03_利用cryptopp写hmacsha256算法

std::string getHash256(string infor, string key , bool flag ){      string mac, encoder , derived ;    /*一切是那么的神奇，前天加了这段代码就出错，所以注释了；    今天重测，又对了，想想还是注释了吧！先看下官方的说法先。*/    /*if( true ) {        HexDecoder  decoder (new StringSink(derived));          decoder.Put((const byte*)key.data(), key.size());          decoder.MessageEnd();      }*/    try{          HMAC<SHA256> hmac((const byte*)key.data(), key.size());          StringSource(infor, true, new HashFilter(hmac, new StringSink(mac)));      }catch(const CryptoPP::Exception& e){          cerr << e.what() << endl;          exit(1);      }      encoder.clear();      StringSource(mac, true, new HexEncoder(new StringSink(encoder)));      transform(encoder.begin(), encoder.end(), encoder.begin(), ::tolower);    qDebug()<<"sign:"<<QString::fromStdString(encoder) ;    return encoder;     //return HMAC  }