在windows中用C++完成以下功能，在主函数中插入TCP socket客户端通讯函数，当程序启动时与主机通讯，当返回特定字符串后进行主函数之后的代码。主函数完成后利用TCP发送特定字符串，并关闭TCP通讯

以下是一个示例代码，实现了上述功能：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <winsock2.h>

#pragma comment(lib, "ws2_32.lib")

#define SERVER_IP "127.0.0.1"
#define SERVER_PORT 12345
#define RESPONSE_MSG "Hello, world!"

void client_communication() {
    WSADATA wsaData;
    if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {
        printf("WSAStartup failed.\n");
        return;
    }

    SOCKET clientSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (clientSocket == INVALID_SOCKET) {
        printf("Failed to create socket.\n");
        WSACleanup();
        return;
    }

    struct sockaddr_in serverAddress;
    memset(&serverAddress, 0, sizeof(serverAddress));
    serverAddress.sin_family = AF_INET;
    serverAddress.sin_addr.s_addr = inet_addr(SERVER_IP);
    serverAddress.sin_port = htons(SERVER_PORT);

    if (connect(clientSocket, (struct sockaddr*)&serverAddress, sizeof(serverAddress)) == SOCKET_ERROR) {
        printf("Failed to connect to server.\n");
        closesocket(clientSocket);
        WSACleanup();
        return;
    }

    char buffer[1024];
    int len = recv(clientSocket, buffer, 1024, 0);
    if (len == SOCKET_ERROR) {
        printf("Failed to receive data.\n");
        closesocket(clientSocket);
        WSACleanup();
        return;
    }
    buffer[len] = '\0';
    if (strcmp(buffer, RESPONSE_MSG) != 0) {
        printf("Received unexpected response: %s\n", buffer);
        closesocket(clientSocket);
        WSACleanup();
        return;
    }

    // Do something after receiving the expected response
    printf("Received expected response: %s\n", buffer);

    // Send a message to the server
    const char* msg = "Hello from client!";
    if (send(clientSocket, msg, strlen(msg), 0) == SOCKET_ERROR) {
        printf("Failed to send data.\n");
    }

    // Close the socket and clean up
    closesocket(clientSocket);
    WSACleanup();
}

int main() {
    // Connect to server and wait for response
    client_communication();

    // Do something after the communication
    printf("Program finished.\n");

    // Send a message to the server to indicate the end of communication
    WSADATA wsaData;
    if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {
        printf("WSAStartup failed.\n");
        return -1;
    }

    SOCKET clientSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (clientSocket == INVALID_SOCKET) {
        printf("Failed to create socket.\n");
        WSACleanup();
        return -1;
    }

    struct sockaddr_in serverAddress;
    memset(&serverAddress, 0, sizeof(serverAddress));
    serverAddress.sin_family = AF_INET;
    serverAddress.sin_addr.s_addr = inet_addr(SERVER_IP);
    serverAddress.sin_port = htons(SERVER_PORT);

    if (connect(clientSocket, (struct sockaddr*)&serverAddress, sizeof(serverAddress)) == SOCKET_ERROR) {
        printf("Failed to connect to server.\n");
        closesocket(clientSocket);
        WSACleanup();
        return -1;
    }

    const char* msg = "End of communication";
    if (send(clientSocket, msg, strlen(msg), 0) == SOCKET_ERROR) {
        printf("Failed to send data.\n");
    }

    closesocket(clientSocket);
    WSACleanup();

    return 0;
}

在这个程序中，`client_communication()`函数实现了与服务器进行通讯的功能。程序启动后，它会创建一个TCP客户端socket，并尝试连接到指定的服务器地址和端口号。一旦连接成功，它会尝试接收数据，如果接收到的数据不是预期的字符串，则会退出函数并关闭socket。如果接收到的数据是预期的字符串，则会打印出来，并执行主函数中的后续代码。在主函数的最后，它会再次创建一个TCP客户端socket，并向服务器发送一个特定的字符串，以表示通讯结束。最终，它会关闭所有socket并清理资源。