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

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

QT TCP服务器实现_服务器
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 <QWidget>
#include <QTcpServer>
#include <QTcpSocket>
 
namespace Ui {
class Widget;
}
 
class Widget : public QWidget
{
    Q_OBJECT
 
public:
    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 <QHostInfo>
 
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
    QList<QHostAddress> addrList = hostInfo.addresses();
    for(int i=0;i<addrList.count();i++)
    {
        QHostAddress host = addrList.at(i);
 
        if(QAbstractSocket::IPv4Protocol == host.protocol())
        {
            QString ip = host.toString();
            ui->comboBox->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ip
    QString 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('\n');
    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

QT TCP服务器实现_#include_02