Qt Configure Options | Qt 6.4

- Qt 6.4
- Qt Configure Options
- Qt 6.4.1 Reference Documentation

# Qt Configure Options

configure is a command-line tool that supports you in building a custom version of Qt from source. It's part of the main Qt source directory.

Since Qt 6, configure is a wrapper around cmake. CMake can also be invoked directly. configure provides additional error checking and compatibility with Qt 5.

This page discusses some of the configure options. For the full list of options, enter the command configure -h.

Note: Unless stated otherwise, the commands on this page are for the Linux platforms. On macOS and Windows, the PATH and directory structure are different, therefore the commands will vary. Also, on Windows systems, the configure script is called configure.bat.

## Configure Workflow

configure must be called in a working build environment where CMake, compilers, and required build tools are readily available. Building Qt Sources lists such dependencies per platform.

After setting up such an environment, the typical workflow is to create a separate build directory, and then first run configure, then build Qt, and then install Qt:

     ~/qt-source/configure
     cmake --build . --parallel
     cmake --install .

You might want to experiment with different configure flags, and therefore run configure multiple times. Note that CMake caches configure options and information about the environment in a file called CMakeCache.txt. Delete this file when you want to start over without cached information.

## Source, Build, and Install Directories

The source directory contains the source code that is obtained from the source package or git repository. The build directory is where the build-related files, such as build system files, object files, and other intermediate files are stored. The install directory is where the binaries and libraries are installed, for use either by the system or by the application.

It's recommended to keep these directories separate by shadow-building and using the -prefix option. This enables you to keep the Qt source tree clean from the build artifacts and binaries, which are stored in a separate directory. This method is very convenient if you want to have multiple builds from the same source tree, but for different configurations. To shadow-build, run configure from a separate directory:

     mkdir ~/qt-build
     cd ~/qt-build
     ~/qt-source/configure -prefix /opt/Qt6

Configuring with the -prefix option means that the Qt binaries and libraries are installed into another directory, which is /opt/Qt6 in this case.

## Examples, Tests, and Tools

By default, configure only configures Qt's libraries and tools. You can use -make examples or -make tests to also build the examples or tests that come with Qt:

     ~/qt-source/configure -make examples -make tests

You can also configure Qt such that examples, tests, and tools are configured, but not built by default. If you set the CMake variables QT_BUILD_EXAMPLES_BY_DEFAULT, QT_BUILD_TESTS_BY_DEFAULT, and QT_BUILD_TOOLS_BY_DEFAULT to OFF, the respective parts will not be built by "cmake --build .". Instead, CMake will generate individual targets that you can then build individually.

Here we build Qt libraries and tools, but also the NotePad Example:

     ~/qt-source/configure -make examples -- -D QT_NO_MAKE_EXAMPLES=ON
     cmake --build . --parallel
     cmake --build . --parallel --target notepad

Note: The -developer-build option builds tests by default. See also Developer Builds below.

## Build Configurations

You can build Qt libraries and tools in various variants, each of them optimized for a different use case.

### Debug and Release Builds

-release tells the compiler to optimize the code, and not provide additional debug symbols alongside Qt and its tools.

-debug skips some optimizations to make it easier to debug Qt and its tools. This option also enables the generation of debug symbols that let you inspect the code and state of the built libraries in a debugger.

Finally, -debug-and-release lets you build both a debug and release variant of Qt libraries in one go. This is only supported if you configure a build for Windows.

There are further options to tweak the configurations:

- -force-debug-info: Creates a release build with debug information.
- -separate-debug-info: Extracts the debug information into a separate file.
- -optimize-size: Optimizes release builds for size instead of speed.

### Static and Shared Builds

Qt Modules can be built as separate libraries that an executable links to and loads at start time (for Qt libraries), or runtime (for Qt plugins). This is called a shared build and is the default configuration on most platforms. The matching configure option is -dynamic.

You can also build Qt such that an executable binary will include all Qt modules it links to and all Qt plugins it needs. This is called a static build and can be selected when configuring with the -static option.

## CMake Generators

When configuring, you can select a CMake generator. Note that CMake supports generators that cannot be used with Qt. Therefore, configure automatically selects a generator for you.

configure always uses the Ninja generator and build tool if a ninja executable is available. Ninja is both cross-platform, feature-rich, and performant, and recommended on all platforms. Use of other generators might work, but is not officially supported.

## Modules and Features

Qt consists of different modules whose sources can be found in different directories inside the top-level source directory. Users can explicitly exclude specific top-level directories to limit build times. Furthermore, each Qt module might have features that can also be explicitly enabled or disabled.

### Excluding Qt Modules

`configure`'s -skip option allows top-level source directories to be excluded from the Qt build. Note that some directories contain multiple Qt modules. For example, to exclude the Qt Wayland Compositor and the Qt Wayland integration plugin from the Qt build, provide -skip qtwayland as an option to configure.

     ~/qt-source/configure -skip qtwayland

### Including or Excluding Features

The -feature-<feature> and -no-feature-<feature> options include and exclude specific features, respectively.

For example, you can use the -no-feature-accessibility configure option to disable Accessibility support in Qt:

     ~/qt-source/configure -no-feature-accessibility

Use configure -list-features to show a list of all available features on the command line. Note that features can depend on other features, so disabling a feature might have side-effects on other features.

## Third-Party Libraries

The Qt source packages include third-party libraries. To set whether Qt should use the system's versions of the libraries or to use the bundled version, pass either -system or -qt before the name of the library to configure.

The table below summarizes some third-party options:

Library Name | Bundled in Qt | Installed in System
--- | --- | ---
zlib | -qt-zlib | -system-zlib
libjpeg | -qt-libjpeg | -system-libjpeg
libpng | -qt-libpng | -system-libpng
freetype | -qt-freetype | -system-freetype
PCRE | -qt-pcre | -system-pcre
HarfBuzz-NG | -qt-harfbuzz | -system-harfbuzz

It's also possible to disable support for these libraries by using -no instead of -qt.

configure in Qt 6 relies on CMake to locate third-party libraries. It does so by checking various system paths. If you installed libraries somewhere else, you can let CMake know this by setting or extending the CMAKE_PREFIX_PATH variable.

For a full list of options, consult the help with configure -help.

### SSL

Qt Network can be configured to support communication for Secure Sockets Layer (SSL) but does not implement the actual algorithms itself. It needs to leverage other libraries instead.

On Windows, Qt can use the system's Secure Channel library for this purpose (configure option -schannel). On macOS and iOS, Qt can be configured to use the SecureTransport API (configure option -securetransport).

The most feature-complete support that also works on almost all target platforms is provided by the OpenSSL Toolkit (option -openssl). Qt does require OpenSSL 1.1.1 or later.

Qt can be configured to use OpenSSL in three ways:

- Qt Network loads OpenSSL libraries (DLLs) when first needed, at runtime. If not found, the application continues to run but fails to handle SSL communication. This is enabled by using the configure option -openssl-runtime.
- Qt Network links against the OpenSSL libraries. If they cannot be found at load time, the application fails to start. This is enabled by using the configure option -openssl-linked.
- Qt Network compiles against a static version of the OpenSSL libraries, and OpenSSL becomes part of the Qt Network library. This is enabled by using the configure option openssl-linked and setting the OPENSSL_USE_STATIC_LIBS variable to ON.

Set the CMake variable OPENSSL_ROOT_DIR if OpenSSL is not installed in a standard location, and therefore not found by configure.

See Secure Sockets Layer (SSL) Classes for further instructions on Qt with SSL support.

## Cross-Compilation Options

To configure Qt for cross-platform development and deployment, you need to have a matching Qt version for the host machine first. Also, the development toolchain for the target platform needs to be set up. This set up varies among the Supported Platforms.

Common options are:

- -external-hostbindir - Path to Qt tools built for this machine.
- -device - Select devices/mkspec for the qmake companion files.
- -device-option - sets additional qmake variables.

Note: Toolchains for non-desktop targets often come with a so-called sysroot that Qt needs to be configured against.

## Developer Builds

The -developer-build configure option is a convenience option that optimizes the build for developing Qt itself. It shouldn't be used for building Qt variants that ship to customers.

Libraries in a developer build contain more exported symbols than a standard build, and all Qt code compiles with a higher warning level. It also changes the default prefix to the build directory, avoiding the need to install Qt before testing things, and finally enables the compilation of Qt's auto-tests by default.

## Specific Options for Platforms

The following pages provide guidelines on how to configure Qt for specific platform development:

- Building Qt for QNX
- Configure an Embedded Linux Device
- Qt for Android - Building from Source
- Qt for Linux/X11 - Building from Source
- Qt for Windows - Building from Source
- Qt for macOS - Building from Source
- Qt for INTEGRITY - Monolith Project Tutorial
- Qt for iOS - Building from Source
- Qt for WebAssembly - Building from Source