如何判断CPU是大端还是小端模式

#include "stdio.h"
int main()
{
  union w
 {
  inta;  //4 bytes
  char b; //1byte
 } c;
  c.a=1;
  if (c.b==1)
  printf("It isLittle_endian!\n");
  else
  printf("It isBig_endian!\n");
  return 1;
}