cmake-generator-expressions(7)¶
Contents
Introduction¶
Generator expressions are evaluated during build system generation to produce information specific to each build configuration.
Generator expressions are allowed in the context of many target properties,
such as LINK_LIBRARIES, INCLUDE_DIRECTORIES,
COMPILE_DEFINITIONS and others. They may also be used when using
commands to populate those properties, such as target_link_libraries(),
target_include_directories(), target_compile_definitions()
and others.
This means that they enable conditional linking, conditional definitions used when compiling, and conditional include directories and more. The conditions may be based on the build configuration, target properties, platform information or any other queryable information.
Logical Expressions¶
Logical expressions are used to create conditional output. The basic
expressions are the 0 and 1 expressions. Because other logical
expressions evaluate to either 0 or 1, they can be composed to
create conditional output:
$<$<CONFIG:Debug>:DEBUG_MODE>
expands to DEBUG_MODE when the Debug configuration is used, and
otherwise expands to nothing.
Available logical expressions are:
$<BOOL:...>1if the...is true, else0$<AND:?[,?]...>1if all?are1, else0The
?must always be either0or1in boolean expressions.$<OR:?[,?]...>0if all?are0, else1$<NOT:?>0if?is1, else1$<STREQUAL:a,b>1ifais STREQUALb, else0$<EQUAL:a,b>1ifais EQUALbin a numeric comparison, else0$<CONFIG:cfg>1if config iscfg, else0. This is a case-insensitive comparison. The mapping inMAP_IMPORTED_CONFIG_<CONFIG>is also considered by this expression when it is evaluated on a property on anIMPORTEDtarget.$<PLATFORM_ID:comp>1if the CMake-id of the platform matchescomp, otherwise0.$<C_COMPILER_ID:comp>1if the CMake-id of the C compiler matchescomp, otherwise0.$<CXX_COMPILER_ID:comp>1if the CMake-id of the CXX compiler matchescomp, otherwise0.$<VERSION_GREATER:v1,v2>1ifv1is a version greater thanv2, else0.$<VERSION_LESS:v1,v2>1ifv1is a version less thanv2, else0.$<VERSION_EQUAL:v1,v2>1ifv1is the same version asv2, else0.$<C_COMPILER_VERSION:ver>1if the version of the C compiler matchesver, otherwise0.$<CXX_COMPILER_VERSION:ver>1if the version of the CXX compiler matchesver, otherwise0.$<TARGET_POLICY:pol>1if the policypolwas NEW when the ‘head’ target was created, else0. If the policy was not set, the warning message for the policy will be emitted. This generator expression only works for a subset of policies.$<COMPILE_FEATURES:feature[,feature]...>1if all of thefeaturefeatures are available for the ‘head’ target, and0otherwise. If this expression is used while evaluating the link implementation of a target and if any dependency transitively increases the requiredC_STANDARDorCXX_STANDARDfor the ‘head’ target, an error is reported. See thecmake-compile-features(7)manual for information on compile features and a list of supported compilers.$<COMPILE_LANGUAGE:lang>1when the language used for compilation unit matcheslang, otherwise0. This expression used to specify compile options for source files of a particular language in a target. For example, to specify the use of the-fno-exceptionscompile option (compiler id checks elided):add_executable(myapp main.cpp foo.c bar.cpp) target_compile_options(myapp PRIVATE $<$<COMPILE_LANGUAGE:CXX>:-fno-exceptions> )
This generator expression has limited use because it is not possible to use it with the Visual Studio generators. Portable buildsystems would not use this expression, and would create separate libraries for each source file language instead:
add_library(myapp_c foo.c) add_library(myapp_cxx foo.c) target_compile_options(myapp_cxx PUBLIC -fno-exceptions) add_executable(myapp main.cpp) target_link_libraries(myapp myapp_c myapp_cxx)
The
MakefileandNinjabased generators can also use this expression to specify compile-language specific compile definitions and include directories:add_executable(myapp main.cpp foo.c bar.cpp) target_compile_definitions(myapp PRIVATE $<$<COMPILE_LANGUAGE:CXX>:COMPILING_CXX> ) target_include_directories(myapp PRIVATE $<$<COMPILE_LANGUAGE:CXX>:/opt/foo/cxx_headers> )
Informational Expressions¶
These expressions expand to some information. The information may be used directly, eg:
include_directories(/usr/include/$<CXX_COMPILER_ID>/)
expands to /usr/include/GNU/ or /usr/include/Clang/ etc, depending on
the Id of the compiler.
These expressions may also may be combined with logical expressions:
$<$<VERSION_LESS:$<CXX_COMPILER_VERSION>,4.2.0>:OLD_COMPILER>
expands to OLD_COMPILER if the
CMAKE_CXX_COMPILER_VERSION is less
than 4.2.0.
Available informational expressions are:
$<CONFIGURATION>- Configuration name. Deprecated. Use
CONFIGinstead. $<CONFIG>- Configuration name
$<PLATFORM_ID>- The CMake-id of the platform.
See also the
CMAKE_SYSTEM_NAMEvariable. $<C_COMPILER_ID>- The CMake-id of the C compiler used.
See also the
CMAKE_<LANG>_COMPILER_IDvariable. $<CXX_COMPILER_ID>- The CMake-id of the CXX compiler used.
See also the
CMAKE_<LANG>_COMPILER_IDvariable. $<C_COMPILER_VERSION>- The version of the C compiler used.
See also the
CMAKE_<LANG>_COMPILER_VERSIONvariable. $<CXX_COMPILER_VERSION>- The version of the CXX compiler used.
See also the
CMAKE_<LANG>_COMPILER_VERSIONvariable. $<TARGET_FILE:tgt>- Full path to main file (.exe, .so.1.2, .a) where
tgtis the name of a target. $<TARGET_FILE_NAME:tgt>- Name of main file (.exe, .so.1.2, .a).
$<TARGET_FILE_DIR:tgt>- Directory of main file (.exe, .so.1.2, .a).
$<TARGET_LINKER_FILE:tgt>- File used to link (.a, .lib, .so) where
tgtis the name of a target. $<TARGET_LINKER_FILE_NAME:tgt>- Name of file used to link (.a, .lib, .so).
$<TARGET_LINKER_FILE_DIR:tgt>- Directory of file used to link (.a, .lib, .so).
$<TARGET_SONAME_FILE:tgt>- File with soname (.so.3) where
tgtis the name of a target. $<TARGET_SONAME_FILE_NAME:tgt>- Name of file with soname (.so.3).
$<TARGET_SONAME_FILE_DIR:tgt>- Directory of with soname (.so.3).
$<TARGET_PDB_FILE:tgt>Full path to the linker generated program database file (.pdb) where
tgtis the name of a target.See also the
PDB_NAMEandPDB_OUTPUT_DIRECTORYtarget properties and their configuration specific variantsPDB_NAME_<CONFIG>andPDB_OUTPUT_DIRECTORY_<CONFIG>.$<TARGET_PDB_FILE_NAME:tgt>- Name of the linker generated program database file (.pdb).
$<TARGET_PDB_FILE_DIR:tgt>- Directory of the linker generated program database file (.pdb).
$<TARGET_PROPERTY:tgt,prop>Value of the property
propon the targettgt.Note that
tgtis not added as a dependency of the target this expression is evaluated on.$<TARGET_PROPERTY:prop>- Value of the property
propon the target on which the generator expression is evaluated. $<INSTALL_PREFIX>- Content of the install prefix when the target is exported via
install(EXPORT)and empty otherwise. $<COMPILE_LANGUAGE>- The compile language of source files when evaluating compile options. See the unary version for notes about portability of this generator expression.
Output Expressions¶
These expressions generate output, in some cases depending on an input. These expressions may be combined with other expressions for information or logical comparison:
-I$<JOIN:$<TARGET_PROPERTY:INCLUDE_DIRECTORIES>, -I>
generates a string of the entries in the INCLUDE_DIRECTORIES target
property with each entry preceeded by -I. Note that a more-complete use
in this situation would require first checking if the INCLUDE_DIRECTORIES
property is non-empty:
$<$<BOOL:${prop}>:-I$<JOIN:${prop}, -I>>
where ${prop} refers to a helper variable:
set(prop "$<TARGET_PROPERTY:INCLUDE_DIRECTORIES>")
Available output expressions are:
$<0:...>- Empty string (ignores
...) $<1:...>- Content of
... $<JOIN:list,...>- Joins the list with the content of
... $<ANGLE-R>- A literal
>. Used to compare strings which contain a>for example. $<COMMA>- A literal
,. Used to compare strings which contain a,for example. $<SEMICOLON>- A literal
;. Used to prevent list expansion on an argument with;. $<TARGET_NAME:...>- Marks
...as being the name of a target. This is required if exporting targets to multiple dependent export sets. The...must be a literal name of a target- it may not contain generator expressions. $<LINK_ONLY:...>- Content of
...except when evaluated in a link interface while propagating Transitive Usage Requirements, in which case it is the empty string. Intended for use only in anINTERFACE_LINK_LIBRARIEStarget property, perhaps via thetarget_link_libraries()command, to specify private link dependencies without other usage requirements. $<INSTALL_INTERFACE:...>- Content of
...when the property is exported usinginstall(EXPORT), and empty otherwise. $<BUILD_INTERFACE:...>- Content of
...when the property is exported usingexport(), or when the target is used by another target in the same buildsystem. Expands to the empty string otherwise. $<LOWER_CASE:...>- Content of
...converted to lower case. $<UPPER_CASE:...>- Content of
...converted to upper case. $<MAKE_C_IDENTIFIER:...>- Content of
...converted to a C identifier. $<TARGET_OBJECTS:objLib>- List of objects resulting from build of
objLib.objLibmust be an object of typeOBJECT_LIBRARY. This expression may only be used in the sources ofadd_library()andadd_executable()commands. $<SHELL_PATH:...>- 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.