通信是个基础的问题，通常要具有连接、断开及消息的发送和接收，一个功能完备的TCP类应该具有连接断开和消息接收的对外接口。现在有一个项目通过TCP实现进程间通信，通过解析发送的字符串识别、执行彼此的命令。现使用c++ Asio独立库实现功能，代码如下。

#pragma once
#include <afxwin.h>         // MFC core and standard components
#include <iostream>
#include <string>
#include <thread>
#include <functional>
#include <asio.hpp>class TCPClient : public std::enable_shared_from_this<TCPClient> {
private:asio::io_context io_context;asio::ip::tcp::socket socket{ io_context };std::function<void(const CString&)> dataReceivedCallback;std::function<void()> disconnectedCallback; // 断开连接回调std::array<char, 10240> buffer;bool connected = false;private:std::string CStringToStdString(CString cstr){// 将 CString 转换为 std::stringCT2A ascii(cstr); // 转换为 ANSI 字符串return std::string(ascii);}char* CStringToChar(CString& cstr){return (char*)CStringToStdString(cstr).data();}public:TCPClient(): socket(io_context) { }bool Connect(const CString& serverIP, int port){return Connect(CStringToStdString(serverIP), port);}bool Connect(const std::string& serverIP, int port) {if (IsConnected()) return true;try {asio::ip::tcp::resolver resolver(io_context);auto endpoints = resolver.resolve(serverIP, std::to_string(port));asio::connect(socket, endpoints);connected = true;StartReceiving();}catch (const std::exception& e) {std::cerr << "Connection error: " << e.what() << std::endl;return false;}}void Disconnect() {if (connected) {asio::error_code ec;socket.shutdown(asio::ip::tcp::socket::shutdown_both, ec);socket.close(ec);connected = false;if (disconnectedCallback) {disconnectedCallback();}}}bool Send(const CString& data) {return Send(CStringToStdString(data));}bool Send(const std::string& data) {if (!IsConnected()) return false;try {asio::write(socket, asio::buffer(data));return true;}catch (const std::exception& e) {std::cerr << "Send error: " << e.what() << std::endl;return false;}}void SetDataReceivedCallback(std::function<void(const CString&)> callback) {dataReceivedCallback = callback;}void SetDisconnectedCallback(std::function<void()> callback) {disconnectedCallback = callback;}bool IsConnected() const {return connected;}private:void StartReceiving() {Receive(); // 开始接收数据std::thread([this]() { io_context.run(); }).detach(); // 在新线程中运行事件循环}void Receive() {auto self = shared_from_this();socket.async_read_some(asio::buffer(buffer),[this, self](const asio::error_code& ec, size_t len) {if (!ec) {std::string data(buffer.data(), len);if (dataReceivedCallback) {// 调用回调函数，将接收到的数据传递给主线程中的类CString receivedData(data.c_str());dataReceivedCallback(receivedData);}Receive(); // 继续接收数据}else {Disconnect();}});}};

上面的Client类作为对外接口的回调函数dataReceivedCallback、dataReceivedCallback均在子线程中执行，现在不想改动该类，想在外部处理实现回调函数在主线程中执行的功能（主要是设计刷新界面）。
关于子、主线程通信，QT的信号槽可以相对方便地实现该功能，至于MFC，一般通过PostMessage加上自定义消息实现，虽然麻烦点，但也能实现功能。现在主线程类中实现子线程传消息到主线程。

1. 自定义消息

// 在某个全局头文件中
#define WM_USER_DATA_RECEIVED (WM_USER + 1)
#define WM_USER_TCP_DISCONNECTED (WM_USER + 2)

2. 响应函数声明
下面的函数将会在主线程执行

//声明
protected:afx_msg LRESULT OnDataReceived(WPARAM wParam, LPARAM lParam);afx_msg LRESULT OnTcpDisconnected(WPARAM wParam, LPARAM lParam);DECLARE_MESSAGE_MAP()
private:void onTcpClientDataReceived(CString data);

3. 响应函数定义

LRESULT CMFCApplication6Dlg::OnDataReceived(WPARAM wParam, LPARAM lParam) {CString* pData = reinterpret_cast<CString*>(lParam);if (pData != nullptr) {// 处理接收到的数据onTcpClientDataReceived(pData->GetString());delete pData; // 清理内存pData = nullptr;}else{AfxMessageBox(_T("pData is nullptr!"));}return 0; // 返回值可以是0或者其他值
}LRESULT CMFCApplication6Dlg::OnTcpDisconnected(WPARAM wParam, LPARAM lParam)
{threadInfo();return 0;
}

4. 建立消息与响应应函数的映射

BEGIN_MESSAGE_MAP(CMFCApplication6Dlg, CDialogEx)ON_MESSAGE(WM_USER_DATA_RECEIVED, &CMFCApplication6Dlg::OnDataReceived)ON_MESSAGE(WM_USER_TCP_DISCONNECTED, &CMFCApplication6Dlg::OnTcpDisconnected)
END_MESSAGE_MAP()

5. 为消息接收、连接断开建立回调函数，并在回调函数中发送自定义消息实现子、主线程通信
需要注意的是，PostMessage第三个参数就是传参的（没怎么研究PostMessage，在此不求甚解），消息接收函数中有个参数，而连接断开不需要参数，第三个参数置为0即可。

std::shared_ptr<TCPClient> m_client = std::make_shared<TCPClient>();m_client->SetDataReceivedCallback([&](const CString& data){CString* pData = new CString(data);BOOL result = PostMessage(WM_USER_DATA_RECEIVED, 0, (LPARAM)pData);if (!result) {// 处理消息发送失败std::cerr << "PostMessage failed: " << GetLastError() << std::endl;}});m_client->SetDisconnectedCallback([&]() {BOOL result = PostMessage(WM_USER_TCP_DISCONNECTED, 0, 0);if (!result) {// 处理消息发送失败std::cerr << "PostMessage failed: " << GetLastError() << std::endl;}});