Base64编码解码

what is base64 coding and decoding is in reference to

https://en.wikipedia.org/wiki/Base64
http://www.cnblogs.com/chengxiaohui/articles/3951129.html
  

//sample code in c++. Please note that the code needs refinements as there is some warning in some analysis tools,e.g. pc-lint, Coverity etc.

// it is just a sample code for study.

//declaration in header

std::string base64Encode(const std::vector<char>& byteData);
std::vector<char> base64Decode(std::string & const inputString);

//implemenation

std::string Cbase64Dlg::base64Encode(const std::vector<char>& byteData)
{
   const std::string codes = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
   std::string base64String;
   int b;
   for (size_t i = 0; i < byteData.size(); i = i+3)
   {
      b = (byteData[i] & 0xFC) >> 2;
      base64String.push_back(codes[b]);
      b = (byteData[i] & 0x03) << 4;
      if (i + 1 < byteData.size())
      {
         b |= (byteData[i + 1] & 0xF0) >> 4;
         base64String.push_back(codes[b]);
         b = (byteData[i + 1] & 0x0F) << 2;
         if (i+2 < byteData.size())
         {
            b |= (byteData[i + 2] & 0xC0) >> 6;
            base64String.push_back(codes[b]);
            b = byteData[i + 2] & 0x3F;
            base64String.push_back(codes[b]);
         }
         else
         {
            base64String.push_back(codes[b]);
            base64String.append("=");
         }
      }
      else
      {
         base64String.push_back(codes[b]);
         base64String.append("==");
      }
   }
   
   return base64String;
}

std::vector<char> Cbase64Dlg::base64Decode(std::string & const inputString)
{   
   static std::string codes = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
   std::vector<char> decoded;

   if (inputString.length() % 4 != 0)    
   {
      return std::vector<char>();
   }

   //The ratio of output bytes to input bytes is 4:3
   int outLen = (inputString.length() * 3 / 4);

   size_t pos = inputString.find_first_of('=');
   if (pos != std::string::npos)
   {
      decoded.resize(outLen - (inputString.length() - pos));
   }
   else
   {
      decoded.resize(outLen);
   }

   int j = 0;
   int b[4] = {};

   const char* p = inputString.c_str();

   while(p && *p && j < outLen)
   {
      bool valid = false;
      for (int i=0; p && i < 4; ++i)
      {
         size_t pos = codes.find_first_of(*p++);
         if ( pos != std::string::npos)
         {
            b[i] = pos;
         }
      }

      if (j < outLen)
      {
         decoded[j++] = (byte) ((b[0] << 2) | (b[1] >> 4));;
         if (j < outLen && b[2] < 64)      
         {
            decoded[j++] = (byte) ((b[1] << 4) | (b[2] >> 2));

            if (j < outLen && b[3] < 64)  
            {
               decoded[j++] = (byte) ((b[2] << 6) | b[3]);
            }
         }
      }
   }

   return decoded;
}

// test code

   char myints[] = "ABC&&&&&&&&&&";
   std::vector<char> byte (myints, myints + sizeof(myints) / sizeof(char) );
   std::string value = base64Encode(byte);
   std::cout << value << std::endl;
   std::vector<char>decode = base64Decode(value);