KDECompilerSettings

Set useful compile and link flags for C++ (and C) code.

Enables many more warnings than the default, and sets stricter modes for some compiler features. By default, exceptions are disabled; kde_target_enable_exceptions() can be used to re-enable them for a specific target.

NB: it is recommended to include this module with the NO_POLICY_SCOPE flag, otherwise you may get spurious warnings with some versions of CMake.

Since 5.85 newer settings are controlled by a variable KDE_COMPILERSETTINGS_LEVEL, taking an ECM version as value. That version can not be greater than the minimum required ECM version. The settings which are default at that version will then be used, but can be overridden by more fine-grained controls (see respective settings). This variable needs to be set before including this module, otherwise defaults to the minimum required ECM version.

Modern code

The following CMake C standard default variables are set:

For KDE_COMPILERSETTINGS_LEVEL >= 5.85:

  • CMAKE_C_STANDARD: 99

  • CMAKE_C_STANDARD_REQUIRED: TRUE

  • CMAKE_C_EXTENSIONS: OFF

Otherwise:

  • CMAKE_C_STANDARD: 90

  • CMAKE_C_STANDARD_REQUIRED: not modified

  • CMAKE_C_EXTENSIONS: not modified

If the variable CMAKE_C_STANDARD is already set when including this module, none of the above variables will be modified.

The following CMake C++ standard default variables are set:

For KDE_COMPILERSETTINGS_LEVEL >= 5.85:

  • CMAKE_CXX_STANDARD: 17

  • CMAKE_CXX_STANDARD_REQUIRED: TRUE

  • CMAKE_CXX_EXTENSIONS: OFF

Otherwise:

  • CMAKE_CXX_STANDARD: 11

  • CMAKE_CXX_STANDARD_REQUIRED: TRUE

  • CMAKE_CXX_EXTENSIONS: not modified.

If the variable CMAKE_CXX_STANDARD is already set when including this module, none of the above variables will be modified.

The following C++ compiler flags are set:

  • -pedantic (GNU and Clang compilers, since 5.85)

    Can be disabled by setting KDE_SKIP_PEDANTIC_WARNINGS_SETTINGS to TRUE before including this module (default is FALSE for KDE_COMPILERSETTINGS_LEVEL >= 5.85, TRUE otherwise).

  • -Wmissing-include-dirs (GNU compilers, since 5.85)

    Can be disabled by setting KDE_SKIP_MISSING_INCLUDE_DIRS_WARNINGS_SETTINGS to TRUE before including this module (default is FALSE for KDE_COMPILERSETTINGS_LEVEL >= 5.85, TRUE otherwise).

  • -Wzero-as-null-pointer-constant (GNU and Clang compilers, since 5.85)

    Can be disabled by setting KDE_SKIP_NULLPTR_WARNINGS_SETTINGS to TRUE before including this module (default is FALSE for KDE_COMPILERSETTINGS_LEVEL >= 5.85, TRUE otherwise).

  • Qt related preprocessor definitions (since 5.85.0):

    • -DQT_NO_CAST_TO_ASCII

    • -DQT_NO_CAST_FROM_ASCII

    • -DQT_NO_URL_CAST_FROM_STRING

    • -DQT_NO_CAST_FROM_BYTEARRAY

    • -DQT_USE_QSTRINGBUILDER

    • -DQT_NO_NARROWING_CONVERSIONS_IN_CONNECT

    • -DQT_NO_KEYWORDS

    • -DQT_NO_FOREACH

    • -DQT_STRICT_ITERATORS

      Strict iterators are not enabled on Windows, because they lead to a link error when application code iterates over a QVector<QPoint> for instance, unless Qt itself was also built with strict iterators. See example at https://bugreports.qt.io/browse/AUTOSUITE-946

    Can be controlled by setting KDE_QT_MODERNCODE_DEFINITIONS_LEVEL to the version of ECM where the wanted set of definitions has been added before including this module (default is KDE_COMPILERSETTINGS_LEVEL). To disable individual definitions instead use remove_definitions() directly after including this module.

Functions

This module provides the following functions:

kde_source_files_enable_exceptions([file1 [file2 [...]]])

Enables exceptions for specific source files. This should not be used on source files in a language other than C++.

kde_target_enable_exceptions(target <INTERFACE|PUBLIC|PRIVATE>)

Enables exceptions for a specific target. This should not be used on a target that has source files in a language other than C++.

kde_enable_exceptions()

Enables exceptions for C++ source files compiled for the CMakeLists.txt file in the current directory and all subdirectories.

Variables

Inclusion of this module defines the following variables:

ENABLE_BSYMBOLICFUNCTIONS

indicates whether we make use of -Bsymbolic-functions for linking. It ensures libraries bind global function references locally rather than at runtime. This option only has an effect on ELF-based systems.

The option is disabled by default except when using KDEFrameworkCompilerSettings.cmake where it’s enabled. Projects can enable it by calling set(ENABLE_BSYMBOLICFUNCTIONS ON) or passing -DENABLE BSYMBOLICFUNCTIONS=ON when configuring the build directory.

Since 5.85

Example usages:

# needing some macro/feature only available with ECM 5.80.0
find_package(ECM 5.80.0 NO_MODULE)

# requiring ECM 5.80.0 above will default KDE_COMPILERSETTINGS_LEVEL also to 5.80.0,
# thus not activate any newer settings
include(KDECompilerSettings NO_POLICY_SCOPE)
# needing some macro/feature only available with ECM 5.87.0
find_package(ECM 5.87.0 NO_MODULE)

# project uses settings default as of KDECompilerSettings in ECM 5.85.0
set(KDE_COMPILERSETTINGS_LEVEL 5.85.0)
include(KDECompilerSettings NO_POLICY_SCOPE)
# needing some macro/feature only available with ECM 5.87.0
find_package(ECM 5.87.0 NO_MODULE)

# project mainly uses settings default as of KDECompilerSettings in ECM 5.85.0
# with some small twisting
set(KDE_COMPILERSETTINGS_LEVEL 5.85.0)
# not ready yet for pedantic compilers
set(KDE_SKIP_PEDANTIC_WARNINGS_SETTINGS TRUE)
# avoid any Qt definitions
set(KDE_QT_MODERNCODE_DEFINITIONS_LEVEL 5.84.0)
include(KDECompilerSettings NO_POLICY_SCOPE)
# needing some macro/feature only available with ECM 5.85.0
find_package(ECM 5.85.0 NO_MODULE)

# requiring ECM 5.85.0 above will default KDE_COMPILERSETTINGS_LEVEL also to 5.85.0,
# which again defaults KDE_QT_MODERNCODE_DEFINITIONS_LEVEL also to 5.85.0
include(KDECompilerSettings NO_POLICY_SCOPE)
# project is fine with almost all added Qt definitions as of 5.85.0, but not these ones:
remove_definitions(
    -DQT_NO_KEYWORDS
    -DQT_NO_FOREACH
)

Since pre-1.0.0.