Question

How do I set the size of a file in c ? Would I do this after I fopen?

Answer 1

Yes you would do it after fopen – you can create what is know as a sparse file

#include <stdio.h>
int main(void) {
        int X = 1024 * 1024 - 1;
        FILE *fp = fopen("myfile", "w");
        fseek(fp, X , SEEK_SET);
        fputc('\0', fp);
        fclose(fp);
}

That should create you a file for X Byte for whatever you need, in this case it’s 1MiB