reorder endian in 32bit words

reorder32.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

unsigned long bswap32 (unsigned long ul)
{
        return ((ul & 0x000000FF) << 24) | ((ul & 0x0000FF00) << 8)  |
                ((ul & 0x00FF0000) >> 8) | ((ul & 0xFF000000) >> 24);
}


int main(int argc, char *argv[])
{
  FILE *from, *to;
  unsigned int word;


  if(argc!=3) {
    printf("Usage: <source> <destination>\n");
    exit(1);
  }

  /* open source file */
  if((from = fopen(argv[1], "rb"))==NULL) {
    printf("Cannot open source file.\n");
    exit(1);
  }

  /* open destination file */
  if((to = fopen(argv[2], "wb"))==NULL) {
    printf("Cannot open destination file.\n");
    exit(1);
  }

  /* copy the file */
  do{

    bzero((void*)&word,sizeof(word));
    fread(&word,sizeof(word),1,from);
    if(ferror(from)) {
      printf("Error reading source file.\n");
      exit(1);
    }
    word = bswap32(word);
    fwrite(&word,4,1,to);
    if(ferror(to)) {
      printf("Error writing destination file.\n");
      exit(1);
    }

  }while(!feof(from));

  fclose(from);
  fclose(to);

  return 0;
}