VC中BASE64编码和解码使用详解

base64可以用来将binary的字节序列数据编码成ASCII字符序列构成的文本。完整的base64定义可见 RFC1421和 RFC2045。编码后的数据比原始数据略长，为原来的4/3。在电子邮件中，根据RFC822规定，每76个字符，还需要加上一个回车换行。

转换的时候，将三个byte的数据，先后放入一个24bit的缓冲区中，先来的byte占高位。数据不足3byte的话，于缓冲区中剩下的Bit用0补足。然后，每次取出6个bit，按照其值选择ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/中的字符作为编码后的输出。不断进行，直到全部输入数据转换完成。如果最后剩下两个输入数据，在编码结果后加1个“=”；如果最后剩下一个输入数据，编码结果后加2个“=”；如果没有剩下任何数据，就什么都不要加，这样才可以保证资料还原的正确性。

base64_API.h  文件内容

#pragma once
#include "stdafx.h"

#include 

#ifdef  __cplusplus
extern "C" {
#endif


INT base64_Encode( const BYTE* inputBuffer, INT inputCount, TCHAR* outputBuffer );


INT base64_Decode( const TCHAR* inputBuffer, INT inputCount, BYTE* outputBuffer );

#ifdef __cplusplus
}
#endif

base64_API.cpp 文件内容

#pragma once

#include "stdafx.h"

#include "base64_API.h"

static const CHAR* DATA_BIN2ASCII = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

INT base64_Encode( const BYTE* inputBuffer, INT inputCount, TCHAR* outputBuffer )
{
  INT i;
  BYTE b0, b1, b2;

  if( (inputBuffer == NULL) || (inputCount < 0) )
  {
    return -1;  // 参数错误
  }

  if( outputBuffer != NULL )
  {
    for( i = inputCount; i > 0; i -= 3 )
    {
      if( i >= 3 )
      {  // 将3字节数据转换成4个ASCII字符
 b0 = *inputBuffer++;
 b1 = *inputBuffer++;
 b2 = *inputBuffer++;

 *outputBuffer++ = DATA_BIN2ASCII[b0 >> 2];
 *outputBuffer++ = DATA_BIN2ASCIi[((b0 << 4) | (b1 >> 4)) & 0x3F];
 *outputBuffer++ = DATA_BIN2ASCIi[((b1 << 2) | (b2 >> 6)) & 0x3F];
 *outputBuffer++ = DATA_BIN2ASCII[b2 & 0x3F];
      }
      else
      {
 b0 = *inputBuffer++;
 if( i == 2 )b1 = *inputBuffer++; else b1 = 0;

 *outputBuffer++ = DATA_BIN2ASCII[b0 >> 2];
 *outputBuffer++ = DATA_BIN2ASCIi[((b0 << 4) | (b1 >> 4)) & 0x3F];
 *outputBuffer++ = (i == 1) ? TEXT('=') : DATA_BIN2ASCIi[(b1 << 2) & 0x3F];
 *outputBuffer++ = TEXT('=');
      }
    } // End for i

    *outputBuffer++ = TEXT('/0');  // 添加字符串结束标记
  }

  return ((inputCount + 2) / 3) * 4;  // 返回有效字符个数
}

#define B64_EOLN      0xF0  // 换行/n
#define B64_CR 0xF1  // 回车/r
#define B64_EOF 0xF2  // 连字符-
#define B64_WS 0xE0  // 跳格或者空格（/t、space）
#define B64_ERROR   0xFF  // 错误字符
#define B64_NOT_base64(a)  (((a)|0x13) == 0xF3)

static const BYTE DATA_ASCII2BIN[128] = {
  0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xE0,0xF0,0xFF,0xFF,0xF1,0xFF,0xFF,
  0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
  0xE0,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x3E,0xFF,0xF2,0xFF,0x3F,
  0x34,0x35,0x36,0x37,0x38,0x39,0x3A,0x3B,0x3C,0x3D,0xFF,0xFF,0xFF,0x00,0xFF,0xFF,
  0xFF,0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E,
  0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,0xFF,0xFF,0xFF,0xFF,0xFF,
  0xFF,0x1A,0x1B,0x1C,0x1D,0x1E,0x1F,0x20,0x21,0x22,0x23,0x24,0x25,0x26,0x27,0x28,
  0x29,0x2A,0x2B,0x2C,0x2D,0x2E,0x2F,0x30,0x31,0x32,0x33,0xFF,0xFF,0xFF,0xFF,0xFF
};

INT base64_Decode( const TCHAR* inputBuffer, INT inputCount, BYTE* outputBuffer )
{
  INT i, j;
  BYTE b[4];
  TCHAR ch;

  if( (inputBuffer == NULL) || (inputCount < 0) )
  {
    return -1;  // 参数错误
  }

  // 去除头部空白字符
  while( inputCount > 0 )
  {
    ch = *inputBuffer;
    if( (ch < 0) || (ch >= 0x80) )
    {
      return -2;  // 数据错误，不在ASCII字符编码范围内
    }
    else
    {
      if( DATA_ASCII2BIN[ch] == B64_WS )
      {
 inputBuffer++;
 inputCount--;
      }
      else
      {
 break;
      }
    }
  }

  // 去除尾部的空白字符、回车换行字符、连字符
  while( inputCount >= 4 )
  {
    ch = inputBuffer[inputCount - 1];
    if( (ch < 0) || (ch >= 0x80) )
    {
      return -2;  // 数据错误，不在ASCII字符编码范围内
    }
    else
    {
      if( B64_NOT_base64(DATA_ASCII2BIN[ch]) )
      {
 inputCount--;
      }
      else
      {
 break;
      }
    }
  }

  // 字符串长度必须为4的倍数
  if( (inputCount % 4) != 0 )
  {
    return -2;  // 数据错误
  }

  if( outputBuffer != NULL )
  {
    for( i = 0; i < inputCount; i += 4 )
    {
      for( j = 0; j < 4; j++ )
      {
 ch = *inputBuffer++;
 if( (ch < 0) || (ch >= 0x80) )
 {
   return -2;  // 数据错误，不在ASCII字符编码范围内
 }
 else
 {
   if( ch == '=' )  // 发现base64编码中的填充字符
   {
     break;
   }
   else
   {
     b[j] = DATA_ASCII2BIN[ch];
     if( b[j] & 0x80 )
     {
return -2;  // 数据错误，无效的base64编码字符
     }
   }   
 }
      } // End for j

      if( j == 4 )
      {
 *outputBuffer++ = (b[0] << 2) | (b[1] >> 4);
 *outputBuffer++ = (b[1] << 4) | (b[2] >> 2 );
 *outputBuffer++ = (b[2] << 6) | b[3];
      }
      else if( j == 3 )
      {  // 有1个填充字节
 *outputBuffer++ = (b[0] << 2) | (b[1] >> 4);
 *outputBuffer++ = (b[1] << 4) | (b[2] >> 2 );

 return (i >> 2) * 3 + 2;
      }
      else if( j == 2 )
      {  // 有2个填充字节
 *outputBuffer++ = (b[0] << 2) | (b[1] >> 4);

 return (i >> 2) * 3 + 1;
      }
      else
      {
 return -2;  // 数据错误，无效的base64编码字符
      }      
    }  // End for i
  }

  return (inputCount >> 2) * 3;
}

采用以上方法就可以将二进制数据转换成可见字符进行传递就可以了.

那么如何使用呢?举以下两个例子

第一个:将一个图片转换成 txt 文本 并保存起来

//选择一个图像文件,将它转为 文本保存至 _T("D:\2.txt"
void CTextPicDlg::OnBnClickedButton2()
{
  // TODO: 在此添加控件通知处理程序代码
  CFileDialog file(TRUE,".jpg","");
  if (file.DoModal() == IDOK)
  {
    CFile data(file.GetPathName(), CFile::modeReadWrite);
    int len = data.GetLength();
    BYTE *dv;
    dv = (BYTE *)malloc(len*sizeof(BYTE));
    data.Read(dv, len);
    data.Close();
    int slen = (len / 3) * 4;
    slen += 10;
    TCHAR * tc;
    tc = (TCHAR *)malloc(slen);
    slen = base64_Encode(dv, len, tc);
    CFile save(_T("D:\2.txt"), CFile::modeCreate | CFile::modeWrite);
    save.Write(tc, slen);
    save.Close();
    free(tc);
    free(dv);
  }
}

第二个例子,将一个文本文件还原为一个图像

void CTextPicDlg::OnBnClickedButton3()
{
  // TODO: 在此添加控件通知处理程序代码
  CFileDialog file(TRUE, ".txt", "");
  if (file.DoModal() == IDOK)
  {
    CFile data(file.GetPathName(), CFile::modeReadWrite);
    int len = data.GetLength();
    TCHAR *dv;
    dv = (TCHAR *)malloc(len*sizeof(TCHAR));
    data.Read(dv, len);
    data.Close();
    int slen = (len / 4) * 3;
    slen += 10;
    BYTE * tc;
    tc = (BYTE *)malloc(slen);
    base64_Decode(dv, len, tc);
    //直接在内存里面构建CIMAGE,需要使用IStream接口,如何使用
    //构建内存环境    
    HGLOBAL hGlobal = GlobalAlloc(GMEM_MOVEABLE, slen);
    void * pData = GlobalLock(hGlobal);
    memcpy(pData, tc, slen); // 拷贝位图数据进去
    GlobalUnlock(hGlobal);
    // 创建IStream
    IStream * pStream = NULL;
    if (CreateStreamonHGlobal(hGlobal, TRUE, &pStream) != S_OK)
      return ;
    //  使用CImage加载位图内存
    CImage img;
    if (SUCCEEDED(img.Load(pStream)) )
    {
      CClientDC dc(this);
//使用内在中构造的图像 直接在对话框上绘图
img.Draw(dc.m_hDC, 0, 0, 500, 300);
    }
     //释放内存
    pStream->Release();
    GlobalFree(hGlobal);
    //如果要保存图像文件的话,那就使用下面的代码
    //CFileDialog savefile(FALSE, ".jpg", "");
    //if (savefile.DoModal()==IDOK)
    //{
    //  CFile save(savefile.GetPathName(), CFile::modeCreate | CFile::modeWrite);
    //  save.Write(tc, slen);
    //  save.Close();
    //}
    free(tc);
    free(dv);
  }
}

至此,利用base64转码的方式,来显示保存显示图片的方法,就算是成功了!

我们再来看一个base64编码解码的例子

首先是编码

const BYTE base64ValTab[65] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

#define AVal(x) base64ValTab[x]
int CSeebase64Dlg::Encodebase64(char * pInput, char * pOutput)
{
    int i = 0;
    int loop = 0;
    int remain = 0;
    int iDstLen = 0;
    int iSrcLen = (int)strlen(pInput);

    loop = iSrcLen/3;
    remain = iSrcLen%3;

    // also can encode native char one by one as decode method
    // but because all of char in native string is to be encoded so encode 3-chars one time is easier.

    for (i=0; i < loop; i++)
    {
 BYTE a1 = (pInput[i*3] >> 2);
 BYTE a2 = ( ((pInput[i*3] & 0x03) << 4) | (pInput[i*3+1] >> 4) );
 BYTE a3 = ( ((pInput[i*3+1] & 0x0F) << 2) | ((pInput[i*3+2] & 0xC0) >> 6) );
 BYTE a4 = (pInput[i*3+2] & 0x3F);

 pOutput[i*4] = AVal(a1);
 pOutput[i*4+1] = AVal(a2);
 pOutput[i*4+2] = AVal(a3);
 pOutput[i*4+3] = AVal(a4);
    }

    iDstLen = i*4;

    if (remain == 1)
    {
 // should pad two equal sign
 i = iSrcLen-1;
 BYTE a1 = (pInput[i] >> 2);
 BYTE a2 = ((pInput[i] & 0x03) << 4);
 
 pOutput[iDstLen++] = AVal(a1);
 pOutput[iDstLen++] = AVal(a2);
 pOutput[iDstLen++] = '=';
 pOutput[iDstLen++] = '=';
 pOutput[iDstLen] = 0x00;
    }
    else if (remain == 2)
    {
 // should pad one equal sign
 i = iSrcLen-2;
 BYTE a1 = (pInput[i] >> 2);
 BYTE a2 = ( ((pInput[i] & 0x03) << 4) | (pInput[i+1] >> 4));
 BYTE a3 = ( (pInput[i+1] & 0x0F) << 2);

 pOutput[iDstLen++] = AVal(a1);
 pOutput[iDstLen++] = AVal(a2);
 pOutput[iDstLen++] = AVal(a3);
 pOutput[iDstLen++] = '=';
 pOutput[iDstLen] = 0x00;
    }
    else
    {
 // just division by 3
 pOutput[iDstLen] = 0x00;
    }

    return iDstLen;
}

下面是解码

const BYTE base64IdxTab[128] =
{
255,255,255,255, 255,255,255,255, 255,255,255,255, 255,255,255,255,
255,255,255,255, 255,255,255,255, 255,255,255,255, 255,255,255,255,
255,255,255,255, 255,255,255,255, 255,255,255,62,  255,255,255,63,
52,53,54,55,   56,57,58,59,   60,61,255,255,  255,255,255,255,
255,0,1,2,    3,4,5,6,     7,8,9,10,     11,12,13,14,
15,16,17,18,   19,20,21,22,   23,24,25,255,   255,255,255,255,
255,26,27,28,   29,30,31,32,   33,34,35,36,   37,38,39,40,
41,42,43,44,   45,46,47,48,   49,50,51,255,   255,255,255,255
};

#define BVal(x) base64IdxTab[x]

int CSeebase64Dlg::Decodebase64(char * pInput, char * pOutput)
{
    int i = 0;
    int iCnt = 0;
    int iSrcLen = (int)strlen(pInput);

    char * p = pOutput;

    for (i=0; i < iSrcLen; i++)
    {
 if (pInput[i] > 127) continue;
 if (pInput[i] == '=') return p-pOutput+1;

 BYTE a = BVal(pInput[i]);
 if (a == 255) continue;
 
 switch (iCnt)
 {
 case 0:
     {
  *p = a << 2;
  iCnt++;
     }
     break;

 case 1:
     {
  *p++ |= a >> 4;
  *p = a << 4;
  iCnt++;
     }
     break;

 case 2:
     {
  *p++ |= a >> 2;
  *p = a << 6;
  iCnt++;
     }
     break;
 case 3:
     {
  *p++ |= a;
  iCnt = 0;
     }
     break;
 } 
    }

    *p = 0x00;
    return p-pOutput;
}