以下是一个基本的多线程网络通信的 C++ 代码案例，其中有一个服务端和多个客户端，它们可以通过TCP/IP协议进行通信。

服务端代码：

#include <iostream>
#include <thread>
#include <cstring>
#include <sys/socket.h>
#include <arpa/inet.h>

using namespace std;

const int PORT = 8080;
const int MAX_CLIENTS = 10;

void clientHandler(int sockfd) {
    char buffer[1024];
    while (true) {
        memset(buffer, 0, sizeof(buffer));
        if (recv(sockfd, buffer, sizeof(buffer), 0) <= 0) {
            cout << "Client disconnected" << endl;
            close(sockfd);
            return;
        } else {
            cout << "Received message: " << buffer << endl;
            send(sockfd, buffer, strlen(buffer), 0);
        }
    }
}

int main() {
    int server_fd, new_sockfd;
    struct sockaddr_in address;
    int addrlen = sizeof(address);

    // Create socket file descriptor
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("Socket creation failed");
        exit(EXIT_FAILURE);
    }

    // Set socket options to reuse address and port
    int opt = 1;
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT,
                   &opt, sizeof(opt))) {
        perror("Setsockopt failed");
        exit(EXIT_FAILURE);
    }

    // Bind socket to a specific port
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {
        perror("Bind failed");
        exit(EXIT_FAILURE);
    }

    // Listen for incoming connections
    if (listen(server_fd, MAX_CLIENTS) < 0) {
        perror("Listen failed");
        exit(EXIT_FAILURE);
    }

    cout << "Server is listening on port " << PORT << endl;

    while (true) {
        // Accept incoming connection
        if ((new_sockfd = accept(server_fd, (struct sockaddr *)&address,
                                 (socklen_t *)&addrlen)) < 0) {
            perror("Accept failed");
            exit(EXIT_FAILURE);
        }

        cout << "New client connected" << endl;

        // Create a new thread to handle the connection
        thread t(clientHandler, new_sockfd);
        t.detach();
    }

    return 0;
}

客户端代码：

#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <arpa/inet.h>

using namespace std;

const char *SERVER_IP = "127.0.0.1";
const int SERVER_PORT = 8080;

int main() {
    int sockfd;
    struct sockaddr_in server_address;

    // Create socket file descriptor
    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        cout << "Socket creation failed" << endl;
        return -1;
    }

    // Set server address and port
    server_address.sin_family = AF_INET;
    server_address.sin_port = htons(SERVER_PORT);

    // Convert IPv4 and IPv6 addresses from text to binary form
    if (inet_pton(AF_INET, SERVER_IP, &server_address.sin_addr) <= 0) {
        cout << "Invalid address/ Address not supported" << endl;
        return -1;
    }

    // Connect to the server
    if (connect(sockfd, (struct sockaddr *)&server_address, sizeof(server_address)) < 0) {
        cout << "Connection failed" << endl;
        return -1;
    }

    cout << "Connected to server" << endl;

    while (true) {
        // Send a message to the server
        char buffer[1024];
        memset(buffer, 0, sizeof(buffer));
        cout << "Enter message: ";
        cin.getline(buffer, sizeof(buffer));
        send(sockfd, buffer, strlen(buffer), 0);

        // Receive a message from the server
        memset(buffer, 0, sizeof(buffer));
        recv(sockfd, buffer, sizeof(buffer), 0);
        cout << "Received message: " << buffer << endl;
    }

    close(sockfd);

    return 0;
}

在这个案例中，服务端与客户端通过 TCP/IP 进行通信，服务端使用一个线程来处理每个连接，而客户端发送消息并接收服务器的响应。当客户端断开连接时，服务端会关闭与该客户端的连接，并释放其线程。

需要注意的是，此代码未考虑一些错误处理和异常情况，仅供参考。