Endianess revertor.

#include<iostream>
#include<cstdio>
#include<unistd.h>
#include<getopt.h>

using namespace std;

int reverse(int);
void help(char *);
void big2lettle(int);
void lettle2big(int);

int main(int argc, char * argv[]) {
    bool reversed = false;
    char c;
    while((c=getopt(argc,argv,"r"))!=-1) {
        switch(c) {
        case 'r':
            reversed = true;
            break;
		case '-':
			goto breakpoint;
        case '?':
            help(argv[0]);
            break;
        default:
            abort();
        }
    }
breakpoint:
    if(argv[optind]==NULL)
        help(argv[0]);
    else {
        int x=atoi(argv[optind]);
        if(reversed) lettle2big(x);
        else big2lettle(x);
    }
    return 0;
}

void help(char * filename) {
    cout << "Usage: " << filename << " [-r] [--] integer" << endl;
    cout << "Convert a number from Big-endian to Small-endian, vise versa." << endl;
	cout << "  --           Separator for options and negative integer argument." << endl;
    cout << "  -r           Convert from Small-endian to Big-endian." << endl;
}

void big2lettle(int orig) {
    int converted = reverse(orig);
    cout << "Origional: " << orig << endl;
    printf("Big-endian: 0x%08X\n",orig);
    printf("Little-endian: 0x%08X\n",converted);
    cout << "Converted: " << converted << endl;
    return;
}

void lettle2big(int orig) {
    int converted = reverse(orig);
    cout << "Origional: " << orig << endl;
    printf("Lettle-endian: 0x%08X\n",converted);
    printf("Big-endian: 0x%08X\n",orig);
    cout << "Converted: " << converted << endl;
    return;
}

int reverse(int orig) {
    int res=0;
    for(int i=0; i<4; i++) {
        int byte=orig&0xff;
        int shifted=byte<<(3-i)*8;
        res|=shifted;
        orig>>=8;
    }
    return res;
}