277 lines
11 KiB
ReStructuredText
277 lines
11 KiB
ReStructuredText
.. cmake-manual-description: CMake Generator Expressions
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cmake-generator-expressions(7)
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******************************
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.. only:: html
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.. contents::
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Introduction
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============
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Generator expressions are evaluated during build system generation to produce
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information specific to each build configuration.
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Generator expressions are allowed in the context of many target properties,
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such as :prop_tgt:`LINK_LIBRARIES`, :prop_tgt:`INCLUDE_DIRECTORIES`,
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:prop_tgt:`COMPILE_DEFINITIONS` and others. They may also be used when using
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commands to populate those properties, such as :command:`target_link_libraries`,
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:command:`target_include_directories`, :command:`target_compile_definitions`
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and others.
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This means that they enable conditional linking, conditional
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definitions used when compiling, and conditional include directories and
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more. The conditions may be based on the build configuration, target
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properties, platform information or any other queryable information.
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Logical Expressions
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===================
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Logical expressions are used to create conditional output. The basic
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expressions are the ``0`` and ``1`` expressions. Because other logical
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expressions evaluate to either ``0`` or ``1``, they can be composed to
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create conditional output::
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$<$<CONFIG:Debug>:DEBUG_MODE>
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expands to ``DEBUG_MODE`` when the ``Debug`` configuration is used, and
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otherwise expands to nothing.
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Available logical expressions are:
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``$<0:...>``
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Empty string (ignores ``...``)
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``$<1:...>``
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Content of ``...``
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``$<BOOL:...>``
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``1`` if the ``...`` is true, else ``0``
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``$<AND:?[,?]...>``
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``1`` if all ``?`` are ``1``, else ``0``
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The ``?`` must always be either ``0`` or ``1`` in boolean expressions.
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``$<OR:?[,?]...>``
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``0`` if all ``?`` are ``0``, else ``1``
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``$<NOT:?>``
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``0`` if ``?`` is ``1``, else ``1``
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``$<STREQUAL:a,b>``
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``1`` if ``a`` is STREQUAL ``b``, else ``0``
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``$<EQUAL:a,b>``
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``1`` if ``a`` is EQUAL ``b`` in a numeric comparison, else ``0``
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``$<CONFIG:cfg>``
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``1`` if config is ``cfg``, else ``0``. This is a case-insensitive comparison.
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The mapping in :prop_tgt:`MAP_IMPORTED_CONFIG_<CONFIG>` is also considered by
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this expression when it is evaluated on a property on an :prop_tgt:`IMPORTED`
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target.
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``$<PLATFORM_ID:comp>``
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``1`` if the CMake-id of the platform matches ``comp``, otherwise ``0``.
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``$<C_COMPILER_ID:comp>``
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``1`` if the CMake-id of the C compiler matches ``comp``, otherwise ``0``.
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``$<CXX_COMPILER_ID:comp>``
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``1`` if the CMake-id of the CXX compiler matches ``comp``, otherwise ``0``.
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``$<VERSION_GREATER:v1,v2>``
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``1`` if ``v1`` is a version greater than ``v2``, else ``0``.
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``$<VERSION_LESS:v1,v2>``
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``1`` if ``v1`` is a version less than ``v2``, else ``0``.
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``$<VERSION_EQUAL:v1,v2>``
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``1`` if ``v1`` is the same version as ``v2``, else ``0``.
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``$<C_COMPILER_VERSION:ver>``
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``1`` if the version of the C compiler matches ``ver``, otherwise ``0``.
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``$<CXX_COMPILER_VERSION:ver>``
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``1`` if the version of the CXX compiler matches ``ver``, otherwise ``0``.
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``$<TARGET_POLICY:pol>``
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``1`` if the policy ``pol`` was NEW when the 'head' target was created,
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else ``0``. If the policy was not set, the warning message for the policy
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will be emitted. This generator expression only works for a subset of
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policies.
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``$<COMPILE_FEATURES:feature[,feature]...>``
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``1`` if all of the ``feature`` features are available for the 'head'
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target, and ``0`` otherwise. If this expression is used while evaluating
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the link implementation of a target and if any dependency transitively
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increases the required :prop_tgt:`C_STANDARD` or :prop_tgt:`CXX_STANDARD`
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for the 'head' target, an error is reported. See the
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:manual:`cmake-compile-features(7)` manual for information on
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compile features.
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``$<COMPILE_LANGUAGE:lang>``
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``1`` when the language used for compilation unit matches ``lang``,
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otherwise ``0``. This expression used to specify compile options for
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source files of a particular language in a target. For example, to specify
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the use of the ``-fno-exceptions`` compile option (compiler id checks
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elided):
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.. code-block:: cmake
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add_executable(myapp main.cpp foo.c bar.cpp)
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target_compile_options(myapp
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PRIVATE $<$<COMPILE_LANGUAGE:CXX>:-fno-exceptions>
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)
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This generator expression has limited use because it is not possible to
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use it with the Visual Studio generators. Portable buildsystems would
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not use this expression, and would create separate libraries for each
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source file language instead:
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.. code-block:: cmake
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add_library(myapp_c foo.c)
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add_library(myapp_cxx foo.c)
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target_compile_options(myapp_cxx PUBLIC -fno-exceptions)
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add_executable(myapp main.cpp)
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target_link_libraries(myapp myapp_c myapp_cxx)
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The ``Makefile`` and ``Ninja`` based generators can also use this
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expression to specify compile-language specific compile definitions:
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.. code-block:: cmake
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add_executable(myapp main.cpp foo.c bar.cpp)
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target_compile_definitions(myapp
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PRIVATE $<$<COMPILE_LANGUAGE:CXX>:COMPILING_CXX>
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)
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Informational Expressions
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=========================
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These expressions expand to some information. The information may be used
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directly, eg::
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include_directories(/usr/include/$<CXX_COMPILER_ID>/)
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expands to ``/usr/include/GNU/`` or ``/usr/include/Clang/`` etc, depending on
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the Id of the compiler.
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These expressions may also may be combined with logical expressions::
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$<$<VERSION_LESS:$<CXX_COMPILER_VERSION>,4.2.0>:OLD_COMPILER>
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expands to ``OLD_COMPILER`` if the
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:variable:`CMAKE_CXX_COMPILER_VERSION <CMAKE_<LANG>_COMPILER_VERSION>` is less
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than 4.2.0.
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Available informational expressions are:
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``$<CONFIGURATION>``
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Configuration name. Deprecated. Use ``CONFIG`` instead.
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``$<CONFIG>``
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Configuration name
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``$<PLATFORM_ID>``
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The CMake-id of the platform.
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See also the :variable:`CMAKE_SYSTEM_NAME` variable.
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``$<C_COMPILER_ID>``
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The CMake-id of the C compiler used.
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See also the :variable:`CMAKE_<LANG>_COMPILER_ID` variable.
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``$<CXX_COMPILER_ID>``
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The CMake-id of the CXX compiler used.
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See also the :variable:`CMAKE_<LANG>_COMPILER_ID` variable.
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``$<C_COMPILER_VERSION>``
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The version of the C compiler used.
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See also the :variable:`CMAKE_<LANG>_COMPILER_VERSION` variable.
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``$<CXX_COMPILER_VERSION>``
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The version of the CXX compiler used.
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See also the :variable:`CMAKE_<LANG>_COMPILER_VERSION` variable.
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``$<TARGET_FILE:tgt>``
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Full path to main file (.exe, .so.1.2, .a) where ``tgt`` is the name of a target.
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``$<TARGET_FILE_NAME:tgt>``
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Name of main file (.exe, .so.1.2, .a).
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``$<TARGET_FILE_DIR:tgt>``
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Directory of main file (.exe, .so.1.2, .a).
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``$<TARGET_LINKER_FILE:tgt>``
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File used to link (.a, .lib, .so) where ``tgt`` is the name of a target.
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``$<TARGET_LINKER_FILE_NAME:tgt>``
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Name of file used to link (.a, .lib, .so).
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``$<TARGET_LINKER_FILE_DIR:tgt>``
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Directory of file used to link (.a, .lib, .so).
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``$<TARGET_SONAME_FILE:tgt>``
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File with soname (.so.3) where ``tgt`` is the name of a target.
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``$<TARGET_SONAME_FILE_NAME:tgt>``
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Name of file with soname (.so.3).
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``$<TARGET_SONAME_FILE_DIR:tgt>``
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Directory of with soname (.so.3).
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``$<TARGET_PDB_FILE:tgt>``
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Full path to the linker generated program database file (.pdb)
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where ``tgt`` is the name of a target.
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See also the :prop_tgt:`PDB_NAME` and :prop_tgt:`PDB_OUTPUT_DIRECTORY`
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target properties and their configuration specific variants
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:prop_tgt:`PDB_NAME_<CONFIG>` and :prop_tgt:`PDB_OUTPUT_DIRECTORY_<CONFIG>`.
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``$<TARGET_PDB_FILE_NAME:tgt>``
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Name of the linker generated program database file (.pdb).
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``$<TARGET_PDB_FILE_DIR:tgt>``
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Directory of the linker generated program database file (.pdb).
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``$<TARGET_PROPERTY:tgt,prop>``
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Value of the property ``prop`` on the target ``tgt``.
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Note that ``tgt`` is not added as a dependency of the target this
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expression is evaluated on.
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``$<TARGET_PROPERTY:prop>``
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Value of the property ``prop`` on the target on which the generator
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expression is evaluated.
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``$<INSTALL_PREFIX>``
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Content of the install prefix when the target is exported via
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:command:`install(EXPORT)` and empty otherwise.
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``$<COMPILE_LANGUAGE>``
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The compile language of source files when evaluating compile options. See
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the unary version for notes about portability of this generator
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expression.
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Output Expressions
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==================
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These expressions generate output, in some cases depending on an input. These
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expressions may be combined with other expressions for information or logical
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comparison::
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-I$<JOIN:$<TARGET_PROPERTY:INCLUDE_DIRECTORIES>, -I>
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generates a string of the entries in the :prop_tgt:`INCLUDE_DIRECTORIES` target
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property with each entry preceeded by ``-I``. Note that a more-complete use
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in this situation would require first checking if the INCLUDE_DIRECTORIES
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property is non-empty::
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$<$<BOOL:${prop}>:-I$<JOIN:${prop}, -I>>
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where ``${prop}`` refers to a helper variable::
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set(prop "$<TARGET_PROPERTY:INCLUDE_DIRECTORIES>")
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Available output expressions are:
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``$<JOIN:list,...>``
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Joins the list with the content of ``...``
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``$<ANGLE-R>``
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A literal ``>``. Used to compare strings which contain a ``>`` for example.
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``$<COMMA>``
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A literal ``,``. Used to compare strings which contain a ``,`` for example.
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``$<SEMICOLON>``
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A literal ``;``. Used to prevent list expansion on an argument with ``;``.
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``$<TARGET_NAME:...>``
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Marks ``...`` as being the name of a target. This is required if exporting
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targets to multiple dependent export sets. The ``...`` must be a literal
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name of a target- it may not contain generator expressions.
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``$<LINK_ONLY:...>``
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Content of ``...`` except when evaluated in a link interface while
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propagating :ref:`Target Usage Requirements`, in which case it is the
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empty string.
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Intended for use only in an :prop_tgt:`INTERFACE_LINK_LIBRARIES` target
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property, perhaps via the :command:`target_link_libraries` command,
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to specify private link dependencies without other usage requirements.
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``$<INSTALL_INTERFACE:...>``
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Content of ``...`` when the property is exported using :command:`install(EXPORT)`,
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and empty otherwise.
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``$<BUILD_INTERFACE:...>``
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Content of ``...`` when the property is exported using :command:`export`, or
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when the target is used by another target in the same buildsystem. Expands to
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the empty string otherwise.
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``$<LOWER_CASE:...>``
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Content of ``...`` converted to lower case.
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``$<UPPER_CASE:...>``
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Content of ``...`` converted to upper case.
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``$<MAKE_C_IDENTIFIER:...>``
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Content of ``...`` converted to a C identifier.
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``$<TARGET_OBJECTS:objLib>``
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List of objects resulting from build of ``objLib``. ``objLib`` must be an
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object of type ``OBJECT_LIBRARY``. This expression may only be used in
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the sources of :command:`add_library` and :command:`add_executable`
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commands.
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