check little or big endian.

gistfile1.c

#include <stdio.h>

int checkEndian(void) {
    union {
        int i;
        char ch;
    }c;
    c.i = 1;
    return (c.ch == 1);
}
int main(int argc, char *argv[]) {
    int rs;
    rs = checkEndian();
    if (rs == 1) {
        printf("little endian");
    } else {
        printf("big endian");
    }
    return 0;
}