How can I clear the contents of a file

Question

I would like to know how the contents of a file can be cleared in C. I know it can be done using truncate, but I can't find any source clearly describing how.

Answer 1

The other answers explain how to use truncate correctly... but if you found yourself on a non-POSIX system that doesn't have unistd.h, then the easiest thing to do is just open the file for writing and immediately close it:

#include <stdio.h>

int main()
{
    FILE *file = fopen("asdf.txt", "w");
    if (!file)
    {
        perror("Could not open file");
    }

    fclose(file);
    return 0;
}

Opening a file with "w" (for write mode) "empties" the file so you can start overwriting it; immediately closing it then results in a 0-length file.