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CMAKE-GENERATOR-EXPRESSIONS(7) CMake CMAKE-GENERATOR-EXPRESSIONS(7)

NAME
cmake-generator-expressions - CMake Generator Expressions

INTRODUCTION
Generator expressions are evaluated during build system generation to
produce information specific to each build configuration. They have
the form $<...>. For example:

target_include_directories(tgt PRIVATE /opt/include/$<CXX_COMPILER_ID>)

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 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 can be nested:

target_compile_definitions(tgt PRIVATE
$<$<VERSION_LESS:$<CXX_COMPILER_VERSION>,4.2.0>:OLD_COMPILER>
)

The above would expand to OLD_COMPILER if the
CMAKE_CXX_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 add_custom_command() or add_custom_target(), use the
VERBATIM and COMMAND_EXPAND_LISTS options to obtain robust argument
splitting and quoting.

# 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$<JOIN:$<TARGET_PROPERTY:tgt,INCLUDE_DIRECTORIES>, -I>
VERBATIM
)

# 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$<JOIN:$<TARGET_PROPERTY:tgt,INCLUDE_DIRECTORIES>, -I>"
VERBATIM
)

# 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$<JOIN:$<TARGET_PROPERTY:tgt,INCLUDE_DIRECTORIES>,;-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:

# The $<BOOL:...> check prevents adding anything if the property is empty,
# assuming the property value cannot be one of CMake's false constants.
set(prop "$<TARGET_PROPERTY:tgt,INCLUDE_DIRECTORIES>")
add_custom_target(run_some_tool
COMMAND some_tool "$<$<BOOL:${prop}>:-I$<JOIN:${prop},;-I>>"
COMMAND_EXPAND_LISTS
VERBATIM
)

A common mistake is to try to split a generator expression across
multiple lines with indenting:

# 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
$<$<AND:
$<CXX_COMPILER_ID:GNU>,
$<VERSION_GREATER_EQUAL:$<CXX_COMPILER_VERSION>,5>
>:HAVE_5_OR_LATER>
)

Again, use helper variables with well-chosen names to build up a
readable expression instead:

set(is_gnu "$<CXX_COMPILER_ID:GNU>")
set(v5_or_later "$<VERSION_GREATER_EQUAL:$<CXX_COMPILER_VERSION>,5>")
set(meet_requirements "$<AND:${is_gnu},${v5_or_later}>")
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 message() command. One
possible way to generate debug messages is to add a custom target:

add_custom_target(genexdebug COMMAND ${CMAKE_COMMAND} -E echo "$<...>")

After running cmake, you can then build the genexdebug target to print
the result of the $<...> expression (i.e. run the command cmake --build
... --target genexdebug).

Another way is to write debug messages to a file with file(GENERATE):

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 Expressions
A fundamental category of generator expressions relates to conditional
logic. Two forms of conditional generator expressions are supported:

$<condition:true_string>
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.

$<IF:condition,true_string,false_string>
New in version 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:

$<$<CONFIG:Debug>:DEBUG_MODE>

Boolean-like condition values other than 1 or 0 can be handled by
wrapping them with the $<BOOL:...> generator expression:

$<BOOL:string>
Converts string to 0 or 1. Evaluates to 0 if any of the
following is true:

o string is empty,

o string is a case-insensitive equal of 0, FALSE, OFF, N, NO,
IGNORE, or NOTFOUND, or

o string ends in the suffix -NOTFOUND (case-sensitive).

Otherwise evaluates to 1.

The $<BOOL:...> generator expression is often used when a condition is
provided by a CMake variable:

$<$<BOOL:${HAVE_SOME_FEATURE}>:-DENABLE_SOME_FEATURE>

Logical Operators
The common boolean logic operators are supported:

$<AND:conditions>
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.

$<OR:conditions>
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.

$<NOT:condition>
condition must be 0 or 1. The result of the expression is 0 if
condition is 1, else 1.

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

$<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. For example, the
following evaluates to 1 if ${foo} is any of BAR, Bar, bar, etc.

$<STREQUAL:$<UPPER_CASE:${foo}>,BAR>

$<EQUAL:value1,value2>
1 if value1 and value2 are numerically equal, else 0.

Version 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>
New in version 3.7.

1 if v1 is a version less than or equal to v2, else 0.

$<VERSION_GREATER_EQUAL:v1,v2>
New in version 3.7.

1 if v1 is a version greater than or equal to v2, else 0.

String Transformations

$<LOWER_CASE:string>
Content of string converted to lower case.

$<UPPER_CASE:string>
Content of string converted to upper case.

$<MAKE_C_IDENTIFIER:...>
Content of ... converted to a C identifier. The conversion
follows the same behavior as string(MAKE_C_IDENTIFIER).

List Expressions

$<IN_LIST:string,list>
New in version 3.12.

1 if string is an item in the semicolon-separated list, else 0.
It uses case-sensitive comparisons.

$<JOIN:list,string>
Joins the list with the content of string inserted between each
item.

$<REMOVE_DUPLICATES:list>
New in version 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.

$<FILTER:list,INCLUDE|EXCLUDE,regex>
New in version 3.15.

Includes or removes items from list that match the regular
expression regex.

Path Expressions
Most of the expressions in this section are closely associated with the
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 $<PATH:CMAKE_PATH> generator expression can
be used to convert a native path to a cmake-style one.

Path Comparisons

$<PATH_EQUAL:path1,path2>
New in version 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 cmake_path(COMPARE) for more details.

Path Queries
These expressions provide the generation-time capabilities equivalent
to the Query options of the cmake_path() command. All paths are
expected to be in cmake-style format.

$<PATH:HAS_*,path>
New in version 3.24.

The following operations return 1 if the particular path
component is present, 0 otherwise. See Path Structure And
Terminology for the meaning of each path component.

$<PATH:HAS_ROOT_NAME,path>
$<PATH:HAS_ROOT_DIRECTORY,path>
$<PATH:HAS_ROOT_PATH,path>
$<PATH:HAS_FILENAME,path>
$<PATH:HAS_EXTENSION,path>
$<PATH:HAS_STEM,path>
$<PATH:HAS_RELATIVE_PART,path>
$<PATH:HAS_PARENT_PATH,path>

Note the following special cases:

o For HAS_ROOT_PATH, a true result will only be returned if at
least one of root-name or root-directory is non-empty.

o 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 filename.

$<PATH:IS_ABSOLUTE,path>
New in version 3.24.

Returns 1 if the path is absolute, 0 otherwise.

$<PATH:IS_RELATIVE,path>
New in version 3.24.

This will return the opposite of IS_ABSOLUTE.

$<PATH:IS_PREFIX[,NORMALIZE],path,input>
New in version 3.24.

Returns 1 if path is the prefix of input, 0 otherwise.

When the NORMALIZE option is specified, path and input are
normalized before the check.

Path Decomposition
These expressions provide the generation-time capabilities equivalent
to the Decomposition options of the cmake_path() command. All paths
are expected to be in cmake-style format.

$<PATH:GET_*,...>
New in version 3.24.

The following operations retrieve a different component or group
of components from a path. See Path Structure And Terminology
for the meaning of each path component.

$<PATH:GET_ROOT_NAME,path>
$<PATH:GET_ROOT_DIRECTORY,path>
$<PATH:GET_ROOT_PATH,path>
$<PATH:GET_FILENAME,path>
$<PATH:GET_EXTENSION[,LAST_ONLY],path>
$<PATH:GET_STEM[,LAST_ONLY],path>
$<PATH:GET_RELATIVE_PART,path>
$<PATH:GET_PARENT_PATH,path>

If a requested component is not present in the path, an empty
string is returned.

Path Transformations
These expressions provide the generation-time capabilities equivalent
to the Modification and Generation options of the cmake_path() command.
All paths are expected to be in cmake-style format.

$<PATH:CMAKE_PATH[,NORMALIZE],path>
New in version 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 normalized
after the conversion.

$<PATH:APPEND,path,input,...>
New in version 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 cmake_path(APPEND) for more details.

$<PATH:REMOVE_FILENAME,path>
New in version 3.24.

Returns path with filename component (as returned by
$<PATH:GET_FILENAME>) removed. After removal, any trailing
directory-separator is left alone, if present.

See cmake_path(REMOVE_FILENAME) for more details.

$<PATH:REPLACE_FILENAME,path,input>
New in version 3.24.

Returns path with the filename component replaced by input. If
path has no filename component (i.e. $<PATH:HAS_FILENAME>
returns 0), path is unchanged.

See cmake_path(REPLACE_FILENAME) for more details.

$<PATH:REMOVE_EXTENSION[,LAST_ONLY],path>
New in version 3.24.

Returns path with the extension removed, if any.

See cmake_path(REMOVE_EXTENSION) for more details.

$<PATH:REPLACE_EXTENSION[,LAST_ONLY],path,input>
New in version 3.24.

Returns path with the extension replaced by input, if any.

See cmake_path(REPLACE_EXTENSION) for more details.

$<PATH:NORMAL_PATH,path>
New in version 3.24.

Returns path normalized according to the steps described in
Normalization.

$<PATH:RELATIVE_PATH,path,base_directory>
New in version 3.24.

Returns path, modified to make it relative to the base_directory
argument.

See cmake_path(RELATIVE_PATH) for more details.

$<PATH:ABSOLUTE_PATH[,NORMALIZE],path,base_directory>
New in version 3.24.

Returns path as absolute. If path is a relative path
($<PATH:IS_RELATIVE> 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 normalized
after the path computation.

See cmake_path(ABSOLUTE_PATH) for more details.

Shell Paths

$<SHELL_PATH:...>
New in version 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.

New in version 3.14: 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.

Configuration Expressions

$<CONFIG>
Configuration name. Use this instead of the deprecated
CONFIGURATION generator expression.

$<CONFIG:cfgs>
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 MAP_IMPORTED_CONFIG_<CONFIG> is also considered by this
expression when it is evaluated on a property of an IMPORTED
target.

Changed in version 3.19: Multiple configurations can be
specified for cfgs. CMake 3.18 and earlier only accepted a
single configuration.

$<OUTPUT_CONFIG:...>
New in version 3.20.

Only valid in add_custom_command() and add_custom_target() as
the outer-most generator expression in an argument. With the
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.

$<COMMAND_CONFIG:...>
New in version 3.20.

Only valid in add_custom_command() and add_custom_target() as
the outer-most generator expression in an argument. With the
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

$<PLATFORM_ID>
The current system's CMake platform id. See also the
CMAKE_SYSTEM_NAME variable.

$<PLATFORM_ID:platform_ids>
1 if CMake's platform id matches any one of the entries in
comma-separated list platform_ids, otherwise 0. See also the
CMAKE_SYSTEM_NAME variable.

Compiler Version
See also the CMAKE_<LANG>_COMPILER_VERSION variable, which is closely
related to the expressions in this sub-section.

$<C_COMPILER_VERSION>
The version of the C compiler used.

$<C_COMPILER_VERSION:version>
1 if the version of the C compiler matches version, otherwise 0.

$<CXX_COMPILER_VERSION>
The version of the CXX compiler used.

$<CXX_COMPILER_VERSION:version>
1 if the version of the CXX compiler matches version, otherwise
0.

$<CUDA_COMPILER_VERSION>
New in version 3.15.

The version of the CUDA compiler used.

$<CUDA_COMPILER_VERSION:version>
New in version 3.15.

1 if the version of the CXX compiler matches version, otherwise
0.

$<OBJC_COMPILER_VERSION>
New in version 3.16.

The version of the OBJC compiler used.

$<OBJC_COMPILER_VERSION:version>
New in version 3.16.

1 if the version of the OBJC compiler matches version, otherwise
0.

$<OBJCXX_COMPILER_VERSION>
New in version 3.16.

The version of the OBJCXX compiler used.

$<OBJCXX_COMPILER_VERSION:version>
New in version 3.16.

1 if the version of the OBJCXX compiler matches version,
otherwise 0.

$<Fortran_COMPILER_VERSION>
The version of the Fortran compiler used.

$<Fortran_COMPILER_VERSION:version>
1 if the version of the Fortran compiler matches version,
otherwise 0.

$<HIP_COMPILER_VERSION>
New in version 3.21.

The version of the HIP compiler used.

$<HIP_COMPILER_VERSION:version>
New in version 3.21.

1 if the version of the HIP compiler matches version, otherwise
0.

$<ISPC_COMPILER_VERSION>
New in version 3.19.

The version of the ISPC compiler used.

$<ISPC_COMPILER_VERSION:version>
New in version 3.19.

1 if the version of the ISPC compiler matches version, otherwise
0.

Compiler Language And ID
See also the CMAKE_<LANG>_COMPILER_ID variable, which is closely
related to most of the expressions in this sub-section.

$<C_COMPILER_ID>
CMake's compiler id of the C compiler used.

$<C_COMPILER_ID:compiler_ids>
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.

$<CXX_COMPILER_ID>
CMake's compiler id of the CXX compiler used.

$<CXX_COMPILER_ID:compiler_ids>
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.

$<CUDA_COMPILER_ID>
New in version 3.15.

CMake's compiler id of the CUDA compiler used.

$<CUDA_COMPILER_ID:compiler_ids>
New in version 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.

$<OBJC_COMPILER_ID>
New in version 3.16.

CMake's compiler id of the OBJC compiler used.

$<OBJC_COMPILER_ID:compiler_ids>
New in version 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.

$<OBJCXX_COMPILER_ID>
New in version 3.16.

CMake's compiler id of the OBJCXX compiler used.

$<OBJCXX_COMPILER_ID:compiler_ids>
New in version 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.

$<Fortran_COMPILER_ID>
CMake's compiler id of the Fortran compiler used.

$<Fortran_COMPILER_ID:compiler_ids>
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.

$<HIP_COMPILER_ID>
New in version 3.21.

CMake's compiler id of the HIP compiler used.

$<HIP_COMPILER_ID:compiler_ids>
New in version 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.

$<ISPC_COMPILER_ID>
New in version 3.19.

CMake's compiler id of the ISPC compiler used.

$<ISPC_COMPILER_ID:compiler_ids>
New in version 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.

$<COMPILE_LANGUAGE>
New in version 3.3.

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.

$<COMPILE_LANGUAGE:languages>
New in version 3.3.

Changed in version 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:

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)

$<COMPILE_LANG_AND_ID:language,compiler_ids>
New in version 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
$<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 Features

$<COMPILE_FEATURES:features>
New in version 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 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.

Linker Language And ID

$<LINK_LANGUAGE>
New in version 3.18.

The link language of the target when evaluating link options.
See the related boolean expression $<LINK_LANGUAGE:languages>
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.

$<LINK_LANGUAGE:languages>
New in version 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:

add_library(api_C ...)
add_library(api_CXX ...)
add_library(api INTERFACE)
target_link_options(api INTERFACE $<$<LINK_LANGUAGE:C>:-opt_c>
$<$<LINK_LANGUAGE:CXX>:-opt_cxx>)
target_link_libraries(api INTERFACE $<$<LINK_LANGUAGE:C>:api_C>
$<$<LINK_LANGUAGE:CXX>: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.

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,
$<LINK_LANGUAGE:..> 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 $<LINK_LANGUAGE:..>
expression. For example:

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$<$<LINK_LANGUAGE:C>:other>)

# correct usage
add_executable(myapp2 main.c)
target_link_libraries(myapp2 PRIVATE $<$<LINK_LANGUAGE:C>: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.

$<LINK_LANG_AND_ID:language,compiler_ids>
New in version 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
$<LINK_LANGUAGE:language> and $<LANG_COMPILER_ID:compiler_ids>.
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:

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 $<$<LINK_LANG_AND_ID:CXX,Clang,AppleClang>:libCXX_Clang>
$<$<LINK_LANG_AND_ID:C,Clang,AppleClang>:libC_Clang>
$<$<LINK_LANG_AND_ID:CXX,Intel>:libCXX_Intel>
$<$<LINK_LANG_AND_ID:C,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 the note related to $<LINK_LANGUAGE:language> for
constraints about the usage of this generator expression.

Link Features

$<LINK_LIBRARY:feature,library-list>
New in version 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:

add_library(lib1 STATIC ...)
add_library(lib2 ...)
target_link_libraries(lib2 PRIVATE "$<LINK_LIBRARY:WHOLE_ARCHIVE,lib1>")

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:

DEFAULT
This feature corresponds to standard linking, essentially
equivalent to using no feature at all. It is typically
only used with the LINK_LIBRARY_OVERRIDE and
LINK_LIBRARY_OVERRIDE_<LIBRARY> target properties.

WHOLE_ARCHIVE
Force inclusion of all members of a static library. This
feature is only supported for the following platforms,
with limitations as noted:

o Linux.

o All BSD variants.

o SunOS.

o All Apple variants. The library must be specified as a
CMake target name, a library file name (such as
libfoo.a), or a library file path (such as
/path/to/libfoo.a). Due to a limitation of the Apple
linker, it cannot be specified as a plain library name
like foo, where foo is not a CMake target.

o Windows. When using a MSVC or MSVC-like toolchain, the
MSVC version must be greater than 1900.

o Cygwin.

o MSYS.

FRAMEWORK
This option tells the linker to search for the specified
framework using the -framework linker option. It can
only be used on Apple platforms, and only with a linker
that understands the option used (i.e. the linker
provided with Xcode, or one compatible with it).

The framework can be specified as a CMake framework
target, a bare framework name, or a file path. If a
target is given, that target must have the FRAMEWORK
target property set to true. For a file path, if it
contains a directory part, that directory will be added
as a framework search path.

add_library(lib SHARED ...)
target_link_libraries(lib PRIVATE "$<LINK_LIBRARY:FRAMEWORK,/path/to/my_framework>")

# The constructed linker command line will contain:
# -F/path/to -framework my_framework

File paths must conform to one of the following patterns
(* is a wildcard, and optional parts are shown as [...]):

o [/path/to/]FwName[.framework]

o [/path/to/]FwName.framework/FwName[suffix]

o [/path/to/]FwName.framework/Versions/*/FwName[suffix]

Note that CMake recognizes and automatically handles
framework targets, even without using the
$<LINK_LIBRARY:FRAMEWORK,...> expression. The generator
expression can still be used with a CMake target if the
project wants to be explicit about it, but it is not
required to do so. The linker command line may have some
differences between using the generator expression or
not, but the final result should be the same. On the
other hand, if a file path is given, CMake will recognize
some paths automatically, but not all cases. The project
may want to use $<LINK_LIBRARY:FRAMEWORK,...> for file
paths so that the expected behavior is clear.

New in version 3.25: The
FRAMEWORK_MULTI_CONFIG_POSTFIX_<CONFIG> target property
as well as the suffix of the framework library name are
now supported by the FRAMEWORK features.

NEEDED_FRAMEWORK
This is similar to the FRAMEWORK feature, except it
forces the linker to link with the framework even if no
symbols are used from it. It uses the -needed_framework
option and has the same linker constraints as FRAMEWORK.

REEXPORT_FRAMEWORK
This is similar to the FRAMEWORK feature, except it tells
the linker that the framework should be available to
clients linking to the library being created. It uses
the -reexport_framework option and has the same linker
constraints as FRAMEWORK.

WEAK_FRAMEWORK
This is similar to the FRAMEWORK feature, except it
forces the linker to mark the framework and all
references to it as weak imports. It uses the
-weak_framework option and has the same linker
constraints as FRAMEWORK.

NEEDED_LIBRARY
This is similar to the NEEDED_FRAMEWORK feature, except
it is for use with non-framework targets or libraries
(Apple platforms only). It uses the -needed_library or
-needed-l option as appropriate, and has the same linker
constraints as NEEDED_FRAMEWORK.

REEXPORT_LIBRARY
This is similar to the REEXPORT_FRAMEWORK feature,
except it is for use with non-framework targets or
libraries (Apple platforms only). It uses the
-reexport_library or -reexport-l option as appropriate,
and has the same linker constraints as
REEXPORT_FRAMEWORK.

WEAK_LIBRARY
This is similar to the WEAK_FRAMEWORK feature, except it
is for use with non-framework targets or libraries (Apple
platforms only). It uses the -weak_library or -weak-l
option as appropriate, and has the same linker
constraints as WEAK_FRAMEWORK.

Built-in and custom library features are defined in terms of the
following variables:

o CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED

o CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>

o CMAKE_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED

o CMAKE_LINK_LIBRARY_USING_<FEATURE>

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
CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED variable
is true, the feature must be defined by the corresponding
CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE> variable.

2. If no language-specific feature is supported, then the
CMAKE_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED variable must be
true and the feature must be defined by the corresponding
CMAKE_LINK_LIBRARY_USING_<FEATURE> variable.

The following limitations should be noted:

o The library-list can specify CMake targets or libraries. Any
CMake target of type OBJECT or INTERFACE will ignore the
feature aspect of the expression and instead be linked in the
standard way.

o The $<LINK_LIBRARY:...> generator expression can only be used
to specify link libraries. In practice, this means it can
appear in the LINK_LIBRARIES, INTERFACE_LINK_LIBRARIES, and
INTERFACE_LINK_LIBRARIES_DIRECT target properties, and be
specified in target_link_libraries() and link_libraries()
commands.

o If a $<LINK_LIBRARY:...> generator expression appears in the
INTERFACE_LINK_LIBRARIES property of a target, it will be
included in the imported target generated by a install(EXPORT)
command. It is the responsibility of the environment
consuming this import to define the link feature used by this
expression.

o Each target or library involved in the link step must have at
most only one kind of library feature. The absence of a
feature is also incompatible with all other features. For
example:

add_library(lib1 ...)
add_library(lib2 ...)
add_library(lib3 ...)

# lib1 will be associated with feature1
target_link_libraries(lib2 PUBLIC "$<LINK_LIBRARY:feature1,lib1>")

# lib1 is being linked with no feature here. This conflicts with the
# use of feature1 in the line above and would result in an error.
target_link_libraries(lib3 PRIVATE lib1 lib2)

Where it isn't possible to use the same feature throughout a
build for a given target or library, the LINK_LIBRARY_OVERRIDE
and LINK_LIBRARY_OVERRIDE_<LIBRARY> target properties can be
used to resolve such incompatibilities.

o The $<LINK_LIBRARY:...> generator expression does not
guarantee that the list of specified targets and libraries
will be kept grouped together. To manage constructs like
--start-group and --end-group, as supported by the GNU ld
linker, use the LINK_GROUP generator expression instead.

$<LINK_GROUP:feature,library-list>
New in version 3.24.

Specify a group of libraries to link to a target, along with a
feature which defines how that group should be linked. For
example:

add_library(lib1 STATIC ...)
add_library(lib2 ...)
target_link_libraries(lib2 PRIVATE "$<LINK_GROUP:RESCAN,lib1,external>")

This specifies that lib2 should link to lib1 and external, and
that both of those two libraries should be included on the
linker command line according to the definition of the RESCAN
feature.

RESCAN Some linkers are single-pass only. For such linkers,
circular references between libraries typically result in
unresolved symbols. This feature instructs the linker to
search the specified static libraries repeatedly until no
new undefined references are created.

Normally, a static library is searched only once in the
order that it is specified on the command line. If a
symbol in that library is needed to resolve an undefined
symbol referred to by an object in a library that appears
later on the command line, the linker would not be able
to resolve that reference. By grouping the static
libraries with the RESCAN feature, they will all be
searched repeatedly until all possible references are
resolved. This will use linker options like
--start-group and --end-group, or on SunOS, -z
rescan-start and -z rescan-end.

Using this feature has a significant performance cost. It
is best to use it only when there are unavoidable
circular references between two or more static libraries.

This feature is available when using toolchains that
target Linux, BSD, and SunOS. It can also be used when
targeting Windows platforms if the GNU toolchain is used.

Built-in and custom group features are defined in terms of the
following variables:

o CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED

o CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>

o CMAKE_LINK_GROUP_USING_<FEATURE>_SUPPORTED

o CMAKE_LINK_GROUP_USING_<FEATURE>

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
CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED variable is
true, the feature must be defined by the corresponding
CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE> variable.

2. If no language-specific feature is supported, then the
CMAKE_LINK_GROUP_USING_<FEATURE>_SUPPORTED variable must be
true and the feature must be defined by the corresponding
CMAKE_LINK_GROUP_USING_<FEATURE> variable.

The LINK_GROUP generator expression is compatible with the
LINK_LIBRARY generator expression. The libraries involved in a
group can be specified using the LINK_LIBRARY generator
expression.

Each target or external library involved in the link step is
allowed to be part of multiple groups, but only if all the
groups involved specify the same feature. Such groups will not
be merged on the linker command line, the individual groups will
still be preserved. Mixing different group features for the
same target or library is forbidden.

add_library(lib1 ...)
add_library(lib2 ...)
add_library(lib3 ...)
add_library(lib4 ...)
add_library(lib5 ...)

target_link_libraries(lib3 PUBLIC "$<LINK_GROUP:feature1,lib1,lib2>")
target_link_libraries(lib4 PRIVATE "$<LINK_GROUP:feature1,lib1,lib3>")
# lib4 will be linked with the groups {lib1,lib2} and {lib1,lib3}.
# Both groups specify the same feature, so this is fine.

target_link_libraries(lib5 PRIVATE "$<LINK_GROUP:feature2,lib1,lib3>")
# An error will be raised here because both lib1 and lib3 are part of two
# groups with different features.

When a target or an external library is involved in the link
step as part of a group and also as not part of any group, any
occurrence of the non-group link item will be replaced by the
groups it belongs to.

add_library(lib1 ...)
add_library(lib2 ...)
add_library(lib3 ...)
add_library(lib4 ...)

target_link_libraries(lib3 PUBLIC lib1)

target_link_libraries(lib4 PRIVATE lib3 "$<LINK_GROUP:feature1,lib1,lib2>")
# lib4 will only be linked with lib3 and the group {lib1,lib2}

Because lib1 is part of the group defined for lib4, that group
then gets applied back to the use of lib1 for lib3. The end
result will be as though the linking relationship for lib3 had
been specified as:

target_link_libraries(lib3 PUBLIC "$<LINK_GROUP:feature1,lib1,lib2>")

Be aware that the precedence of the group over the non-group
link item can result in circular dependencies between groups.
If this occurs, a fatal error is raised because circular
dependencies are not allowed for groups.

add_library(lib1A ...)
add_library(lib1B ...)
add_library(lib2A ...)
add_library(lib2B ...)
add_library(lib3 ...)

# Non-group linking relationships, these are non-circular so far
target_link_libraries(lib1A PUBLIC lib2A)
target_link_libraries(lib2B PUBLIC lib1B)

# The addition of these groups creates circular dependencies
target_link_libraries(lib3 PRIVATE
"$<LINK_GROUP:feat,lib1A,lib1B>"
"$<LINK_GROUP:feat,lib2A,lib2B>"
)

Because of the groups defined for lib3, the linking
relationships for lib1A and lib2B effectively get expanded to
the equivalent of:

target_link_libraries(lib1A PUBLIC "$<LINK_GROUP:feat,lib2A,lib2B>")
target_link_libraries(lib2B PUBLIC "$<LINK_GROUP:feat,lib1A,lib1B>")

This creates a circular dependency between groups: lib1A -->
lib2B --> lib1A.

The following limitations should also be noted:

o The library-list can specify CMake targets or libraries. Any
CMake target of type OBJECT or INTERFACE will ignore the
feature aspect of the expression and instead be linked in the
standard way.

o The $<LINK_GROUP:...> generator expression can only be used to
specify link libraries. In practice, this means it can appear
in the LINK_LIBRARIES, INTERFACE_LINK_LIBRARIES,and
INTERFACE_LINK_LIBRARIES_DIRECT target properties, and be
specified in target_link_libraries() and link_libraries()
commands.

o If a $<LINK_GROUP:...> generator expression appears in the
INTERFACE_LINK_LIBRARIES property of a target, it will be
included in the imported target generated by a install(EXPORT)
command. It is the responsibility of the environment
consuming this import to define the link feature used by this
expression.

Link Context

$<LINK_ONLY:...>
New in version 3.1.

Content of ..., except while collecting Transitive Usage
Requirements, in which case it is the empty string. This is
intended for use in an INTERFACE_LINK_LIBRARIES target property,
typically populated via the target_link_libraries() command, to
specify private link dependencies without other usage
requirements.

New in version 3.24: LINK_ONLY may also be used in a
LINK_LIBRARIES target property. See policy CMP0131.

$<DEVICE_LINK:list>
New in version 3.18.

Returns the list if it is the device link step, an empty list
otherwise. The device link step is controlled by
CUDA_SEPARABLE_COMPILATION and CUDA_RESOLVE_DEVICE_SYMBOLS
properties and policy CMP0105. This expression can only be used
to specify link options.

$<HOST_LINK:list>
New in version 3.18.

Returns the list if it is the normal link step, an empty list
otherwise. This expression is mainly useful when a device link
step is also involved (see $<DEVICE_LINK:list> generator
expression). This expression can only be used to specify link
options.

Target-Dependent Expressions
These queries refer to a target tgt. Unless otherwise stated, this can
be any runtime artifact, namely:

o An executable target created by add_executable().

o A shared library target (.so, .dll but not their .lib import library)
created by add_library().

o A static library target created by add_library().

In the following, the phrase "the tgt filename" means the name of the
tgt binary file. This has to be distinguished from the phrase "the
target name", which is just the string tgt.

$<TARGET_EXISTS:tgt>
New in version 3.12.

1 if tgt exists as a CMake target, else 0.

$<TARGET_NAME_IF_EXISTS:tgt>
New in version 3.12.

The target name tgt if the target exists, an empty string
otherwise.

Note that tgt is not added as a dependency of the target this
expression is evaluated on.

$<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.

$<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.

Changed in version 3.26: When encountered during evaluation of
Transitive Usage Requirements, typically in an INTERFACE_*
target property, lookup of the tgt name occurs in the directory
of the target specifying the requirement, rather than the
directory of the consuming target for which the expression is
being evaluated.

$<TARGET_PROPERTY:prop>
Value of the property prop on the target for which the
expression is being evaluated. Note that for generator
expressions in Transitive Usage Requirements this is the
consuming target rather than the target specifying the
requirement.

$<TARGET_OBJECTS:tgt>
New in version 3.1.

List of objects resulting from building tgt. This would
typically be used on object library targets.

$<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.

$<TARGET_FILE:tgt>
Full path to the tgt binary file.

Note that tgt is not added as a dependency of the target this
expression is evaluated on, unless the expression is being used
in add_custom_command() or add_custom_target().

$<TARGET_FILE_BASE_NAME:tgt>
New in version 3.15.

Base name of tgt, i.e. $<TARGET_FILE_NAME:tgt> without prefix
and suffix. For example, if the tgt filename 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>
New in version 3.15.

Prefix of the tgt filename (such as lib).

DragonFly On-Line Manual Pages

NAME

INTRODUCTION

WHITESPACE AND QUOTING

DEBUGGING

GENERATOR EXPRESSION REFERENCE

COPYRIGHT