TCP 服务器

在 Qt 中创建 TCP 服务器也很容易，的确，类 QTcpServer 已经提供了我们所需要做的所有服务器。

首先，我们需要监听任何 ip，一个随机端口，并在连接客户端时执行某些操作。像那样：

 _server.listen(QHostAddress::Any, 4242);
 connect(&_server, SIGNAL(newConnection()), this, SLOT(onNewConnection()));

然后，当这是一个新连接时，我们可以将它添加到客户端列表并准备读取/写入套接字。像那样：

   QTcpSocket *clientSocket = _server.nextPendingConnection();
   connect(clientSocket, SIGNAL(readyRead()), this, SLOT(onReadyRead()));
   connect(clientSocket, SIGNAL(stateChanged(QAbstractSocket::SocketState)), this, SLOT(onSocketStateChanged(QAbstractSocket::SocketState)));
   _sockets.push_back(clientSocket);

当客户端断开连接时，stateChanged(QAbstractSocket::SocketState) 允许我们将套接字删除到列表中。

这是一个基本的聊天服务器：

main.cpp 中：

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

mainwindow.h：

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QTcpServer>
#include <QTcpSocket>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

public slots:
    void onNewConnection();
    void onSocketStateChanged(QAbstractSocket::SocketState socketState);
    void onReadyRead();
private:
    Ui::MainWindow *ui;
    QTcpServer  _server;
    QList<QTcpSocket*>  _sockets;
};

#endif // MAINWINDOW_H

mainwindow.cpp：

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QDebug>
#include <QHostAddress>
#include <QAbstractSocket>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow),
    _server(this)
{
    ui->setupUi(this);
    _server.listen(QHostAddress::Any, 4242);
    connect(&_server, SIGNAL(newConnection()), this, SLOT(onNewConnection()));
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::onNewConnection()
{
   QTcpSocket *clientSocket = _server.nextPendingConnection();
   connect(clientSocket, SIGNAL(readyRead()), this, SLOT(onReadyRead()));
   connect(clientSocket, SIGNAL(stateChanged(QAbstractSocket::SocketState)), this, SLOT(onSocketStateChanged(QAbstractSocket::SocketState)));

    _sockets.push_back(clientSocket);
    for (QTcpSocket* socket : _sockets) {
        socket->write(QByteArray::fromStdString(clientSocket->peerAddress().toString().toStdString() + " connected to server !\n"));
    }
}

void MainWindow::onSocketStateChanged(QAbstractSocket::SocketState socketState)
{
    if (socketState == QAbstractSocket::UnconnectedState)
    {
        QTcpSocket* sender = static_cast<QTcpSocket*>(QObject::sender());
        _sockets.removeOne(sender);
    }
}

void MainWindow::onReadyRead()
{
    QTcpSocket* sender = static_cast<QTcpSocket*>(QObject::sender());
    QByteArray datas = sender->readAll();
    for (QTcpSocket* socket : _sockets) {
        if (socket != sender)
            socket->write(QByteArray::fromStdString(sender->peerAddress().toString().toStdString() + ": " + datas.toStdString()));
    }
}

（使用与前一个示例相同的 mainwindow.ui）