Qt Qt Network TCP Client

Example

To create a TCP connection in Qt, we will use QTcpSocket. First, we need to connect with connectToHost.

So for example, to connect to a local tcp serveur: _socket.connectToHost(QHostAddress("127.0.0.1"), 4242);

Then, if we need to read datas from the server, we need to connect the signal readyRead with a slot. Like that:

connect(&_socket, SIGNAL(readyRead()), this, SLOT(onReadyRead()));

and finally, we can read the datas like that:

void MainWindow::onReadyRead()
{
    QByteArray datas = _socket.readAll();
    qDebug() << datas;
}

To write datas, you can use the write(QByteArray) method:

_socket.write(QByteArray("ok !\n"));

So a basic TCP Client can look like that:

main.cpp:

#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 <QTcpSocket>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

public slots:
    void onReadyRead();

private:
    Ui::MainWindow *ui;
    QTcpSocket  _socket;
};

#endif // MAINWINDOW_H

mainwindow.cpp:

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

#include <QDebug>
#include <QHostAddress>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow),
    _socket(this)
{
    ui->setupUi(this);
    _socket.connectToHost(QHostAddress("127.0.0.1"), 4242);
    connect(&_socket, SIGNAL(readyRead()), this, SLOT(onReadyRead()));
}

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

void MainWindow::onReadyRead()
{
    QByteArray datas = _socket.readAll();
    qDebug() << datas;
    _socket.write(QByteArray("ok !\n"));
}

mainwindow.ui: (empty here)

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>400</width>
    <height>300</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralWidget"/>
  <widget class="QMenuBar" name="menuBar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>400</width>
     <height>25</height>
    </rect>
   </property>
  </widget>
  <widget class="QToolBar" name="mainToolBar">
   <attribute name="toolBarArea">
    <enum>TopToolBarArea</enum>
   </attribute>
   <attribute name="toolBarBreak">
    <bool>false</bool>
   </attribute>
  </widget>
  <widget class="QStatusBar" name="statusBar"/>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <resources/>
 <connections/>
</ui>