Base64算法

Base64算法是一种基于64个字符的编码算法，仅是一种算法，并不是加密算法（因为算法是公开的）。

经过Base64编码后的数据会比原始数据略长，为原来的4/3倍。经过Base64编码后的字符串的字符数是以4为单位的整数倍。

算法使用：添加头文件和实现文件

QString c="203609";
QString str=base64Encode(c.toStdString().c_str(), c.length());

头文件：

/********** 
This library is free software; you can redistribute it and/or modify it under 
the terms of the GNU Lesser General Public License as published by the 
Free Software Foundation; either version 2.1 of the License, or (at your 
option) any later version. (See <http://www.gnu.org/copyleft/lesser.html>.) 
 
This library is distributed in the hope that it will be useful, but WITHOUT 
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS 
FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for 
more details. 
 
You should have received a copy of the GNU Lesser General Public License 
along with this library; if not, write to the Free Software Foundation, Inc., 
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA 
**********/  
// "liveMedia"  
// Copyright (c) 1996-2010 Live Networks, Inc.  All rights reserved.  
// Base64 encoding and decoding  
// C++ header  
  
#ifndef _BASE64_HH  
#define _BASE64_HH  
  
//#ifndef _BOOLEAN_HH  
//#include "Boolean.hh"  
//#endif  
  
#ifdef __cplusplus  
extern "C" {  
#endif  
  
unsigned char* base64Decode(char* in, unsigned int& resultSize, bool trimTrailingZeros = true);  
    // returns a newly allocated array - of size "resultSize" - that  
    // the caller is responsible for delete[]ing.  
  
char* base64Encode(char const* orig, unsigned origLength);  
    // returns a 0-terminated string that  
    // the caller is responsible for delete[]ing.  
  
  
#ifdef __cplusplus  
}  
#endif  
  
#endif

实现文件：

/********** 
This library is free software; you can redistribute it and/or modify it under 
the terms of the GNU Lesser General Public License as published by the 
Free Software Foundation; either version 2.1 of the License, or (at your 
option) any later version. (See <http://www.gnu.org/copyleft/lesser.html>.) 
 
This library is distributed in the hope that it will be useful, but WITHOUT 
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS 
FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for 
more details. 
 
You should have received a copy of the GNU Lesser General Public License 
along with this library; if not, write to the Free Software Foundation, Inc., 
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA 
**********/  
// "liveMedia"  
// Copyright (c) 1996-2010 Live Networks, Inc.  All rights reserved.  
// Base64 encoding and decoding  
// implementation  
  
#include "base64.h"  
  
#include <string.h>  
  
static char base64DecodeTable[256];  
  
  
char* strDup(char const* str)   
{  
    if (str == NULL) return NULL;  
    size_t len = strlen(str) + 1;  
    char* copy = new char[len];  
  
    if (copy != NULL)   
    {  
        memcpy(copy, str, len);  
    }  
    return copy;  
}  
  
char* strDupSize(char const* str)   
{  
    if (str == NULL) return NULL;  
    size_t len = strlen(str) + 1;  
    char* copy = new char[len];  
  
    return copy;  
}  
  
  
  
static void initBase64DecodeTable()  
{  
  int i;  
  for (i = 0; i < 256; ++i) base64DecodeTable[i] = (char)0x80;  
      // default value: invalid  
  
  for (i = 'A'; i <= 'Z'; ++i) base64DecodeTable[i] = 0 + (i - 'A');  
  for (i = 'a'; i <= 'z'; ++i) base64DecodeTable[i] = 26 + (i - 'a');  
  for (i = '0'; i <= '9'; ++i) base64DecodeTable[i] = 52 + (i - '0');  
  base64DecodeTable[(unsigned char)'+'] = 62;  
  base64DecodeTable[(unsigned char)'/'] = 63;  
  base64DecodeTable[(unsigned char)'='] = 0;  
}  
  
unsigned char* base64Decode(char* in, unsigned int& resultSize, bool trimTrailingZeros)   
{  
  static bool haveInitedBase64DecodeTable = false;  
  if (!haveInitedBase64DecodeTable)  
  {  
    initBase64DecodeTable();  
    haveInitedBase64DecodeTable = true;  
  }  
  
  unsigned char* out = (unsigned char*)strDupSize(in); // ensures we have enough space  
  int k = 0;  
  int const jMax = strlen(in) - 3;  
     // in case "in" is not a multiple of 4 bytes (although it should be)  
  for (int j = 0; j < jMax; j += 4)   
  {  
    char inTmp[4], outTmp[4];  
    for (int i = 0; i < 4; ++i)   
    {  
      inTmp[i] = in[i+j];  
      outTmp[i] = base64DecodeTable[(unsigned char)inTmp[i]];  
      if ((outTmp[i]&0x80) != 0) outTmp[i] = 0; // pretend the input was 'A'  
    }  
  
    out[k++] = (outTmp[0]<<2) | (outTmp[1]>>4);  
    out[k++] = (outTmp[1]<<4) | (outTmp[2]>>2);  
    out[k++] = (outTmp[2]<<6) | outTmp[3];  
  }  
  
  if (trimTrailingZeros)   
  {  
    while (k > 0 && out[k-1] == '/0') --k;  
  }  
  resultSize = k;  
  unsigned char* result = new unsigned char[resultSize];  
  memmove(result, out, resultSize);  
  delete[] out;  
  
  return result;  
}  
  
static const char base64Char[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";  
  
char* base64Encode(char const* origSigned, unsigned origLength)   
{  
  unsigned char const* orig = (unsigned char const*)origSigned; // in case any input bytes have the MSB set  
  if (orig == NULL) return NULL;  
  
  unsigned const numOrig24BitValues = origLength/3;  
  bool havePadding = origLength > numOrig24BitValues*3;  
  bool havePadding2 = origLength == numOrig24BitValues*3 + 2;  
  unsigned const numResultBytes = 4*(numOrig24BitValues + havePadding);  
  char* result = new char[numResultBytes+1]; // allow for trailing '/0'  
  
  // Map each full group of 3 input bytes into 4 output base-64 characters:  
  unsigned i;  
  for (i = 0; i < numOrig24BitValues; ++i)   
  {  
    result[4*i+0] = base64Char[(orig[3*i]>>2)&0x3F];  
    result[4*i+1] = base64Char[(((orig[3*i]&0x3)<<4) | (orig[3*i+1]>>4))&0x3F];  
    result[4*i+2] = base64Char[((orig[3*i+1]<<2) | (orig[3*i+2]>>6))&0x3F];  
    result[4*i+3] = base64Char[orig[3*i+2]&0x3F];  
  }  
  
  // Now, take padding into account.  (Note: i == numOrig24BitValues)  
  if (havePadding)   
  {  
    result[4*i+0] = base64Char[(orig[3*i]>>2)&0x3F];  
    if (havePadding2)  
    {  
      result[4*i+1] = base64Char[(((orig[3*i]&0x3)<<4) | (orig[3*i+1]>>4))&0x3F];  
      result[4*i+2] = base64Char[(orig[3*i+1]<<2)&0x3F];  
    }   
    else   
    {  
      result[4*i+1] = base64Char[((orig[3*i]&0x3)<<4)&0x3F];  
      result[4*i+2] = '=';  
    }  
    result[4*i+3] = '=';  
  }  
  
  result[numResultBytes] = '';  
  return result;  
}