#include <stdio.h>

long int filesize( FILE *fp )
  {
    long int save_pos, size_of_file;

    save_pos = ftell( fp );
    fseek( fp, 0L, SEEK_END );
    size_of_file = ftell( fp );
    fseek( fp, save_pos, SEEK_SET );
    return( size_of_file );
  }

void main()
  {
    FILE *fp;

    fp = fopen( "file", "r" );
    if( fp != NULL ) {
      printf( "File size=%ld\n", filesize( fp ) );
      fclose( fp );
    }
  }