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Minimal CMake

In order to generate the project, we will use cmake. This tool will generate a build system of your choice using configuration files named CMakeLists.txt.

You can launch cmake using the basic command cmake, or use the GUI apps like ccmake or cmake-gui.

Requirements

You will need:

The version 6 of Qt requires at least c++17, in the following example we will ask for c++20 because why not.

Minimal cmake project

First we will need to initialize the cmake project.

Folder structure

Technically, for a minimum project need only a single CMakeFile.txt and your source files. But for this project, we propose the following structure:

qml-template
    ├─ CMakeLists.txt #will be called the `root CMakeLists`
    └─ src
        ├─ CMakeLists.txt
        └─ qmlApp
            ├─ app
            ├─ assets
            ├─ widgets
            └─ CMakeLists.txt #will be called the `app CMakeLists`

This structure will be used all along this course, but feel free to use your own.

Additional cmake file

If you followed the proposed folder structure, you will need to add a CMakeLists in the src folder that contains the following line:

add_subdirectory(qmlApp)

To do that, we need at least the following lines in the root CMakeLists:

cmake_minimum_required(VERSION 3.21)

project(qml-template LANGUAGES C CXX VERSION 1.0.0)

You will also need to have at least a library or an executable, but we will see that in the next part.

Find Qt

As any other third parties, we will need to first find it using a find_package.

To do that, you can add the following line in the root CMakeLists

find_package(Qt6 6.8 REQUIRED COMPONENTS Core Qml Quick Widgets)

If Qt is not found, you will have to set the Qt6_DIR manually.

How to set the Qt6_DIR

Usually the path is /path/to/qt/dir/{qt_version}/{compiler}/lib/cmake/Qt6.

With qt_version the full version (ex: 6.8.6) and compiler the name of the compiler used (ex: gcc_64)

To set it in the cmake build, you can either:

  • Use cmake-gui

image

  • Add the option in the cmake command:

cmake . -DQt6_DIR=/path/to/qt/dir/{qt_version}/{compiler}/lib/cmake/Qt6

Setup project

Once the library is found, we will need to call qt_standard_project_setup in order to set the default values of some cmake variables (see the full list here)

Thanks to this function, we no longer need to set CMAKE_AUTOMOC or CMAKE_AUTOUIC as we did when using Qt5.

Note

This function will also include GNUInstallDirs

Example

In the end, here is the full content of the root CMakeLists:

cmake_minimum_required(VERSION 3.21)

project(qml-template LANGUAGES C CXX VERSION 1.0.0)

set(CMAKE_CXX_STANDARD 20) #Qt6 requires at least cpp17
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 6.8 REQUIRED COMPONENTS Core Qml Quick Widgets)
if(Qt6_FOUND)
    message(STATUS "Qt found, version ${Qt6_VERSION}")
    qt_standard_project_setup(REQUIRES 6.8)
endif()

Note

If you followed the proposed folder structure, you will need to add another line:

add_subdirectory(src)

This line will notify cmake that there is a CMakeLists in the given folder (here the src folder)

So this gives us the following code:

cmake_minimum_required(VERSION 3.21)

project(qml-template LANGUAGES C CXX VERSION 1.0.0)

set(CMAKE_CXX_STANDARD 20) #Qt6 requires at least cpp17
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 6.8 REQUIRED COMPONENTS Core Qml Quick Widgets)
if(Qt6_FOUND)
    message(STATUS "Qt found, version ${Qt6_VERSION}")
    qt_standard_project_setup(REQUIRES 6.8)
endif()

add_subdirectory(src)