CODEWITHSUNDEEP
cstdinfgetslibc
emily
emily

Reputation: 161

fgets() function in C

I know everybody has told me to use fgets and not gets because of buffer overflow. However, I am a bit confused about the third parameter in fgets(). As I understand it, fgets is dependent on:

char * fgets ( char * str, int num, FILE * stream );

char* str is the ptr to where my input will be stored.

num is the max number of character to be read.

but what is FILE *stream? If I am just prompting the user to enter a string (like a sentence) should I just type "stdin" ?

And should I type FILE *stdin at the top, near main()?

Upvotes: 16

Views: 40608

Answers (4)

Carl Norum
Carl Norum

Reputation: 225202

You are correct. stream is a pointer to a FILE structure, like that returned from fopen. stdin, stdout, and stderr are already defined for your program, so you can use them directly instead of opening or declaring them on your own.

For example, you can read from the standard input with:

fgets(buffer, 10, stdin);

Or from a specific file with:

FILE *f = fopen("filename.txt", "r");
fgets(buffer, 10, f);

Upvotes: 17

user108127
user108127

Reputation: 486

Broadly there are two ways you can communicate with files in C. One is using the low-level OS dependent system calls such as open(), read(), write() etc which work with file descriptors. Another one is using FILE structures which are used in C library functions like fread(), fwrite() etc including the one you mentioned above.

As it is with the UNIX philosophy, everything is a file. So even the standard input (stdin) is treated as a pointer to a FILE structure.

tl;dr Yes, you should use stdin for FILE* stream in your call to fgets()

Upvotes: 3

Brian Campbell
Brian Campbell

Reputation: 333266

Yes, you should just use stdin. That is a predefined FILE * that reads from the standard input of your program. And it should already be defined if you have a #include <stdio.h> at the top of your file (which you'll need for fgets).

Upvotes: 4

David Nehme
David Nehme

Reputation: 21597

FILE is the standard C file. Yes, if you want to read from standard input, stdin is the correct symbol.

Upvotes: 1

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