CSAPP 习题2.46 xbyte

// 取出unsigned中的某一byte

#include <iostream>

using namespace std;

int xbyte (unsigned ui, int byte)
{
  int bias = (3 - byte) * 8 ;
  unsigned mask = ( 0xff<<24 );
  // cout << hex << mask << endl;
  int mediat = (ui << bias) & mask ;
  // cout << hex << mediat << endl;
  return ( mediat >> 24);
}

int main()
{
  cout << hex << xbyte(0x12345678, 2) << endl;
  return 0;
}