client server UDP C++ example

main.cpp

CLIENT SIDE:

#include <iostream>
#include <winsock2.h>
using namespace std;

#pragma comment(lib,"ws2_32.lib") 
#pragma warning(disable:4996) 

#define SERVER "127.0.0.1"  // or "localhost" - ip address of UDP server
#define BUFLEN 512  // max length of answer
#define PORT 8888  // the port on which to listen for incoming data

int main()
{
    system("title UDP Client");

    // initialise winsock
    WSADATA ws;
    printf("Initialising Winsock...");
    if (WSAStartup(MAKEWORD(2, 2), &ws) != 0)
    {
        printf("Failed. Error Code: %d", WSAGetLastError());
        return 1;
    }
    printf("Initialised.\n");

    // create socket
    sockaddr_in server;
    int client_socket;
    if ((client_socket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == SOCKET_ERROR) // <<< UDP socket
    {
        printf("socket() failed with error code: %d", WSAGetLastError());
        return 2;
    }

    // setup address structure
    memset((char*)&server, 0, sizeof(server));
    server.sin_family = AF_INET;
    server.sin_port = htons(PORT);
    server.sin_addr.S_un.S_addr = inet_addr(SERVER);

    // start communication
    while (true)
    {
        char message[BUFLEN];
        printf("Enter message: ");
        cin.getline(message, BUFLEN);

        // send the message
        if (sendto(client_socket, message, strlen(message), 0, (sockaddr*)&server, sizeof(sockaddr_in)) == SOCKET_ERROR)
        {
            printf("sendto() failed with error code: %d", WSAGetLastError());
            return 3;
        }

        // receive a reply and print it
        // clear the answer by filling null, it might have previously received data
        char answer[BUFLEN] = {};

        // try to receive some data, this is a blocking call
        int slen = sizeof(sockaddr_in);
        int answer_length;
        if (answer_length = recvfrom(client_socket, answer, BUFLEN, 0, (sockaddr*)&server, &slen) == SOCKET_ERROR)
        {
            printf("recvfrom() failed with error code: %d", WSAGetLastError());
            exit(0);
        }

        cout << answer << "\n";
    }

    closesocket(client_socket);
    WSACleanup();
}

==========================================================================================================================
  
SERVER SIDE:

#include <iostream>
#include <winsock2.h>
using namespace std;

#pragma comment(lib,"ws2_32.lib") // Winsock Library
#pragma warning(disable:4996) 

#define BUFLEN 512
#define PORT 8888

int main()
{
    system("title UDP Server");

    sockaddr_in server, client;

    // initialise winsock
    WSADATA wsa;
    printf("Initialising Winsock...");
    if (WSAStartup(MAKEWORD(2, 2), &wsa) != 0)
    {
        printf("Failed. Error Code: %d", WSAGetLastError());
        exit(0);
    }
    printf("Initialised.\n");

    // create a socket
    SOCKET server_socket;
    if ((server_socket = socket(AF_INET, SOCK_DGRAM, 0)) == INVALID_SOCKET)
    {
        printf("Could not create socket: %d", WSAGetLastError());
    }
    printf("Socket created.\n");

    // prepare the sockaddr_in structure
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = INADDR_ANY;
    server.sin_port = htons(PORT);

    // bind
    if (bind(server_socket, (sockaddr*)&server, sizeof(server)) == SOCKET_ERROR)
    {
        printf("Bind failed with error code: %d", WSAGetLastError());
        exit(EXIT_FAILURE);
    }
    puts("Bind done.");

    while (true)
    {
        printf("Waiting for data...");
        fflush(stdout);
        char message[BUFLEN] = {};

        // try to receive some data, this is a blocking call
        int message_len;
        int slen = sizeof(sockaddr_in);
        if (message_len = recvfrom(server_socket, message, BUFLEN, 0, (sockaddr*)&client, &slen) == SOCKET_ERROR)
        {
            printf("recvfrom() failed with error code: %d", WSAGetLastError());
            exit(0);
        }

        // print details of the client/peer and the data received
        printf("Received packet from %s:%d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
        printf("Data: %s\n", message);

        cin.getline(message, BUFLEN);

        // reply the client with 2the same data
        if (sendto(server_socket, message, strlen(message), 0, (sockaddr*)&client, sizeof(sockaddr_in)) == SOCKET_ERROR)
        {
            printf("sendto() failed with error code: %d", WSAGetLastError());
            return 3;
        }
    }

    closesocket(server_socket);
    WSACleanup();
}