.. cmake-manual-description: CMake Generator Expressions cmake-generator-expressions(7) ****************************** .. only:: html .. contents:: Introduction ============ Generator expressions are evaluated during build system generation to produce information specific to each build configuration. They have the form ``$<...>``. For example: .. code-block:: cmake target_include_directories(tgt PRIVATE /opt/include/$) This would expand to ``/opt/include/GNU``, ``/opt/include/Clang``, etc. depending on the C++ compiler used. Generator expressions are allowed in the context of many target properties, such as :prop_tgt:`LINK_LIBRARIES`, :prop_tgt:`INCLUDE_DIRECTORIES`, :prop_tgt:`COMPILE_DEFINITIONS` and others. They may also be used when using commands to populate those properties, such as :command:`target_link_libraries`, :command:`target_include_directories`, :command:`target_compile_definitions` and others. They enable conditional linking, conditional definitions used when compiling, conditional include directories, and more. The conditions may be based on the build configuration, target properties, platform information, or any other queryable information. Generator expressions can be nested: .. code-block:: cmake target_compile_definitions(tgt PRIVATE $<$,4.2.0>:OLD_COMPILER> ) The above would expand to ``OLD_COMPILER`` if the :variable:`CMAKE_CXX_COMPILER_VERSION _COMPILER_VERSION>` is less than 4.2.0. Whitespace And Quoting ====================== Generator expressions are typically parsed after command arguments. If a generator expression contains spaces, new lines, semicolons or other characters that may be interpreted as command argument separators, the whole expression should be surrounded by quotes when passed to a command. Failure to do so may result in the expression being split and it may no longer be recognized as a generator expression. When using :command:`add_custom_command` or :command:`add_custom_target`, use the ``VERBATIM`` and ``COMMAND_EXPAND_LISTS`` options to obtain robust argument splitting and quoting. .. code-block:: cmake # WRONG: Embedded space will be treated as an argument separator. # This ends up not being seen as a generator expression at all. add_custom_target(run_some_tool COMMAND some_tool -I$, -I> VERBATIM ) .. code-block:: cmake # Better, but still not robust. Quotes prevent the space from splitting the # expression. However, the tool will receive the expanded value as a single # argument. add_custom_target(run_some_tool COMMAND some_tool "-I$, -I>" VERBATIM ) .. code-block:: cmake # Nearly correct. Using a semicolon to separate arguments and adding the # COMMAND_EXPAND_LISTS option means that paths with spaces will be handled # correctly. Quoting the whole expression ensures it is seen as a generator # expression. But if the target property is empty, we will get a bare -I # with nothing after it. add_custom_target(run_some_tool COMMAND some_tool "-I$,;-I>" COMMAND_EXPAND_LISTS VERBATIM ) Using variables to build up a more complex generator expression is also a good way to reduce errors and improve readability. The above example can be improved further like so: .. code-block:: cmake # The $ check prevents adding anything if the property is empty, # assuming the property value cannot be one of CMake's false constants. set(prop "$") add_custom_target(run_some_tool COMMAND some_tool "$<$:-I$>" COMMAND_EXPAND_LISTS VERBATIM ) Finally, the above example can be expressed in a more simple and robust way using an alternate generator expression: .. code-block:: cmake add_custom_target(run_some_tool COMMAND some_tool "$,PREPEND,-I>" COMMAND_EXPAND_LISTS VERBATIM ) A common mistake is to try to split a generator expression across multiple lines with indenting: .. code-block:: cmake # WRONG: New lines and spaces all treated as argument separators, so the # generator expression is split and not recognized correctly. target_compile_definitions(tgt PRIVATE $<$, $,5> >:HAVE_5_OR_LATER> ) Again, use helper variables with well-chosen names to build up a readable expression instead: .. code-block:: cmake set(is_gnu "$") set(v5_or_later "$,5>") set(meet_requirements "$") target_compile_definitions(tgt PRIVATE "$<${meet_requirements}:HAVE_5_OR_LATER>" ) Debugging ========= Since generator expressions are evaluated during generation of the buildsystem, and not during processing of ``CMakeLists.txt`` files, it is not possible to inspect their result with the :command:`message()` command. One possible way to generate debug messages is to add a custom target: .. code-block:: cmake add_custom_target(genexdebug COMMAND ${CMAKE_COMMAND} -E echo "$<...>") After running :program:`cmake`, you can then build the ``genexdebug`` target to print the result of the ``$<...>`` expression (i.e. run the command :option:`cmake --build ... --target genexdebug `). Another way is to write debug messages to a file with :command:`file(GENERATE)`: .. code-block:: cmake file(GENERATE OUTPUT filename CONTENT "$<...>") Generator Expression Reference ============================== .. note:: This reference deviates from most of the CMake documentation in that it omits angular brackets ``<...>`` around placeholders like ``condition``, ``string``, ``target``, etc. This is to prevent an opportunity for those placeholders to be misinterpreted as generator expressions. .. _`Conditional Generator Expressions`: Conditional Expressions ----------------------- A fundamental category of generator expressions relates to conditional logic. Two forms of conditional generator expressions are supported: .. genex:: $ Evaluates to ``true_string`` if ``condition`` is ``1``, or an empty string if ``condition`` evaluates to ``0``. Any other value for ``condition`` results in an error. .. genex:: $ .. versionadded:: 3.8 Evaluates to ``true_string`` if ``condition`` is ``1``, or ``false_string`` if ``condition`` is ``0``. Any other value for ``condition`` results in an error. Typically, the ``condition`` is itself a generator expression. For instance, the following expression expands to ``DEBUG_MODE`` when the ``Debug`` configuration is used, and the empty string for all other configurations: .. code-block:: cmake $<$:DEBUG_MODE> Boolean-like ``condition`` values other than ``1`` or ``0`` can be handled by wrapping them with the ``$`` generator expression: .. genex:: $ Converts ``string`` to ``0`` or ``1``. Evaluates to ``0`` if any of the following is true: * ``string`` is empty, * ``string`` is a case-insensitive equal of ``0``, ``FALSE``, ``OFF``, ``N``, ``NO``, ``IGNORE``, or ``NOTFOUND``, or * ``string`` ends in the suffix ``-NOTFOUND`` (case-sensitive). Otherwise evaluates to ``1``. The ``$`` generator expression is often used when a ``condition`` is provided by a CMake variable: .. code-block:: cmake $<$:-DENABLE_SOME_FEATURE> .. _`Boolean Generator Expressions`: Logical Operators ----------------- The common boolean logic operators are supported: .. genex:: $ where ``conditions`` is a comma-separated list of boolean expressions, all of which must evaluate to either ``1`` or ``0``. The whole expression evaluates to ``1`` if all conditions are ``1``. If any condition is ``0``, the whole expression evaluates to ``0``. .. genex:: $ where ``conditions`` is a comma-separated list of boolean expressions. all of which must evaluate to either ``1`` or ``0``. The whole expression evaluates to ``1`` if at least one of the ``conditions`` is ``1``. If all ``conditions`` evaluate to ``0``, the whole expression evaluates to ``0``. .. genex:: $ ``condition`` must be ``0`` or ``1``. The result of the expression is ``0`` if ``condition`` is ``1``, else ``1``. .. _`Comparison Expressions`: Primary Comparison Expressions ------------------------------ CMake supports a variety of generator expressions that compare things. This section covers the primary and most widely used comparison types. Other more specific comparison types are documented in their own separate sections further below. String Comparisons ^^^^^^^^^^^^^^^^^^ .. genex:: $ ``1`` if ``string1`` and ``string2`` are equal, else ``0``. The comparison is case-sensitive. For a case-insensitive comparison, combine with a :ref:`string transforming generator expression `. For example, the following evaluates to ``1`` if ``${foo}`` is any of ``BAR``, ``Bar``, ``bar``, etc. .. code-block:: cmake $,BAR> .. genex:: $ ``1`` if ``value1`` and ``value2`` are numerically equal, else ``0``. Version Comparisons ^^^^^^^^^^^^^^^^^^^ .. genex:: $ ``1`` if ``v1`` is a version less than ``v2``, else ``0``. .. genex:: $ ``1`` if ``v1`` is a version greater than ``v2``, else ``0``. .. genex:: $ ``1`` if ``v1`` is the same version as ``v2``, else ``0``. .. genex:: $ .. versionadded:: 3.7 ``1`` if ``v1`` is a version less than or equal to ``v2``, else ``0``. .. genex:: $ .. versionadded:: 3.7 ``1`` if ``v1`` is a version greater than or equal to ``v2``, else ``0``. .. _`String Transforming Generator Expressions`: String Transformations ---------------------- .. genex:: $ Content of ``string`` converted to lower case. .. genex:: $ Content of ``string`` converted to upper case. .. genex:: $ Content of ``...`` converted to a C identifier. The conversion follows the same behavior as :command:`string(MAKE_C_IDENTIFIER)`. List Expressions ---------------- Most of the expressions in this section are closely associated with the :command:`list` command, providing the same capabilities, but in the form of a generator expression. .. _GenEx List Comparisons: List Comparisons ^^^^^^^^^^^^^^^^ .. genex:: $ .. versionadded:: 3.12 ``1`` if ``string`` is an item in the semicolon-separated ``list``, else ``0``. It uses case-sensitive comparisons. .. _GenEx List Queries: List Queries ^^^^^^^^^^^^ .. genex:: $ .. versionadded:: 3.27 Returns the list's length. .. genex:: $ .. versionadded:: 3.27 Returns the list of elements specified by indices from the list. .. genex:: $ .. versionadded:: 3.27 Returns a sublist of the given list. If is 0, an empty list will be returned. If is -1 or the list is smaller than + then the remaining elements of the list starting at will be returned. .. genex:: $ .. versionadded:: 3.27 Returns the index of the element specified in the list or -1 if it wasn't found. .. _GenEx List Transformations: List Transformations ^^^^^^^^^^^^^^^^^^^^ .. genex:: $ .. versionadded:: 3.27 Returns a string which joins the list with the content of the ``glue`` string inserted between each item. .. genex:: $ .. versionadded:: 3.27 Returns a list with the elements appended. .. genex:: $ .. versionadded:: 3.27 Returns a list with the elements inserted at the beginning of the list. .. genex:: $ .. versionadded:: 3.27 Returns a list with the elements inserted at the specified index. It is an error to specify an out-of-range index. Valid indexes are 0 to N where N is the length of the list, inclusive. An empty list has length 0. .. genex:: $ .. versionadded:: 3.27 Returns a list with the last element was removed. .. genex:: $ .. versionadded:: 3.27 Returns a list with the first element was removed. .. genex:: $ .. versionadded:: 3.27 Returns a list with all instances of the given values were removed. .. genex:: $ .. versionadded:: 3.27 Returns a list with all values at given indices were removed. .. genex:: $ .. versionadded:: 3.27 Returns a list where duplicated items were removed. The relative order of items is preserved, but if duplicates are encountered, only the first instance is preserved. .. genex:: $ .. versionadded:: 3.27 Returns a list with the items that match the regular expression ``regex`` were included or removed. .. genex:: $ .. versionadded:: 3.27 Returns the list transformed by applying an ``ACTION`` to all or, by specifying a ``SELECTOR``, to the selected elements of the list. .. note:: The ``TRANSFORM`` sub-command does not change the number of elements in the list. If a ``SELECTOR`` is specified, only some elements will be changed, the other ones will remain the same as before the transformation. ``ACTION`` specifies the action to apply to the elements of the list. The actions have exactly the same semantics as of the :command:`list(TRANSFORM)` command. ``ACTION`` must be one of the following: :command:`APPEND `, :command:`PREPEND ` Append, prepend specified value to each element of the list. .. code-block:: cmake $ :command:`TOLOWER `, :command:`TOUPPER ` Convert each element of the list to lower, upper characters. .. code-block:: cmake $ :command:`STRIP ` Remove leading and trailing spaces from each element of the list. .. code-block:: cmake $ :command:`REPLACE `: Match the regular expression as many times as possible and substitute the replacement expression for the match for each element of the list. .. code-block:: cmake $ ``SELECTOR`` determines which elements of the list will be transformed. Only one type of selector can be specified at a time. When given, ``SELECTOR`` must be one of the following: ``AT`` Specify a list of indexes. .. code-block:: cmake $ ``FOR`` Specify a range with, optionally, an increment used to iterate over the range. .. code-block:: cmake $ ``REGEX`` Specify a regular expression. Only elements matching the regular expression will be transformed. .. code-block:: cmake $ .. genex:: $ Joins the list with the content of the ``glue`` string inserted between each item. .. genex:: $ .. versionadded:: 3.15 Removes duplicated items in the given ``list``. The relative order of items is preserved, but if duplicates are encountered, only the first instance is preserved. .. genex:: $ .. versionadded:: 3.15 Includes or removes items from ``list`` that match the regular expression ``regex``. .. _GenEx List Ordering: List Ordering ^^^^^^^^^^^^^ .. genex:: $ .. versionadded:: 3.27 Returns the list with the elements in reverse order. .. genex:: $ .. versionadded:: 3.27 Returns the list sorted according the specified options. Use one of the ``COMPARE`` options to select the comparison method for sorting: ``STRING`` Sorts a list of strings alphabetically. This is the default behavior if the ``COMPARE`` option is not given. ``FILE_BASENAME`` Sorts a list of pathnames of files by their basenames. ``NATURAL`` Sorts a list of strings using natural order (see ``strverscmp(3)`` manual), i.e. such that contiguous digits are compared as whole numbers. For example: the following list `10.0 1.1 2.1 8.0 2.0 3.1` will be sorted as `1.1 2.0 2.1 3.1 8.0 10.0` if the ``NATURAL`` comparison is selected where it will be sorted as `1.1 10.0 2.0 2.1 3.1 8.0` with the ``STRING`` comparison. Use one of the ``CASE`` options to select a case sensitive or case insensitive sort mode: ``SENSITIVE`` List items are sorted in a case-sensitive manner. This is the default behavior if the ``CASE`` option is not given. ``INSENSITIVE`` List items are sorted case insensitively. The order of items which differ only by upper/lowercase is not specified. To control the sort order, one of the ``ORDER`` options can be given: ``ASCENDING`` Sorts the list in ascending order. This is the default behavior when the ``ORDER`` option is not given. ``DESCENDING`` Sorts the list in descending order. This is an error to specify multiple times the same option. Various options can be specified in any order: .. code-block:: cmake $ Path Expressions ---------------- Most of the expressions in this section are closely associated with the :command:`cmake_path` command, providing the same capabilities, but in the form of a generator expression. For all generator expressions in this section, paths are expected to be in cmake-style format. The :ref:`$\ ` generator expression can be used to convert a native path to a cmake-style one. .. _GenEx Path Comparisons: Path Comparisons ^^^^^^^^^^^^^^^^ .. genex:: $ .. versionadded:: 3.24 Compares the lexical representations of two paths. No normalization is performed on either path. Returns ``1`` if the paths are equal, ``0`` otherwise. See :ref:`cmake_path(COMPARE) ` for more details. .. _GenEx Path Queries: Path Queries ^^^^^^^^^^^^ These expressions provide the generation-time capabilities equivalent to the :ref:`Query ` options of the :command:`cmake_path` command. All paths are expected to be in cmake-style format. .. genex:: $ .. versionadded:: 3.24 The following operations return ``1`` if the particular path component is present, ``0`` otherwise. See :ref:`Path Structure And Terminology` for the meaning of each path component. :: $ $ $ $ $ $ $ $ Note the following special cases: * For ``HAS_ROOT_PATH``, a true result will only be returned if at least one of ``root-name`` or ``root-directory`` is non-empty. * For ``HAS_PARENT_PATH``, the root directory is also considered to have a parent, which will be itself. The result is true except if the path consists of just a :ref:`filename `. .. genex:: $ .. versionadded:: 3.24 Returns ``1`` if the path is :ref:`absolute `, ``0`` otherwise. .. genex:: $ .. versionadded:: 3.24 This will return the opposite of ``IS_ABSOLUTE``. .. genex:: $ .. versionadded:: 3.24 Returns ``1`` if ``path`` is the prefix of ``input``, ``0`` otherwise. When the ``NORMALIZE`` option is specified, ``path`` and ``input`` are :ref:`normalized ` before the check. .. _GenEx Path Decomposition: Path Decomposition ^^^^^^^^^^^^^^^^^^ These expressions provide the generation-time capabilities equivalent to the :ref:`Decomposition ` options of the :command:`cmake_path` command. All paths are expected to be in cmake-style format. .. genex:: $ .. versionadded:: 3.24 The following operations retrieve a different component or group of components from a path. See :ref:`Path Structure And Terminology` for the meaning of each path component. .. versionchanged:: 3.27 All operations now accept a list of paths as argument. When a list of paths is specified, the operation will be applied to each path. :: $ $ $ $ $ $ $ $ If a requested component is not present in the path, an empty string is returned. .. _GenEx Path Transformations: Path Transformations ^^^^^^^^^^^^^^^^^^^^ These expressions provide the generation-time capabilities equivalent to the :ref:`Modification ` and :ref:`Generation ` options of the :command:`cmake_path` command. All paths are expected to be in cmake-style format. .. versionchanged:: 3.27 All operations now accept a list of paths as argument. When a list of paths is specified, the operation will be applied to each path. .. _GenEx PATH-CMAKE_PATH: .. genex:: $ .. versionadded:: 3.24 Returns ``path``. If ``path`` is a native path, it is converted into a cmake-style path with forward-slashes (``/``). On Windows, the long filename marker is taken into account. When the ``NORMALIZE`` option is specified, the path is :ref:`normalized ` after the conversion. .. genex:: $ .. versionadded:: 3.24 Returns all the ``input`` arguments appended to ``path`` using ``/`` as the ``directory-separator``. Depending on the ``input``, the value of ``path`` may be discarded. See :ref:`cmake_path(APPEND) ` for more details. .. genex:: $ .. versionadded:: 3.24 Returns ``path`` with filename component (as returned by ``$``) removed. After removal, any trailing ``directory-separator`` is left alone, if present. See :ref:`cmake_path(REMOVE_FILENAME) ` for more details. .. genex:: $ .. versionadded:: 3.24 Returns ``path`` with the filename component replaced by ``input``. If ``path`` has no filename component (i.e. ``$`` returns ``0``), ``path`` is unchanged. See :ref:`cmake_path(REPLACE_FILENAME) ` for more details. .. genex:: $ .. versionadded:: 3.24 Returns ``path`` with the :ref:`extension ` removed, if any. See :ref:`cmake_path(REMOVE_EXTENSION) ` for more details. .. genex:: $ .. versionadded:: 3.24 Returns ``path`` with the :ref:`extension ` replaced by ``input``, if any. See :ref:`cmake_path(REPLACE_EXTENSION) ` for more details. .. genex:: $ .. versionadded:: 3.24 Returns ``path`` normalized according to the steps described in :ref:`Normalization`. .. genex:: $ .. versionadded:: 3.24 Returns ``path``, modified to make it relative to the ``base_directory`` argument. See :ref:`cmake_path(RELATIVE_PATH) ` for more details. .. genex:: $ .. versionadded:: 3.24 Returns ``path`` as absolute. If ``path`` is a relative path (``$`` returns ``1``), it is evaluated relative to the given base directory specified by ``base_directory`` argument. When the ``NORMALIZE`` option is specified, the path is :ref:`normalized ` after the path computation. See :ref:`cmake_path(ABSOLUTE_PATH) ` for more details. Shell Paths ^^^^^^^^^^^ .. genex:: $ .. versionadded:: 3.4 Content of ``...`` converted to shell path style. For example, slashes are converted to backslashes in Windows shells and drive letters are converted to posix paths in MSYS shells. The ``...`` must be an absolute path. .. versionadded:: 3.14 The ``...`` may be a :ref:`semicolon-separated list ` of paths, in which case each path is converted individually and a result list is generated using the shell path separator (``:`` on POSIX and ``;`` on Windows). Be sure to enclose the argument containing this genex in double quotes in CMake source code so that ``;`` does not split arguments. Configuration Expressions ------------------------- .. genex:: $ Configuration name. Use this instead of the deprecated :genex:`CONFIGURATION` generator expression. .. genex:: $ ``1`` if config is any one of the entries in comma-separated list ``cfgs``, else ``0``. This is a case-insensitive comparison. The mapping in :prop_tgt:`MAP_IMPORTED_CONFIG_` is also considered by this expression when it is evaluated on a property of an :prop_tgt:`IMPORTED` target. .. versionchanged:: 3.19 Multiple configurations can be specified for ``cfgs``. CMake 3.18 and earlier only accepted a single configuration. .. genex:: $ .. versionadded:: 3.20 Only valid in :command:`add_custom_command` and :command:`add_custom_target` as the outer-most generator expression in an argument. With the :generator:`Ninja Multi-Config` generator, generator expressions in ``...`` are evaluated using the custom command's "output config". With other generators, the content of ``...`` is evaluated normally. .. genex:: $ .. versionadded:: 3.20 Only valid in :command:`add_custom_command` and :command:`add_custom_target` as the outer-most generator expression in an argument. With the :generator:`Ninja Multi-Config` generator, generator expressions in ``...`` are evaluated using the custom command's "command config". With other generators, the content of ``...`` is evaluated normally. Toolchain And Language Expressions ---------------------------------- Platform ^^^^^^^^ .. genex:: $ The current system's CMake platform id. See also the :variable:`CMAKE_SYSTEM_NAME` variable. .. genex:: $ ``1`` if CMake's platform id matches any one of the entries in comma-separated list ``platform_ids``, otherwise ``0``. See also the :variable:`CMAKE_SYSTEM_NAME` variable. Compiler Version ^^^^^^^^^^^^^^^^ See also the :variable:`CMAKE__COMPILER_VERSION` variable, which is closely related to the expressions in this sub-section. .. genex:: $ The version of the C compiler used. .. genex:: $ ``1`` if the version of the C compiler matches ``version``, otherwise ``0``. .. genex:: $ The version of the CXX compiler used. .. genex:: $ ``1`` if the version of the CXX compiler matches ``version``, otherwise ``0``. .. genex:: $ .. versionadded:: 3.15 The version of the CUDA compiler used. .. genex:: $ .. versionadded:: 3.15 ``1`` if the version of the CXX compiler matches ``version``, otherwise ``0``. .. genex:: $ .. versionadded:: 3.16 The version of the OBJC compiler used. .. genex:: $ .. versionadded:: 3.16 ``1`` if the version of the OBJC compiler matches ``version``, otherwise ``0``. .. genex:: $ .. versionadded:: 3.16 The version of the OBJCXX compiler used. .. genex:: $ .. versionadded:: 3.16 ``1`` if the version of the OBJCXX compiler matches ``version``, otherwise ``0``. .. genex:: $ The version of the Fortran compiler used. .. genex:: $ ``1`` if the version of the Fortran compiler matches ``version``, otherwise ``0``. .. genex:: $ .. versionadded:: 3.21 The version of the HIP compiler used. .. genex:: $ .. versionadded:: 3.21 ``1`` if the version of the HIP compiler matches ``version``, otherwise ``0``. .. genex:: $ .. versionadded:: 3.19 The version of the ISPC compiler used. .. genex:: $ .. versionadded:: 3.19 ``1`` if the version of the ISPC compiler matches ``version``, otherwise ``0``. Compiler Language And ID ^^^^^^^^^^^^^^^^^^^^^^^^ See also the :variable:`CMAKE__COMPILER_ID` variable, which is closely related to most of the expressions in this sub-section. .. genex:: $ CMake's compiler id of the C compiler used. .. genex:: $ where ``compiler_ids`` is a comma-separated list. ``1`` if CMake's compiler id of the C compiler matches any one of the entries in ``compiler_ids``, otherwise ``0``. .. genex:: $ CMake's compiler id of the CXX compiler used. .. genex:: $ where ``compiler_ids`` is a comma-separated list. ``1`` if CMake's compiler id of the CXX compiler matches any one of the entries in ``compiler_ids``, otherwise ``0``. .. genex:: $ .. versionadded:: 3.15 CMake's compiler id of the CUDA compiler used. .. genex:: $ .. versionadded:: 3.15 where ``compiler_ids`` is a comma-separated list. ``1`` if CMake's compiler id of the CUDA compiler matches any one of the entries in ``compiler_ids``, otherwise ``0``. .. genex:: $ .. versionadded:: 3.16 CMake's compiler id of the OBJC compiler used. .. genex:: $ .. versionadded:: 3.16 where ``compiler_ids`` is a comma-separated list. ``1`` if CMake's compiler id of the Objective-C compiler matches any one of the entries in ``compiler_ids``, otherwise ``0``. .. genex:: $ .. versionadded:: 3.16 CMake's compiler id of the OBJCXX compiler used. .. genex:: $ .. versionadded:: 3.16 where ``compiler_ids`` is a comma-separated list. ``1`` if CMake's compiler id of the Objective-C++ compiler matches any one of the entries in ``compiler_ids``, otherwise ``0``. .. genex:: $ CMake's compiler id of the Fortran compiler used. .. genex:: $ where ``compiler_ids`` is a comma-separated list. ``1`` if CMake's compiler id of the Fortran compiler matches any one of the entries in ``compiler_ids``, otherwise ``0``. .. genex:: $ .. versionadded:: 3.21 CMake's compiler id of the HIP compiler used. .. genex:: $ .. versionadded:: 3.21 where ``compiler_ids`` is a comma-separated list. ``1`` if CMake's compiler id of the HIP compiler matches any one of the entries in ``compiler_ids``, otherwise ``0``. .. genex:: $ .. versionadded:: 3.19 CMake's compiler id of the ISPC compiler used. .. genex:: $ .. versionadded:: 3.19 where ``compiler_ids`` is a comma-separated list. ``1`` if CMake's compiler id of the ISPC compiler matches any one of the entries in ``compiler_ids``, otherwise ``0``. .. genex:: $ .. versionadded:: 3.3 The compile language of source files when evaluating compile options. See :ref:`the related boolean expression ` ``$`` for notes about the portability of this generator expression. .. _`Boolean COMPILE_LANGUAGE Generator Expression`: .. genex:: $ .. versionadded:: 3.3 .. versionchanged:: 3.15 Multiple languages can be specified for ``languages``. CMake 3.14 and earlier only accepted a single language. ``1`` when the language used for compilation unit matches any of the comma-separated entries in ``languages``, otherwise ``0``. This expression may be used to specify compile options, compile definitions, and include directories for source files of a particular language in a target. For example: .. code-block:: cmake add_executable(myapp main.cpp foo.c bar.cpp zot.cu) target_compile_options(myapp PRIVATE $<$:-fno-exceptions> ) target_compile_definitions(myapp PRIVATE $<$:COMPILING_CXX> $<$:COMPILING_CUDA> ) target_include_directories(myapp PRIVATE $<$:/opt/foo/headers> ) This specifies the use of the ``-fno-exceptions`` compile option, ``COMPILING_CXX`` compile definition, and ``cxx_headers`` include directory for C++ only (compiler id checks elided). It also specifies a ``COMPILING_CUDA`` compile definition for CUDA. Note that with :ref:`Visual Studio Generators` and :generator:`Xcode` there is no way to represent target-wide compile definitions or include directories separately for ``C`` and ``CXX`` languages. Also, with :ref:`Visual Studio Generators` there is no way to represent target-wide flags separately for ``C`` and ``CXX`` languages. Under these generators, expressions for both C and C++ sources will be evaluated using ``CXX`` if there are any C++ sources and otherwise using ``C``. A workaround is to create separate libraries for each source file language instead: .. code-block:: cmake add_library(myapp_c foo.c) add_library(myapp_cxx bar.cpp) target_compile_options(myapp_cxx PUBLIC -fno-exceptions) add_executable(myapp main.cpp) target_link_libraries(myapp myapp_c myapp_cxx) .. genex:: $ .. versionadded:: 3.15 ``1`` when the language used for compilation unit matches ``language`` and CMake's compiler id of the ``language`` compiler matches any one of the comma-separated entries in ``compiler_ids``, otherwise ``0``. This expression is a short form for the combination of ``$`` and ``$``. This expression may be used to specify compile options, compile definitions, and include directories for source files of a particular language and compiler combination in a target. For example: .. code-block:: cmake add_executable(myapp main.cpp foo.c bar.cpp zot.cu) target_compile_definitions(myapp PRIVATE $<$:COMPILING_CXX_WITH_CLANG> $<$:COMPILING_CXX_WITH_INTEL> $<$:COMPILING_C_WITH_CLANG> ) This specifies the use of different compile definitions based on both the compiler id and compilation language. This example will have a ``COMPILING_CXX_WITH_CLANG`` compile definition when Clang is the CXX compiler, and ``COMPILING_CXX_WITH_INTEL`` when Intel is the CXX compiler. Likewise, when the C compiler is Clang, it will only see the ``COMPILING_C_WITH_CLANG`` definition. Without the ``COMPILE_LANG_AND_ID`` generator expression, the same logic would be expressed as: .. code-block:: cmake target_compile_definitions(myapp PRIVATE $<$,$>:COMPILING_CXX_WITH_CLANG> $<$,$>:COMPILING_CXX_WITH_INTEL> $<$,$>:COMPILING_C_WITH_CLANG> ) Compile Features ^^^^^^^^^^^^^^^^ .. genex:: $ .. versionadded:: 3.1 where ``features`` is a comma-separated list. Evaluates to ``1`` if all of the ``features`` are available for the 'head' target, and ``0`` otherwise. If this expression is used while evaluating the link implementation of a target and if any dependency transitively increases the required :prop_tgt:`C_STANDARD` or :prop_tgt:`CXX_STANDARD` for the 'head' target, an error is reported. See the :manual:`cmake-compile-features(7)` manual for information on compile features and a list of supported compilers. Compile Context ^^^^^^^^^^^^^^^ .. genex:: $ .. versionadded:: 3.27 Content of ``...``, when collecting :ref:`Target Usage Requirements`, otherwise it is the empty string. This is intended for use in an :prop_tgt:`INTERFACE_LINK_LIBRARIES` and :prop_tgt:`LINK_LIBRARIES` target properties, typically populated via the :command:`target_link_libraries` command. Provides compilation usage requirements without any linking requirements. Use cases include header-only usage where all usages are known to not have linking requirements (e.g., all-``inline`` or C++ template libraries). Note that for proper evaluation of this expression requires policy :policy:`CMP0099` to be set to `NEW`. Linker Language And ID ^^^^^^^^^^^^^^^^^^^^^^ .. genex:: $ .. versionadded:: 3.18 The link language of the target when evaluating link options. See :ref:`the related boolean expression ` ``$`` for notes about the portability of this generator expression. .. note:: This generator expression is not supported by the link libraries properties to avoid side-effects due to the double evaluation of these properties. .. _`Boolean LINK_LANGUAGE Generator Expression`: .. genex:: $ .. versionadded:: 3.18 ``1`` when the language used for link step matches any of the comma-separated entries in ``languages``, otherwise ``0``. This expression may be used to specify link libraries, link options, link directories and link dependencies of a particular language in a target. For example: .. code-block:: cmake add_library(api_C ...) add_library(api_CXX ...) add_library(api INTERFACE) target_link_options(api INTERFACE $<$:-opt_c> $<$:-opt_cxx>) target_link_libraries(api INTERFACE $<$:api_C> $<$:api_CXX>) add_executable(myapp1 main.c) target_link_options(myapp1 PRIVATE api) add_executable(myapp2 main.cpp) target_link_options(myapp2 PRIVATE api) This specifies to use the ``api`` target for linking targets ``myapp1`` and ``myapp2``. In practice, ``myapp1`` will link with target ``api_C`` and option ``-opt_c`` because it will use ``C`` as link language. And ``myapp2`` will link with ``api_CXX`` and option ``-opt_cxx`` because ``CXX`` will be the link language. .. _`Constraints LINK_LANGUAGE Generator Expression`: .. note:: To determine the link language of a target, it is required to collect, transitively, all the targets which will be linked to it. So, for link libraries properties, a double evaluation will be done. During the first evaluation, ``$`` expressions will always return ``0``. The link language computed after this first pass will be used to do the second pass. To avoid inconsistency, it is required that the second pass do not change the link language. Moreover, to avoid unexpected side-effects, it is required to specify complete entities as part of the ``$`` expression. For example: .. code-block:: cmake add_library(lib STATIC file.cxx) add_library(libother STATIC file.c) # bad usage add_executable(myapp1 main.c) target_link_libraries(myapp1 PRIVATE lib$<$:other>) # correct usage add_executable(myapp2 main.c) target_link_libraries(myapp2 PRIVATE $<$:libother>) In this example, for ``myapp1``, the first pass will, unexpectedly, determine that the link language is ``CXX`` because the evaluation of the generator expression will be an empty string so ``myapp1`` will depends on target ``lib`` which is ``C++``. On the contrary, for ``myapp2``, the first evaluation will give ``C`` as link language, so the second pass will correctly add target ``libother`` as link dependency. .. genex:: $ .. versionadded:: 3.18 ``1`` when the language used for link step matches ``language`` and the CMake's compiler id of the language linker matches any one of the comma-separated entries in ``compiler_ids``, otherwise ``0``. This expression is a short form for the combination of ``$`` and ``$``. This expression may be used to specify link libraries, link options, link directories and link dependencies of a particular language and linker combination in a target. For example: .. code-block:: cmake add_library(libC_Clang ...) add_library(libCXX_Clang ...) add_library(libC_Intel ...) add_library(libCXX_Intel ...) add_executable(myapp main.c) if (CXX_CONFIG) target_sources(myapp PRIVATE file.cxx) endif() target_link_libraries(myapp PRIVATE $<$:libCXX_Clang> $<$:libC_Clang> $<$:libCXX_Intel> $<$:libC_Intel>) This specifies the use of different link libraries based on both the compiler id and link language. This example will have target ``libCXX_Clang`` as link dependency when ``Clang`` or ``AppleClang`` is the ``CXX`` linker, and ``libCXX_Intel`` when ``Intel`` is the ``CXX`` linker. Likewise when the ``C`` linker is ``Clang`` or ``AppleClang``, target ``libC_Clang`` will be added as link dependency and ``libC_Intel`` when ``Intel`` is the ``C`` linker. See :ref:`the note related to ` ``$`` for constraints about the usage of this generator expression. Link Features ^^^^^^^^^^^^^ .. genex:: $ .. versionadded:: 3.24 Specify a set of libraries to link to a target, along with a ``feature`` which provides details about *how* they should be linked. For example: .. code-block:: cmake add_library(lib1 STATIC ...) add_library(lib2 ...) target_link_libraries(lib2 PRIVATE "$") This specifies that ``lib2`` should link to ``lib1`` and use the ``WHOLE_ARCHIVE`` feature when doing so. Feature names are case-sensitive and may only contain letters, numbers and underscores. Feature names defined in all uppercase are reserved for CMake's own built-in features. The pre-defined built-in library features are: .. include:: ../variable/LINK_LIBRARY_PREDEFINED_FEATURES.txt Built-in and custom library features are defined in terms of the following variables: * :variable:`CMAKE__LINK_LIBRARY_USING__SUPPORTED` * :variable:`CMAKE__LINK_LIBRARY_USING_` * :variable:`CMAKE_LINK_LIBRARY_USING__SUPPORTED` * :variable:`CMAKE_LINK_LIBRARY_USING_` The value used for each of these variables is the value as set at the end of the directory scope in which the target was created. The usage is as follows: 1. If the language-specific :variable:`CMAKE__LINK_LIBRARY_USING__SUPPORTED` variable is true, the ``feature`` must be defined by the corresponding :variable:`CMAKE__LINK_LIBRARY_USING_` variable. 2. If no language-specific ``feature`` is supported, then the :variable:`CMAKE_LINK_LIBRARY_USING__SUPPORTED` variable must be true and the ``feature`` must be defined by the corresponding :variable:`CMAKE_LINK_LIBRARY_USING_` variable. The following limitations should be noted: * The ``library-list`` can specify CMake targets or libraries. Any CMake target of type :ref:`OBJECT