Detecting byte order for cases where you need to know. Originally in Obj-C, adapted from iOS macOS Network Cookbook available on Safaribooks.com

byte_order.c

typedef enum {
    ET_Unknown,
    ET_Little,
    ET_Big
} endian_type_e;

endian_type_e byte_order()
{
    union {
        short num_as_short;
        char  num_as_char[sizeof(short)];
    } test;
    test.num_as_short = 0x0102;

    if (sizeof(short) == 2) {
        if (test.num_as_char[0] == 1 && test.num_as_char[1] == 2) {
            return ET_Big;
        }
        else if (test.num_as_char[0] == 2 && test.num_as_char[1] == 1) {
            return ET_Little;
        }
        else {
            return ET_Unknown;
        }
    }
    else
        return ET_Unknown;
}

int main(int argc, const char* argv[])
{
    const endian_type_e et = byte_order();
    (void)et;
    return 0;
}