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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. de-
pending on the C++ compiler used.

Generator expressions are allowed in the context of many target proper-
ties, 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 com-
piling, conditional include directories, and more. The conditions may
be based on the build configuration, target properties, platform infor-
mation, 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 com-
mand. 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 VERBA-
TIM and COMMAND_EXPAND_LISTS options to obtain robust argument split-
ting 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
)

Finally, the above example can be expressed in a more simple and robust
way using an alternate generator expression:

add_custom_target(run_some_tool
COMMAND some_tool "$<LIST:TRANSFORM,$<TARGET_PROPERTY:tgt,INCLUDE_DIRECTORIES>,PREPEND,-I>"
COMMAND_EXPAND_LISTS
VERBATIM
)

A common mistake is to try to split a generator expression across mul-
tiple 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 read-
able 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 re-
sults 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 er-
ror.

New in version 3.28: This generator expression short-circuits
such that generator expressions in false_string will not evalu-
ate when condition is 1, and generator expressions in
true_string will not evaluate when condition is 0.

Typically, the condition is itself a generator expression. For in-
stance, the following expression expands to DEBUG_MODE when the Debug
configuration is used, and the empty string for all other configura-
tions:

$<$<CONFIG:Debug>:DEBUG_MODE>

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

$<BOOL:string>
Converts string to 0 or 1. Evaluates to 0 if any of the follow-
ing 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 $<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 expres-
sions, all of which must evaluate to either 1 or 0. The whole
expression evaluates to 1 if all conditions are 1. If any con-
dition is 0, the whole expression evaluates to 0.

$<OR:conditions>
where conditions is a comma-separated list of boolean expres-
sions. 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 evalu-
ates to 0.

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

New in version 3.28: Logical operators short-circuit such that genera-
tor expressions in the arguments list will not be evaluated once a re-
turn value can be determined.

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 sepa-
rate 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 fol-
lows the same behavior as string(MAKE_C_IDENTIFIER).

List Expressions
Most of the expressions in this section are closely associated with the
list() command, providing the same capabilities, but in the form of a
generator expression.

In each of the following list-related generator expressions, the list
must not contain any commas if that generator expression expects some-
thing to be provided after the list. For example, the expression
$<LIST:FIND,list,value> requires a value after the list. Since a comma
is used to separate the list and the value, the list cannot itself con-
tain a comma. This restriction does not apply to the list() command,
it is specific to the list-handling generator expressions only.

List Comparisons
$<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.

List Queries
$<LIST:LENGTH,list>
New in version 3.27.

The number of items in the list.

$<LIST:GET,list,index,...>
New in version 3.27.

Expands to the list of items specified by indices from the list.

$<LIST:SUBLIST,list,begin,length>
New in version 3.27.

A sublist of the given list. If length is 0, an empty list will
be returned. If length is -1 or the list is smaller than begin
+ length, the remaining items of the list starting at begin will
be returned.

$<LIST:FIND,list,value>
New in version 3.27.

The index of the first item in list with the specified value, or
-1 if value is not in the list.

List Transformations
$<LIST:JOIN,list,glue>
New in version 3.27.

Converts list to a single string with the content of the glue
string inserted between each item. This is conceptually the
same operation as $<JOIN:list,glue>, but the two have different
behavior with regard to empty items. $<LIST:JOIN,list,glue>
preserves all empty items, whereas $<JOIN:list,glue> drops all
empty items from the list.

$<LIST:APPEND,list,item,...>
New in version 3.27.

The list with each item appended. Multiple items should be sep-
arated by commas.

$<LIST:PREPEND,list,item,...>
New in version 3.27.

The list with each item inserted at the beginning. If there are
multiple items, they should be separated by commas, and the or-
der of the prepended items will be preserved.

$<LIST:INSERT,list,index,item,...>
New in version 3.27.

The list with the item (or multiple items) inserted at the spec-
ified index. Multiple items should be separated by commas.

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.

$<LIST:POP_BACK,list>
New in version 3.27.

The list with the last item removed.

$<LIST:POP_FRONT,list>
New in version 3.27.

The list with the first item removed.

$<LIST:REMOVE_ITEM,list,value,...>
New in version 3.27.

The list with all instances of the given value (or values) re-
moved. If multiple values are given, they should be separated
by commas.

$<LIST:REMOVE_AT,list,index,...>
New in version 3.27.

The list with the item at each given index removed.

$<LIST:REMOVE_DUPLICATES,list>
New in version 3.27.

The list with all duplicated items removed. The relative order
of items is preserved, but if duplicates are encountered, only
the first instance is preserved. The result is the same as
$<REMOVE_DUPLICATES:list>.

$<LIST:FILTER,list,INCLUDE|EXCLUDE,regex>
New in version 3.27.

A list of items from the list which match (INCLUDE) or do not
match (EXCLUDE) the regular expression regex. The result is the
same as $<FILTER:list,INCLUDE|EXCLUDE,regex>.

$<LIST:TRANSFORM,list,ACTION[,SELECTOR]>
New in version 3.27.

The list transformed by applying an ACTION to all or, by speci-
fying a SELECTOR, to the selected list items.

NOTE:
The TRANSFORM sub-command does not change the number of items
in the list. If a SELECTOR is specified, only some items will
be changed, the other ones will remain the same as before the
transformation.

ACTION specifies the action to apply to the items of the list.
The actions have exactly the same semantics as for the
list(TRANSFORM) command. ACTION must be one of the following:

APPEND, PREPEND
Append, prepend specified value to each item of the
list.

$<LIST:TRANSFORM,list,(APPEND|PREPEND),value[,SELECTOR]>

TOLOWER, TOUPPER
Convert each item of the list to lower, upper charac-
ters.

$<LIST:TRANSFORM,list,(TOLOWER|TOUPPER)[,SELECTOR]>

STRIP Remove leading and trailing spaces from each item of
the list.

$<LIST:TRANSFORM,list,STRIP[,SELECTOR]>

REPLACE:
Match the regular expression as many times as possible
and substitute the replacement expression for the
match for each item of the list.

$<LIST:TRANSFORM,list,REPLACE,regular_expression,replace_expression[,SELECTOR]>

SELECTOR determines which items 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.

$<LIST:TRANSFORM,list,ACTION,AT,index[,index...]>

FOR Specify a range with, optionally, an increment used to
iterate over the range.

$<LIST:TRANSFORM,list,ACTION,FOR,start,stop[,step]>

REGEX Specify a regular expression. Only items matching the
regular expression will be transformed.

$<LIST:TRANSFORM,list,ACTION,REGEX,regular_expression>

$<JOIN:list,glue>
Joins the list with the content of the glue string inserted be-
tween each item. This is conceptually the same operation as
$<LIST:JOIN,list,glue>, but the two have different behavior with
regard to empty items. $<LIST:JOIN,list,glue> preserves all
empty items, whereas $<JOIN,list,glue> drops all empty items
from the list.

$<REMOVE_DUPLICATES:list>
New in version 3.15.

Removes duplicated items in the given list. The relative order
of items is preserved, and if duplicates are encountered, only
the first instance is retained. The result is the same as
$<LIST:REMOVE_DUPLICATES,list>.

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

Includes or removes items from list that match the regular ex-
pression regex. The result is the same as
$<LIST:FILTER,list,INCLUDE|EXCLUDE,regex>.

List Ordering
$<LIST:REVERSE,list>
New in version 3.27.

The list with the items in reverse order.

$<LIST:SORT,list[,(COMPARE:option|CASE:option|ORDER:option)]...>
New in version 3.27.

The list sorted according to 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 file paths by their basenames.

NATURAL
Sorts a list of strings using natural order (see the
man page for strverscmp(3)), such that contiguous dig-
its 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, whereas 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 in a case-insensitive manner.
The order of items which differ only by upper/lower-
case 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 de-
fault behavior when the ORDER option is not given.

DESCENDING
Sorts the list in descending order.

Options can be specified in any order, but it is an error to
specify the same option multiple times.

$<LIST:SORT,list,CASE:SENSITIVE,COMPARE:STRING,ORDER:DESCENDING>

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 normaliza-
tion 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 ex-
pected to be in cmake-style format.

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

The following operations return 1 if the particular path compo-
nent 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:

• 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 ex-
cept 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.

Changed in version 3.27: All operations now accept a list of
paths as argument. When a list of paths is specified, the opera-
tion will be applied to each path.

$<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.

Changed in version 3.27: All operations now accept a list of paths as
argument. When a list of paths is specified, the operation will be ap-
plied to each path.

$<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 di-
rectory-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> re-
turns 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 con-
taining 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 ex-
pression when it is evaluated on a property of an IMPORTED tar-
get.

Changed in version 3.19: Multiple configurations can be speci-
fied 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 C++ 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 C++ compiler matches version, otherwise
0.

$<OBJC_COMPILER_VERSION>
New in version 3.16.

The version of the Objective-C compiler used.

$<OBJC_COMPILER_VERSION:version>
New in version 3.16.

1 if the version of the Objective-C compiler matches version,
otherwise 0.

$<OBJCXX_COMPILER_VERSION>
New in version 3.16.

The version of the Objective-C++ compiler used.

$<OBJCXX_COMPILER_VERSION:version>
New in version 3.16.

1 if the version of the Objective-C++ 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, other-
wise 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, ID, and Frontend-Variant
See also the CMAKE_<LANG>_COMPILER_ID and
CMAKE_<LANG>_COMPILER_FRONTEND_VARIANT variables, which are closely re-
lated 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 com-
piler id of the C compiler matches any one of the entries in
compiler_ids, otherwise 0.

Changed in version 3.15: Multiple compiler_ids can be specified.
CMake 3.14 and earlier only accepted a single compiler ID.

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

$<CXX_COMPILER_ID:compiler_ids>
where compiler_ids is a comma-separated list. 1 if CMake's com-
piler id of the C++ compiler matches any one of the entries in
compiler_ids, otherwise 0.

Changed in version 3.15: Multiple compiler_ids can be specified.
CMake 3.14 and earlier only accepted a single compiler ID.

$<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 com-
piler 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 Objective-C compiler used.

$<OBJC_COMPILER_ID:compiler_ids>
New in version 3.16.

where compiler_ids is a comma-separated list. 1 if CMake's com-
piler id of the Objective-C compiler matches any one of the en-
tries in compiler_ids, otherwise 0.

$<OBJCXX_COMPILER_ID>
New in version 3.16.

CMake's compiler id of the Objective-C++ compiler used.

$<OBJCXX_COMPILER_ID:compiler_ids>
New in version 3.16.

where compiler_ids is a comma-separated list. 1 if CMake's com-
piler 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 com-
piler id of the Fortran compiler matches any one of the entries
in compiler_ids, otherwise 0.

Changed in version 3.15: Multiple compiler_ids can be specified.
CMake 3.14 and earlier only accepted a single compiler ID.

$<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 com-
piler 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 com-
piler id of the ISPC compiler matches any one of the entries in
compiler_ids, otherwise 0.

$<C_COMPILER_FRONTEND_VARIANT>
New in version 3.30.

CMake's compiler frontend variant of the C compiler used.

$<C_COMPILER_FRONTEND_VARIANT:compiler_ids>
New in version 3.30.

where compiler_ids is a comma-separated list. 1 if CMake's com-
piler frontend variant of the C compiler matches any one of the
entries in compiler_ids, otherwise 0.

$<CXX_COMPILER_FRONTEND_VARIANT>
New in version 3.30.

CMake's compiler frontend variant of the C++ compiler used.

$<CXX_COMPILER_FRONTEND_VARIANT:compiler_ids>
New in version 3.30.

where compiler_ids is a comma-separated list. 1 if CMake's com-
piler frontend variant of the C++ compiler matches any one of
the entries in compiler_ids, otherwise 0.

$<CUDA_COMPILER_FRONTEND_VARIANT>
New in version 3.30.

CMake's compiler id of the CUDA compiler used.

$<CUDA_COMPILER_FRONTEND_VARIANT:compiler_ids>
New in version 3.30.

where compiler_ids is a comma-separated list. 1 if CMake's com-
piler frontend variant of the CUDA compiler matches any one of
the entries in compiler_ids, otherwise 0.

$<OBJC_COMPILER_FRONTEND_VARIANT>
New in version 3.30.

CMake's compiler frontend variant of the Objective-C compiler
used.

$<OBJC_COMPILER_FRONTEND_VARIANT:compiler_ids>
New in version 3.30.

where compiler_ids is a comma-separated list. 1 if CMake's com-
piler frontend variant of the Objective-C compiler matches any
one of the entries in compiler_ids, otherwise 0.

$<OBJCXX_COMPILER_FRONTEND_VARIANT>
New in version 3.30.

CMake's compiler frontend variant of the Objective-C++ compiler
used.

$<OBJCXX_COMPILER_FRONTEND_VARIANT:compiler_ids>
New in version 3.30.

where compiler_ids is a comma-separated list. 1 if CMake's com-
piler frontend variant of the Objective-C++ compiler matches any
one of the entries in compiler_ids, otherwise 0.

$<Fortran_COMPILER_FRONTEND_VARIANT>
New in version 3.30.

CMake's compiler id of the Fortran compiler used.

$<Fortran_COMPILER_FRONTEND_VARIANT:compiler_ids>
New in version 3.30.

where compiler_ids is a comma-separated list. 1 if CMake's com-
piler frontend variant of the Fortran compiler matches any one
of the entries in compiler_ids, otherwise 0.

$<HIP_COMPILER_FRONTEND_VARIANT>
New in version 3.30.

CMake's compiler id of the HIP compiler used.

$<HIP_COMPILER_FRONTEND_VARIANT:compiler_ids>
New in version 3.30.

where compiler_ids is a comma-separated list. 1 if CMake's com-
piler frontend variant of the HIP compiler matches any one of
the entries in compiler_ids, otherwise 0.

$<ISPC_COMPILER_FRONTEND_VARIANT>
New in version 3.30.

CMake's compiler id of the ISPC compiler used.

$<ISPC_COMPILER_FRONTEND_VARIANT:compiler_ids>
New in version 3.30.

where compiler_ids is a comma-separated list. 1 if CMake's com-
piler frontend variant 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 op-
tions. See the related boolean expression $<COMPILE_LAN-
GUAGE:language> for notes about the portability of this genera-
tor 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 lan-
guage.

1 when the language used for compilation unit matches any of the
comma-separated entries in languages, otherwise 0. This expres-
sion may be used to specify compile options, compile defini-
tions, 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 direc-
tory for C++ only (compiler id checks elided). It also speci-
fies 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 di-
rectories 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, ex-
pressions 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 $<COM-
PILE_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 par-
ticular language and compiler combination in a target. For ex-
ample:

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 oth-
erwise. If this expression is used while evaluating the link im-
plementation of a target and if any dependency transitively in-
creases 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 sup-
ported compilers.

Compile Context
$<COMPILE_ONLY:...>
New in version 3.27.

Content of ..., when collecting transitive compile properties,
otherwise it is the empty string. This is intended for use in
an INTERFACE_LINK_LIBRARIES and LINK_LIBRARIES target proper-
ties, typically populated via the target_link_libraries() com-
mand. Provides compilation usage requirements without any link-
ing requirements.

Use cases include header-only usage where all usages are known
to not have linking requirements (e.g., all-inline or C++ tem-
plate libraries).

Note that for proper evaluation of this expression requires pol-
icy CMP0099 to be set to NEW.

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 li-
braries 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 expres-
sion 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_LAN-
GUAGE:..> expressions will always return 0. The link lan-
guage 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 com-
plete 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, unexpect-
edly, 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_LAN-
GUAGE:language> and $<LANG_COMPILER_ID:compiler_ids>. This ex-
pression 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 con-
straints 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:

• Linux.

• All BSD variants.

• SunOS.

• All Apple variants. The library must be specified as a
CMake target name, a library file name (such as lib-
foo.a), or a library file path (such as /path/to/lib-
foo.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.

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

• Cygwin.

• 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 pro-
vided with Xcode, or one compatible with it).

The framework can be specified as a CMake framework tar-
get, 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 frame-
work 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 [...]):

• [/path/to/]FwName[.framework]

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

• [/path/to/]FwName.framework/Versions/*/FwName[suf-
fix]

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 re-
quired 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 refer-
ences 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, ex-
cept it is for use with non-framework targets or li-
braries (Apple platforms only). It uses the -reex-
port_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 con-
straints as WEAK_FRAMEWORK.

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

• CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED

• CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>

• CMAKE_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED

• 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 cre-
ated. 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:

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

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

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

• Each target or library involved in the link step must have at
most only one kind of library feature. The absence of a fea-
ture is also incompatible with all other features. For exam-
ple:

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.

• The $<LINK_LIBRARY:...> generator expression does not guaran-
tee 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 ex-
ample:

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 li-
braries with the RESCAN feature, they will all be
searched repeatedly until all possible references are re-
solved. This will use linker options like --start-group
and --end-group, or on SunOS, -z rescan-start and -z res-
can-end.

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

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

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

• CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED

• CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>

• CMAKE_LINK_GROUP_USING_<FEATURE>_SUPPORTED

• 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 cre-
ated. 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 expres-
sion.

Each target or external library involved in the link step is al-
lowed 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 re-
sult 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 depen-
dencies 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 relation-
ships for lib1A and lib2B effectively get expanded to the equiv-
alent 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:

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

• 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() com-
mands.

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

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

Content of ..., except while collecting usage requirements from
transitive compile properties, 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 depen-
dencies without other usage requirements such as include direc-
tories or compile options.

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 prop-
erties 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 expres-
sion). This expression can only be used to specify link options.

Target-Dependent Expressions
Target Meta-Data
These expressions look up information about a target.

$<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 other-
wise.

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

$<TARGET_NAME:tgt>
The target name tgt as written. This marks tgt as being the
name of a target inside a larger expression, which is required
if exporting targets to multiple dependent export sets. The tgt
text must be a literal name of a target; it may not contain gen-
erator expressions. The target does not have to exist.

$<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 pol-
icy will be emitted. This generator expression only works for a
subset of policies.

Target Properties
These expressions look up the values of target properties.

$<TARGET_PROPERTY:tgt,prop>
Value of the property prop on the target tgt, or empty if the
property is not set.

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
Target 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 evalu-
ated.

$<TARGET_PROPERTY:prop>
Value of the property prop on the target for which the expres-
sion is being evaluated, or empty if the property is not set.
Note that for generator expressions in Target Usage Requirements
this is the consuming target rather than the target specifying
the requirement.

The expressions have special evaluation rules for some properties:

Target Build Specification Properties
These evaluate as a semicolon-separated list representing the
union of the value on the target itself with the values of the
corresponding Target Usage Requirements on targets named by the
target's LINK_LIBRARIES:

• For Target Compile Properties, evaluation of corresponding us-
age requirements is transitive over the closure of the linked
targets' INTERFACE_LINK_LIBRARIES excluding entries guarded by
the LINK_ONLY generator expression.

• For Target Link Properties, evaluation of corresponding usage
requirements is transitive over the closure of the linked tar-
gets' INTERFACE_LINK_LIBRARIES including entries guarded by
the LINK_ONLY generator expression. See policy CMP0166.

Evaluation of LINK_LIBRARIES itself is not transitive.

Target Usage Requirement Properties
These evaluate as a semicolon-separated list representing the
union of the value on the target itself with the values of the
same properties on targets named by the target's
INTERFACE_LINK_LIBRARIES:

• For Transitive Compile Properties, evaluation is transitive
over the closure of the target's INTERFACE_LINK_LIBRARIES ex-
cluding entries guarded by the LINK_ONLY generator expression.

• For Transitive Link Properties, evaluation is transitive over
the closure of the target's INTERFACE_LINK_LIBRARIES including
entries guarded by the LINK_ONLY generator expression. See
policy CMP0166.

Evaluation of INTERFACE_LINK_LIBRARIES itself is not transitive.

Custom Transitive Properties
New in version 3.30.

These are processed during evaluation as follows:

• Evaluation of $<TARGET_PROPERTY:tgt,PROP> for some property
PROP, named without an INTERFACE_ prefix, checks the
TRANSITIVE_COMPILE_PROPERTIES and TRANSITIVE_LINK_PROPERTIES
properties on target tgt, on targets named by its
LINK_LIBRARIES, and on the transitive closure of targets named
by the linked targets' INTERFACE_LINK_LIBRARIES.

If PROP is listed by one of those properties, then it evalu-
ates as a semicolon-separated list representing the union of
the value on the target itself with the values of the corre-
sponding INTERFACE_PROP on targets named by the target's
LINK_LIBRARIES:

• If PROP is named by TRANSITIVE_COMPILE_PROPERTIES, evalua-
tion of the corresponding INTERFACE_PROP is transitive over
the closure of the linked targets' INTERFACE_LINK_LIBRARIES,
excluding entries guarded by the LINK_ONLY generator expres-
sion.

• If PROP is named by TRANSITIVE_LINK_PROPERTIES, evaluation
of the corresponding INTERFACE_PROP is transitive over the
closure of the linked targets' INTERFACE_LINK_LIBRARIES, in-
cluding entries guarded by the LINK_ONLY generator expres-
sion.

• Evaluation of $<TARGET_PROPERTY:tgt,INTERFACE_PROP> for some
property INTERFACE_PROP, named with an INTERFACE_ prefix,
checks the TRANSITIVE_COMPILE_PROPERTIES and
TRANSITIVE_LINK_PROPERTIES properties on target tgt, and on
the transitive closure of targets named by its
INTERFACE_LINK_LIBRARIES.

If the corresponding PROP is listed by one of those proper-
ties, then INTERFACE_PROP evaluates as a semicolon-separated
list representing the union of the value on the target itself
with the value of the same property on targets named by the
target's INTERFACE_LINK_LIBRARIES:

• If PROP is named by TRANSITIVE_COMPILE_PROPERTIES, evalua-
tion of the corresponding INTERFACE_PROP is transitive over
the closure of the target's INTERFACE_LINK_LIBRARIES, ex-
cluding entries guarded by the LINK_ONLY generator expres-
sion.

• If PROP is named by TRANSITIVE_LINK_PROPERTIES, evaluation
of the corresponding INTERFACE_PROP is transitive over the
closure of the target's INTERFACE_LINK_LIBRARIES, including
entries guarded by the LINK_ONLY generator expression.

If a PROP is named by both TRANSITIVE_COMPILE_PROPERTIES and
TRANSITIVE_LINK_PROPERTIES, the latter takes precedence.

Compatible Interface Properties
These evaluate as a single value combined from the target it-
self, from targets named by the target's LINK_LIBRARIES, and
from the transitive closure of the linked targets'
INTERFACE_LINK_LIBRARIES. Values of a compatible interface
property from multiple targets combine based on the type of com-
patibility required by the COMPATIBLE_INTERFACE_* property
defining it.

Target Artifacts
These expressions look up information about artifacts associated with a
given target tgt. Unless otherwise stated, this can be any runtime ar-
tifact, namely:

• An executable target created by add_executable().

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

• 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 tar-
get name", which is just the string tgt.

$<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).

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