1.TCP通信概述

tcp是一种用于数据传输的低级网络协议，它是可靠的、面向流、面向连接的传输协议，特别适合于连续数据传输。

服务器端使用QTcpServer用于端口监听，建立服务器；QTcpSocket用于建立连接后使用套接字进行通信。

2.常用API

void close() 关闭服务器，停止网络监听

(相关资料图)

bool listen() 在给定IP地址和端口上进行监听

QTcpSocket *nextPendingConnection() 返回下一个等待接入的连接

bool waitForNewConnection() 以阻塞方式等待新连接

3.示例

服务器端程序首先使用listen()开始服务器监听，可以指定IP和端口，一般一个服务器程序只监听某个端口的网络连接。

当有新的客户端接入时，QTcpServer内部的incomingConnection()函数会创建一个与客户端连接的QTcpSocket对象，然后发射信号newConnection()。

所以在客户端与服务器建立TCP连接后，具体的数据通信是通过QTcpSocket完成的。

#ifndef WIDGET_H#define WIDGET_H#include #include #include namespace Ui {class Widget;}class Widget : public QWidget{Q_OBJECTpublic:explicit Widget(QWidget *parent = 0);~Widget();private slots:void on_btnStart_clicked();void on_btnStop_clicked();void on_btnClear_clicked();void on_newConnection();void onConnected();void onDisConnected();void onStateChanged(QAbstractSocket::SocketState socketState);void onReadyRead();void on_btnSend_clicked();private:Ui::Widget *ui;QTcpServer *m_tcpServer = nullptr;QTcpSocket *m_tcpSocket = nullptr;};#endif // WIDGET_H

#include "widget.h"#include "ui_widget.h"#include Widget::Widget(QWidget *parent) :QWidget(parent),ui(new Ui::Widget){ui->setupUi(this);//本地主机名QString hostName = QHostInfo::localHostName();//本机IP地址QHostInfo hostInfo = QHostInfo::fromName(hostName);//IP地址列表QListaddrList = hostInfo.addresses();for(int i=0;icomboBox->addItem(ip);}}m_tcpServer = new QTcpServer(this);connect(m_tcpServer,&QTcpServer::newConnection,this,&Widget::on_newConnection);}Widget::~Widget(){delete ui;}void Widget::on_btnStart_clicked(){//当前选择的ipQString ip = ui->comboBox->currentText();//端口int port = ui->lineEditPort->text().toInt();QHostAddress addr(ip);//监听m_tcpServer->listen(addr,port);ui->plainTextEdit->appendPlainText("**开始监听...");ui->plainTextEdit->appendPlainText("**服务器地址: "+m_tcpServer->serverAddress().toString());ui->plainTextEdit->appendPlainText("**服务器端口: "+QString::number(m_tcpServer->serverPort()));ui->btnStart->setEnabled(false);ui->btnStop->setEnabled(true);ui->lbListen->setText("正在监听");}void Widget::on_btnStop_clicked(){if(m_tcpServer->isListening()){m_tcpServer->close();ui->btnStart->setEnabled(true);ui->btnStop->setEnabled(false);ui->lbListen->setText("停止监听");ui->plainTextEdit->appendPlainText("**停止监听**");}}void Widget::on_btnClear_clicked(){ui->plainTextEdit->clear();}void Widget::on_newConnection(){m_tcpSocket = m_tcpServer->nextPendingConnection();connect(m_tcpSocket,&QTcpSocket::connected,this,&Widget::onConnected);connect(m_tcpSocket,&QTcpSocket::disconnected,this,&Widget::onDisConnected);connect(m_tcpSocket,&QTcpSocket::stateChanged,this,&Widget::onStateChanged);connect(m_tcpSocket,&QTcpSocket::readyRead,this,&Widget::onReadyRead);ui->plainTextEdit->appendPlainText("** client socket connected");ui->plainTextEdit->appendPlainText("** peer address: "+m_tcpSocket->peerAddress().toString());ui->plainTextEdit->appendPlainText("** peer port: "+QString::number(m_tcpSocket->peerPort()));}void Widget::onConnected(){ui->plainTextEdit->appendPlainText("** client socket connected");ui->plainTextEdit->appendPlainText("** peer address: "+m_tcpSocket->peerAddress().toString());ui->plainTextEdit->appendPlainText("** peer port: "+QString::number(m_tcpSocket->peerPort()));}void Widget::onDisConnected(){ui->plainTextEdit->appendPlainText("** client socket disconnected");m_tcpSocket->deleteLater();}void Widget::onStateChanged(QAbstractSocket::SocketState socketState){switch (socketState){case QAbstractSocket::UnconnectedState:ui->lbListen->setText("UnconnectedState");break;case QAbstractSocket::HostLookupState:ui->lbListen->setText("HostLookupState");break;case QAbstractSocket::ConnectedState:ui->lbListen->setText("ConnectedState");break;case QAbstractSocket::ConnectingState:ui->lbListen->setText("ConnectingState");break;case QAbstractSocket::BoundState:ui->lbListen->setText("BoundState");break;case QAbstractSocket::ClosingState:ui->lbListen->setText("ClosingState");break;case QAbstractSocket::ListeningState:ui->lbListen->setText("ListeningState");break;}}void Widget::onReadyRead(){while(m_tcpSocket->canReadLine()){ui->plainTextEdit->appendPlainText("[in] "+m_tcpSocket->readLine());}}void Widget::on_btnSend_clicked(){QString msg =ui->lineEdit->text();ui->plainTextEdit->appendPlainText("[out]"+msg);QByteArray str = msg.toUtf8();str.append("
");m_tcpSocket->write(str);}

一般TCP服务器程序允许多个客户端接入，本例只演示了一个客户端接入，为了使每个socket连接通信互不影响，一般采用多线程，即为一个socket连接创建一个线程。

4.与客户端通信

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