为什么从我的代码中删除TextBox.AppendText（）会更改此处的套接字通信？

Question

I have a simple client/server communication between C++ and C# where the C# program sends a string to the C++. Sending of a string is done on 3 stages. Send the length of the length of the string--> Send the length of string --> Send the String. For debugging purposes I have a TextBox called textbox1 on my C# program to print the sent values using textbox1.AppendText() three times for the three values sent. Everything was sent and received correctly, When I remove two of the three AppendText() lines from my code it still works but the strange thing is when I remove the third one (Commented as //<--This Line , The C++ server receives 0!

C# Client (Code Snippet):

 private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                MemoryStream ms;
                NetworkStream ns;
                TcpClient client;
                BinaryWriter br;
                byte[] tosend;
                string AndroidId = "2468101214161820";
                string len = AndroidId.Length.ToString();
                string lol = len.Length.ToString();

                ms = new MemoryStream();
                client = new TcpClient("127.0.0.1", 8888);                
                ns = client.GetStream();
                br = new BinaryWriter(ns);
                //****************Send Length Of Length***************
                tosend = System.Text.Encoding.ASCII.GetBytes(lol);
                br.Write(tosend);
                textBox1.AppendText(Encoding.ASCII.GetString(tosend));//<---THIS LINE
                //****************Send Length***************
                tosend = System.Text.Encoding.ASCII.GetBytes(len);
                br.Write(tosend);
                //****************Send Length Of Length***************
                tosend = System.Text.Encoding.ASCII.GetBytes(AndroidId);
                br.Write(tosend);

                ns.Close();
                client.Close();
            }

C++ Server Code Snippet:

//***********Recieve Length Of Length*****************
                char* lol_buff0 = new char[1];
                int nullpoint=  recv(s, lol_buff0, strlen(lol_buff0), 0);
                lol_buff0[nullpoint] = '\0';
                int lengthoflength = atoi(lol_buff0);
                //***********Recieve Length*****************
                char* l_buff0 = new char[lengthoflength];
                int nullpoint2=recv(s, l_buff0, strlen(l_buff0), 0);
                l_buff0[nullpoint2] = '\0';
                int length = atoi(l_buff0);
                //***********Recieve AndroidID*****************
                char* AndroidID = new char[length];
                valread0 = recv(s, AndroidID, strlen(AndroidID), 0);

                if (valread0 == SOCKET_ERROR)
                {
                    int error_code = WSAGetLastError();
                    if (error_code == WSAECONNRESET)
                    {
                        //Somebody disconnected , get his details and print
                        printf("Host disconnected unexpectedly , ip %s , port %d \n", inet_ntoa(address.sin_addr), ntohs(address.sin_port));

                        //Close the socket and mark as 0 in list for reuse
                        closesocket(s);
                        client_socket[i] = 0;
                    }
                    else
                    {
                        printf("recv failed with error code : %d", error_code);
                    }
                }
                if (valread0 == 0)
                {
                    //Somebody disconnected , get his details and print
                    printf("Host disconnected , ip %s , port %d \n", inet_ntoa(address.sin_addr), ntohs(address.sin_port));

                    //Close the socket and mark as 0 in list for reuse
                    closesocket(s);
                    client_socket[i] = 0;
                }
                else
                {
                    //add null character, if you want to use with printf/puts or other string handling functions
                    AndroidID[valread0] = '\0';
                    printf("%s:%d  Your Android ID is - %s \n", inet_ntoa(address.sin_addr), ntohs(address.sin_port), AndroidID);
                }

I know I can accommodate the TextBox as long as it works but It is so weird and I'd like to know what is the explanation for that. Thanks.

Answer 1

You're assuming that the data will be received in one recv call (or alternatively, that one send corresponds to one receive). That is a false assumption. You need to keep reading until you read length of bytes of data. TCP doesn't have any messaging built in, it only deals with streams.

Adding the line may mean that some small delay is added which makes the receive happen in a single call - it's hard to tell, since you're dealing with something that isn't quite deterministic. Handle TCP properly, and see if the problem persists.