title
CS50 2021 in HDR - Lecture 4 - Memory

description
This is CS50, Harvard University's Introduction to the intellectual enterprises of computer science and the art of programming. Enroll for free at https://cs50.edx.org/. Slides, source code, and more at https://cs50.harvard.edu/x. Playlist at https://www.youtube.com/playlist?list=PLhQjrBD2T383f9scHRNYJkior2VvYjpSL. TABLE OF CONTENTS 00:00:00 - Introduction 00:01:17 - Memory 00:04:16 - RGB 00:06:15 - Hexadecimal 00:14:12 - Memory Addresses 00:17:27 - address.c 00:19:47 - Pointers 00:22:12 - Address Of 00:26:36 - Dereference Operator 00:31:13 - Visualizing Pointers 00:39:18 - Assignment Operator 00:40:52 - Strings in Memory 00:44:47 - char * 00:59:09 - Pointer Arithmetic 01:09:52 - compare.c 01:20:52 - copy.c 01:25:46 - malloc and free 01:39:24 - Valgrind 01:46:06 - Garbage Values 01:48:50 - Binky Pointer Fun 01:54:31 - Swap 01:58:00 - swap.c 02:01:39 - Stack and Heap 02:03:52 - Visualizing swap.c 02:07:22 - Pointer Helpers 02:12:22 - scanf 02:16:55 - Segmentation Fault 02:19:18 - File Input/Output 02:25:08 - This was CS50 *** This is CS50, Harvard University's introduction to the intellectual enterprises of computer science and the art of programming. *** HOW TO SUBSCRIBE http://www.youtube.com/subscription_center?add_user=cs50tv HOW TO TAKE CS50 edX: https://cs50.edx.org/ Harvard Extension School: https://cs50.harvard.edu/extension Harvard Summer School: https://cs50.harvard.edu/summer OpenCourseWare: https://cs50.harvard.edu/x HOW TO JOIN CS50 COMMUNITIES Discord: https://discord.gg/cs50 Ed: https://cs50.harvard.edu/x/ed Facebook Group: https://www.facebook.com/groups/cs50/ Faceboook Page: https://www.facebook.com/cs50/ GitHub: https://github.com/cs50 Gitter: https://gitter.im/cs50/x Instagram: https://instagram.com/cs50 LinkedIn Group: https://www.linkedin.com/groups/7437240/ LinkedIn Page: https://www.linkedin.com/school/cs50/ Medium: https://cs50.medium.com/ Quora: https://www.quora.com/topic/CS50 Reddit: https://www.reddit.com/r/cs50/ Slack: https://cs50.edx.org/slack Snapchat: https://www.snapchat.com/add/cs50 SoundCloud: https://soundcloud.com/cs50 Stack Exchange: https://cs50.stackexchange.com/ TikTok: https://www.tiktok.com/@cs50 Twitter: https://twitter.com/cs50 YouTube: http://www.youtube.com/cs50 HOW TO FOLLOW DAVID J. MALAN Facebook: https://www.facebook.com/dmalan GitHub: https://github.com/dmalan Instagram: https://www.instagram.com/davidjmalan/ LinkedIn: https://www.linkedin.com/in/malan/ Quora: https://www.quora.com/profile/David-J-Malan TikTok: https://www.tiktok.com/@davidjmalan Twitter: https://twitter.com/davidjmalan *** CS50 SHOP https://cs50.harvardshop.com/ *** LICENSE CC BY-NC-SA 4.0 Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International Public License https://creativecommons.org/licenses/by-nc-sa/4.0/ David J. Malan https://cs.harvard.edu/malan malan@harvard.edu

detail
{'title': 'CS50 2021 in HDR - Lecture 4 - Memory', 'heatmap': [{'end': 1321.75, 'start': 1136.365, 'weight': 0.754}, {'end': 3503.904, 'start': 3413.159, 'weight': 0.777}, {'end': 5255.348, 'start': 5073.87, 'weight': 0.705}, {'end': 5430.386, 'start': 5336.769, 'weight': 0.73}, {'end': 5607.41, 'start': 5511.231, 'weight': 0.744}, {'end': 6222.317, 'start': 6126.287, 'weight': 0.749}, {'end': 6489.257, 'start': 6391.191, 'weight': 1}, {'end': 7449.973, 'start': 7265.413, 'weight': 0.785}, {'end': 7884.398, 'start': 7705.057, 'weight': 0.766}, {'end': 8146.46, 'start': 8053.571, 'weight': 0.866}, {'end': 8495.131, 'start': 8313.014, 'weight': 0.756}], 'summary': 'Lecture explores computer memory, hexadecimal number system, pointers, string comparison, dynamic memory allocation, and memory management in c, addressing potential security threats and practical examples in memory manipulation.', 'chapters': [{'end': 424.058, 'segs': [{'end': 184.918, 'src': 'embed', 'start': 154.38, 'weight': 0, 'content': [{'end': 159.865, 'text': "because if you're only using a finite amount of memory, then at the end of the day you can only store a finite amount of information.", 'start': 154.38, 'duration': 5.485}, {'end': 166.611, 'text': "And at least I don't really see in this grid here any glint of a license plate or something like that that you might otherwise see in in Hollywood.", 'start': 159.905, 'duration': 6.706}, {'end': 169.652, 'text': "So today we'll explore sort of these kinds of representations,", 'start': 166.631, 'duration': 3.021}, {'end': 175.474, 'text': 'of how you might use memory in new and interesting ways to represent now very familiar things,', 'start': 169.652, 'duration': 5.822}, {'end': 178.836, 'text': 'but also start to explore what some of the limitations are of this representation.', 'start': 175.474, 'duration': 3.362}, {'end': 184.918, 'text': "But consider after all that this doesn't need to be even as high resolution as many pixels as something like this other image.", 'start': 179.156, 'duration': 5.762}], 'summary': 'Exploring new memory representations with limitations and lower resolution.', 'duration': 30.538, 'max_score': 154.38, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI154380.jpg'}, {'end': 256.44, 'src': 'embed', 'start': 226.098, 'weight': 3, 'content': [{'end': 232.023, 'text': "If you go to this URL here, we've put together an opportunity to do a sort of a bit of pixel art.", 'start': 226.098, 'duration': 5.925}, {'end': 235.747, 'text': 'If you go to this URL here that will redirect you to a google spreadsheet.', 'start': 232.103, 'duration': 3.644}, {'end': 241.392, 'text': "If you have a laptop with you today that will look a little something like this, which we've sort of organized in rows and columns.", 'start': 235.767, 'duration': 5.625}, {'end': 249.318, 'text': "So, if you'd like to go ahead and use google spreadsheets colorization feature to coloring those individual squares, if you'd like,", 'start': 241.432, 'duration': 7.886}, {'end': 256.44, 'text': "see if you can't make something a little creative and then email it to carter and we'll exhibit some of the best or favorites on the website thereafter.", 'start': 249.318, 'duration': 7.122}], 'summary': 'Create pixel art using google sheets, email to carter for website exhibit.', 'duration': 30.342, 'max_score': 226.098, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI226098.jpg'}, {'end': 291.843, 'src': 'embed', 'start': 259.682, 'weight': 2, 'content': [{'end': 262.203, 'text': 'images, and not all of you have used, presumably, photoshop,', 'start': 259.682, 'duration': 2.521}, {'end': 267.405, 'text': "but you're probably generally familiar with photoshop as a program for editing and creating images or photos or the like.", 'start': 262.203, 'duration': 5.202}, {'end': 270.726, 'text': "And here is a screenshot of photoshop's color picker,", 'start': 267.705, 'duration': 3.021}, {'end': 276.788, 'text': "via which you can change like what color you're going to draw with the paintbrush or what color you're going to fill in with the paint bucket.", 'start': 270.726, 'duration': 6.062}, {'end': 278.73, 'text': 'representative of any kind of graphical tool.', 'start': 277.048, 'duration': 1.682}, {'end': 284.395, 'text': "And there's kind of a lot of information in here, but there's perhaps some familiar terms now R.", 'start': 279.05, 'duration': 5.345}, {'end': 285.236, 'text': 'G And B.', 'start': 284.395, 'duration': 0.841}, {'end': 291.843, 'text': "In fact, right now, this is photoshop's way of saying you're about to fill in your background or foreground with the color black,", 'start': 285.236, 'duration': 6.607}], 'summary': 'Introduction to photoshop color picker and r, g, b color representation', 'duration': 32.161, 'max_score': 259.682, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI259682.jpg'}, {'end': 411.37, 'src': 'embed', 'start': 385.874, 'weight': 1, 'content': [{'end': 390.537, 'text': 'any RGB value red green blue just combine some amount of red or green or blue.', 'start': 385.874, 'duration': 4.663}, {'end': 400.063, 'text': 'So here we have 72 73 33 which in the context of an email or text of course said what a couple of weeks back just high with an exclamation point.', 'start': 390.657, 'duration': 9.406}, {'end': 407.648, 'text': 'But in the context of a photoshop like program, this might instead be representing collectively this shade of yellow, for instance,', 'start': 400.083, 'duration': 7.565}, {'end': 409.789, 'text': 'when you combine that much red, that much green, that much blue.', 'start': 407.648, 'duration': 2.141}, {'end': 411.37, 'text': 'So here is the same idea.', 'start': 410.169, 'duration': 1.201}], 'summary': 'Rgb values can combine to create different colors, e.g. 72 73 33 could represent a shade of yellow in a photoshop program.', 'duration': 25.496, 'max_score': 385.874, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI385874.jpg'}], 'start': 11.303, 'title': 'Exploring computer memory and photoshop color picker', 'summary': "Explores computer memory for image representation and introduces a pixel art activity, along with discussing photoshop's color picker for manipulating colors using rgb and hexadecimal values.", 'chapters': [{'end': 259.682, 'start': 11.303, 'title': 'Cs 50 week four: exploring computer memory', 'summary': 'Discusses the representation of images using memory, exploring the limitations of such representation and introduces a hands-on activity for creating pixel art using a google spreadsheet.', 'duration': 248.379, 'highlights': ['The chapter discusses the representation of images using memory The chapter delves into how images are represented using memory and explains the concept of using pixels as dots on the screen to represent images.', 'Introduces a hands-on activity for creating pixel art using a google spreadsheet The chapter introduces an opportunity for the audience to create pixel art using a google spreadsheet, allowing them to color individual squares and submit their creations for potential exhibition on the website.', 'Explores the limitations of image representation using memory The chapter explores the limitations of representing images using memory, emphasizing that there is a finite amount of information that can be stored due to the finite amount of memory available.']}, {'end': 424.058, 'start': 259.682, 'title': 'Understanding photoshop color picker', 'summary': "Discusses how to use photoshop's color picker to manipulate colors, including the representation of colors in rgb and hexadecimal values, and how different combinations of red, green, and blue create various colors.", 'duration': 164.376, 'highlights': ['Explanation of color representation in RGB and hexadecimal values The chapter explains the representation of colors in both RGB and hexadecimal values, providing insight into how different combinations of red, green, and blue create various colors.', "Demonstration of using Photoshop's color picker to change colors The speaker demonstrates the use of Photoshop's color picker to change colors, exemplifying the manipulation of colors using different tools.", 'Comparison of RGB values in the context of web design and Photoshop The comparison of RGB values in web design (using HTML and CSS) and in Photoshop, highlighting the similarity in the representation of colors through RGB values.', 'Introduction to the concept of hexadecimal color representation The introduction to the concept of hexadecimal color representation as a different base system, in addition to binary and decimal, laying the groundwork for further exploration.']}], 'duration': 412.755, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI11303.jpg', 'highlights': ['The chapter explores the limitations of representing images using memory, emphasizing the finite amount of information that can be stored.', 'The chapter explains the representation of colors in both RGB and hexadecimal values, providing insight into how different combinations of red, green, and blue create various colors.', "The speaker demonstrates the use of Photoshop's color picker to change colors, exemplifying the manipulation of colors using different tools.", 'The chapter introduces an opportunity for the audience to create pixel art using a google spreadsheet, allowing them to color individual squares and submit their creations for potential exhibition on the website.']}, {'end': 1841.746, 'segs': [{'end': 475.813, 'src': 'embed', 'start': 445.812, 'weight': 0, 'content': [{'end': 447.893, 'text': 'So think back here was binary in the world of binary.', 'start': 445.812, 'duration': 2.081}, {'end': 452.895, 'text': 'You had just two digits zero and one could have been anything else a or B X or Y.', 'start': 447.913, 'duration': 4.982}, {'end': 458.979, 'text': "But the world standardized on these numerals zero and one in our world's decimal system.", 'start': 452.895, 'duration': 6.084}, {'end': 460.779, 'text': 'Of course, you have zero through nine.', 'start': 458.999, 'duration': 1.78}, {'end': 468.146, 'text': "as of today, though, we're going to start using hexadecimal, sometimes in the context of images and also files, just because it's a convention.", 'start': 460.779, 'duration': 7.367}, {'end': 475.813, 'text': "There's some conveniences to it where now you're going to be able to count up to F in a notation called hexadecimal from zero through nine.", 'start': 468.406, 'duration': 7.407}], 'summary': 'Introducing hexadecimal notation, counting up to f from 0-9 for conveniences in images and files.', 'duration': 30.001, 'max_score': 445.812, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI445812.jpg'}, {'end': 589.416, 'src': 'embed', 'start': 556.89, 'weight': 1, 'content': [{'end': 558.472, 'text': 'It would be 01 in this case.', 'start': 556.89, 'duration': 1.582}, {'end': 564.942, 'text': 'This would be 23456789 in decimal.', 'start': 558.813, 'duration': 6.129}, {'end': 578.172, 'text': "We're about to go to 10 but in hexadecimal to be clear what comes next? So apparently a so zero a zero b which is now 10 or 11 or 12 13 14 15.", 'start': 564.962, 'duration': 13.21}, {'end': 582.634, 'text': 'So using hexadecimal is just kind of an interesting way of using single symbols.', 'start': 578.173, 'duration': 4.461}, {'end': 589.416, 'text': "now, zero through F to count from zero through 15, and we'll see why it's 15 in a moment.", 'start': 582.634, 'duration': 6.782}], 'summary': 'Using hexadecimal, counting from 0 to f equals 0 to 15, with 01 as the starting point.', 'duration': 32.526, 'max_score': 556.89, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI556890.jpg'}, {'end': 795.829, 'src': 'embed', 'start': 771.361, 'weight': 7, 'content': [{'end': 777.363, 'text': "And if we wanted to count to 255 in binary, that's as high as you can count, recall, with eight bits,", 'start': 771.361, 'duration': 6.002}, {'end': 784.105, 'text': "and there's only a few of these numbers that are useful to memorize, like, 255 is as high as you can count with eight bits if you start at zero,", 'start': 777.363, 'duration': 6.742}, {'end': 786.086, 'text': 'because two to the eighth is 256..', 'start': 784.105, 'duration': 1.981}, {'end': 789.607, 'text': "But if you start at zero, it's zero through 255.", 'start': 786.086, 'duration': 3.521}, {'end': 795.829, 'text': "So in binary recall if you have eight bits, all of which were ones and I won't do out the math pedantically here.", 'start': 789.607, 'duration': 6.222}], 'summary': 'Counting to 255 in binary with 8 bits, 256 total possible values, 0 to 255.', 'duration': 24.468, 'max_score': 771.361, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI771361.jpg'}, {'end': 916.998, 'src': 'embed', 'start': 892.845, 'weight': 6, 'content': [{'end': 904.63, 'text': "So what comes after F here? Well if I think about the computer's memory I normally might do after F which is 15 16 but instead 10 11 12 13.", 'start': 892.845, 'duration': 11.785}, {'end': 910.074, 'text': 'This is not 10, 11, 12, 13, because I claim them in the context of hexadecimal.', 'start': 904.632, 'duration': 5.442}, {'end': 913.876, 'text': "now, as per the previous slide, we already started going into A's through F's.", 'start': 910.074, 'duration': 3.802}, {'end': 916.998, 'text': 'So you immediately see here a possible problem.', 'start': 914.537, 'duration': 2.461}], 'summary': 'Discussion of hexadecimal numbers and memory sequencing', 'duration': 24.153, 'max_score': 892.845, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI892845.jpg'}, {'end': 1352.61, 'src': 'heatmap', 'start': 1136.365, 'weight': 4, 'content': [{'end': 1138.726, 'text': "So that's what's going on inside of the computer's memory.", 'start': 1136.365, 'duration': 2.361}, {'end': 1146.01, 'text': 'So what if I actually wanted to start tinkering with its location or maybe just knowing its location.', 'start': 1139.247, 'duration': 6.763}, {'end': 1151.691, 'text': "Well, this variable n indeed has a name and that's a label of sorts for it.", 'start': 1146.07, 'duration': 5.621}, {'end': 1158.314, 'text': "But at the end of the day that 50 is technically at a specific address and I'm going to make one up zero x 123.", 'start': 1152.032, 'duration': 6.282}, {'end': 1159.994, 'text': "and it's 123 because I really don't care what it is.", 'start': 1158.314, 'duration': 1.68}, {'end': 1161.995, 'text': 'I just want an address for the sake of discussion.', 'start': 1160.054, 'duration': 1.941}, {'end': 1168.998, 'text': 'So way over here off screen might be bite zero way down here is bite O X 123.', 'start': 1162.475, 'duration': 6.523}, {'end': 1172.179, 'text': "It's in hexadecimal notation just by convention.", 'start': 1168.998, 'duration': 3.181}, {'end': 1177.081, 'text': 'So how can I actually see where my variables are ending up in memory?', 'start': 1172.919, 'duration': 4.162}, {'end': 1178.261, 'text': "if I'm curious to do so?", 'start': 1177.081, 'duration': 1.18}, {'end': 1183.663, 'text': 'Well, let me go back to my code here and let me actually change this just a little bit.', 'start': 1178.321, 'duration': 5.342}, {'end': 1192.918, 'text': 'Let me go ahead and introduce for instance another symbol here and another topic altogether, namely pointers.', 'start': 1184.103, 'duration': 8.815}, {'end': 1202.481, 'text': 'So a pointer is a variable that stores the address of some value, the location of some value or, more specifically,', 'start': 1193.718, 'duration': 8.763}, {'end': 1205.501, 'text': 'the specific bite in which that value is stored.', 'start': 1202.481, 'duration': 3.02}, {'end': 1211.683, 'text': 'So again, if you think of your memory as being a whole bunch of bites zero at top left, 2 billion or whatever at bottom right,', 'start': 1205.561, 'duration': 6.122}, {'end': 1212.803, 'text': 'depending on how much ram you have.', 'start': 1211.683, 'duration': 1.12}, {'end': 1215.044, 'text': 'Each of those things has a location in our address.', 'start': 1213.283, 'duration': 1.761}, {'end': 1218.866, 'text': 'A pointer is just a variable storing one such address.', 'start': 1215.564, 'duration': 3.302}, {'end': 1228.673, 'text': "So it turns out that in the world of C there's a couple of new symbols we can use if we want to see what it is we're talking about here.", 'start': 1219.727, 'duration': 8.946}, {'end': 1231.695, 'text': 'And those two operators as of today are these.', 'start': 1229.193, 'duration': 2.502}, {'end': 1235.657, 'text': 'You can use the ampersand operator and see in a couple of ways.', 'start': 1232.175, 'duration': 3.482}, {'end': 1243.422, 'text': 'We already saw it very briefly to do ampersand ampersand to kind of and to to Boolean expressions together in the context of a conditional.', 'start': 1235.697, 'duration': 7.725}, {'end': 1244.502, 'text': 'This is different.', 'start': 1243.822, 'duration': 0.68}, {'end': 1248.365, 'text': 'A single ampersand is the address of operator.', 'start': 1244.903, 'duration': 3.462}, {'end': 1254.988, 'text': "So, literally in your code, if you've got a variable like n or anything else and you write ampersand n,", 'start': 1248.805, 'duration': 6.183}, {'end': 1261.412, 'text': "c is going to figure out for you what is the address of that variable n in the computer's memory, and it's going to give you a number,", 'start': 1254.988, 'duration': 6.424}, {'end': 1265.254, 'text': 'a number otherwise known as the address of that.', 'start': 1261.412, 'duration': 3.842}, {'end': 1273.77, 'text': "If you want to store that address in a variable even though, yes, it's a number like O, X, 1, 2, 3,", 'start': 1266.187, 'duration': 7.583}, {'end': 1284.054, 'text': 'you have to tell see in advance that you want to store not an inch per se, but the address of an end and the syntax for doing that somewhat.', 'start': 1273.77, 'duration': 10.284}, {'end': 1290.876, 'text': 'non, obviously, is, to use an asterisk here, a star operator, and you say this when creating the variable.', 'start': 1284.054, 'duration': 6.822}, {'end': 1294.858, 'text': 'if you want p to be a pointer, that is the address of some other variable,', 'start': 1290.876, 'duration': 3.982}, {'end': 1300.94, 'text': 'You do in star p and the star just tells the computer this is not an integer per se.', 'start': 1295.498, 'duration': 5.442}, {'end': 1305.862, 'text': "This is the address of something that yes is an end but we're just being more precise.", 'start': 1301.36, 'duration': 4.502}, {'end': 1312.265, 'text': 'So, on the right hand side, you have the address of operator, as always with the equal sign you copy from right to left.', 'start': 1306.443, 'duration': 5.822}, {'end': 1316.947, 'text': 'because ampersand n is by definition the address of something, you have to store it in a pointer.', 'start': 1312.265, 'duration': 4.682}, {'end': 1321.75, 'text': 'And the way to declare a pointer is to specify the type of value,', 'start': 1317.387, 'duration': 4.363}, {'end': 1327.954, 'text': "whose address you're storing and then use the star to indicate that this is indeed a pointer and not just a regular old int.", 'start': 1321.75, 'duration': 6.204}, {'end': 1330.745, 'text': "So let's see this in practice.", 'start': 1329.505, 'duration': 1.24}, {'end': 1335.786, 'text': 'Let me go back to my own source code here and let me make just a couple of tweaks.', 'start': 1330.765, 'duration': 5.021}, {'end': 1341.367, 'text': "I'm gonna leave n alone here but I'm gonna go ahead and initially just do this.", 'start': 1335.866, 'duration': 5.501}, {'end': 1352.61, 'text': "Uh, let me say int star p equals ampersand n, and then down here I'm gonna print out, not end this time, but p the variable p.", 'start': 1341.387, 'duration': 11.223}], 'summary': 'The transcript discusses memory addresses and pointers in c programming, explaining how to store and retrieve variable addresses.', 'duration': 216.245, 'max_score': 1136.365, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI1136365.jpg'}, {'end': 1392.609, 'src': 'embed', 'start': 1365.723, 'weight': 5, 'content': [{'end': 1371.389, 'text': "So now let's go ahead and recompile this make address so far so good dot slash address enter.", 'start': 1365.723, 'duration': 5.666}, {'end': 1375.653, 'text': 'And a little weirdly, but perhaps understandably now,', 'start': 1372.27, 'duration': 3.383}, {'end': 1384.001, 'text': "the address in my computer's memory at which the variable and happened to be stored was not quite as simple as O X 123..", 'start': 1375.653, 'duration': 8.348}, {'end': 1385.582, 'text': 'This computer has a lot more memory.', 'start': 1384.001, 'duration': 1.581}, {'end': 1392.609, 'text': 'So technically it was stored at O X 7 F F C B 4 5 7 8 E 5 C.', 'start': 1385.642, 'duration': 6.967}], 'summary': 'Address recompiled successfully, variable stored at ox7ffcb4578e5c', 'duration': 26.886, 'max_score': 1365.723, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI1365723.jpg'}, {'end': 1566.816, 'src': 'embed', 'start': 1531.457, 'weight': 8, 'content': [{'end': 1533.759, 'text': "you touched memory that you shouldn't have.", 'start': 1531.457, 'duration': 2.302}, {'end': 1541.948, 'text': 'And odds are, you did it most recently by going too far in an array, going to the left or negative in an array or somehow looking at memory.', 'start': 1533.88, 'duration': 8.068}, {'end': 1542.608, 'text': "you shouldn't have.", 'start': 1541.948, 'duration': 0.66}, {'end': 1546.092, 'text': "And we'll explain today why it is you were able to do that.", 'start': 1542.848, 'duration': 3.244}, {'end': 1549.475, 'text': 'Other questions on these primitive so far.', 'start': 1547.013, 'duration': 2.462}, {'end': 1550.276, 'text': 'Yeah From carter later.', 'start': 1549.515, 'duration': 0.761}, {'end': 1557.208, 'text': 'Good question.', 'start': 1556.667, 'duration': 0.541}, {'end': 1558.549, 'text': 'Earlier we used star P.', 'start': 1557.288, 'duration': 1.261}, {'end': 1566.816, 'text': 'Let me rewind in time to the previous version of this code where I actually had a variable called P just like with variable declarations in the past.', 'start': 1558.549, 'duration': 8.267}], 'summary': 'The transcript discusses accessing memory incorrectly and explains the reason behind it.', 'duration': 35.359, 'max_score': 1531.457, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI1531457.jpg'}], 'start': 424.098, 'title': 'Hexadecimal number system, computer memory and variable storage, and pointers in c', 'summary': 'Introduces the hexadecimal number system, highlighting its efficiency in representing numbers, explores computer memory and variable storage through an example program, and explains pointers in c, including their potential security threats and implications of using the ampersand operator.', 'chapters': [{'end': 1013.814, 'start': 424.098, 'title': 'Hexadecimal number system', 'summary': 'Introduces the hexadecimal number system, explaining its usage in representing color codes in images and files, highlighting its efficiency in representing numbers up to 255 using just two digits instead of three in decimal, and its convention in computer memory addressing as a more succinct and efficient way to represent memory locations.', 'duration': 589.716, 'highlights': ['Hexadecimal system efficiently represents numbers up to 255 with just two digits, compared to three in decimal, offering a 50% reduction in digits required for the same value. Hexadecimal system allows counting up to 255 using just two digits (FF), providing a 50% reduction in the number of digits required compared to decimal representation for the same value.', 'Hexadecimal is conventionally used in computer memory addressing for succinctly representing memory locations, with each digit representing four bits, making it more efficient than decimal. In the context of computer memory addressing, hexadecimal is used for representing memory locations, with each digit representing four bits, offering a more succinct and efficient way to represent memory addresses compared to decimal.', "The convention of representing hexadecimal numbers with '0x' signals to readers that the number is in hexadecimal, resolving potential confusion between decimal and hexadecimal representations. The convention of representing hexadecimal numbers with '0x' signals to readers that the number is in hexadecimal, resolving potential confusion between decimal and hexadecimal representations."]}, {'end': 1172.179, 'start': 1013.814, 'title': 'Exploring computer memory and variable storage', 'summary': "Explores how variables are stored in a computer's memory, including the allocation of memory for a variable and the use of addresses to manipulate or locate the variable, illustrated through an example program that assigns the value 50 to a variable called n.", 'duration': 158.365, 'highlights': ["Variables are stored in a computer's memory, with an int typically using 4 bytes or 32 bits. The variable 'n' is stored in the computer's memory as an int, typically using 4 bytes or 32 bits.", "The value 50 is stored in the variable 'N' and represented in 32 zeros and ones, but is written as a decimal in the code. The value 50 is stored in the variable 'N' and represented in 32 zeros and ones in the computer's memory, while being written as a decimal in the code.", "The variable 'N' has a specific address, in this case represented as 0x123 in hexadecimal notation. The variable 'N' is located at a specific address, presented as 0x123 in hexadecimal notation."]}, {'end': 1530.937, 'start': 1172.919, 'title': 'Understanding pointers in c', 'summary': 'Introduces pointers in c, explaining how to use the ampersand operator to get the address of a variable, and the potential security threats associated with accessing memory directly in c.', 'duration': 358.018, 'highlights': ['Pointers in C store the address of a value, allowing access to specific bytes of memory. A pointer in C is a variable that stores the address of some value, allowing access to specific bytes in memory.', "The ampersand operator in C is used to get the address of a variable in the computer's memory. The ampersand operator in C is used to obtain the address of a variable in the computer's memory, providing a way to access its location.", 'Accessing memory directly in C can pose security threats, such as potential buffer overflows and segmentation faults. Directly accessing memory in C can lead to security threats like buffer overflows and segmentation faults, which are frequent issues in the language.']}, {'end': 1841.746, 'start': 1531.457, 'title': 'Understanding pointers in c', 'summary': 'Explores the concept of pointers in c, their declaration, usage, dereferencing, and the implications of using the ampersand operator, highlighting the confusion and importance of knowing the type of data being pointed to.', 'duration': 310.289, 'highlights': ['The star operator in C is used for pointer declaration, multiplication, and dereferencing, which can be confusing to beginners, but practice leads to comfort.', 'Declaring a pointer in C involves specifying the type of data it points to, which provides the compiler with enough information to correctly interpret and print the data at that address.', 'The ampersand operator is used to get the address of a variable in C, and it is crucial to know the type of data being addressed for accurate interpretation by the compiler.', 'Pointers in C can have pointers, indicated by using the star operator twice, but this concept is not explored in detail in this chapter.']}], 'duration': 1417.648, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI424098.jpg', 'highlights': ['Hexadecimal system efficiently represents numbers up to 255 with just two digits, offering a 50% reduction in digits required for the same value.', "The convention of representing hexadecimal numbers with '0x' signals to readers that the number is in hexadecimal, resolving potential confusion between decimal and hexadecimal representations.", 'In the context of computer memory addressing, hexadecimal is used for representing memory locations, with each digit representing four bits, offering a more succinct and efficient way to represent memory addresses compared to decimal.', "The value 50 is stored in the variable 'N' and represented in 32 zeros and ones in the computer's memory, while being written as a decimal in the code.", "The variable 'N' is located at a specific address, presented as 0x123 in hexadecimal notation.", 'A pointer in C is a variable that stores the address of some value, allowing access to specific bytes in memory.', 'Directly accessing memory in C can lead to security threats like buffer overflows and segmentation faults, which are frequent issues in the language.', 'Declaring a pointer in C involves specifying the type of data it points to, which provides the compiler with enough information to correctly interpret and print the data at that address.', 'The ampersand operator is used to get the address of a variable in C, and it is crucial to know the type of data being addressed for accurate interpretation by the compiler.', 'The star operator in C is used for pointer declaration, multiplication, and dereferencing, which can be confusing to beginners, but practice leads to comfort.']}, {'end': 3550.719, 'segs': [{'end': 2235.877, 'src': 'embed', 'start': 2211.208, 'weight': 3, 'content': [{'end': 2222.185, 'text': "Sure What's your name? And say again and food.", 'start': 2211.208, 'duration': 10.977}, {'end': 2224.967, 'text': 'Okay Come on up to the edge of the stage there.', 'start': 2223.186, 'duration': 1.781}, {'end': 2228.911, 'text': 'And just to be clear if this is p that is apparently end.', 'start': 2225.028, 'duration': 3.883}, {'end': 2230.653, 'text': "But to make clear what we're talking about.", 'start': 2228.991, 'duration': 1.662}, {'end': 2235.877, 'text': "when we're storing O X, whatever values like O X 123, that's essentially equivalent to my.", 'start': 2230.653, 'duration': 5.224}], 'summary': 'Clarifying the process for storing values like o x 123 as equivalent to my.', 'duration': 24.669, 'max_score': 2211.208, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI2211208.jpg'}, {'end': 2507.998, 'src': 'embed', 'start': 2472.457, 'weight': 2, 'content': [{'end': 2478.441, 'text': 'And we I claimed or revealed last week that string is not technically a feature built into C.', 'start': 2472.457, 'duration': 5.984}, {'end': 2487.187, 'text': "Like. it's not an official data type, but every programmer, in most any language, refers to sequences of characters, words, letters, paragraphs as strings.", 'start': 2478.441, 'duration': 8.746}, {'end': 2492.61, 'text': "So the vernacular exists, but the data type doesn't typically exist per se in C.", 'start': 2487.407, 'duration': 5.203}, {'end': 2496.873, 'text': "So what we're about to do if you will for dramatic effect is take off some training wheels today.", 'start': 2492.61, 'duration': 4.263}, {'end': 2501.596, 'text': 'The CS 50 library implemented in the form of the header file CS 50 dot H.', 'start': 2496.913, 'duration': 4.683}, {'end': 2507.998, 'text': 'We claim has had a bunch of things in it prototypes for get string prototypes for get into and all of those other functions.', 'start': 2501.596, 'duration': 6.402}], 'summary': 'In c, string is not an official data type, but cs50 library provides prototypes for get string and get into functions.', 'duration': 35.541, 'max_score': 2472.457, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI2472457.jpg'}, {'end': 2562.751, 'src': 'embed', 'start': 2530.79, 'weight': 4, 'content': [{'end': 2532.051, 'text': "I don't care about all the other bites.", 'start': 2530.79, 'duration': 1.261}, {'end': 2533.532, 'text': "Let's just focus on these.", 'start': 2532.091, 'duration': 1.441}, {'end': 2537.815, 'text': 'and this per last week is how high might be stored H I exclamation point.', 'start': 2533.532, 'duration': 4.283}, {'end': 2546.7, 'text': 'and then one more, as someone already observed, that sentinel value that no character, which just means 80 bits to demarcate the end of that string,', 'start': 2537.815, 'duration': 8.885}, {'end': 2548.341, 'text': "just in case there's something to the right of it.", 'start': 2546.7, 'duration': 1.641}, {'end': 2551.203, 'text': 'The computer can now distinguish one string from another.', 'start': 2548.781, 'duration': 2.422}, {'end': 2554.745, 'text': 'So last week we introduced this new syntax.', 'start': 2551.883, 'duration': 2.862}, {'end': 2562.751, 'text': 'Well, if strings are just a raise of characters, you can then very cleverly use that square bracket notation and go to location zero or one or two,', 'start': 2555.085, 'duration': 7.666}], 'summary': 'Introduced new syntax; using square bracket notation to locate characters in a string.', 'duration': 31.961, 'max_score': 2530.79, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI2530790.jpg'}, {'end': 2734.84, 'src': 'embed', 'start': 2706.974, 'weight': 8, 'content': [{'end': 2712.617, 'text': 'So if s is got points at the first character and you can trust that backslash zero is at the end of the string,', 'start': 2706.974, 'duration': 5.643}, {'end': 2717.56, 'text': "that's literally all you need to figure out where a string begins and ends.", 'start': 2712.617, 'duration': 4.943}, {'end': 2722.223, 'text': "So what do I mean by this? Well, let's be a little more concrete in terms of this picture.", 'start': 2718.22, 'duration': 4.003}, {'end': 2724.064, 'text': "If I've started with this line of code here,", 'start': 2722.263, 'duration': 1.801}, {'end': 2734.84, 'text': 'It turns out all this time since week one that the word string has just semi secretly been an alias for char star.', 'start': 2724.984, 'duration': 9.856}], 'summary': "Backslash zero marks end of the string, 'string' is an alias for char star.", 'duration': 27.866, 'max_score': 2706.974, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI2706974.jpg'}, {'end': 2808.158, 'src': 'embed', 'start': 2784.909, 'weight': 0, 'content': [{'end': 2793.752, 'text': "Let me go back to my code here and let's get rid of this integer stuff and let's instead now do for instance this, let me add in the CS 50 library.", 'start': 2784.909, 'duration': 8.843}, {'end': 2796.953, 'text': "So we'll include CS 50 dot H for now.", 'start': 2794.372, 'duration': 2.581}, {'end': 2801.935, 'text': "I'm gonna go ahead and inside of main give myself a string s equals high exclamation point.", 'start': 2797.513, 'duration': 4.422}, {'end': 2805.276, 'text': "I don't type the backslash zero C does that for me automatically.", 'start': 2801.975, 'duration': 3.301}, {'end': 2808.158, 'text': 'by using my double quotes like this.', 'start': 2806.536, 'duration': 1.622}], 'summary': "Modifying code to include cs50 library and initializing a string 's' with a value 'high!'", 'duration': 23.249, 'max_score': 2784.909, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI2784909.jpg'}, {'end': 3436.17, 'src': 'embed', 'start': 3413.159, 'weight': 5, 'content': [{'end': 3421.042, 'text': 'Let me go ahead and claim that we implemented char star or rather string as a char star as follows.', 'start': 3413.159, 'duration': 7.883}, {'end': 3423.824, 'text': 'As of last week, we were writing this code.', 'start': 3421.603, 'duration': 2.221}, {'end': 3431.387, 'text': 'as of this week, we can now start writing this code because char star specifically, we invented in the CS 50 library.', 'start': 3423.824, 'duration': 7.563}, {'end': 3434.329, 'text': "But it turns out you've seen a way of inventing your own data types.", 'start': 3431.407, 'duration': 2.922}, {'end': 3436.17, 'text': 'recall this thing here.', 'start': 3435.009, 'duration': 1.161}], 'summary': 'Implemented char star as string, enabling new code writing. discovered method for inventing data types.', 'duration': 23.011, 'max_score': 3413.159, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI3413159.jpg'}, {'end': 3503.904, 'src': 'heatmap', 'start': 3413.159, 'weight': 0.777, 'content': [{'end': 3421.042, 'text': 'Let me go ahead and claim that we implemented char star or rather string as a char star as follows.', 'start': 3413.159, 'duration': 7.883}, {'end': 3423.824, 'text': 'As of last week, we were writing this code.', 'start': 3421.603, 'duration': 2.221}, {'end': 3431.387, 'text': 'as of this week, we can now start writing this code because char star specifically, we invented in the CS 50 library.', 'start': 3423.824, 'duration': 7.563}, {'end': 3434.329, 'text': "But it turns out you've seen a way of inventing your own data types.", 'start': 3431.407, 'duration': 2.922}, {'end': 3436.17, 'text': 'recall this thing here.', 'start': 3435.009, 'duration': 1.161}, {'end': 3444.396, 'text': 'We played around last time with data structures or the struct keyword and see and briefly the type def keyword which defines a type for you.', 'start': 3436.77, 'duration': 7.626}, {'end': 3446.697, 'text': "And if I highlight what's interesting here,", 'start': 3444.716, 'duration': 1.981}, {'end': 3458.125, 'text': 'the way we invented a person data type last time was to define a person as having two variables inside of it a structure that encapsulates a name and encapsulates a number.', 'start': 3446.697, 'duration': 11.428}, {'end': 3467.511, 'text': 'Now, even though the syntax is a little different today because of the star thing, notice that This could be a similar application of that idea.', 'start': 3458.846, 'duration': 8.665}, {'end': 3476.054, 'text': 'If I want to create a type called string highlighted in yellow here, then I use type def to make it defined to be char star.', 'start': 3467.911, 'duration': 8.143}, {'end': 3479.916, 'text': 'So this is literally all that has ever been in CS 50 dot H.', 'start': 3476.314, 'duration': 3.602}, {'end': 3483.417, 'text': "In addition to those prototypes of functions we've talked about type def.", 'start': 3479.916, 'duration': 3.501}, {'end': 3490.32, 'text': 'char star string is a one line code that brings the word string as a data type into existence.', 'start': 3483.417, 'duration': 6.903}, {'end': 3491.962, 'text': "And that's all that's ever been there.", 'start': 3490.74, 'duration': 1.222}, {'end': 3495.028, 'text': 'But the star, the char star is just too much in week one.', 'start': 3492.002, 'duration': 3.026}, {'end': 3503.904, 'text': 'We wait until this point to sort of peel back that layer or any questions then on what a string is, what star or the ampersand are doing? Yeah.', 'start': 3495.429, 'duration': 8.475}], 'summary': 'Cs 50 library now includes char star as string data type, allowing for easy creation of new data types.', 'duration': 90.745, 'max_score': 3413.159, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI3413159.jpg'}], 'start': 1848.072, 'title': 'Understanding pointers, strings, and memory in c', 'summary': 'Covers the concepts of pointers and strings in c, discussing 64-bit pointers, memory limitations with 32-bit pointers, and their functionality. it also explores the representation of strings in memory, use of cs 50 library, and manipulation of strings without the library, along with their relationship with pointers and memory addresses.', 'chapters': [{'end': 2448.317, 'start': 1848.072, 'title': 'Understanding pointers in computer memory', 'summary': 'Discusses the concept of pointers in computer memory, highlighting that pointers are typically 64 bits, addressing the history of memory limitations with 32-bit pointers, and likening pointers to the postal system, emphasizing their use and functionality. the chapter concludes with a discussion on the use of assignment operators and the lack of automatic updates for pointers in c.', 'duration': 600.245, 'highlights': ['Pointers are typically 64 bits or 8 bytes, addressing the limitations of 32-bit pointers and the increased memory capacity of modern computers.', 'The analogy of pointers to the postal system is used to explain how memory locations store values and addresses, emphasizing the practical use and functionality of pointers.', 'The discussion includes the use of assignment operators and the lack of automatic updates for pointers in C, highlighting the need for manual updates to pointer values.']}, {'end': 2784.869, 'start': 2448.317, 'title': 'Understanding strings in c', 'summary': 'Discusses the concept of strings in c, how they are represented in memory, and how they are essentially represented as a char pointer, using the cs 50 library as an example.', 'duration': 336.552, 'highlights': ['Strings in C are not technically a feature built into the language, but are commonly referred to as sequences of characters, and are represented as an array of characters. The concept of strings in C is explained as not being an official data type, but rather commonly referred to as sequences of characters, and are represented as an array of characters.', 'The CS 50 library, implemented in the form of the header file CS 50 dot H, provides prototypes for functions such as get string and get into, and also defines the word string, allowing its use in programs. The CS 50 library provides prototypes for functions and defines the word string, enabling its use in programs through the inclusion of CS 50 dot H header file.', "Strings in C are represented in the computer's memory as a pointer to the first character in the string, and the null character is used to demarcate the end of the string. Strings in C are represented in memory as a pointer to the first character in the string, with the null character being used to indicate the end of the string."]}, {'end': 3061.967, 'start': 2784.909, 'title': 'Understanding c strings and pointers', 'summary': 'Covers the process of manipulating strings in c without the cs 50 library, demonstrating the concept of pointers and memory addresses, and how creating a copy of a variable results in a different memory address.', 'duration': 277.058, 'highlights': ['The chapter covers the process of manipulating strings in C without the CS 50 library The speaker removes the CS 50 library, making changes to the code to manipulate strings in C without any external library support.', 'Demonstrating the concept of pointers and memory addresses The speaker introduces the concept of pointers and memory addresses by showcasing the process of obtaining and printing memory addresses of variables in C.', 'Creating a copy of a variable results in a different memory address A demonstration is provided where creating a copy of a variable results in a different memory address, despite both containing the same value.']}, {'end': 3550.719, 'start': 3062.408, 'title': 'Understanding strings and pointers in c', 'summary': 'Focuses on understanding the relationship between strings and pointers in c, demonstrating how strings are represented as pointers to the first character in the string, and the use of ampersand and star in manipulating memory addresses and values, providing insights on the implementation of string as a char star and the potential issues with comparing strings due to comparing memory addresses.', 'duration': 488.311, 'highlights': ["Strings in C are represented as pointers to the first character in the string, demonstrated by printing the address of the first character in the string 'S'. Demonstrates the relationship between strings and pointers, clarifies that strings are represented as pointers to the first character in the string.", "The use of ampersand and star in manipulating memory addresses and values is illustrated by printing the address of every character in the string 'S' and explaining the functionality of percent P and percent S in the context of printing pointer values and characters. Explains the use of ampersand and star in manipulating memory addresses and values, provides insight into the functionality of percent P and percent S in printing pointer values and characters.", 'Insights on the implementation of string as a char star are provided, showcasing the use of type def to define string as char star and drawing a parallel with the invention of data types using struct keyword. Demonstrates the implementation of string as a char star using type def, draws a parallel with the invention of data types using the struct keyword.', 'Potential issues with comparing strings due to comparing memory addresses are highlighted, pointing out the deliberate use of strcmp over comparing memory addresses directly. Highlights potential issues with comparing strings due to comparing memory addresses, emphasizes the deliberate use of strcmp over comparing memory addresses directly.']}], 'duration': 1702.647, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI1848072.jpg', 'highlights': ['Pointers are typically 64 bits or 8 bytes, addressing the limitations of 32-bit pointers and the increased memory capacity of modern computers.', 'The analogy of pointers to the postal system is used to explain how memory locations store values and addresses, emphasizing the practical use and functionality of pointers.', "Strings in C are represented in the computer's memory as a pointer to the first character in the string, and the null character is used to demarcate the end of the string.", 'The CS 50 library provides prototypes for functions and defines the word string, enabling its use in programs through the inclusion of CS 50 dot H header file.', 'Creating a copy of a variable results in a different memory address, despite both containing the same value.', 'Demonstrates the relationship between strings and pointers, clarifies that strings are represented as pointers to the first character in the string.', 'Explains the use of ampersand and star in manipulating memory addresses and values, provides insight into the functionality of percent P and percent S in printing pointer values and characters.', 'Demonstrates the implementation of string as a char star using type def, draws a parallel with the invention of data types using the struct keyword.', 'Highlights potential issues with comparing strings due to comparing memory addresses, emphasizes the deliberate use of strcmp over comparing memory addresses directly.']}, {'end': 4183.386, 'segs': [{'end': 3626.938, 'src': 'embed', 'start': 3592.578, 'weight': 0, 'content': [{'end': 3595.92, 'text': "That is the word string and I'll redefine S as a string.", 'start': 3592.578, 'duration': 3.342}, {'end': 3601.544, 'text': "And what I didn't mention before is that these double quotes that you've been using for some time are actually a little special.", 'start': 3596.24, 'duration': 5.304}, {'end': 3609.288, 'text': 'The double quotes are a clue to the compiler that what is between them is in fact a string as we now know it,', 'start': 3601.644, 'duration': 7.644}, {'end': 3615.332, 'text': 'which means the compiler will do all the work of figuring out where to put the H, the I, the exclamation point,', 'start': 3609.288, 'duration': 6.044}, {'end': 3618.093, 'text': 'and even adding for you automatically a backslash zero.', 'start': 3615.332, 'duration': 2.761}, {'end': 3626.938, 'text': 'And what the compiler will do for you too is figure out what address all four of those chars ended up at and stored for you in the variable s.', 'start': 3618.473, 'duration': 8.465}], 'summary': 'Compiler identifies string in double quotes, adds backslash zero, and stores chars in variable s.', 'duration': 34.36, 'max_score': 3592.578, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI3592578.jpg'}, {'end': 3659.159, 'src': 'embed', 'start': 3627.458, 'weight': 1, 'content': [{'end': 3633.061, 'text': "So that's why it just kind of happens with strings without using ampersands or even stars explicitly.", 'start': 3627.458, 'duration': 5.603}, {'end': 3638.283, 'text': 'But the star at least has been there because again string is just synonymous now with char star.', 'start': 3633.401, 'duration': 4.882}, {'end': 3642.025, 'text': "It's not really as readable but it is now the same idea.", 'start': 3638.323, 'duration': 3.702}, {'end': 3648.408, 'text': "So I'll leave string in place just to do something sort of week one style here for a moment and let's go ahead and print out a few characters.", 'start': 3642.365, 'duration': 6.043}, {'end': 3659.159, 'text': "So I'm going to use percent C this time and I'm going to print out S bracket zero And then I'm going to print out s bracket one and s bracket to,", 'start': 3648.448, 'duration': 10.711}], 'summary': 'Explaining the usage of strings and characters in c programming.', 'duration': 31.701, 'max_score': 3627.458, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI3627458.jpg'}, {'end': 4168.702, 'src': 'embed', 'start': 4136.886, 'weight': 5, 'content': [{'end': 4139.448, 'text': "So this is something we're going to take advantage of to before long.", 'start': 4136.886, 'duration': 2.562}, {'end': 4147.712, 'text': "There's this sort of inter relationship between addresses and arrays that just generally allows you to treat one as though it is the other.", 'start': 4139.828, 'duration': 7.884}, {'end': 4149.895, 'text': 'But the math is taken care of for you.', 'start': 4148.254, 'duration': 1.641}, {'end': 4154.895, 'text': 'Or any questions then on on this before we start to solve some some bigger problems.', 'start': 4150.535, 'duration': 4.36}, {'end': 4168.702, 'text': 'Yeah potentially if you go beyond the end of an array, you might get a segmentation fault.', 'start': 4154.916, 'duration': 13.786}], 'summary': 'Addresses and arrays can be interrelated, enabling math operations, but may lead to segmentation faults.', 'duration': 31.816, 'max_score': 4136.886, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI4136886.jpg'}], 'start': 3551.319, 'title': 'Using pointers in data structures', 'summary': 'Explores using pointers and addresses to stitch together complicated data structures, including images and videos, using the cs 50 library. it also delves into the concept of pointers, pointer arithmetic, and string representation, highlighting the relationship between arrays and addresses.', 'chapters': [{'end': 3592.098, 'start': 3551.319, 'title': 'Using pointers to stitch data structures', 'summary': 'Explores the use of pointers and addresses to stitch together more complicated data structures, representing not just images, but also videos and other two-dimensional structures, using the cs 50 library.', 'duration': 40.779, 'highlights': ['The goal is to use addresses to stitch together more complicated data structures than just persons or candidates, representing not just images, but also videos and other two-dimensional structures.', 'The chapter focuses on using pointers and addresses to represent more versatile data structures, such as videos and other two-dimensional structures.', 'The use of the CS 50 library is mentioned as a tool for exploring the concept of using pointers and addresses in data structures.']}, {'end': 4183.386, 'start': 3592.578, 'title': 'Understanding pointers and strings', 'summary': 'Explores the concept of pointers, pointer arithmetic, and string representation, touching on how double quotes denote strings, pointer arithmetic to access individual characters, and the relationship between arrays and addresses.', 'duration': 590.808, 'highlights': ['The chapter explores the concept of pointers, pointer arithmetic, and string representation. The transcript delves into the fundamental concept of pointers, pointer arithmetic, and the representation of strings in memory.', 'Double quotes denote strings, and the compiler automatically handles the string representation and memory allocation. The use of double quotes serves as a clue to the compiler to identify the enclosed characters as a string, leading to automatic memory allocation and proper representation of the string.', 'Pointer arithmetic is used to access individual characters in a string. The chapter demonstrates the use of pointer arithmetic to access individual characters within a string by incrementing the pointer to access subsequent characters.', 'Arrays can be treated as pointers, allowing for the manipulation of array elements as memory addresses. An array can be treated as the address of its first element, enabling the manipulation of array elements as memory addresses, simplifying the process of working with arrays.']}], 'duration': 632.067, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI3551319.jpg', 'highlights': ['The chapter focuses on using pointers and addresses to represent more versatile data structures, such as videos and other two-dimensional structures.', 'The goal is to use addresses to stitch together more complicated data structures than just persons or candidates, representing not just images, but also videos and other two-dimensional structures.', 'The use of the CS 50 library is mentioned as a tool for exploring the concept of using pointers and addresses in data structures.', 'The chapter explores the concept of pointers, pointer arithmetic, and string representation.', 'Arrays can be treated as pointers, allowing for the manipulation of array elements as memory addresses.', 'Double quotes denote strings, and the compiler automatically handles the string representation and memory allocation.', 'Pointer arithmetic is used to access individual characters in a string.']}, {'end': 4796.092, 'segs': [{'end': 4293.708, 'src': 'embed', 'start': 4262.922, 'weight': 3, 'content': [{'end': 4266.685, 'text': 'So so far so good in this first version of comparison.', 'start': 4262.922, 'duration': 3.763}, {'end': 4274.852, 'text': "But as you might see where I'm going with this, let's move away from integers and let's actually change these things to char to strings.", 'start': 4267.506, 'duration': 7.346}, {'end': 4280.037, 'text': 'So I could do string s over here, get string s over here.', 'start': 4275.333, 'duration': 4.704}, {'end': 4286.662, 'text': 'Then I could do string t over here and get string over here.', 'start': 4280.657, 'duration': 6.005}, {'end': 4293.708, 'text': 'asking the user for T this time here and then I can compare the two if S equals equals T.', 'start': 4287.483, 'duration': 6.225}], 'summary': 'First version compares integers, then converts to strings for comparison.', 'duration': 30.786, 'max_score': 4262.922, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI4262922.jpg'}, {'end': 4502.705, 'src': 'embed', 'start': 4477.647, 'weight': 5, 'content': [{'end': 4484.25, 'text': "So that's an easy fix include string dot h which despite its name does not create a data type called string.", 'start': 4477.647, 'duration': 6.603}, {'end': 4487.191, 'text': 'It just has string related functions in it like stir compare.', 'start': 4484.35, 'duration': 2.841}, {'end': 4488.492, 'text': "Let's make compare again.", 'start': 4487.611, 'duration': 0.881}, {'end': 4490.994, 'text': 'Now it compiles dot slash compare.', 'start': 4489.292, 'duration': 1.702}, {'end': 4494.617, 'text': "Now let's type in high exclamation point and even the same thing again.", 'start': 4491.374, 'duration': 3.243}, {'end': 4498.561, 'text': 'These are now oh I used it wrong.', 'start': 4495.178, 'duration': 3.383}, {'end': 4502.705, 'text': "Okay user error that was supposed to be impressive but it's the opposite.", 'start': 4498.641, 'duration': 4.064}], 'summary': 'Including string.h for string-related functions led to a user error.', 'duration': 25.058, 'max_score': 4477.647, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI4477647.jpg'}, {'end': 4796.092, 'src': 'embed', 'start': 4754.678, 'weight': 0, 'content': [{'end': 4761.402, 'text': 'One is over here, one is over here and per a moment ago, one is O X 123, the other is O X 456.', 'start': 4754.678, 'duration': 6.724}, {'end': 4767.626, 'text': "Yes, technically they're pointing at something that's the same, but that just reveals how stir compare works.", 'start': 4761.402, 'duration': 6.224}, {'end': 4776.094, 'text': 'stir compare is apparently a function that takes in the address of a string as its argument and the address of another string as its argument.', 'start': 4768.166, 'duration': 7.928}, {'end': 4785.244, 'text': 'It goes to the first character in each of those strings respectively and probably has like a for loop or a while loop and just goes from left to right,', 'start': 4776.595, 'duration': 8.649}, {'end': 4788.267, 'text': 'comparing, looking for the same charge left and right.', 'start': 4785.244, 'duration': 3.023}, {'end': 4791.79, 'text': "And if it doesn't notice any differences, boom, it returns zero.", 'start': 4788.768, 'duration': 3.022}, {'end': 4796.092, 'text': 'If it does notice a difference, it returns a positive or a negative value.', 'start': 4792.351, 'duration': 3.741}], 'summary': 'Stir compare function compares strings and returns 0 for no differences, positive/negative values for differences.', 'duration': 41.414, 'max_score': 4754.678, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI4754678.jpg'}], 'start': 4183.426, 'title': 'Comparing integers and strings in c', 'summary': 'Introduces a program in c to compare two data types, demonstrating differences with examples of identical and different values. it also discusses string comparison in c, including memory representation, pointer usage, and the functionality of the stir compare function, providing insights into comparison results.', 'chapters': [{'end': 4332.238, 'start': 4183.426, 'title': 'Comparing integers and strings in c', 'summary': 'Introduces a program in c that compares the values of two integers and then modifies it to compare two strings, demonstrating the differences in comparing data types, with examples of identical and different values.', 'duration': 148.812, 'highlights': ["The chapter introduces a program in C that compares the values of two integers The program is initially designed to compare the values of two integers using the '==' operator, demonstrating the process of asking for user input and printing results based on the comparison.", "The program is modified to compare two strings, demonstrating the differences in comparing data types The program is then modified to compare two strings using the '==' operator, showcasing the process of asking for user input for strings and the differences in comparing string values.", 'Examples of identical and different values are used to showcase the comparison process Examples of identical and different string values are used to demonstrate the comparison process, providing clear outcomes to illustrate the differences when comparing strings in the C program.']}, {'end': 4796.092, 'start': 4332.438, 'title': 'Understanding string comparison in c', 'summary': 'Discusses the fundamental issue of string comparison in c, highlighting how strings are represented in memory, the use of pointers, and the functionality of the stir compare function to compare strings and return zero for equality, a positive value if the first string comes before the second, and a negative value if the opposite is true.', 'duration': 463.654, 'highlights': ['String representation in memory The chapter explains how strings are represented in memory using pointers, illustrating how each character in a string is stored at a different address, leading to different memory locations for seemingly identical strings.', 'Functionality of stir compare The functionality of the stir compare function is detailed, emphasizing its use to compare strings by iterating through each character and returning zero for equality, a positive value if the first string comes before the second, and a negative value if the opposite is true.', 'Explanation of pointers The concept of pointers is clarified with the example of how S and T are pointers to characters, highlighting the addresses of the first characters in S and T, and the subsequent comparison and functionality of stir compare.']}], 'duration': 612.666, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI4183426.jpg', 'highlights': ["The program is modified to compare two strings, demonstrating the differences in comparing data types The program is then modified to compare two strings using the '==' operator, showcasing the process of asking for user input for strings and the differences in comparing string values.", 'Examples of identical and different values are used to showcase the comparison process Examples of identical and different string values are used to demonstrate the comparison process, providing clear outcomes to illustrate the differences when comparing strings in the C program.', 'Functionality of stir compare The functionality of the stir compare function is detailed, emphasizing its use to compare strings by iterating through each character and returning zero for equality, a positive value if the first string comes before the second, and a negative value if the opposite is true.', 'String representation in memory The chapter explains how strings are represented in memory using pointers, illustrating how each character in a string is stored at a different address, leading to different memory locations for seemingly identical strings.', "The chapter introduces a program in C that compares the values of two integers The program is initially designed to compare the values of two integers using the '==' operator, demonstrating the process of asking for user input and printing results based on the comparison.", 'Explanation of pointers The concept of pointers is clarified with the example of how S and T are pointers to characters, highlighting the addresses of the first characters in S and T, and the subsequent comparison and functionality of stir compare.']}, {'end': 5456.593, 'segs': [{'end': 4974.074, 'src': 'embed', 'start': 4926.172, 'weight': 2, 'content': [{'end': 4928.874, 'text': 'There was a bunch of helpful functions in that library as well.', 'start': 4926.172, 'duration': 2.702}, {'end': 4934.237, 'text': "Now at the very last line of the program, let's just print out with both S and T.", 'start': 4929.374, 'duration': 4.863}, {'end': 4941.863, 'text': 'R by simply printing out percent s for each of them and t is percent s also not percent t of course.', 'start': 4934.237, 'duration': 7.626}, {'end': 4944.264, 'text': "And let's see what happens here.", 'start': 4942.643, 'duration': 1.621}, {'end': 4945.946, 'text': 'So let me make copy.', 'start': 4944.725, 'duration': 1.221}, {'end': 4947.767, 'text': 'Oh my God, so many mistakes.', 'start': 4945.966, 'duration': 1.801}, {'end': 4953.109, 'text': 'What did I do wrong? Oh, Okay, that was unintended string T equals S sorry.', 'start': 4947.847, 'duration': 5.262}, {'end': 4959.27, 'text': "So I'm creating two variables S and T respectively and I'm copying S into T make copy enter.", 'start': 4953.589, 'duration': 5.681}, {'end': 4968.733, 'text': "There we go dot, slash copy and let's now type in for instance, how about high exclamation point in all lower case this time?", 'start': 4959.45, 'duration': 9.283}, {'end': 4970.473, 'text': 'and now what gets printed?', 'start': 4968.733, 'duration': 1.74}, {'end': 4974.074, 'text': "Huh?. I don't think that's what I intended.", 'start': 4970.493, 'duration': 3.581}], 'summary': "Mistake made in copying string s to t. unintended output with 'high' in lowercase.", 'duration': 47.902, 'max_score': 4926.172, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI4926172.jpg'}, {'end': 5255.348, 'src': 'heatmap', 'start': 5073.87, 'weight': 0.705, 'content': [{'end': 5084.936, 'text': 'But when I copy S into T by doing T equals S semicolon that literally just copies S into T which puts the value O X 1 2 3 there.', 'start': 5073.87, 'duration': 11.066}, {'end': 5088.999, 'text': 'So if we now abstract away all these numbers and just think about a picture with arrows,', 'start': 5084.976, 'duration': 4.023}, {'end': 5096.404, 'text': "what we've drawn in the computer's memory is this two different pointers but storing the same address,", 'start': 5089.739, 'duration': 6.665}, {'end': 5099.346, 'text': 'which means the breadcrumbs lead to the same place.', 'start': 5096.404, 'duration': 2.942}, {'end': 5102.949, 'text': 'And so if you follow the T breadcrumb and capitalize the first letter,', 'start': 5099.746, 'duration': 3.203}, {'end': 5111.075, 'text': 'it is functionally the same as copying the changing the first letter in the version s as well.', 'start': 5102.949, 'duration': 8.126}, {'end': 5115.298, 'text': "So what's the solution, then, to this kind of problem?", 'start': 5112.476, 'duration': 2.822}, {'end': 5126.156, 'text': "Like, even if you have no idea how to do it in code, like, what's the gist of what I really intended, which I want a genuine copy of S called T?", 'start': 5117.028, 'duration': 9.128}, {'end': 5129.278, 'text': 'I want a new H I exclamation point backslash zero.', 'start': 5126.156, 'duration': 3.122}, {'end': 5141.271, 'text': 'What do I need to do to make that happen? Thoughts So there is a function called stir copy S T R C P Y which is a possible answer to this question.', 'start': 5130.279, 'duration': 10.992}, {'end': 5148.295, 'text': 'The catch with stir copy is that you have to tell in advance not only what the source string is the one you want to copy.', 'start': 5141.571, 'duration': 6.724}, {'end': 5152.257, 'text': 'you also need to pass in the address of a chunk of memory into which you can copy.', 'start': 5148.295, 'duration': 3.962}, {'end': 5157.702, 'text': "the string and here's one thing we haven't seen yet and we need one more building block today if you will.", 'start': 5152.717, 'duration': 4.985}, {'end': 5165.03, 'text': "We haven't yet seen a way to create new chunks of memory then then let some other function copy into them.", 'start': 5158.043, 'duration': 6.987}, {'end': 5171.397, 'text': "And for this we're going to introduce something called dynamic memory allocation and this is the last and most powerful feature,", 'start': 5165.19, 'duration': 6.207}, {'end': 5174.28, 'text': "perhaps today whereby we're going to introduce two functions.", 'start': 5171.397, 'duration': 2.883}, {'end': 5179.361, 'text': 'malloc and free where malloc means memory allocate which literally does just that.', 'start': 5174.74, 'duration': 4.621}, {'end': 5181.062, 'text': "It's a function that takes a number is input.", 'start': 5179.502, 'duration': 1.56}, {'end': 5186.284, 'text': 'How many bytes of memory do you want the operating system to find for you somewhere in that big grid?', 'start': 5181.342, 'duration': 4.942}, {'end': 5190.805, 'text': "It's going to find it and it's going to return to the address of the first bite of contiguous memory.", 'start': 5186.664, 'duration': 4.141}, {'end': 5193.806, 'text': 'back to back to back, and then you can do anything you want with that chunk of memory.', 'start': 5190.805, 'duration': 3.001}, {'end': 5195.727, 'text': 'free is going to do the opposite.', 'start': 5194.426, 'duration': 1.301}, {'end': 5199.95, 'text': "when you're done using a chunk of memory that Malik has given you, you can say free it,", 'start': 5195.727, 'duration': 4.223}, {'end': 5204.973, 'text': 'and that means you hand it back to the operating system and then the operating system can use it for something else later.', 'start': 5199.95, 'duration': 5.023}, {'end': 5208.796, 'text': 'So this is actually evidence of a common problem in programming.', 'start': 5205.514, 'duration': 3.282}, {'end': 5209.896, 'text': "If you're Mac, your P.", 'start': 5208.836, 'duration': 1.06}, {'end': 5216.399, 'text': "C has ever been in the habit of starting to get like really really slow or it's kind of slowing to a crawl.", 'start': 5209.896, 'duration': 6.503}, {'end': 5217.639, 'text': 'Heck maybe it even freezes.', 'start': 5216.439, 'duration': 1.2}, {'end': 5224.621, 'text': "One of the possible explanations could be that the program you're running by apple or Microsoft or whoever.", 'start': 5218.139, 'duration': 6.482}, {'end': 5230.143, 'text': "maybe they're using malloc or some equivalent, asking the operating system mac os or windows for give me more memory.", 'start': 5224.621, 'duration': 5.522}, {'end': 5230.923, 'text': 'I need more memory.', 'start': 5230.183, 'duration': 0.74}, {'end': 5232.303, 'text': 'The user is creating more images.', 'start': 5230.963, 'duration': 1.34}, {'end': 5233.763, 'text': 'The user is typing a longer essay.', 'start': 5232.343, 'duration': 1.42}, {'end': 5235.144, 'text': 'Give me more memory, more memory.', 'start': 5233.803, 'duration': 1.341}, {'end': 5242.605, 'text': 'If the program has a bug and never actually freeze any of that memory, your computer might end up using all of the available memory.', 'start': 5235.624, 'duration': 6.981}, {'end': 5246.486, 'text': 'And honestly humans are not very good at handling corner cases like that.', 'start': 5242.705, 'duration': 3.781}, {'end': 5250.147, 'text': 'Very often programs computers just freeze at that point or get really,', 'start': 5246.546, 'duration': 3.601}, {'end': 5255.348, 'text': "really slow because they start trying to be creative when there's not enough memory left.", 'start': 5250.147, 'duration': 5.201}], 'summary': 'Using dynamic memory allocation through malloc and free can resolve memory issues in programming.', 'duration': 181.478, 'max_score': 5073.87, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI5073870.jpg'}, {'end': 5179.361, 'src': 'embed', 'start': 5117.028, 'weight': 0, 'content': [{'end': 5126.156, 'text': "Like, even if you have no idea how to do it in code, like, what's the gist of what I really intended, which I want a genuine copy of S called T?", 'start': 5117.028, 'duration': 9.128}, {'end': 5129.278, 'text': 'I want a new H I exclamation point backslash zero.', 'start': 5126.156, 'duration': 3.122}, {'end': 5141.271, 'text': 'What do I need to do to make that happen? Thoughts So there is a function called stir copy S T R C P Y which is a possible answer to this question.', 'start': 5130.279, 'duration': 10.992}, {'end': 5148.295, 'text': 'The catch with stir copy is that you have to tell in advance not only what the source string is the one you want to copy.', 'start': 5141.571, 'duration': 6.724}, {'end': 5152.257, 'text': 'you also need to pass in the address of a chunk of memory into which you can copy.', 'start': 5148.295, 'duration': 3.962}, {'end': 5157.702, 'text': "the string and here's one thing we haven't seen yet and we need one more building block today if you will.", 'start': 5152.717, 'duration': 4.985}, {'end': 5165.03, 'text': "We haven't yet seen a way to create new chunks of memory then then let some other function copy into them.", 'start': 5158.043, 'duration': 6.987}, {'end': 5171.397, 'text': "And for this we're going to introduce something called dynamic memory allocation and this is the last and most powerful feature,", 'start': 5165.19, 'duration': 6.207}, {'end': 5174.28, 'text': "perhaps today whereby we're going to introduce two functions.", 'start': 5171.397, 'duration': 2.883}, {'end': 5179.361, 'text': 'malloc and free where malloc means memory allocate which literally does just that.', 'start': 5174.74, 'duration': 4.621}], 'summary': 'Introduction to dynamic memory allocation with malloc and free functions.', 'duration': 62.333, 'max_score': 5117.028, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI5117028.jpg'}, {'end': 5430.386, 'src': 'heatmap', 'start': 5336.769, 'weight': 0.73, 'content': [{'end': 5342.952, 'text': "It returns the length of the string you see plus one also takes into account the fact that I'm going to need that backslash end.", 'start': 5336.769, 'duration': 6.183}, {'end': 5345.353, 'text': 'Now let me do this old school style first.', 'start': 5343.392, 'duration': 1.961}, {'end': 5348.935, 'text': 'Let me go ahead and manually copy the string T.', 'start': 5345.673, 'duration': 3.262}, {'end': 5350.096, 'text': 'S into T first.', 'start': 5348.935, 'duration': 1.161}, {'end': 5363.806, 'text': "So for into I equals zero I is less than the string length of S I plus plus Then inside my for loop I'm gonna do T bracket I equals S bracket I.", 'start': 5350.516, 'duration': 13.29}, {'end': 5367.1, 'text': 'But actually I want the no character too.', 'start': 5363.806, 'duration': 3.294}, {'end': 5369.621, 'text': 'So I want to do the length of the string plus one more.', 'start': 5367.2, 'duration': 2.421}, {'end': 5372.562, 'text': 'And heck, I think I learned an optimization last time.', 'start': 5370.201, 'duration': 2.361}, {'end': 5380.847, 'text': "If I'm doing this again and again, I could really do n equals sterling of S plus one, and then do I is less than end,", 'start': 5372.683, 'duration': 8.164}, {'end': 5382.848, 'text': 'just as a nice design optimization.', 'start': 5380.847, 'duration': 2.001}, {'end': 5392.473, 'text': 'I think this for loop will actually handle the process then of copying every character from S into every available bite of memory in T.', 'start': 5383.428, 'duration': 9.045}, {'end': 5398.178, 'text': 'Or I could get rid of all of that and take your suggestion, which is to use stir copy,', 'start': 5393.693, 'duration': 4.485}, {'end': 5402.923, 'text': 'which takes as its first argument the destination and its second argument the source.', 'start': 5398.178, 'duration': 4.745}, {'end': 5410.391, 'text': "So copy from right to left in this case to that's going to do all of that automatically for me as well.", 'start': 5403.484, 'duration': 6.907}, {'end': 5413.033, 'text': "Now I think I'm good.", 'start': 5411.232, 'duration': 1.801}, {'end': 5420.359, 'text': 'I can now capitalize safely the first character in T, which is now a different chunk of memory than S,', 'start': 5413.454, 'duration': 6.905}, {'end': 5425.522, 'text': 'and then I can print them both out to see that one has not changed but the other has, so make copy.', 'start': 5420.359, 'duration': 5.163}, {'end': 5430.386, 'text': 'All right, what did I do wrong? Implicitly declaring library function malloc dot dot dot.', 'start': 5425.542, 'duration': 4.844}], 'summary': 'Copying string s into string t using manual and optimized methods, exploring library function stir copy.', 'duration': 93.617, 'max_score': 5336.769, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI5336769.jpg'}], 'start': 4796.472, 'title': 'String comparison, pointers, and dynamic memory allocation in c', 'summary': 'Covers string comparison with `strcmp`, pointers, and dynamic memory allocation in c, including the use of ampersand operator, pointer storage in memory, limitations of copying strings, malloc and free functions, and the importance of including the standard lib library.', 'chapters': [{'end': 4842.332, 'start': 4796.472, 'title': 'String comparison and pointers', 'summary': 'Covers string comparison using `strcmp` and the concept of pointers, discussing the use of the ampersand operator and the storage of pointer addresses in memory.', 'duration': 45.86, 'highlights': ['The chapter covers string comparison using `strcmp` and the concept of pointers.', 'The ampersand operator can be used on pointers to get the equivalent of a `char**` that could be stored elsewhere in memory.', 'The implementation of string length using a for loop and the usage of `strcmp` for comparing strings are discussed.']}, {'end': 5456.593, 'start': 4842.632, 'title': 'Dynamic memory allocation in c', 'summary': 'Introduces dynamic memory allocation in c, discussing the limitations of copying strings using assignment operator, the use of malloc and free functions, and the implications of not freeing memory, emphasizing the need for including the standard lib library.', 'duration': 613.961, 'highlights': ['Dynamic memory allocation using malloc and free functions The chapter introduces malloc and free functions, which are used to allocate and deallocate memory, respectively, in C, providing a solution for copying strings and emphasizing the importance of freeing memory to avoid performance issues.', 'Limitations of copying strings using assignment operator The chapter discusses the limitations of copying strings using the assignment operator, highlighting that it only copies the pointers, resulting in both variables pointing to the same memory address, and explains the need for a genuine copy of the string.', 'Importance of including the standard lib library The chapter emphasizes the importance of including the standard lib library to address errors related to implicitly declaring library functions, such as malloc, highlighting the need for proper library inclusion in C programming.']}], 'duration': 660.121, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI4796472.jpg', 'highlights': ['The chapter introduces malloc and free functions for dynamic memory allocation.', 'The chapter emphasizes the importance of including the standard lib library.', 'The chapter covers string comparison using `strcmp` and the concept of pointers.', 'The ampersand operator can be used on pointers to get the equivalent of a `char**`.', 'The limitations of copying strings using the assignment operator are discussed.', 'The implementation of string length using a for loop and the usage of `strcmp` for comparing strings are discussed.']}, {'end': 6501.321, 'segs': [{'end': 5607.41, 'src': 'heatmap', 'start': 5511.231, 'weight': 0.744, 'content': [{'end': 5518.593, 'text': "I don't need to do free s, and I shouldn't, because that is handled automatically by the CS 50 library s recall came from get string,", 'start': 5511.231, 'duration': 7.362}, {'end': 5525.435, 'text': "and we actually have some fancy code in place that makes sure that at the end of your program's execution we free any memory that we allocated,", 'start': 5518.593, 'duration': 6.842}, {'end': 5528.196, 'text': "so we don't actually waste memory like I described earlier.", 'start': 5525.435, 'duration': 2.761}, {'end': 5532.318, 'text': "But there's actually a couple of other things if I really want to be pedantic I should put in here.", 'start': 5528.576, 'duration': 3.742}, {'end': 5540.84, 'text': "It turns out that sometimes malloc can fail and sometimes malloc doesn't have enough memory available because maybe your computer is doing so much stuff.", 'start': 5532.798, 'duration': 8.042}, {'end': 5542.38, 'text': "There's just no more ram available.", 'start': 5540.86, 'duration': 1.52}, {'end': 5544.62, 'text': 'So technically I should do something like this.', 'start': 5542.82, 'duration': 1.8}, {'end': 5552.702, 'text': "If T equals equals null with two L's today, then I should just return one or something to say that there was a problem.", 'start': 5545.181, 'duration': 7.521}, {'end': 5554.123, 'text': 'I should probably print an error message too.', 'start': 5552.722, 'duration': 1.401}, {'end': 5555.403, 'text': "But for now I'm going to keep it simple.", 'start': 5554.143, 'duration': 1.26}, {'end': 5558.283, 'text': 'I should also probably check this.', 'start': 5556.323, 'duration': 1.96}, {'end': 5560.384, 'text': 'This is a little risky of me.', 'start': 5558.764, 'duration': 1.62}, {'end': 5565.328, 'text': "If I'm doing T bracket zero, this is assuming that there is a letter there.", 'start': 5561.044, 'duration': 4.284}, {'end': 5571.113, 'text': "But what if the human the human just hit enter at the prompt and didn't even type H let alone H I exclamation point.", 'start': 5565.368, 'duration': 5.745}, {'end': 5573.315, 'text': 'What if there is no T bracket zero.', 'start': 5571.354, 'duration': 1.961}, {'end': 5581.762, 'text': 'So technically what I should probably do here is if the length of T is at least greater than zero.', 'start': 5573.816, 'duration': 7.946}, {'end': 5586.143, 'text': 'Then go ahead and safely capitalize the first letter of it.', 'start': 5581.982, 'duration': 4.161}, {'end': 5592.485, 'text': 'And then at the very end, if all goes well, I can return zero thereby signifying that indeed this thing was successful.', 'start': 5586.563, 'duration': 5.922}, {'end': 5596.366, 'text': 'So yes, these two functions malloc and free should be in concert.', 'start': 5592.865, 'duration': 3.501}, {'end': 5601.568, 'text': 'And so if you call malloc, you should call free eventually.', 'start': 5596.746, 'duration': 4.822}, {'end': 5604.089, 'text': 'But you did not call malloc for S.', 'start': 5601.668, 'duration': 2.421}, {'end': 5607.41, 'text': 'So you should not call free for S.', 'start': 5604.089, 'duration': 3.321}], 'summary': 'Cs50 library handles automatic memory deallocation, malloc failure check, and input validation for capitalization. no memory wastage and proper error handling demonstrated.', 'duration': 96.179, 'max_score': 5511.231, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI5511231.jpg'}, {'end': 6222.317, 'src': 'heatmap', 'start': 6126.287, 'weight': 0.749, 'content': [{'end': 6131.391, 'text': "The second mistake that I've made as a side effect is I'm also touching memory that I shouldn't.", 'start': 6126.287, 'duration': 5.104}, {'end': 6137.678, 'text': 'X bracket three would mean go to the fourth inch in the chunk of memory that came back.', 'start': 6132.376, 'duration': 5.302}, {'end': 6141.02, 'text': 'I only asked for enough memory for three inch, not four.', 'start': 6138.179, 'duration': 2.841}, {'end': 6143.661, 'text': "So this is what's called a buffer overflow.", 'start': 6141.48, 'duration': 2.181}, {'end': 6150.624, 'text': 'I am accidentally but deliberately at the moment going beyond boundaries of this array, this chunk of memory.', 'start': 6143.781, 'duration': 6.843}, {'end': 6154.486, 'text': 'So bad things happen but not necessarily by just running your program.', 'start': 6150.944, 'duration': 3.542}, {'end': 6157.187, 'text': 'Let me go ahead and just try this make memory.', 'start': 6154.506, 'duration': 2.681}, {'end': 6160.308, 'text': "and you'll see here that it compiles.", 'start': 6158.047, 'duration': 2.261}, {'end': 6166.112, 'text': 'Okay dot slash memory and it actually does not segmentation fault which comes back to that point of non determinism.', 'start': 6160.388, 'duration': 5.724}, {'end': 6167.572, 'text': "Sometimes it does, sometimes it doesn't.", 'start': 6166.172, 'duration': 1.4}, {'end': 6169.373, 'text': 'It depends on how bad of a mistake you made.', 'start': 6167.612, 'duration': 1.761}, {'end': 6178.238, 'text': "But there's a program that can spot these kinds of mistakes and I'm gonna go ahead and expand my terminal window for a moment and I'm gonna run not just dot slash memory,", 'start': 6169.814, 'duration': 8.424}, {'end': 6180.86, 'text': 'but a program called Valgrind dot slash memory.', 'start': 6178.238, 'duration': 2.622}, {'end': 6186.926, 'text': "This is a command that comes with a lot of computer systems that's designed to find memory related bugs in code.", 'start': 6181.3, 'duration': 5.626}, {'end': 6190.81, 'text': "So it's a new tool in your toolkit today and you'll use it with the coming problem sets.", 'start': 6186.966, 'duration': 3.844}, {'end': 6192.011, 'text': "I'm gonna run this now.", 'start': 6191.17, 'duration': 0.841}, {'end': 6194.894, 'text': "It's output, honestly, is hideous,", 'start': 6192.512, 'duration': 2.382}, {'end': 6201.561, 'text': "but there's a few things that will start to jump out and will help you with tools in the problem set to see these kinds of things.", 'start': 6194.894, 'duration': 6.667}, {'end': 6203.102, 'text': "Here's the first mistake.", 'start': 6202.001, 'duration': 1.101}, {'end': 6210.148, 'text': "invalid right of size four that's on memory dot C line nine per my highlights.", 'start': 6203.783, 'duration': 6.365}, {'end': 6211.849, 'text': 'So let me go look at line nine.', 'start': 6210.528, 'duration': 1.321}, {'end': 6215.712, 'text': 'In what sense is this an invalid right of size four?', 'start': 6212.489, 'duration': 3.223}, {'end': 6222.317, 'text': "Well, I'm touching memory that I shouldn't, and I'm touching it as though it's an int, and an int is four bytes size four.", 'start': 6216.172, 'duration': 6.145}], 'summary': 'Improper memory handling causes buffer overflow and potential segmentation faults, detectable using valgrind tool.', 'duration': 96.03, 'max_score': 6126.287, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI6126287.jpg'}, {'end': 6167.572, 'src': 'embed', 'start': 6143.781, 'weight': 7, 'content': [{'end': 6150.624, 'text': 'I am accidentally but deliberately at the moment going beyond boundaries of this array, this chunk of memory.', 'start': 6143.781, 'duration': 6.843}, {'end': 6154.486, 'text': 'So bad things happen but not necessarily by just running your program.', 'start': 6150.944, 'duration': 3.542}, {'end': 6157.187, 'text': 'Let me go ahead and just try this make memory.', 'start': 6154.506, 'duration': 2.681}, {'end': 6160.308, 'text': "and you'll see here that it compiles.", 'start': 6158.047, 'duration': 2.261}, {'end': 6166.112, 'text': 'Okay dot slash memory and it actually does not segmentation fault which comes back to that point of non determinism.', 'start': 6160.388, 'duration': 5.724}, {'end': 6167.572, 'text': "Sometimes it does, sometimes it doesn't.", 'start': 6166.172, 'duration': 1.4}], 'summary': 'Accidentally exceeding memory boundaries can lead to non-deterministic segmentation faults.', 'duration': 23.791, 'max_score': 6143.781, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI6143781.jpg'}, {'end': 6305.717, 'src': 'embed', 'start': 6275.063, 'weight': 2, 'content': [{'end': 6276.464, 'text': "But there's still something in there.", 'start': 6275.063, 'duration': 1.401}, {'end': 6280.147, 'text': 'Notice this 12 bytes in one blocks.', 'start': 6276.785, 'duration': 3.362}, {'end': 6281.248, 'text': 'No regard for grammar.', 'start': 6280.448, 'duration': 0.8}, {'end': 6283.35, 'text': 'There are definitely lost in lost record.', 'start': 6281.268, 'duration': 2.082}, {'end': 6284.671, 'text': 'One of one super cryptic.', 'start': 6283.43, 'duration': 1.241}, {'end': 6287.293, 'text': 'But this is hinting at a so called memory leak.', 'start': 6285.252, 'duration': 2.041}, {'end': 6291.357, 'text': 'The blocks of memory are lost in the sense that I malloc them.', 'start': 6287.774, 'duration': 3.583}, {'end': 6293.359, 'text': 'I asked for them but I never take a guess.', 'start': 6291.417, 'duration': 1.942}, {'end': 6294.951, 'text': 'free them.', 'start': 6294.471, 'duration': 0.48}, {'end': 6298.253, 'text': "I have a memory leak and this is the arcane way of saying you've screwed up.", 'start': 6295.091, 'duration': 3.162}, {'end': 6299.254, 'text': 'You have a memory leak.', 'start': 6298.273, 'duration': 0.981}, {'end': 6300.814, 'text': 'So this is an easy fix.', 'start': 6299.534, 'duration': 1.28}, {'end': 6305.717, 'text': "Fortunately, once I'm done with this memory, I just need to free it at the end.", 'start': 6300.874, 'duration': 4.843}], 'summary': 'Identified a memory leak of 12 bytes in one block, needs to be freed at the end.', 'duration': 30.654, 'max_score': 6275.063, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI6275063.jpg'}, {'end': 6349.739, 'src': 'embed', 'start': 6315.262, 'weight': 0, 'content': [{'end': 6319.004, 'text': 'Valgrind of dot slash memory enter Now this is pretty good.', 'start': 6315.262, 'duration': 3.742}, {'end': 6320.826, 'text': 'All heat blocks were freed.', 'start': 6319.525, 'duration': 1.301}, {'end': 6321.446, 'text': 'Whatever that means.', 'start': 6320.866, 'duration': 0.58}, {'end': 6322.947, 'text': 'No leaks are possible.', 'start': 6321.546, 'duration': 1.401}, {'end': 6326.43, 'text': "And even though it's still a little cryptic, there's no other error here.", 'start': 6323.448, 'duration': 2.982}, {'end': 6331.354, 'text': "And in fact it's pretty explicit error summary, zero errors from zero contexts dot dot dot.", 'start': 6326.45, 'duration': 4.904}, {'end': 6338.14, 'text': "So, even though this is one of the most arcane tools we'll use, it's also one of the most powerful, because it can see things that you, the human,", 'start': 6331.855, 'duration': 6.285}, {'end': 6340.582, 'text': 'might not and maybe even that the debugger might not.', 'start': 6338.14, 'duration': 2.442}, {'end': 6346.907, 'text': "It does a much closer reading of your code while it's running to figure out exactly what is going on.", 'start': 6340.682, 'duration': 6.225}, {'end': 6348.417, 'text': 'All right.', 'start': 6348.217, 'duration': 0.2}, {'end': 6349.739, 'text': 'Any questions, then,', 'start': 6348.497, 'duration': 1.242}], 'summary': 'Valgrind tool reports zero errors and is powerful for code analysis.', 'duration': 34.477, 'max_score': 6315.262, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI6315262.jpg'}, {'end': 6489.257, 'src': 'heatmap', 'start': 6391.191, 'weight': 1, 'content': [{'end': 6394.615, 'text': 'I equals zero, I less than three, I plus plus.', 'start': 6391.191, 'duration': 3.424}, {'end': 6397.359, 'text': 'then let me go ahead and print out percent.', 'start': 6394.615, 'duration': 2.744}, {'end': 6400.843, 'text': 'I backslash in scores bracket I, semi colon.', 'start': 6397.359, 'duration': 3.484}, {'end': 6401.264, 'text': "That's it.", 'start': 6400.943, 'duration': 0.321}, {'end': 6408.139, 'text': "This code pretty sure is going to compile and it's going to run.", 'start': 6403.493, 'duration': 4.646}, {'end': 6415.628, 'text': "But what is my logical bug? I've sort of forgotten a step even though the code that's written is not so wrong.", 'start': 6408.84, 'duration': 6.788}, {'end': 6420.098, 'text': "Yeah Yeah, I didn't provide the score.", 'start': 6415.648, 'duration': 4.45}, {'end': 6424.562, 'text': "So I didn't actually initialize the array called scores to have any scores whatsoever.", 'start': 6420.178, 'duration': 4.384}, {'end': 6429.007, 'text': "What's curious about this though is that the computer technically doesn't mind.", 'start': 6424.983, 'duration': 4.024}, {'end': 6434.433, 'text': "Let me go ahead and sort of playfully make garbage enter, and it's kind of an app description,", 'start': 6429.067, 'duration': 5.366}, {'end': 6437.837, 'text': "because what I'm about to see are so called garbage values.", 'start': 6434.433, 'duration': 3.404}, {'end': 6443.482, 'text': 'when you the programmer do not initialize your codes variables to have values.', 'start': 6438.417, 'duration': 5.065}, {'end': 6447.466, 'text': "Sometimes who knows what's going to be there? The computer has been doing some other things.", 'start': 6443.943, 'duration': 3.523}, {'end': 6450.929, 'text': "There's a bit of work that happens even before your code runs in the computer.", 'start': 6447.706, 'duration': 3.223}, {'end': 6455.894, 'text': 'So there might be remnants of past inch char strings floats anything else in there.', 'start': 6451.23, 'duration': 4.664}, {'end': 6466.003, 'text': "And what you're seeing is those garbage values, which is to say, you should never forget, as I just did, to initialize the value of some variable,", 'start': 6456.235, 'duration': 9.768}, {'end': 6472.627, 'text': 'and this is actually pretty dangerous, and there have been many examples of software being compromised because of one of these issues,', 'start': 6466.003, 'duration': 6.624}, {'end': 6483.593, 'text': "where a variable wasn't initialized and all of a sudden users maybe people on the internet in the context of web applications could suddenly see the contents of someone else's memory or remnants,", 'start': 6472.627, 'duration': 10.966}, {'end': 6489.257, 'text': "maybe someone's password that had been previously typed in, or some other value, like a credit card number that had been previously typed in.", 'start': 6483.593, 'duration': 5.664}], 'summary': 'Uninitialized variables can lead to security vulnerabilities and exposure of sensitive data; always initialize variables to avoid such issues.', 'duration': 98.066, 'max_score': 6391.191, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI6391191.jpg'}], 'start': 5456.593, 'title': 'Memory management in c', 'summary': 'Covers memory management in c, including the use of malloc and free, automatic handling of memory by the cs 50 library, error handling for malloc failure, necessity of using malloc with functions like strcpy, significance of proper memory allocation and string manipulation, potential memory problems, and usage of valgrind tool for bug detection.', 'chapters': [{'end': 5518.593, 'start': 5456.593, 'title': 'Memory management in c', 'summary': 'Discusses memory management in c, covering the use of malloc and free, and the automatic handling of memory by the cs 50 library.', 'duration': 62, 'highlights': ["The computer automatically remembers the size of allocated memory, allowing for the proper deallocation of memory by using free, exemplified by the handling of 'T' in the code.", "Explanation of the automatic handling of memory for 'S' by the CS 50 library when using get string."]}, {'end': 5823.874, 'start': 5518.593, 'title': 'Memory management and functions', 'summary': 'Discusses the importance of memory management in c programming, including the use of malloc and free functions, error handling for malloc failure, and the necessity of using malloc with functions like strcpy. the transcript also emphasizes the significance of proper memory allocation and string manipulation to avoid memory wastage and program errors.', 'duration': 305.281, 'highlights': ['The importance of memory management in C programming is emphasized, including the use of malloc and free functions for memory allocation and deallocation, ensuring efficient memory usage and preventing memory leaks.', 'The necessity of error handling for malloc failure is discussed, highlighting the need to check for null return value and provide appropriate error messages in case of memory allocation failure, ensuring robust program behavior in resource-constrained environments.', 'The significance of using malloc with functions like strcpy is explained, emphasizing the need for properly allocated memory space to accommodate the copied characters and the trailing null character, preventing memory wastage and potential program errors.']}, {'end': 6501.321, 'start': 5824.215, 'title': 'Memory management and debugging tools', 'summary': 'Discusses memory management, including the use of malloc and strcpy for copying strings and the potential memory problems that can arise, as well as the usage of the valgrind tool to detect memory-related bugs in code. it also highlights the concept of garbage values and the importance of initializing variables to avoid potential security vulnerabilities.', 'duration': 677.106, 'highlights': ['The chapter discusses the usage of malloc and strcpy for copying strings and the potential memory problems that can arise. The speaker explains the usage of malloc and strcpy for copying strings and the potential memory problems that can arise, such as buffer overflow, when insufficient memory is allocated for the copied string.', 'The chapter introduces the Valgrind tool and its capability to detect memory-related bugs in code. The speaker introduces the Valgrind tool as a means to detect memory-related bugs in code, demonstrating its output and the ability to identify issues such as invalid memory accesses and memory leaks.', 'The concept of garbage values and the importance of initializing variables to avoid potential security vulnerabilities are discussed. The concept of garbage values is explained, emphasizing the importance of initializing variables to avoid potential security vulnerabilities, such as exposing sensitive information stored in memory.']}], 'duration': 1044.728, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI5456593.jpg', 'highlights': ['The necessity of error handling for malloc failure is discussed, highlighting the need to check for null return value and provide appropriate error messages in case of memory allocation failure, ensuring robust program behavior in resource-constrained environments.', 'The importance of memory management in C programming is emphasized, including the use of malloc and free functions for memory allocation and deallocation, ensuring efficient memory usage and preventing memory leaks.', "The computer automatically remembers the size of allocated memory, allowing for the proper deallocation of memory by using free, exemplified by the handling of 'T' in the code.", 'The chapter introduces the Valgrind tool and its capability to detect memory-related bugs in code. The speaker introduces the Valgrind tool as a means to detect memory-related bugs in code, demonstrating its output and the ability to identify issues such as invalid memory accesses and memory leaks.', 'The concept of garbage values and the importance of initializing variables to avoid potential security vulnerabilities are discussed. The concept of garbage values is explained, emphasizing the importance of initializing variables to avoid potential security vulnerabilities, such as exposing sensitive information stored in memory.', 'The chapter discusses the usage of malloc and strcpy for copying strings and the potential memory problems that can arise. The speaker explains the usage of malloc and strcpy for copying strings and the potential memory problems that can arise, such as buffer overflow, when insufficient memory is allocated for the copied string.', 'The significance of using malloc with functions like strcpy is explained, emphasizing the need for properly allocated memory space to accommodate the copied characters and the trailing null character, preventing memory wastage and potential program errors.', "Explanation of the automatic handling of memory for 'S' by the CS 50 library when using get string."]}, {'end': 7279.6, 'segs': [{'end': 6581.265, 'src': 'embed', 'start': 6554.268, 'weight': 0, 'content': [{'end': 6561.654, 'text': "It's another if you actually mistake a garbage value for a valid pointer because garbage values are just zeros and one somewhere numbers that is.", 'start': 6554.268, 'duration': 7.386}, {'end': 6569.961, 'text': "But if you use that new D reference operator the star and try to go to a garbage value thinking incorrectly that it's a valid pointer.", 'start': 6561.994, 'duration': 7.967}, {'end': 6571.461, 'text': 'Bad things can happen.', 'start': 6570.521, 'duration': 0.94}, {'end': 6572.362, 'text': 'Computers can crash.', 'start': 6571.501, 'duration': 0.861}, {'end': 6576.323, 'text': 'Or more familiarly, segmentation faults can happen.', 'start': 6572.462, 'duration': 3.861}, {'end': 6581.265, 'text': 'So allow me to introduce, if we could dim the lights for two minutes, our friend Binky from Stanford.', 'start': 6576.403, 'duration': 4.862}], 'summary': 'Using the new d reference operator can prevent crashes and segmentation faults when dealing with garbage values in pointers.', 'duration': 26.997, 'max_score': 6554.268, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI6554268.jpg'}, {'end': 6633.112, 'src': 'embed', 'start': 6601.266, 'weight': 3, 'content': [{'end': 6604.948, 'text': "Okay, well, I see the two pointers, but they don't seem to be pointing to anything.", 'start': 6601.266, 'duration': 3.682}, {'end': 6605.709, 'text': "That's right.", 'start': 6605.248, 'duration': 0.461}, {'end': 6607.91, 'text': "Initially, pointers don't point to anything.", 'start': 6606.109, 'duration': 1.801}, {'end': 6611.912, 'text': 'The things they point to are called pointees, and setting them up is a separate step.', 'start': 6608.21, 'duration': 3.702}, {'end': 6613.813, 'text': 'Oh, right, right, I knew that.', 'start': 6612.572, 'duration': 1.241}, {'end': 6615.113, 'text': 'The pointees are separate.', 'start': 6614.073, 'duration': 1.04}, {'end': 6623.958, 'text': 'So, how do you allocate a pointee? Okay, well, this code allocates a new integer pointee, and this part sets x to point to it.', 'start': 6615.954, 'duration': 8.004}, {'end': 6626.026, 'text': 'Hey, that looks better.', 'start': 6625.165, 'duration': 0.861}, {'end': 6627.387, 'text': 'So make it do something.', 'start': 6626.386, 'duration': 1.001}, {'end': 6633.112, 'text': "Okay I'll dereference the pointer X to store the number 42 into its pointee.", 'start': 6628.048, 'duration': 5.064}], 'summary': 'Understanding pointers and allocating pointees in code.', 'duration': 31.846, 'max_score': 6601.266, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI6601266.jpg'}, {'end': 6805.272, 'src': 'embed', 'start': 6779.332, 'weight': 1, 'content': [{'end': 6783.495, 'text': "That's fine because again malloc returns the address of some chunk of memory.", 'start': 6779.332, 'duration': 4.163}, {'end': 6786.097, 'text': 'This chunk of memory is big enough for an int.', 'start': 6783.796, 'duration': 2.301}, {'end': 6788.479, 'text': 'x is therefore going to store the address of that chunk.', 'start': 6786.097, 'duration': 2.382}, {'end': 6789.9, 'text': "that's big enough for an int.", 'start': 6788.479, 'duration': 1.421}, {'end': 6795.124, 'text': 'star. x recalls the dereference operator means go to that address and put 42 in it.', 'start': 6789.9, 'duration': 5.224}, {'end': 6800.949, 'text': "It's like going to the mailbox and putting the number 42 in it instead of taking the number 50 out like we did before.", 'start': 6795.384, 'duration': 5.565}, {'end': 6805.272, 'text': 'But why is this line bad? This is where binky sort of lost his head so to speak.', 'start': 6801.529, 'duration': 3.743}], 'summary': 'Malloc returns memory address for x to store 42, a pointer concept.', 'duration': 25.94, 'max_score': 6779.332, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI6779332.jpg'}], 'start': 6501.321, 'title': 'Memory and pointer concepts', 'summary': 'Delves into memory manipulation, hacking, and pointer concepts, emphasizing the dangers of misuse and providing practical examples. it includes a programmer humor reference from xkcd and addresses pass by value vs. pass by reference in function calls.', 'chapters': [{'end': 6539.677, 'start': 6501.321, 'title': 'Memory manipulation and hacking', 'summary': 'Discusses the ability to manipulate memory and hack into its contents, providing a powerful tool for exploitation, as well as a programmer humor reference from xkcd.', 'duration': 38.356, 'highlights': ['The ability to manipulate memory and hack into its contents provides great power for exploitation.', 'Programmer humor reference from XKCD is also discussed.', 'The chapter introduces the concept of having a great power to manipulate memory.']}, {'end': 7279.6, 'start': 6539.677, 'title': 'Understanding pointers and pointer misuse', 'summary': 'Explains the concepts of pointers and their misuse, highlighting the dangers of misunderstanding garbage values and the importance of proper pointer allocation and referencing, as demonstrated through a code example. it also addresses the common issue of pass by value vs. pass by reference in function calls, showcasing a practical example and its implications.', 'duration': 739.923, 'highlights': ['The dangers of misunderstanding garbage values and the importance of proper pointer allocation and referencing Misunderstanding garbage values as valid pointers can lead to computer crashes or segmentation faults, emphasizing the need for proper allocation and referencing of pointers.', 'Practical example showcasing the issue of pass by value vs. pass by reference in function calls The code example of a swap function illustrates the implications of pass by value in function calls, highlighting the importance of understanding the differences between passing variables by value and by reference.', 'Demonstration of pointer allocation and dereferencing through code examples The transcript provides code examples demonstrating pointer allocation and dereferencing, showing the step-by-step process of setting up pointers and pointees and using the dereference operator to access and modify pointee values.']}], 'duration': 778.279, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI6501321.jpg', 'highlights': ['The chapter introduces the concept of having a great power to manipulate memory.', 'Practical example showcasing the issue of pass by value vs. pass by reference in function calls.', 'Demonstration of pointer allocation and dereferencing through code examples.', 'The ability to manipulate memory and hack into its contents provides great power for exploitation.', 'The dangers of misunderstanding garbage values and the importance of proper pointer allocation and referencing.']}, {'end': 8719.91, 'segs': [{'end': 7884.398, 'src': 'heatmap', 'start': 7705.057, 'weight': 0.766, 'content': [{'end': 7707.698, 'text': 'whatever is at locations B contents.', 'start': 7705.057, 'duration': 2.641}, {'end': 7712.819, 'text': 'And then lastly we want to copy temp into whatever is at location B.', 'start': 7708.338, 'duration': 4.481}, {'end': 7718.221, 'text': "So again, we're very deliberately introducing all of these stars because we don't want to change any of these addresses.", 'start': 7712.819, 'duration': 5.402}, {'end': 7725.523, 'text': 'We want to go to these addresses per the D reference operator and put values there or get values from.', 'start': 7718.501, 'duration': 7.022}, {'end': 7727.504, 'text': 'So what does this actually mean??', 'start': 7726.283, 'duration': 1.221}, {'end': 7733.807, 'text': "Well, if I kind of rewind in this story and I go back here, I still have temp, although I'm going to delete its value to begin with.", 'start': 7727.544, 'duration': 6.263}, {'end': 7743.513, 'text': "I still have B and I still have a but what's going to be different this time is how I use a and B.", 'start': 7734.328, 'duration': 9.185}, {'end': 7744.754, 'text': 'So let me finish erasing those.', 'start': 7743.513, 'duration': 1.241}, {'end': 7745.974, 'text': "That's a on the left.", 'start': 7745.134, 'duration': 0.84}, {'end': 7748.296, 'text': 'This is B on the right at this point in the story.', 'start': 7746.014, 'duration': 2.282}, {'end': 7752.718, 'text': "We're rerunning swap with this new and improved version and let's see what happens.", 'start': 7748.516, 'duration': 4.202}, {'end': 7756.718, 'text': 'Well, X is presumably at some address.', 'start': 7753.299, 'duration': 3.419}, {'end': 7759.921, 'text': "Maybe it's like O X 123 as always.", 'start': 7756.898, 'duration': 3.023}, {'end': 7767.308, 'text': "What then does a get when I'm using this code? The value of a is O X 123.", 'start': 7760.582, 'duration': 6.726}, {'end': 7768.329, 'text': 'What is the value of B??', 'start': 7767.308, 'duration': 1.021}, {'end': 7771.712, 'text': 'Maybe why is that O X 456?', 'start': 7768.409, 'duration': 3.303}, {'end': 7772.433, 'text': 'What goes in B??', 'start': 7771.712, 'duration': 0.721}, {'end': 7776.917, 'text': "Well, I'm gonna put O X 456.", 'start': 7772.733, 'duration': 4.184}, {'end': 7779.72, 'text': 'And then what am I going to do based on these three lines of code??', 'start': 7776.917, 'duration': 2.803}, {'end': 7783.783, 'text': "I'm going to store in temp whatever is at the address in a.", 'start': 7780.2, 'duration': 3.583}, {'end': 7784.944, 'text': 'what is the address in a?', 'start': 7783.783, 'duration': 1.161}, {'end': 7785.725, 'text': "that's this thing here.", 'start': 7784.944, 'duration': 0.781}, {'end': 7788.407, 'text': "So I'm gonna put one in temp line two.", 'start': 7785.945, 'duration': 2.462}, {'end': 7790.549, 'text': "I'm gonna go to be all right.", 'start': 7788.968, 'duration': 1.581}, {'end': 7791.17, 'text': 'B is 456.', 'start': 7790.749, 'duration': 0.421}, {'end': 7798.656, 'text': "So I'm going to be and I'm gonna store two at whatever is at location a and at location a is 123.", 'start': 7791.17, 'duration': 7.486}, {'end': 7799.116, 'text': "So that's this.", 'start': 7798.656, 'duration': 0.46}, {'end': 7802.94, 'text': "So what am I going to do? I'm going to change this one to a two.", 'start': 7799.156, 'duration': 3.784}, {'end': 7809.413, 'text': 'last line of code, get the value of temp which is one and then put it at whatever the location B is.', 'start': 7804.008, 'duration': 5.405}, {'end': 7815.739, 'text': 'So B 456 go there and change it to be the value of temp tmp which puts one here.', 'start': 7809.473, 'duration': 6.266}, {'end': 7817.421, 'text': "That's it for the code.", 'start': 7816.46, 'duration': 0.961}, {'end': 7818.822, 'text': "There's still no return value.", 'start': 7817.481, 'duration': 1.341}, {'end': 7823.544, 'text': 'swap returns which means these three temporary variables are sort of garbage values.', 'start': 7819.182, 'duration': 4.362}, {'end': 7826.304, 'text': 'Now they can be reused by subsequent function calls.', 'start': 7823.604, 'duration': 2.7}, {'end': 7834.187, 'text': "But now I've actually swapped the values of X and Y, which is to say what came as naturally as the real world here,", 'start': 7826.345, 'duration': 7.842}, {'end': 7840.609, 'text': 'for Mariana is not quite as simply done in C, because again functions are sort of isolated from each other.', 'start': 7834.187, 'duration': 6.422}, {'end': 7843.75, 'text': 'You can pass in values but you get copies of those values.', 'start': 7840.869, 'duration': 2.881}, {'end': 7851.216, 'text': "If you want one function to affect the value of a variable somewhere else, You have to one understand what's going on.", 'start': 7844.151, 'duration': 7.065}, {'end': 7854.498, 'text': 'but to pass things in as by a pointer here,', 'start': 7851.216, 'duration': 3.282}, {'end': 7858.32, 'text': 'So if I go back to my code here, I need to make a few changes.', 'start': 7854.958, 'duration': 3.362}, {'end': 7860.001, 'text': 'Now let me get rid of these extra print deaths.', 'start': 7858.38, 'duration': 1.621}, {'end': 7862.562, 'text': 'Let me go in and add all these stars.', 'start': 7860.721, 'duration': 1.841}, {'end': 7869.025, 'text': "So I'm dereferencing these actual addresses here and here and I've got to make one more change.", 'start': 7863.523, 'duration': 5.502}, {'end': 7878.735, 'text': 'How do I now call swap if swap is expecting an in star and an in star that is the address of an end and the address of another end.', 'start': 7869.866, 'duration': 8.869}, {'end': 7884.398, 'text': 'What do I change on line 11 here? Yeah, sorry.', 'start': 7879.515, 'duration': 4.883}], 'summary': 'Explanation of using pointers in c and swapping values.', 'duration': 179.341, 'max_score': 7705.057, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI7705057.jpg'}, {'end': 7743.513, 'src': 'embed', 'start': 7708.338, 'weight': 3, 'content': [{'end': 7712.819, 'text': 'And then lastly we want to copy temp into whatever is at location B.', 'start': 7708.338, 'duration': 4.481}, {'end': 7718.221, 'text': "So again, we're very deliberately introducing all of these stars because we don't want to change any of these addresses.", 'start': 7712.819, 'duration': 5.402}, {'end': 7725.523, 'text': 'We want to go to these addresses per the D reference operator and put values there or get values from.', 'start': 7718.501, 'duration': 7.022}, {'end': 7727.504, 'text': 'So what does this actually mean??', 'start': 7726.283, 'duration': 1.221}, {'end': 7733.807, 'text': "Well, if I kind of rewind in this story and I go back here, I still have temp, although I'm going to delete its value to begin with.", 'start': 7727.544, 'duration': 6.263}, {'end': 7743.513, 'text': "I still have B and I still have a but what's going to be different this time is how I use a and B.", 'start': 7734.328, 'duration': 9.185}], 'summary': 'Introducing stars to preserve addresses, accessing values using d reference operator.', 'duration': 35.175, 'max_score': 7708.338, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI7708338.jpg'}, {'end': 8146.46, 'src': 'heatmap', 'start': 8053.571, 'weight': 0.866, 'content': [{'end': 8058.435, 'text': 'This is what you would have had to type essentially in week one just to get an end from the user.', 'start': 8053.571, 'duration': 4.864}, {'end': 8061.117, 'text': "And there's a whole bunch of things that can go wrong still.", 'start': 8058.755, 'duration': 2.362}, {'end': 8064.7, 'text': "But that's the cryptic syntax we would have had to show you in week one.", 'start': 8061.677, 'duration': 3.023}, {'end': 8066.541, 'text': 'Let me go ahead and make scan F here.', 'start': 8064.98, 'duration': 1.561}, {'end': 8069.784, 'text': 'Oops Uh user error.', 'start': 8066.561, 'duration': 3.223}, {'end': 8071.345, 'text': 'Put the semi colon in the wrong place.', 'start': 8069.964, 'duration': 1.381}, {'end': 8073.347, 'text': 'Make scan F enter.', 'start': 8072.025, 'duration': 1.322}, {'end': 8074.247, 'text': 'Oh my God.', 'start': 8073.827, 'duration': 0.42}, {'end': 8076.789, 'text': "Non void doesn't return a value.", 'start': 8075.288, 'duration': 1.501}, {'end': 8081.233, 'text': 'Oh thank you.', 'start': 8080.452, 'duration': 0.781}, {'end': 8085.213, 'text': 'Start to make scan F.', 'start': 8082.611, 'duration': 2.602}, {'end': 8085.733, 'text': 'There we go.', 'start': 8085.213, 'duration': 0.52}, {'end': 8087.034, 'text': 'Okay So scan F.', 'start': 8085.833, 'duration': 1.201}, {'end': 8089.776, 'text': "I'm gonna type in a number like 50 and it just prints it back out.", 'start': 8087.034, 'duration': 2.742}, {'end': 8093.819, 'text': 'So that is the sort of traditional way of implementing something like get in.', 'start': 8089.876, 'duration': 3.943}, {'end': 8099.043, 'text': 'The problem though is when you start to get into strings, things get dangerous quickly.', 'start': 8094.159, 'duration': 4.884}, {'end': 8102.405, 'text': 'Let me delete all this and give myself a string s.', 'start': 8099.103, 'duration': 3.302}, {'end': 8104.106, 'text': "Although wait a minute, we don't call it strings anymore.", 'start': 8102.405, 'duration': 1.701}, {'end': 8106.588, 'text': 'Char star to store a string.', 'start': 8104.507, 'duration': 2.081}, {'end': 8110.271, 'text': 'Then let me go ahead and just prompt the user for a string using just print F.', 'start': 8107.048, 'duration': 3.223}, {'end': 8117.736, 'text': 'Then let me go ahead and use scan f ask them for a string this time with percent s and store it at that address.', 'start': 8110.871, 'duration': 6.865}, {'end': 8123.199, 'text': 'Then let me go ahead and print out whatever the human typed in just by using the same notation.', 'start': 8118.216, 'duration': 4.983}, {'end': 8127.542, 'text': 'So here line five is the same thing as string s.', 'start': 8123.74, 'duration': 3.802}, {'end': 8129.523, 'text': "But we've taken back that layer today.", 'start': 8127.542, 'duration': 1.981}, {'end': 8131.385, 'text': "So it's char star s.", 'start': 8129.584, 'duration': 1.801}, {'end': 8132.485, 'text': 'This is just week one.', 'start': 8131.385, 'duration': 1.1}, {'end': 8141.833, 'text': "This is just week one line seven is new scan f will also read from the human's keyboard a string and store it at S.", 'start': 8133.126, 'duration': 8.707}, {'end': 8143.495, 'text': "But that's okay because S is an address.", 'start': 8141.833, 'duration': 1.662}, {'end': 8146.46, 'text': "It's correct not to do the ampersand.", 'start': 8143.676, 'duration': 2.784}], 'summary': 'Demonstration of traditional implementation of input in c, with potential errors and syntax issues.', 'duration': 92.889, 'max_score': 8053.571, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI8053571.jpg'}, {'end': 8512.066, 'src': 'heatmap', 'start': 8313.014, 'weight': 1, 'content': [{'end': 8319.397, 'text': "But if we hadn't given you get string, you would have had to do stuff like this knowing about malloc already or knowing about strings being a raise.", 'start': 8313.014, 'duration': 6.383}, {'end': 8326.8, 'text': "And even now there's a danger if the human types in five letters, six letters, 100 letters, this code like with the hello input,", 'start': 8319.458, 'duration': 7.342}, {'end': 8328.842, 'text': 'will probably just crash, which is bad.', 'start': 8326.8, 'duration': 2.042}, {'end': 8330.022, 'text': 'So get string.', 'start': 8329.262, 'duration': 0.76}, {'end': 8338.304, 'text': 'also has this functionality built in, where we have a fancy loop inside such that we allocate, using malloc, as many bytes as you physically type in,', 'start': 8330.022, 'duration': 8.282}, {'end': 8343.025, 'text': 'and we use malloc essentially every keystroke the moment you type in H, E, L, L, O.', 'start': 8338.304, 'duration': 4.721}, {'end': 8350.386, 'text': "We're sort of like laying the tracks as we go and we keep allocating more and more memory so that we theoretically will never crash with get string,", 'start': 8343.025, 'duration': 7.361}, {'end': 8357.567, 'text': "even though it's this easy to crap, this easy to crash your code using scan F if you again did it without the help of a library.", 'start': 8350.386, 'duration': 7.181}, {'end': 8360.111, 'text': 'So where are we all going with this?', 'start': 8358.308, 'duration': 1.803}, {'end': 8364.678, 'text': 'Well, let me show you a few final examples that will pave the way for what will be problem set, for.', 'start': 8360.151, 'duration': 4.527}, {'end': 8369.325, 'text': "let me go ahead and open up from today's code, which is available on the course's website.", 'start': 8364.678, 'duration': 4.647}, {'end': 8377.996, 'text': 'For instance, a program like this uh called phone book dot C.', 'start': 8370.005, 'duration': 7.991}, {'end': 8382.52, 'text': "And I'm just gonna give you a quick tour of it that you'll see more details on in the context of P set for itself.", 'start': 8377.996, 'duration': 4.524}, {'end': 8384.221, 'text': "We're gonna introduce a few new functions.", 'start': 8382.799, 'duration': 1.422}, {'end': 8389.544, 'text': "You're gonna see you're gonna see a function called F open which stands for file open and it takes two arguments.", 'start': 8384.341, 'duration': 5.203}, {'end': 8391.544, 'text': 'the name of a file to open like a C.', 'start': 8389.764, 'duration': 1.78}, {'end': 8391.904, 'text': 'S V.', 'start': 8391.544, 'duration': 0.36}, {'end': 8400.346, 'text': 'That you might manipulate in excel or google spreadsheets or the like comma separated values and then something like a for append or for read W.', 'start': 8391.904, 'duration': 8.442}, {'end': 8404.287, 'text': 'For right depending on whether you want to add to the file, just open it up or change it.', 'start': 8400.346, 'duration': 3.941}, {'end': 8407.548, 'text': "We're going to introduce you to a file pointer.", 'start': 8405.287, 'duration': 2.261}, {'end': 8413.569, 'text': "You'll see that capital file which is a little non conventional capital file is a pointer to an actual file.", 'start': 8407.908, 'duration': 5.661}, {'end': 8418.731, 'text': "on the computer's hard drive so that you can actually access something like a csv file or heck even images.", 'start': 8413.929, 'duration': 4.802}, {'end': 8424.774, 'text': "And we're going to see down below that you're also going to have the ability to write files as well or print to files.", 'start': 8419.072, 'duration': 5.702}, {'end': 8430.998, 'text': "You'll see functions like print f, print f for file, print f or f right file right?", 'start': 8425.115, 'duration': 5.883}, {'end': 8439.923, 'text': "Which, now that you will begin to understand pointers, you'll have the ability to actually not only read files, text files, images, other things,", 'start': 8431.338, 'duration': 8.585}, {'end': 8441.144, 'text': 'but also write them out.', 'start': 8439.923, 'duration': 1.221}, {'end': 8447.929, 'text': 'In fact, for instance, just as a teaser here, JPEGs will be one of the things we focus on this week,', 'start': 8441.404, 'duration': 6.525}, {'end': 8455.376, 'text': 'where we give you a forensic image and your goal is to recover as many photographs from this forensic image of like a digital camera as you possibly can.', 'start': 8447.929, 'duration': 7.447}, {'end': 8464.263, 'text': "And the way you're going to do that is by knowing in advance that every JPEG in the world starts with these three bites written in hexadecimal.", 'start': 8455.756, 'duration': 8.507}, {'end': 8465.363, 'text': 'But these three numbers.', 'start': 8464.303, 'duration': 1.06}, {'end': 8471.107, 'text': "And so in fact, just as a teaser, let me open up an example you'll see on the course's website for today.", 'start': 8465.844, 'duration': 5.263}, {'end': 8475.73, 'text': "If I scroll through here, you'll see a program that does a little something like this.", 'start': 8471.888, 'duration': 3.842}, {'end': 8476.691, 'text': 'And again, more on this.', 'start': 8475.93, 'duration': 0.761}, {'end': 8480.755, 'text': 'And if we could hit the There we go.', 'start': 8476.751, 'duration': 4.004}, {'end': 8486.121, 'text': "So here we have the notion of a bite we're going to create for ourselves.", 'start': 8481.095, 'duration': 5.026}, {'end': 8488.884, 'text': "We'll see a data type called bite, which is a common convention.", 'start': 8486.161, 'duration': 2.723}, {'end': 8495.131, 'text': "This gives me three bites and you're going to learn about a function called every, which reads from a file some number of bites,", 'start': 8489.144, 'duration': 5.987}, {'end': 8496.172, 'text': 'for instance three bites.', 'start': 8495.131, 'duration': 1.041}, {'end': 8503.819, 'text': 'We might then use code like this if bytes bracket zero equals equals O, X, F, F and bytes bracket one equals zero, X,', 'start': 8496.713, 'duration': 7.106}, {'end': 8507.062, 'text': 'D eight and bytes bracket two equals zero X, F, F.', 'start': 8503.819, 'duration': 3.243}, {'end': 8509.624, 'text': 'All three of those bites I just claimed represent a JPEG.', 'start': 8507.062, 'duration': 2.562}, {'end': 8512.066, 'text': "You'll see an output like this.", 'start': 8510.044, 'duration': 2.022}], 'summary': 'Introduction to file handling and memory allocation in c programming, with a teaser on recovering jpeg images.', 'duration': 199.052, 'max_score': 8313.014, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI8313013.jpg'}, {'end': 8611.096, 'src': 'embed', 'start': 8587.178, 'weight': 0, 'content': [{'end': 8593.562, 'text': "And just to end on a note here, I have a version of this code ready to go that doesn't implement all of those filters.", 'start': 8587.178, 'duration': 6.384}, {'end': 8598.606, 'text': 'It just implements one filter initially Let me go ahead and just ready this on my computer here.', 'start': 8593.622, 'duration': 4.984}, {'end': 8605.091, 'text': "I'm gonna go into my own version of filter and you'll see a few files that will give you a tour of this coming week in bitmap.", 'start': 8599.126, 'duration': 5.965}, {'end': 8611.096, 'text': 'dot H, for instance, is a version of this structure that I claimed existed a moment ago.', 'start': 8605.091, 'duration': 6.005}], 'summary': 'Code version ready with one filter, files for tour in bitmap', 'duration': 23.918, 'max_score': 8587.178, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI8587178.jpg'}], 'start': 7279.68, 'title': 'Memory management, pointers, user input dangers, and file handling in c', 'summary': 'Covers conventional memory usage, stack and heap memory implications, memory overflow issues, flawed logic in the swap function, pointers for memory management, dangers of user input using scanf, and file handling for image processing in c.', 'chapters': [{'end': 7579.293, 'start': 7279.68, 'title': 'Memory management and function logic', 'summary': 'Explains the conventional memory usage within a computer, highlighting the implications of using stack and heap memory, and the potential issues of memory overflow, emphasizing the flawed logic in the swap function and the significance of memory conventions.', 'duration': 299.613, 'highlights': ['The conventional memory usage within a computer involves storing machine code at the top, followed by global variables, heap, and stack memory. The computer stores machine code at the top of memory, followed by global variables, heap, and stack memory.', 'The potential issue of memory overflow is highlighted, emphasizing the consequences of excessive usage of heap and stack memory, leading to program crashes or errors. Excessive usage of heap and stack memory can lead to memory overflow, causing program crashes or errors.', 'The flawed logic in the swap function is explained through a visual representation of memory blocks, showcasing the incorrect handling of variables and the absence of a return value. The flawed logic in the swap function is demonstrated through a visual representation of memory blocks, illustrating the incorrect handling of variables and the absence of a return value.']}, {'end': 7934.673, 'start': 7579.593, 'title': 'Memory management in c', 'summary': 'Explains the use of pointers in c to manage memory and swap values, emphasizing the need to pass addresses to modify variables and the drawbacks of passing values to functions.', 'duration': 355.08, 'highlights': ['The chapter explains the use of pointers in C to manage memory and swap values. The transcript highlights the use of pointers in C for memory management and value swapping, illustrating the concept of passing addresses to modify variables.', 'Emphasizes the need to pass addresses to modify variables in C. It emphasizes the need to pass addresses, or pointers, rather than values to modify variables in C, showcasing the limitations of passing values to functions.', 'Illustrates the drawbacks of passing values to functions in C. The transcript illustrates the drawbacks of passing values to functions in C, highlighting the need to understand memory management and use pointers for efficient variable modification.']}, {'end': 8350.386, 'start': 7935.053, 'title': 'The dangers of user input in c', 'summary': 'Discusses the potential dangers of using traditional input functions like scanf for user input in c, highlighting the vulnerabilities and potential crashes that can occur due to insufficient memory allocation when dealing with strings.', 'duration': 415.333, 'highlights': ['Traditional input functions like scanf for user input in C can lead to potential crashes and vulnerabilities due to insufficient memory allocation, as illustrated by the examples involving string inputs. The chapter discusses the dangers of using traditional input functions like scanf for user input in C, highlighting the vulnerabilities and potential crashes that can occur due to insufficient memory allocation when dealing with strings. It demonstrates the issues with string inputs and the need for proper memory allocation to avoid crashes.', 'The use of get_string with its built-in functionality for dynamic memory allocation using malloc is emphasized as a safer alternative for handling user input, as it allocates memory for each keystroke to prevent crashes. The chapter emphasizes the use of get_string as a safer alternative for handling user input, highlighting its built-in functionality for dynamic memory allocation using malloc. It explains how get_string allocates memory for each keystroke, preventing potential crashes and ensuring safer handling of user input.']}, {'end': 8719.91, 'start': 8350.386, 'title': 'File handling and image processing in c', 'summary': 'Introduces file handling in c, including the use of functions like f open and file pointers, and provides examples of image processing through file manipulation and implementation of filters, paving the way for the upcoming problem set.', 'duration': 369.524, 'highlights': ['The chapter introduces file handling in C, including the use of functions like F open and file pointers. Functions like F open and file pointers are introduced, providing a foundation for file manipulation in C.', 'Examples of image processing through file manipulation and implementation of filters are provided. The chapter presents examples of file manipulation for image processing, including the implementation of filters and image file format conversion.', 'The chapter paves the way for the upcoming problem set. The content prepares the audience for the upcoming problem set by providing a glimpse of the concepts and tools that will be utilized.']}], 'duration': 1440.23, 'thumbnail': 'https://coursnap.oss-ap-southeast-1.aliyuncs.com/video-capture/nvO1sq_b_zI/pics/nvO1sq_b_zI7279680.jpg', 'highlights': ['The potential issue of memory overflow is highlighted, emphasizing the consequences of excessive usage of heap and stack memory, leading to program crashes or errors.', 'The chapter discusses the dangers of using traditional input functions like scanf for user input in C, highlighting the vulnerabilities and potential crashes that can occur due to insufficient memory allocation when dealing with strings.', 'The chapter presents examples of file manipulation for image processing, including the implementation of filters and image file format conversion.', 'The chapter explains the use of pointers in C to manage memory and swap values, illustrating the concept of passing addresses to modify variables.']}], 'highlights': ['The chapter introduces malloc and free functions for dynamic memory allocation.', 'The importance of memory management in C programming is emphasized, including the use of malloc and free functions for memory allocation and deallocation, ensuring efficient memory usage and preventing memory leaks.', "The computer automatically remembers the size of allocated memory, allowing for the proper deallocation of memory by using free, exemplified by the handling of 'T' in the code.", 'The chapter introduces the Valgrind tool and its capability to detect memory-related bugs in code. The speaker introduces the Valgrind tool as a means to detect memory-related bugs in code, demonstrating its output and the ability to identify issues such as invalid memory accesses and memory leaks.', 'The concept of garbage values and the importance of initializing variables to avoid potential security vulnerabilities are discussed. The concept of garbage values is explained, emphasizing the importance of initializing variables to avoid potential security vulnerabilities, such as exposing sensitive information stored in memory.', 'The chapter discusses the usage of malloc and strcpy for copying strings and the potential memory problems that can arise. The speaker explains the usage of malloc and strcpy for copying strings and the potential memory problems that can arise, such as buffer overflow, when insufficient memory is allocated for the copied string.', 'The significance of using malloc with functions like strcpy is explained, emphasizing the need for properly allocated memory space to accommodate the copied characters and the trailing null character, preventing memory wastage and potential program errors.', 'The chapter explores the concept of pointers, pointer arithmetic, and string representation.', "The program is modified to compare two strings, demonstrating the differences in comparing data types The program is then modified to compare two strings using the '==' operator, showcasing the process of asking for user input for strings and the differences in comparing string values.", 'The potential issue of memory overflow is highlighted, emphasizing the consequences of excessive usage of heap and stack memory, leading to program crashes or errors.']}