Checking Endianness of your Operating System

Sometimes when trying to debug oddities in your C programs, especially when doing cross-compilation to other architectures it is good to know when going from an x86 (Little Endian) to say an ARM processor running in Big Endian.  This is doubly useful when dealing with encryption keys or network packets.  If you have an encryption key on a desktop machine running in Little Endian, and the decryption key on a Big Endian system, you have to take into account the differing byte order.  There is a great Wikipedia article about Endianness if you would like to learn more. There is also a nifty C program you can compile to check the Endianess of your OS.

#include <stdio.h>
#include <stdlib.h>
 
int main()
{
    int x = 1;
 
    if (*(char *)&x == 1)
        fprintf(stderr, "Little Endian\n");
    else
        fprintf(stderr, "Big Endian\n");
 
    return 0;
}

To compile:

gcc -o endian endian.c

Then run:

erik@debian:~$ ./endian
Little Endian

Voila, now you know the Endianness of your Operating System.