Convert a file from little endian to big endian and vice versa

endian_swap.cpp

// usage: 
// ./endian_swap infile.lsb.ext outfile.msb.ext
// ./endian_swap infile.msb.ext outfile.lsb.ext 

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

int main(int argc, char** argv)
{
    FILE* input = NULL;
    FILE* output = NULL;
    unsigned long size = 0;
    unsigned long itr = 0;
    unsigned char* buffer;

    if(argc != 3)
        return 0;
    input = fopen(argv[1],"rb");
    output = fopen(argv[2],"wb");

    if(!input || !output)
        fprintf(stderr,"could not open file");
    fseek(input,0,SEEK_END);
    size = ftell(input);
    fseek(input,0,SEEK_SET);

    buffer = (unsigned char*)malloc(size);

    fread(buffer,1,size,input);
    fclose(input);
    for(itr = 0; itr<size; itr=itr+4)
    {
        fwrite(&buffer[itr + 3],1,1,output);
        fwrite(&buffer[itr + 2],1,1,output);
        fwrite(&buffer[itr + 1],1,1,output);
        fwrite(&buffer[itr + 0],1,1,output);
    }
    fclose(output);
    return 0;
}