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cstringfilememory

C: How to read an entire file into a buffer

I want to read the contents of a file into a buffer.

What would be the most efficient and portable option?

Solution

  • Portability between Linux and Windows is a headache, since Linux is a POSIX-conformant system with high-quality toolchain for C; whereas, Windows does not.

    If you stick to the standard and don't mind a race condition (between getting the file's size and reading the contents), this may suffice:

    #include <stdio.h>
#include <stdlib.h>

FILE *f = fopen("textfile.txt", "rb");
fseek(f, 0, SEEK_END);
long fsize = ftell(f);
fseek(f, 0, SEEK_SET);  /* same as rewind(f); */

char *string = malloc(fsize + 1);
fread(string, fsize, 1, f);
fclose(f);

string[fsize] = 0;

// use the string, then ...

free(string);

    Here string will contain the contents of the text file as a properly 0-terminated C string. This code is just standard C, it's not POSIX-specific (although that it doesn't guarantee it will work/compile on Windows).

    If you do care about the race condition, see this other answer.