Provided by: cmake-data_3.16.3-1ubuntu1.20.04.1_all 
NAME
cmake-generator-expressions - CMake Generator Expressions
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.
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 have the form $<...>. To avoid confusion, this page deviates from
most of the CMake documentation in that it omits angular brackets <...> around
placeholders like condition, string, target, among others.
Generator expressions can be nested, as shown in most of the examples below.
BOOLEAN GENERATOR EXPRESSIONS
Boolean expressions evaluate to either 0 or 1. They are typically used to construct the
condition in a conditional generator expression.
Available boolean expressions are:
Logical Operators
$<BOOL:string>
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.
$<AND:conditions>
where conditions is a comma-separated list of boolean expressions. Evaluates to 1
if all conditions are 1. Otherwise evaluates to 0.
$<OR:conditions>
where conditions is a comma-separated list of boolean expressions. Evaluates to 1
if at least one of the conditions is 1. Otherwise evaluates to 0.
$<NOT:condition>
0 if condition is 1, else 1.
String Comparisons
$<STREQUAL:string1,string2>
1 if string1 and string2 are equal, else 0. The comparison is case-sensitive. For
a case-insensitive comparison, combine with a string transforming generator
expression,
$<STREQUAL:$<UPPER_CASE:${foo}>,"BAR"> # "1" if ${foo} is any of "BAR", "Bar", "bar", ...
$<EQUAL:value1,value2>
1 if value1 and value2 are numerically equal, else 0.
$<IN_LIST:string,list>
1 if string is member of the semicolon-separated list, else 0. Uses case-sensitive
comparisons.
$<VERSION_LESS:v1,v2>
1 if v1 is a version less than v2, else 0.
$<VERSION_GREATER:v1,v2>
1 if v1 is a version greater than v2, else 0.
$<VERSION_EQUAL:v1,v2>
1 if v1 is the same version as v2, else 0.
$<VERSION_LESS_EQUAL:v1,v2>
1 if v1 is a version less than or equal to v2, else 0.
$<VERSION_GREATER_EQUAL:v1,v2>
1 if v1 is a version greater than or equal to v2, else 0.
Variable Queries
$<TARGET_EXISTS:target>
1 if target exists, else 0.
$<CONFIG:cfg>
1 if config is cfg, else 0. This is a case-insensitive comparison. The mapping in
MAP_IMPORTED_CONFIG_<CONFIG> is also considered by this expression when it is
evaluated on a property on an IMPORTED target.
$<PLATFORM_ID:platform_ids>
where platform_ids is a comma-separated list. 1 if the CMake’s platform id matches
any one of the entries in platform_ids, otherwise 0. See also the
CMAKE_SYSTEM_NAME variable.
$<C_COMPILER_ID:compiler_ids>
where compiler_ids is a comma-separated list. 1 if the CMake’s compiler id of the
C compiler matches any one of the entries in compiler_ids, otherwise 0. See also
the CMAKE_<LANG>_COMPILER_ID variable.
$<CXX_COMPILER_ID:compiler_ids>
where compiler_ids is a comma-separated list. 1 if the CMake’s compiler id of the
CXX compiler matches any one of the entries in compiler_ids, otherwise 0. See also
the CMAKE_<LANG>_COMPILER_ID variable.
$<CUDA_COMPILER_ID:compiler_ids>
where compiler_ids is a comma-separated list. 1 if the CMake’s compiler id of the
CUDA compiler matches any one of the entries in compiler_ids, otherwise 0. See
also the CMAKE_<LANG>_COMPILER_ID variable.
$<OBJC_COMPILER_ID:compiler_ids>
where compiler_ids is a comma-separated list. 1 if the CMake’s compiler id of the
Objective-C compiler matches any one of the entries in compiler_ids, otherwise 0.
See also the CMAKE_<LANG>_COMPILER_ID variable.
$<OBJCXX_COMPILER_ID:compiler_ids>
where compiler_ids is a comma-separated list. 1 if the CMake’s compiler id of the
Objective-C++ compiler matches any one of the entries in compiler_ids, otherwise 0.
See also the CMAKE_<LANG>_COMPILER_ID variable.
$<Fortran_COMPILER_ID:compiler_ids>
where compiler_ids is a comma-separated list. 1 if the CMake’s compiler id of the
Fortran compiler matches any one of the entries in compiler_ids, otherwise 0. See
also the CMAKE_<LANG>_COMPILER_ID variable.
$<C_COMPILER_VERSION:version>
1 if the version of the C compiler matches version, otherwise 0. See also the
CMAKE_<LANG>_COMPILER_VERSION variable.
$<CXX_COMPILER_VERSION:version>
1 if the version of the CXX compiler matches version, otherwise 0. See also the
CMAKE_<LANG>_COMPILER_VERSION variable.
$<CUDA_COMPILER_VERSION:version>
1 if the version of the CXX compiler matches version, otherwise 0. See also the
CMAKE_<LANG>_COMPILER_VERSION variable.
$<OBJC_COMPILER_VERSION:version>
1 if the version of the OBJC compiler matches version, otherwise 0. See also the
CMAKE_<LANG>_COMPILER_VERSION variable.
$<OBJCXX_COMPILER_VERSION:version>
1 if the version of the OBJCXX compiler matches version, otherwise 0. See also the
CMAKE_<LANG>_COMPILER_VERSION variable.
$<Fortran_COMPILER_VERSION:version>
1 if the version of the Fortran compiler matches version, otherwise 0. See also
the CMAKE_<LANG>_COMPILER_VERSION variable.
$<TARGET_POLICY:policy>
1 if the policy was NEW when the ‘head’ target was created, else 0. 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:features>
where features is a comma-spearated 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 C_STANDARD or CXX_STANDARD for the ‘head’
target, an error is reported. See the cmake-compile-features(7) manual for
information on compile features and a list of supported compilers.
$<COMPILE_LANG_AND_ID:language,compiler_ids>
1 when the language used for compilation unit matches language and the CMake’s
compiler id of the language compiler matches any one of the entries in
compiler_ids, otherwise 0. This expression is a short form for the combination of
$<COMPILE_LANGUAGE:language> and $<LANG_COMPILER_ID:compiler_ids>. 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:
add_executable(myapp main.cpp foo.c bar.cpp zot.cu)
target_compile_definitions(myapp
PRIVATE $<$<COMPILE_LANG_AND_ID:CXX,AppleClang,Clang>:COMPILING_CXX_WITH_CLANG>
$<$<COMPILE_LANG_AND_ID:CXX,Intel>:COMPILING_CXX_WITH_INTEL>
$<$<COMPILE_LANG_AND_ID:C,Clang>: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:
target_compile_definitions(myapp
PRIVATE $<$<AND:$<COMPILE_LANGUAGE:CXX>,$<CXX_COMPILER_ID:AppleClang,Clang>>:COMPILING_CXX_WITH_CLANG>
$<$<AND:$<COMPILE_LANGUAGE:CXX>,$<CXX_COMPILER_ID:Intel>>:COMPILING_CXX_WITH_INTEL>
$<$<AND:$<COMPILE_LANGUAGE:C>,$<C_COMPILER_ID:Clang>>:COMPILING_C_WITH_CLANG>
)
$<COMPILE_LANGUAGE:languages>
1 when the language used for compilation unit matches any of the 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:
add_executable(myapp main.cpp foo.c bar.cpp zot.cu)
target_compile_options(myapp
PRIVATE $<$<COMPILE_LANGUAGE:CXX>:-fno-exceptions>
)
target_compile_definitions(myapp
PRIVATE $<$<COMPILE_LANGUAGE:CXX>:COMPILING_CXX>
$<$<COMPILE_LANGUAGE:CUDA>:COMPILING_CUDA>
)
target_include_directories(myapp
PRIVATE $<$<COMPILE_LANGUAGE:CXX,CUDA>:/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 Visual Studio Generators and Xcode there is no way to represent
target-wide compile definitions or include directories separately for C and CXX
languages. Also, with 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:
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)
STRING-VALUED GENERATOR EXPRESSIONS
These expressions expand to some string. For example,
include_directories(/usr/include/$<CXX_COMPILER_ID>/)
expands to /usr/include/GNU/ or /usr/include/Clang/ etc, depending on the compiler
identifier.
String-valued expressions may also be combined with other expressions. Here an example
for a string-valued expression within a boolean expressions within a conditional
expression:
$<$<VERSION_LESS:$<CXX_COMPILER_VERSION>,4.2.0>:OLD_COMPILER>
expands to OLD_COMPILER if the CMAKE_CXX_COMPILER_VERSION is less than 4.2.0.
And here two nested string-valued expressions:
-I$<JOIN:$<TARGET_PROPERTY:INCLUDE_DIRECTORIES>, -I>
generates a string of the entries in the INCLUDE_DIRECTORIES target property with each
entry preceded by -I.
Expanding on the previous example, if one first wants to check if the INCLUDE_DIRECTORIES
property is non-empty, then it is advisable to introduce a helper variable to keep the
code readable:
set(prop "$<TARGET_PROPERTY:INCLUDE_DIRECTORIES>") # helper variable
$<$<BOOL:${prop}>:-I$<JOIN:${prop}, -I>>
The following string-valued generator expressions are available:
Escaped Characters
String literals to escape the special meaning a character would otherwise have:
$<ANGLE-R>
A literal >. Used for example to compare strings that contain a >.
$<COMMA>
A literal ,. Used for example to compare strings which contain a ,.
$<SEMICOLON>
A literal ;. Used to prevent list expansion on an argument with ;.
Conditional Expressions
Conditional generator expressions depend on a boolean condition that must be 0 or 1.
$<condition:true_string>
Evaluates to true_string if condition is 1. Otherwise evaluates to the empty
string.
$<IF:condition,true_string,false_string>
Evaluates to true_string if condition is 1. Otherwise evaluates to false_string.
Typically, the condition is a boolean generator expression. For instance,
$<$<CONFIG:Debug>:DEBUG_MODE>
expands to DEBUG_MODE when the Debug configuration is used, and otherwise expands to the
empty string.
String Transformations
$<JOIN:list,string>
Joins the list with the content of string.
$<REMOVE_DUPLICATES:list>
Removes duplicated items in the given list.
$<FILTER:list,INCLUDE|EXCLUDE,regex>
Includes or removes items from list that match the regular expression regex.
$<LOWER_CASE:string>
Content of string converted to lower case.
$<UPPER_CASE:string>
Content of string converted to upper case.
$<GENEX_EVAL:expr>
Content of expr evaluated as a generator expression in the current context. This
enables consumption of generator expressions whose evaluation results itself in
generator expressions.
$<TARGET_GENEX_EVAL:tgt,expr>
Content of expr evaluated as a generator expression in the context of tgt target.
This enables consumption of custom target properties that themselves contain
generator expressions.
Having the capability to evaluate generator expressions is very useful when you
want to manage custom properties supporting generator expressions. For example:
add_library(foo ...)
set_property(TARGET foo PROPERTY
CUSTOM_KEYS $<$<CONFIG:DEBUG>:FOO_EXTRA_THINGS>
)
add_custom_target(printFooKeys
COMMAND ${CMAKE_COMMAND} -E echo $<TARGET_PROPERTY:foo,CUSTOM_KEYS>
)
This naive implementation of the printFooKeys custom command is wrong because
CUSTOM_KEYS target property is not evaluated and the content is passed as is (i.e.
$<$<CONFIG:DEBUG>:FOO_EXTRA_THINGS>).
To have the expected result (i.e. FOO_EXTRA_THINGS if config is Debug), it is
required to evaluate the output of $<TARGET_PROPERTY:foo,CUSTOM_KEYS>:
add_custom_target(printFooKeys
COMMAND ${CMAKE_COMMAND} -E
echo $<TARGET_GENEX_EVAL:foo,$<TARGET_PROPERTY:foo,CUSTOM_KEYS>>
)
Variable Queries
$<CONFIG>
Configuration name.
$<CONFIGURATION>
Configuration name. Deprecated since CMake 3.0. Use CONFIG instead.
$<PLATFORM_ID>
The current system’s CMake platform id. See also the CMAKE_SYSTEM_NAME variable.
$<C_COMPILER_ID>
The CMake’s compiler id of the C compiler used. See also the
CMAKE_<LANG>_COMPILER_ID variable.
$<CXX_COMPILER_ID>
The CMake’s compiler id of the CXX compiler used. See also the
CMAKE_<LANG>_COMPILER_ID variable.
$<CUDA_COMPILER_ID>
The CMake’s compiler id of the CUDA compiler used. See also the
CMAKE_<LANG>_COMPILER_ID variable.
$<OBJC_COMPILER_ID>
The CMake’s compiler id of the OBJC compiler used. See also the
CMAKE_<LANG>_COMPILER_ID variable.
$<OBJCXX_COMPILER_ID>
The CMake’s compiler id of the OBJCXX compiler used. See also the
CMAKE_<LANG>_COMPILER_ID variable.
$<Fortran_COMPILER_ID>
The CMake’s compiler id of the Fortran compiler used. See also the
CMAKE_<LANG>_COMPILER_ID variable.
$<C_COMPILER_VERSION>
The version of the C compiler used. See also the CMAKE_<LANG>_COMPILER_VERSION
variable.
$<CXX_COMPILER_VERSION>
The version of the CXX compiler used. See also the CMAKE_<LANG>_COMPILER_VERSION
variable.
$<CUDA_COMPILER_VERSION>
The version of the CUDA compiler used. See also the CMAKE_<LANG>_COMPILER_VERSION
variable.
$<OBJC_COMPILER_VERSION>
The version of the OBJC compiler used. See also the CMAKE_<LANG>_COMPILER_VERSION
variable.
$<OBJCXX_COMPILER_VERSION>
The version of the OBJCXX compiler used. See also the
CMAKE_<LANG>_COMPILER_VERSION variable.
$<Fortran_COMPILER_VERSION>
The version of the Fortran compiler used. See also the
CMAKE_<LANG>_COMPILER_VERSION variable.
$<COMPILE_LANGUAGE>
The compile language of source files when evaluating compile options. See the
related boolean expression $<COMPILE_LANGUAGE:language> for notes about the
portability of this generator expression.
Target-Dependent Queries
$<TARGET_NAME_IF_EXISTS:tgt>
Expands to the tgt if the given target exists, an empty string otherwise.
$<TARGET_FILE:tgt>
Full path to main file (.exe, .so.1.2, .a) where tgt is the name of a target.
$<TARGET_FILE_BASE_NAME:tgt>
Base name of main file where tgt is the name of a target.
The base name corresponds to the target file name (see $<TARGET_FILE_NAME:tgt>)
without prefix and suffix. For example, if target file name is libbase.so, the base
name is base.
See also the OUTPUT_NAME, ARCHIVE_OUTPUT_NAME, LIBRARY_OUTPUT_NAME and
RUNTIME_OUTPUT_NAME target properties and their configuration specific variants
OUTPUT_NAME_<CONFIG>, ARCHIVE_OUTPUT_NAME_<CONFIG>, LIBRARY_OUTPUT_NAME_<CONFIG>
and RUNTIME_OUTPUT_NAME_<CONFIG>.
The <CONFIG>_POSTFIX and DEBUG_POSTFIX target properties can also be considered.
Note that tgt is not added as a dependency of the target this expression is
evaluated on.
$<TARGET_FILE_PREFIX:tgt>
Prefix of main file where tgt is the name of a target.
See also the PREFIX target property.
Note that tgt is not added as a dependency of the target this expression is
evaluated on.
$<TARGET_FILE_SUFFIX:tgt>
Suffix of main file where tgt is the name of a target.
The suffix corresponds to the file extension (such as “.so” or “.exe”).
See also the SUFFIX target property.
Note that tgt is not added as a dependency of the target this expression is
evaluated on.
$<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 tgt is the name of a target.
$<TARGET_LINKER_FILE_BASE_NAME:tgt>
Base name of file used to link where tgt is the name of a target.
The base name corresponds to the target linker file name (see
$<TARGET_LINKER_FILE_NAME:tgt>) without prefix and suffix. For example, if target
file name is libbase.a, the base name is base.
See also the OUTPUT_NAME, ARCHIVE_OUTPUT_NAME, and LIBRARY_OUTPUT_NAME target
properties and their configuration specific variants OUTPUT_NAME_<CONFIG>,
ARCHIVE_OUTPUT_NAME_<CONFIG> and LIBRARY_OUTPUT_NAME_<CONFIG>.
The <CONFIG>_POSTFIX and DEBUG_POSTFIX target properties can also be considered.
Note that tgt is not added as a dependency of the target this expression is
evaluated on.
$<TARGET_LINKER_FILE_PREFIX:tgt>
Prefix of file used to link where tgt is the name of a target.
See also the PREFIX and IMPORT_PREFIX target properties.
Note that tgt is not added as a dependency of the target this expression is
evaluated on.
$<TARGET_LINKER_FILE_SUFFIX:tgt>
Suffix of file used to link where tgt is the name of a target.
The suffix corresponds to the file extension (such as “.so” or “.lib”).
See also the SUFFIX and IMPORT_SUFFIX target properties.
Note that tgt is not added as a dependency of the target this expression is
evaluated on.
$<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 tgt is 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 tgt is the
name of a target.
See also the PDB_NAME and PDB_OUTPUT_DIRECTORY target properties and their
configuration specific variants PDB_NAME_<CONFIG> and
PDB_OUTPUT_DIRECTORY_<CONFIG>.
$<TARGET_PDB_FILE_BASE_NAME:tgt>
Base name of the linker generated program database file (.pdb) where tgt is the
name of a target.
The base name corresponds to the target PDB file name (see
$<TARGET_PDB_FILE_NAME:tgt>) without prefix and suffix. For example, if target file
name is base.pdb, the base name is base.
See also the PDB_NAME target property and its configuration specific variant
PDB_NAME_<CONFIG>.
The <CONFIG>_POSTFIX and DEBUG_POSTFIX target properties can also be considered.
Note that tgt is not added as a dependency of the target this expression is
evaluated on.
$<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_BUNDLE_DIR:tgt>
Full path to the bundle directory (my.app, my.framework, or my.bundle) where tgt is
the name of a target.
$<TARGET_BUNDLE_CONTENT_DIR:tgt>
Full path to the bundle content directory where tgt is the name of a target. For
the macOS SDK it leads to my.app/Contents, my.framework, or my.bundle/Contents. For
all other SDKs (e.g. iOS) it leads to my.app, my.framework, or my.bundle due to the
flat bundle structure.
$<TARGET_PROPERTY:tgt,prop>
Value of the property prop on the target tgt.
Note that tgt is not added as a dependency of the target this expression is
evaluated on.
$<TARGET_PROPERTY:prop>
Value of the property prop on the target on which the generator expression is
evaluated. Note that for generator expressions in Target Usage Requirements this is
the value of the property on the consuming target rather than the target specifying
the requirement.
$<INSTALL_PREFIX>
Content of the install prefix when the target is exported via install(EXPORT) and
empty otherwise.
Output-Related Expressions
$<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 Target
Usage Requirements, in which case it is the empty string. Intended for use only in
an INTERFACE_LINK_LIBRARIES target property, perhaps via the
target_link_libraries() command, to specify private link dependencies without other
usage requirements.
$<INSTALL_INTERFACE:...>
Content of ... when the property is exported using install(EXPORT), and empty
otherwise.
$<BUILD_INTERFACE:...>
Content of ... when the property is exported using export(), or when the target is
used by another target in the same buildsystem. Expands to the empty string
otherwise.
$<MAKE_C_IDENTIFIER:...>
Content of ... converted to a C identifier. The conversion follows the same
behavior as string(MAKE_C_IDENTIFIER).
$<TARGET_OBJECTS:objLib>
List of objects resulting from build of objLib.
$<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. The ... may be a
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.
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 message() command.
One possible way to generate debug messages is to add a custom target,
add_custom_target(genexdebug COMMAND ${CMAKE_COMMAND} -E echo "$<...>")
The shell command make genexdebug (invoked after execution of cmake) would then print the
result of $<...>.
Another way is to write debug messages to a file:
file(GENERATE OUTPUT filename CONTENT "$<...>")
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