QT 实现TCP通信

概述

使用QT来实现TCP连接并通信

实现

第一步，在.pro文件中添加network库

QT += network

服务端
服务端使用了QTcpSever和QTcpSocket类，QTcpSever用于创建TCP服务，QTcpSocket用于控制建立的socket连接。其实现的步骤如下：
1、创建TCPserver对象

m_server = new QTcpServer();

2、使用listen()监听IP端口

m_server->listen(QHostAddress::Any, tcp_port);

QHostAddress::Any表示任意IP地址，QT中QHostAddress类用于提供一个IP地址，常用的还有：QHostAddress::LocalHost(本地主机地址)、QHostAddress::AnyIPv4(任意的IPv4地址)等等
tcp_port即端口号

3、当有新的连接时，会发出newConnection信号，触发槽函数接受连接并获取连接的套接字QTcpSocket

connect(m_server, SIGNAL(newConnection()), SLOT(onNewConnection()));

m_socket = m_server->nextPendingConnection();  //获取连接套接字

4、绑定disconnected和readyRead信号

connect(m_socket, SIGNAL(disconnected()), SLOT(onDisconnected()));
connect(m_socket, SIGNAL(readyRead()), SLOT(onReadyRead()));

disconnected：表示有连接断开
readyRead：表示Socket缓存接收到新的数据

5、读取客户端发来的数据

m_socket->readAll();

服务端整体代码如下：

//TcpServer.h
#ifndef TCPSERVER_H
#define TCPSERVER_H

#include <QObject>
#include <QTcpServer>
#include <QTcpSocket>

class TcpServer : public QObject {
    Q_OBJECT

public:
    explicit TcpServer(uint16_t tcp_port);
    ~TcpServer() {};

public:

private slots:
    void onDisconnected();
    void onNewConnection();
    void onReadyRead();

private:
    QTcpServer* m_server;
    QTcpSocket* m_socket;

};

#endif // TCPSERVER_H

//TcpServer.cpp
#include "TcpServer.h"
#include <QTcpServer>
#include <QTcpSocket>

TcpServer::TcpServer(uint16_t tcp_port):
    m_server(new QTcpServer(this))  //创建TCP服务
{
    m_server->listen(QHostAddress::Any, tcp_port);  //监听IP端口
    connect(m_server, SIGNAL(newConnection()), this, SLOT(onNewConnection()));
}

void TcpServer::onNewConnection()
{
    m_socket = m_server->nextPendingConnection();  //获取连接套接字

    connect(m_socket, SIGNAL(disconnected()), SLOT(onDisconnected()));
    connect(m_socket, SIGNAL(readyRead()), SLOT(onReadyRead()));
    qDebug() << "new connection accepted!!";

}

void TcpServer::onReadyRead()
{
    qDebug() << m_socket->readAll();  //读取socket中的数据并打印
}

void TcpServer::onDisconnected()
{
    qDebug() << "client disconnected!!";
}

客户端
客户端的实现就相对简单很多，只使用了QTcpSocket类，其实现的步骤如下：
1、创建QTcpSocket对象

m_clientSocket = new QTcpSocket();

2、使用connectToHost()连接服务器IP和端口号

m_clientSocket->connectToHost(QHostAddress::LocalHost, tcp_port);

3、绑定connected和disconnected信号

connect(m_clientSocket, SIGNAL(connected()), SLOT(onConnected()));
connect(m_clientSocket, SIGNAL(disconnected()), SLOT(onDisconnected()));

connected：表示连接成功

4、发送数据给服务端

m_clientSocket->write("hello");

客户端整体代码如下：

//TcpClient.h
#ifndef TCPCLIENT_H
#define TCPCLIENT_H

#include <QTcpSocket>

class Tcpclient : public QObject
{
    Q_OBJECT
public:
    Tcpclient(uint16_t tcp_port);
    virtual ~Tcpclient() {}

private slots:
    void onConnected();
    void onDisconnected();

private:
    QTcpSocket* m_clientSocket;
};

#endif // TCPCLIENT_H

//TcpClient.cpp
#include "Tcpclient.h"

Tcpclient::Tcpclient(uint16_t tcp_port)
{
    m_clientSocket = new QTcpSocket();
    m_clientSocket->connectToHost(QHostAddress::LocalHost, tcp_port);

    connect(m_clientSocket, SIGNAL(connected()), SLOT(onConnected()));
    connect(m_clientSocket, SIGNAL(disconnected()), SLOT(onDisconnected()));
}

void Tcpclient::onConnected()
{
    qDebug() << "connect ok!";
    m_clientSocket->write("hello");
}

void Tcpclient::onDisconnected()
{
    m_clientSocket->disconnectFromHost();  //断开与服务端的连接
}

此外，服务端也可以发送数据给客户端，客户端绑定readyRead信号来接收

进一步讨论

我们都知道，在使用原生socket来实现TCP时，为了满足多个客户端的连接，通常会使用select()、epoll()来实现IO复用。在这一点上QT封装的TCP已经帮我们实现了。但是我们如何在槽函数中获取当前发出此信号的socket呢？
我们可以使用QObject::sender()

QObject::Sender()返回发送信号的对象的指针，返回类型为QObject *

例如在上文服务端的onDisconnected()槽函数中，可以使用sender()来获取当前发出断开信号disconnected的socket对象，并销毁它

void TcpServer::onDisconnected()
{
    sender()->deleteLater();  //获取断开连接的socket对象并销毁
    qDebug() << "client disconnected!!";
}

因此在槽函数中可以根据sender()的不同来进行不同的处理