check whether the system is little or big endian

check_endian.c

#include <stdio.h>

int main(int argc, const char *argv[])
{
    int x = 1;
    char *y = (char*)&x;
    printf("If next line prints 1, then it's little-endian.\n")
    printf("%c\n", (*y)+48);
    return 0;
}


// Suppose we are on a 32-bit machine.
// 
// If it is little endian, the x in the memory will be something like:
// 
//        higher memory
//           ----->
//     +----+----+----+----+
//     |0x01|0x00|0x00|0x00|
//     +----+----+----+----+
//     A
//     |
//    &x
// so (char*)(*x) == 1, and *y+48 == '1'.
// 
// If it is big endian, it will be:
// 
//     +----+----+----+----+
//     |0x00|0x00|0x00|0x01|
//     +----+----+----+----+
//     A
//     |
//    &x
// so this one will be '0'.