int main(int argh,char ** argue){
  union uni{
       short s;
       char c[2];
   } un;
   un.s = 0x0102;
   std::cout << un.c[0] << "\t" << un.c[1] << std::endl;
   if(un.c[0] == 1 && un.c[1] == 2){
       std::cout << "大端字节序" << std::endl;
   } else if (un.c[0] == 2 && un.c[1] == 1){
       std::cout << "小端字节序" << std::endl;
   }
}

共用体共用一块内存，short 占 8 位，最大存储为 0XFF （255)， 0x0102 = 208会占两个字节