Two way communication between Client and Server using Win32 Threads
Last Updated :
12 Jul, 2025
It is possible to send data from the server and receive a response from the client. Similarly, the client can also send and receive data to-and-from. Here we will discuss the approach using Win32 Threads in C/C++.
Approach
- Use CreateThread function which creates a new thread for a process.
- The CreateThread method must specify the starting address of the code that the new thread is to execute. Following is the prototype of CreateThread function:
C++
HANDLE CreateThread(
LPSECURITY_ATTRIBUTES lpThreadAttributes,
DWORD dwStackSize,
LPTHREAD_START_ROUTINE lpStartAddress,
LPVOID lpParameter, DWORD dwCreationFlags,
LPDWORD lpThreadId
);
- Then using WaitForSingleObject function that returns message in form of object received from client, to receive data from client. Following is the prototype of WaitForSingleObject function:
C++
DWORD WaitForSingleObject(
HANDLE hHandle,
DWORD dwMilliseconds
);
Creating the Server program
In the Server Program, we will be using two threads, one for Sending data to the client and another for Receiving data from the client. The process of communication stops when both Client and Server type exit.
Server
// C++ program to create Server
#include <iostream>
#include <string.h>
#include <winsock2.h>
using namespace std;
// Function that receive data
// from client
DWORD WINAPI serverReceive(LPVOID lpParam)
{
// Created buffer[] to
// receive message
char buffer[1024] = { 0 };
// Created client socket
SOCKET client = *(SOCKET*)lpParam;
// Server executes continuously
while (true) {
// If received buffer gives
// error then return -1
if (recv(client, buffer, sizeof(buffer), 0)
== SOCKET_ERROR) {
cout << "recv function failed with error "
<< WSAGetLastError() << endl;
return -1;
}
// If Client exits
if (strcmp(buffer, "exit") == 0) {
cout << "Client Disconnected."
<< endl;
break;
}
// Print the message
// given by client that
// was stored in buffer
cout << "Client: " << buffer << endl;
// Clear buffer message
memset(buffer, 0,
sizeof(buffer));
}
return 1;
}
// Function that sends data to client
DWORD WINAPI serverSend(LPVOID lpParam)
{
// Created buffer[] to
// receive message
char buffer[1024] = { 0 };
// Created client socket
SOCKET client = *(SOCKET*)lpParam;
// Server executes continuously
while (true) {
// Input message server
// wants to send to client
gets(buffer);
// If sending failed
// return -1
if (send(client,
buffer,
sizeof(buffer), 0)
== SOCKET_ERROR) {
cout << "send failed with error "
<< WSAGetLastError() << endl;
return -1;
}
// If server exit
if (strcmp(buffer, "exit") == 0) {
cout << "Thank you for using the application"
<< endl;
break;
}
}
return 1;
}
// Driver Code
int main()
{
// Data
WSADATA WSAData;
// Created socket server
// and client
SOCKET server, client;
// Socket address for server
// and client
SOCKADDR_IN serverAddr, clientAddr;
WSAStartup(MAKEWORD(2, 0), &WSAData);
// Making server
server = socket(AF_INET,
SOCK_STREAM, 0);
// If invalid socket created,
// return -1
if (server == INVALID_SOCKET) {
cout << "Socket creation failed with error:"
<< WSAGetLastError() << endl;
return -1;
}
serverAddr.sin_addr.s_addr = INADDR_ANY;
serverAddr.sin_family = AF_INET;
serverAddr.sin_port = htons(5555);
// If socket error occurred,
// return -1
if (bind(server,
(SOCKADDR*)&serverAddr,
sizeof(serverAddr))
== SOCKET_ERROR) {
cout << "Bind function failed with error: "
<< WSAGetLastError() << endl;
return -1;
}
// Get the request from
// server
if (listen(server, 0)
== SOCKET_ERROR) {
cout << "Listen function failed with error:"
<< WSAGetLastError() << endl;
return -1;
}
cout << "Listening for
incoming connections...." << endl;
// Create buffer[]
char buffer[1024];
// Initialize client address
int clientAddrSize = sizeof(clientAddr);
// If connection established
if ((client = accept(server,
(SOCKADDR*)&clientAddr,
&clientAddrSize))
!= INVALID_SOCKET) {
cout << "Client connected!" << endl;
cout << "Now you can use our live chat application."
<< "Enter \"exit\" to disconnect" << endl;
// Create variable of
// type DWORD
DWORD tid;
// Create Thread t1
HANDLE t1 = CreateThread(NULL,
0,
serverReceive,
&client,
0,
&tid);
// If created thread
// is not created
if (t1 == NULL) {
cout << "Thread Creation Error: "
<< WSAGetLastError() << endl;
}
// Create Thread t2
HANDLE t2 = CreateThread(NULL,
0,
serverSend,
&client,
0,
&tid);
// If created thread
// is not created
if (t2 == NULL) {
cout << "Thread Creation Error: "
<< WSAGetLastError() << endl;
}
// Received Objects
// from client
WaitForSingleObject(t1,
INFINITE);
WaitForSingleObject(t2,
INFINITE);
// Close the socket
closesocket(client);
// If socket closing
// failed.
if (closesocket(server)
== SOCKET_ERROR) {
cout << "Close socket failed with error: "
<< WSAGetLastError() << endl;
return -1;
}
WSACleanup();
}
}
Run the ServerApplication.cpp file using the command:
g++ ServerApplication.cpp -lws2_32
Creating the Client Program
In the Client Program, we will be using two threads one for Sending data to the server and another for Receiving data from the server. The process of communication stops when both Server and Client type exit.
Client
// C++ program to create client
#include <iostream>
#include <string.h>
#include <winsock2.h>
using namespace std;
// Function that receive data from server
DWORD WINAPI clientReceive(LPVOID lpParam)
{
// Created buffer[] to
// receive message
char buffer[1024] = { 0 };
// Created server socket
SOCKET server = *(SOCKET*)lpParam;
// Client executes continuously
while (true) {
// If received buffer gives
// error then return -1
if (recv(server, buffer,
sizeof(buffer), 0)
== SOCKET_ERROR) {
cout << "recv function failed with error: "
<< WSAGetLastError()
<< endl;
return -1;
}
// If Server exits
if (strcmp(buffer, "exit") == 0) {
cout << "Server disconnected."
<< endl;
return 1;
}
// Print the message
// given by server that
// was stored in buffer
cout << "Server: " << buffer << endl;
// Clear buffer message
memset(buffer, 0, sizeof(buffer));
}
return 1;
}
// Function that sends data to server
DWORD WINAPI clientSend(LPVOID lpParam)
{
// Created buffer[] to
// receive message
char buffer[1024] = { 0 };
// Created server socket
SOCKET server = *(SOCKET*)lpParam;
// Client executes continuously
while (true) {
// Input message client
// wants to send to server
gets(buffer);
// If sending failed
// return -1
if (send(server,
buffer,
sizeof(buffer), 0)
== SOCKET_ERROR) {
cout << "send failed with error: "
<< WSAGetLastError() << endl;
return -1;
}
// If client exit
if (strcmp(buffer, "exit")
== 0) {
cout << "Thank you for using the application"
<< endl;
break;
}
}
return 1;
}
// Driver Code
int main()
{
// Input data
WSADATA WSAData;
// Created socket server
SOCKET server;
SOCKADDR_IN addr;
WSAStartup(MAKEWORD(2, 0), &WSAData);
// If invalid socket created,
// return -1
if ((server = socket(AF_INET,
SOCK_STREAM, 0))
== INVALID_SOCKET) {
cout << "Socket creation failed with error: "
<< WSAGetLastError() << endl;
return -1;
}
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
addr.sin_family = AF_INET;
addr.sin_port = htons(5555);
// If connection failed
if (connect(server,
(SOCKADDR*)&addr,
sizeof(addr))
== SOCKET_ERROR) {
cout << "Server connection failed with error: "
<< WSAGetLastError() << endl;
return -1;
}
// If connection established
cout << "Connected to server!"
<< endl;
cout << "Now you can use our live chat application."
<< " Enter \"exit\" to disconnect"
<< endl;
DWORD tid;
// Create Thread t1
HANDLE t1 = CreateThread(NULL,
0,
clientReceive,
&server,
0, &tid);
// If created thread
// is not created
if (t1 == NULL)
cout << "Thread creation error: "
<< GetLastError();
// Create Thread t2
HANDLE t2 = CreateThread(NULL,
0,
clientSend,
&server,
0, &tid);
// If created thread
// is not created
if (t2 == NULL)
cout << "Thread creation error: "
<< GetLastError();
// Received Objects
// from client
WaitForSingleObject(t1, INFINITE);
WaitForSingleObject(t2, INFINITE);
// Socket closed
closesocket(server);
WSACleanup();
}
Run the ClientApplication.cpp file using the command:
g++ ClientApplication.cpp -lws2_32
Output:
After communication between Server and Client
The left side command prompt is the ServerApplication and the right side command prompt is the ClientApplication.
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