File Pointers - CS50 Shorts

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CC BY-NC-SA 4.0
Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International Public License

David J. Malan

[JoeHartshorn]

fopen: 3:04
fclose 5:17
fgetc: 6:05
fputc: 9:35
fread: 11:24
fwrite: 15:20

@CS50 timestamps per topic on each of the shorts and walk-throughs, like with the lectures, would be great :)

[el_kraken]

Love these CS50 shorts. Doug has an incredible talent for teaching.

[labradoryshockdart]

Doug Lloyd is the Superman of CS50. He explained things very well that I don't understand from the lectures!

[jjhj_]

I'm really grateful for these free, incredibly high-quality online courses. Harvard's my hero for 2020

[krys]

I cant tell you how much these videos have helped me 😭😭😭😭 THANK YOU SO MUCH

[wade]

This is super informative. You summed up so much in such a short time.

[dinoman]

This is really helpful for understanding the recover problem in pset4

[colonizatorgg]

Nice tutorial man, very straightforward

[calintatar]

You gotta love Doug's T-shirts though

[annamaniuk]

The following code is incorrect:
char ch;
while ((ch = fgetc(file)) != EOF)
printf("%c", ch);

If we assume EOF <= 255, then there's a problem if the file contains the byte EOF: we would end the while loop as soon as we encounter this magic byte.
Otherwise (EOF > 255), then `ch`, because it is of type char, cannot possibly be > 255. therefore, ch will never be equal to EOF. The loop will never end.

This would be correct:
int ch;
while ((ch = fgetc(file)) != EOF)
printf("%c", ch);

[coffeeisthepathtovictory]

Definition of Ephemeral: lasting for a very short time
via google

[TornikeBatavani]

It is possible to use r+, w+ or a+ modes of fopen as well. They open a file for reading and writing, or reading and appending.

[amosp]

Thank you Doug for another informative short. But one thing in this video has me confused and I need a clarification from someone with a better understanding.
The statement made at the beginning of the video: "File pointers and pointers, while interrelated, are not exactly the same thing." What is being referred to as a 'file pointer' here? Is it the structure, i.e. FILE or the pointer to the structure i.e. FILE*? If it is the latter, isn't it the exact same thing as a pointer? If it is the former, then why in this case alone we've deviating from the convention used in CS50 to place the * closer to the data type and not the variable name? I've read up on the topic and I don't think I have a clear understanding yet, but... as far as I have seen, the FILE structure stores the data about the file, its position in memory on the disk and information for read/write operations such as the point up to which read/write has taken place and so on. Because it points to the file [even if the pointing isn't exactly of the same nature of a regular pointer], this struct is called a 'file pointer'. Our usage of that 'file pointer' i.e. the struct FILE always includes a pointer to that struct, i.e. FILE* because we will be passing it to functions, and because we need to pass by reference and not by value it is important to use 'file pointers' with a pointer to 'file pointers'. Now, I'm not sure if I have grasped this concept. If someone could clarify, I'd be grateful.

[Mrkichanpark]

finals is 2 days, this video is a life saver

[OK-rieu]

Thank you so much, I was in need for that little bit of information regarding fread, fwrite which you've helped me acquire.

[conraduouou]

it's my 5th time to watch this video and I can't seem to wrap my head around recover

[ejif]

Мне очень нравится, как доносит информацию Doug Lloyd. Интересно, понятно, плюс примеры Хорошего кода. Спасибо!!!

[Maen]

Thank you so much this is so useful and simple 🌹

[xrafter]

But that loop don't move the pointer?

[DogginsFroggins]

Honestly how are you supposed to do lab 4 without knowing this? I feel they over-estimate our ability to read documentation, but then again this makes me nervous for documentation in general.