Getting filesize the Expert Way

#include <stdio.h>

#define MAXNUMBER 1024

int main()
{
    int i;
    char a[MAXNUMBER];

    FILE *fp = popen("du -b  /bin/bash", "r");

    while((a[i++] = getc(fp))!= 9)
        ;

    a[i] ='\0';

    printf(" a is %s\n", a);

    pclose(fp);
    return 0;
}

Is executing an other process "the expert way"?

#include <stdio.h>

long file_size(FILE* f, int discard_pos)
{
  long tmp;
  long ret;
  if (!discard_pos)
    tmp = ftell(f);

  fseek(f, 0, SEEK_END);
  ret = ftell(f);

  if (!discard_pos)
    fseek(f, tmp, SEEK_SET);

  return ret;
}

>>3
This is from: http://stackoverflow.com/questions/238603/how-can-i-get-a-files-size-in-c/246855#246855