qt tcp客户端的例子

下面是一个简单的QT TCP客户端的例子，可以用来连接服务器并发送、接收数据。

#include <QtNetwork>
#include <QTcpSocket>

class TcpClient : public QObject
{
    Q_OBJECT

public:
    TcpClient(QObject *parent = 0);

public slots:
    void connectToServer();
    void sendMessage(const QString &message);

private slots:
    void readData();
    void displayError(QAbstractSocket::SocketError socketError);

private:
    QTcpSocket *tcpSocket;
};

TcpClient::TcpClient(QObject *parent)
    : QObject(parent)
{
    tcpSocket = new QTcpSocket(this);

    connect(tcpSocket, SIGNAL(readyRead()), this, SLOT(readData()));
    connect(tcpSocket, SIGNAL(error(QAbstractSocket::SocketError)), this, SLOT(displayError(QAbstractSocket::SocketError)));
}

void TcpClient::connectToServer()
{
    tcpSocket->connectToHost("localhost", 8000);
}

void TcpClient::sendMessage(const QString &message)
{
    QByteArray block;
    QDataStream out(&block, QIODevice::WriteOnly);
    out.setVersion(QDataStream::Qt_5_9);
    out << quint16(0) << message;

    out.device()->seek(0);
    out << quint16(block.size() - sizeof(quint16));

    tcpSocket->write(block);
}

void TcpClient::readData()
{
    QDataStream in(tcpSocket);
    in.setVersion(QDataStream::Qt_5_9);

    if (tcpSocket->bytesAvailable() < (int)sizeof(quint16))
        return;

    quint16 blockSize;
    in >> blockSize;

    if (tcpSocket->bytesAvailable() < blockSize)
        return;

    QString message;
    in >> message;

    qDebug() << "Received message: " << message;
}

void TcpClient::displayError(QAbstractSocket::SocketError socketError)
{
    qDebug() << "Socket error: " << tcpSocket->errorString();
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    TcpClient client;
    client.connectToServer();
    client.sendMessage("Hello, server!");

    return a.exec();
}

这个例子中，TcpClient 类继承自 QObject，包含了连接服务器、发送消息、读取数据和处理错误等功能。其中，connectToServer() 方法用于连接服务器，sendMessage() 方法用于发送消息，readData() 方法用于读取数据，displayError() 方法用于处理错误。

在 main() 函数中，首先创建了 TcpClient 的实例，然后调用 connectToServer() 方法连接服务器，并通过 sendMessage() 方法发送一条消息。最后调用 a.exec() 进入事件循环，等待数据的读取和错误的处理。