C++ Base64 编码 解码

C++实现 base64 字符串编码解码(GCC编译)。

 /**
 * @brief C++ base64 编解码
 * @author wid
 * @date 2013-20-25
 *
 * @note 若代码存在 bug 或程序缺陷, 请留言反馈, 谢谢!
 */

 #include <iostream>
 #include <string>
 #include <ctime>

 //base64 编解码函数声明
 std::string b64encodestring(const std::string &strString);      //对 ASCII 字符串进行 base64 编码
 std::string b64decodestring(const std::string &strString);      //对 base64 编码后的字符串进行解码

 //base64 编解码函数实现
 /**
 * @brief 对 ASCII 字符串进行 base64 编码
 *
 * @param strString 待编码的字符串
 *
 * @return srs::string 返回编码后的字符串
 *
 * @note 对于字符串中含有非 ASCII 字符串型的字符, 代码将抛出 std::string 型异常, 请捕获
 */
 std::string b64encodestring(const std::string &strString)
 {
     int nByteSrc = strString.length();
     std::string pszSource = strString;

     int i = ;
     for(i; i < nByteSrc; i++)
         if( pszSource[i] <  || pszSource[i] >  )
             throw "can not encode Non-ASCII characters";

     const char *enkey = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
     std::string pszEncode(nByteSrc*/ + , '\0');
     int nLoop = nByteSrc % ==  ? nByteSrc : nByteSrc - ;
     int n = ;
     for(i=; i < nLoop; i+= )
     {
         pszEncode[n] = enkey[pszSource[i]>>];
         pszEncode[n+] = enkey[((pszSource[i]&)<<) | ((pszSource[i+] & 0xF0)>>)];
         pszEncode[n+] = enkey[((pszSource[i+] & 0x0f)<<) | ((pszSource[i+] & 0xc0 )>>)];
         pszEncode[n+] = enkey[pszSource[i+] & 0x3F];
         n += ;
     }

     switch(nByteSrc%)
     {
     case :
         pszEncode[n] = '\0';
         break;

     case :
         pszEncode[n] = enkey[pszSource[i]>>];
         pszEncode[n+] = enkey[((pszSource[i]&)<<) | ((&0xf0)>>)];
         pszEncode[n+] = '=';
         pszEncode[n+] = '=';
         pszEncode[n+] = '\0';
         break;

     case :
         pszEncode[n] = enkey[pszSource[i]>>];
         pszEncode[n+] = enkey[((pszSource[i]&)<<) | ((pszSource[i+]&0xf0)>>)];
         pszEncode[n+] = enkey[(( pszSource[i+]&0xf)<< ) | ((&0xc0)>>)];
         pszEncode[n+] = '=';
         pszEncode[n+] = '\0';
         break;
     }

     return pszEncode.c_str();
 }

 /**
 * @brief 对 base64 编码后的字符串进行解码
 *
 * @param strString 待解码的字符串
 *
 * @return std::string 返回解码后的字符串
 *
 * @note 对于非base64编码的字符串或已损坏的base64字符串进行解码会抛出 std::string 型异常, 请捕获
 */
 std::string b64decodestring(const std::string &strString)
 {
     int nByteSrc = strString.length();
     std::string pszSource = strString;

     const int dekey[] = {
         -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -,
         -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -, -,
         , // '+'
         -, -, -,
         , // '/'
         , , , , , , , , , , // '0'-'9'
         -, -, -, -, -, -, -,
         , , , , , , , , , , , , ,
         , , , , , , , , , , , , , // 'A'-'Z'
         -, -, -, -, -, -,
         , , , , , , , , , , , , ,
         , , , , , , , , , , , , , // 'a'-'z'
     };

     if(nByteSrc% != )
         throw "bad base64 string";

     std::string pszDecode(nByteSrc*/+, '\0');
     int nLoop = pszSource[nByteSrc-]  == '=' ? nByteSrc -  : nByteSrc;
     int b[];
     int i = , n = ;
     for(i = ; i < nLoop; i +=  )
     {
         b[] = dekey[pszSource[i]];        b[] = dekey[pszSource[i+]];
         b[] = dekey[pszSource[i+]];    b[] = dekey[pszSource[i+]];
         if(b[] == - || b[] == - || b[] == - || b[] == -)
             throw "bad base64 string";

         pszDecode[n] = (b[] << ) | ((b[] & 0x30) >> );
         pszDecode[n+] = ((b[] & 0xf) << ) | ((b[] & 0x3c) >> );
         pszDecode[n+] =  ((b[] & 0x3) << ) | b[];

         n+=;
     }

     if( pszSource[nByteSrc-] == '=' && pszSource[nByteSrc-] == '=' )
     {
         b[] = dekey[pszSource[i]];        b[] = dekey[pszSource[i+]];
         if(b[] == - || b[] == -)
             throw "bad base64 string";

         pszDecode[n] = (b[] << ) | ((b[] & 0x30) >> );
         pszDecode[n+] = '\0';
     }

     if( pszSource[nByteSrc-] == '=' && pszSource[nByteSrc-] != '=' )
     {
         b[] = dekey[pszSource[i]];        b[] = dekey[pszSource[i+]];
         b[] = dekey[pszSource[i+]];
         if(b[] == - || b[] == - || b[] == -)
             throw "bad base64 string";

         pszDecode[n] = (b[] << ) | ((b[] & 0x30) >> );
         pszDecode[n+] = ((b[] & 0xf) << ) | ((b[] & 0x3c) >> );
         pszDecode[n+] = '\0';
     }

     if( pszSource[nByteSrc-] != '=' && pszSource[nByteSrc-] != '=' )
         pszDecode[n] = '\0';

     return pszDecode;
 }

 //测试
 int main()
 {
     ///编码测试
     std::string str1 = "Hello, world!";
     std::cout << "对Hello, world!进行base64编码: " << b64encodestring(str1) << std::endl;

     ///解码测试
     std::string str2 = "SGVsbG8sIHdvcmxkIQ==";
     std::cout << "对SGVsbG8sIHdvcmxkIQ==进行base64解码: " << b64decodestring(str2) << std::endl;

     ///编码耗时测试
     std::string str3(, 'A');    //生成 10000000 长的字符串
     std::cout << std::endl << "对 10000000 长的字符串进行编码耗时测试.." << std::endl;
     size_t t0 = clock();        //编码计时开始
     b64encodestring(str3);
     std::cout << "测试结束, 耗时 " << clock() - t0 << "ms" << std::endl;

     ///解码耗时测试
     std::string str4 = b64encodestring(str3);        //得到长度为 10000000 的字符串base64编码后的字符串
     std::cout << std::endl << "对 " << str4.length() << " 长的base64字符串进行解码耗时测试.." << std::endl;
     size_t t1 = clock();        //解码计时开始
     b64decodestring(str3);
     std::cout << "测试结束, 耗时 " << clock() - t1 << "ms" << std::endl;

     return ;
 }

运行测试结果:

若代码存在 bug 或程序缺陷, 请留言反馈, 谢谢。