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Qt

The most complete cross-platform C++ application framework — GUI and much else.

Developer UtilitiesCLI/UtilsC++
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What it is

Qt is a comprehensive C++ framework for developing cross-platform applications and graphical user interfaces (GUIs). It provides tools for GUI design, event handling, networking, threading, and more.

Qt provides modules for GUI, networking, multimedia, database access, and more. It follows an object-oriented and signal-slot architecture to handle events and interactions efficiently.

Licence
LGPL 3 or commercial
Watch for
The moc preprocessor means Qt shapes your build system too

When to use it

The question documentation cannot answer for you — because it cannot recommend something else.

Reach for it when

  • Desktop applications that must look native on Windows, macOS and Linux
  • Embedded devices with a graphical interface
  • You want widgets, networking, threading and serialisation from one coherent framework

Look elsewhere when

  • Licensing is a constraint — the commercial and LGPL terms need real consideration for closed-source products
  • You want a small library rather than a framework that shapes your whole codebase

Installation

sudo apt install qt5-default qtcreator

Getting started

The smallest useful thing you can do with it, and what each part means.

Simple GUI application
#include <QApplication>
#include <QLabel>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);
    QLabel label("Hello, Qt!");
    label.show();
    return app.exec();
}
Creates a basic Qt application with a window displaying 'Hello, Qt!'.
Button click with signal-slot
#include <QApplication>
#include <QPushButton>
#include <QObject>
#include <iostream>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);
    QPushButton button("Click Me");
    QObject::connect(&button, &QPushButton::clicked, [](){ std::cout << "Button clicked!" << std::endl; });
    button.show();
    return app.exec();
}
Demonstrates Qt's signal-slot mechanism by printing a message when a button is clicked.

Advanced usage

Where the library earns its place over a simpler alternative.

Using Qt for networking
// Use QTcpSocket, QUdpSocket, or QNetworkAccessManager for network operations.
Multithreading in Qt
// Use QThread or QtConcurrent for running tasks in parallel.
Database access
// Use QSqlDatabase and QSqlQuery to connect and interact with SQL databases.

Errors and fixes

The failures you are most likely to hit, and what actually resolves them.

QSqlError
Check database connection, credentials, and SQL query syntax.
QNetworkReply error
Handle network errors by checking error codes and implementing retries.

Best practices

  • Use signal-slot mechanism for event-driven programming instead of polling.
  • Keep UI code and business logic separate.
  • Use layouts instead of fixed coordinates for flexible GUI design.
  • Prefer modern C++ features when writing Qt applications.
  • Utilize Qt's resource system for managing assets like images and icons.

Alternatives

Comparable options, and the reason you would pick one over the other.

Background

Why it exists, and what it was reacting to.

Qt was first developed by Haavard Nord and Eirik Chambe-Eng in 1991. It became widely popular for building desktop, mobile, and embedded applications due to its cross-platform capabilities and rich set of libraries. Qt supports modern C++ and integrates with QML for declarative UI design.

Related libraries

Others in Developer Utilities for C++.

← All C++ librariesC++ guide