Endianness test for C (untested)

endian.c

#include <stdio.h>

int is_little_endian(void)
{
        char buf[sizeof(unsigned int)];

        *(unsigned int *)buf = 1u;
        return (int)buf[0];
}

int main(void)
{
        printf("This host is %s endian.\n",
            is_little_endian() ? "little" : "big");

        return 0;
}