Changing one byte in a file in C

Question

Let's say I have a file stream open and ready.

How do I seek a single byte in the stream and change it so that change is reflected on the file?

Answer 1

FILE* fileHandle = fopen("filename", "r+b"); // r+ if you need char mode
fseek(fileHandle, position_of_byte, SEEK_SET);
fwrite("R" /* the value to replace with */, 1, 1, fileHandle);

Answer 2

#include "stdio.h"

int main(void)
{
    FILE* f = fopen("so-data.dat", "r+b"); // Error checking omitted
    fseek(f, 5, SEEK_SET);
    fwrite("x", 1, 1, f);
    fclose(f);
}

Answer 3

#include <stdio.h> /* standard header, use the angle brackets */

int main(void)
{
    char somechar = 'x'; /* one-byte data */
    FILE* fp = fopen("so-data.txt", "r+");
    if (fp) {
      fseek(fp, 5, SEEK_SET);
      fwrite(&somechar, 1, 1, fp);
      fclose(fp);
    }
    return 0; /* if you are on non-C99 systems */
}