最近做了一个网络编程的DLL给C#调用，DLL中封装了一个TCP Client的函数接口，如下所示

//C++ TCP报文发送接口
int TcpClient_send(unsigned char* buffSend, unsigned int nLen)
{unsigned char buff[1024];int len = StringToHex(buffSend, buff);int nRet = 0;if (Connect()){int sendRes = send(m_hTcpClientSocket, (char*)buff, nLen, 0);if (sendRes == SOCKET_ERROR){nRet = -2;closesocket(m_hTcpClientSocket);m_hTcpClientSocket = NULL;}else{nRet = sendRes;}}else{nRet = -1;}return nRet;
}char ConvertHexChar(char ch)
{if ((ch >= '0') && (ch <= '9'))return   ch - 0x30;else   if ((ch >= 'A') && (ch <= 'F'))return   ch - 'A' + 10;else   if ((ch >= 'a') && (ch <= 'f'))return   ch - 'a' + 10;else   return   (-1);}int StringToHex(CString str, unsigned char* senddata)
{int hexdata, lowhexdata;int hexdatalen = 0;int len = str.GetLength();for (int i = 0; i < len;){char lstr, hstr = str[i];if (hstr == ' '){i++;continue;}i++;if (i >= len)break;lstr = str[i];hexdata = ConvertHexChar(hstr);lowhexdata = ConvertHexChar(lstr);if ((hexdata == 16) || (lowhexdata == 16))break;elsehexdata = hexdata * 16 + lowhexdata;i++;senddata[hexdatalen] = (char)hexdata;hexdatalen++;}return hexdatalen;
}

   在C#中调用该接口的时候，刚开始我是通过string down = System.Text.Encoding.Default.GetString()或者System.Text.Encoding.UTF8.GetString()的方式将字节数组转换成string然后传递给TcpClientSyn_send函数，但是这两种方法传递的字节数组到达DLL中时大于127的字节都会变为0x3f也就是63。后来果断抛弃该种方法，转而通过自定义函数BytesToHexString()将字节数组变为类似于“AA AA A0 01”这样的字符串，然后再DLL中通过另一个自定义函数StringToHex()来再次转换成字节数组。

//C#调用DLL中的TcpClient_send函数
private static void SendThread(object n)
{//发送byte[] buffSend = { 0xAA, 0xAA, 0x70, 0x01, 0x00, 0x00, 0x00, 0x01, 0x00, 0x80, 0x17, 0xC5, 0x51, 0xE2, 0xEE, 0xEE };//string down = System.Text.Encoding.Default.GetString(buffSend);//string down = System.Text.Encoding.UTF8.GetString(buffSend);string HexString_down = BytesToHexString(buffSend);int sendLen=TcpClient_send(HexString_down, 16);if (sendLen> 0){}//接收     uint nRecvLen;nRecvLen = 0;StringBuilder buffRecv = new StringBuilder(1024);buffRecv.Clear();int recvLen=TcpClientSyn_recv(buffRecv,ref nRecvLen);if (recvLen> 0){}}private static string BytesToHexString(byte[] byteDatas)
{StringBuilder builder = new StringBuilder();for (int i = 0; i < byteDatas.Length; i++){builder.Append(string.Format("{0:X2} ", byteDatas[i]));}return builder.ToString().Trim();
}