整型变量(int)与字节数组(byte[])的相互转换

// int2byte.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <Windows.h>

/*
#define MAKEWORD(a, b)  ((WORD)(((BYTE)(((DWORD_PTR)(a)) & 0xff)) | ((WORD)((BYTE)(((DWORD_PTR)(b)) & 0xff))) << 8))
#define MAKELONG(a, b)  ((LONG)(((WORD)(((DWORD_PTR)(a)) & 0xffff)) | ((DWORD)((WORD)(((DWORD_PTR)(b)) & 0xffff))) << 16))
#define LOWORD(l)   ((WORD)(((DWORD_PTR)(l)) & 0xffff))
#define HIWORD(l)   ((WORD)((((DWORD_PTR)(l)) >> 16) & 0xffff))
#define LOBYTE(w)   ((BYTE)(((DWORD_PTR)(w)) & 0xff))
#define HIBYTE(w)   ((BYTE)((((DWORD_PTR)(w)) >> 8) & 0xff))
*/

// ==========================================================
//   Big Endian / Small Endian utility functions
// ==========================================================
BOOL IsSmallEndian()
{
  DWORD wd = 0x22; 
  if( *((BYTE *)&wd) == 0x22 )  // Small Endian
    return TRUE;
  else
    return FALSE;
}

void SwapShort(WORD *sp) {
    BYTE *cp = (BYTE *)sp, t = cp[0]; cp[0] = cp[1]; cp[1] = t;
}

void SwapLong(DWORD *lp) {
    BYTE *cp = (BYTE *)lp, t = cp[0]; cp[0] = cp[3]; cp[3] = t;
    t = cp[1]; cp[1] = cp[2]; cp[2] = t;
}

// int 2 byte
BYTE *Int2Byte(int nVal)
{
  BYTE *pByte = new BYTE[4];
  for (int i = 0; i<4;i++)
  {
    pByte[i] = (BYTE)(nVal >> 8*(3-i) & 0xff);
  }
  return pByte;
}

// byte 2 int
int Byte2Int(BYTE *pb)
{
  // assume the length of pb is 4
  int nValue=0;
  for(int i=0;i < 4; i++)
  {
    nValue += ( pb[i] & 0xFF)<<(8*(3-i));
  }
  return nValue;
}

int _tmain(int argc, _TCHAR* argv[])
{
  //PC， 小端字节

  //
  BYTE *byte = Int2Byte(0x12345678);
  printf("byte[0]=0x%xh,byte[1]=0x%xh,byte[2]=0x%xh, byte[3]=0x%xh\n", byte[0], byte[1], byte[2],byte[3]);

  int nVal = Byte2Int(byte);
  printf("nVal=0x%xh\n\n",nVal);



  //
  // 小端字节应该是得到 0xefcdab89, 大端得到0x89abcdef
  WORD wLow, wHigh;
  DWORD dwData;

  BYTE b[4] = {0x89, 0xab, 0xcd, 0xef};
  DWORD dwVal = 0xefcdab89;

  // DWORD分解成BYTE数组
  WORD lo = LOWORD(dwVal),
    hi = HIWORD(dwVal);

  printf("lo=0x%xh,hi=0x%xh\n", lo, hi);

  //BYTE数组组合成DWORD
  wLow = MAKEWORD(b[0],b[1]);
  wHigh = MAKEWORD(b[2], b[3]);
  dwData = MAKELONG(wLow, wHigh);
  printf("wLow=0x%xh,wHigh=0x%xh,dwData=0x%xh\n", wLow, wHigh, dwData);

  getchar();
  return 0;
}