cmake-generator-expressions.7.rst 22 KB

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  1. .. cmake-manual-description: CMake Generator Expressions
  2. cmake-generator-expressions(7)
  3. ******************************
  4. .. only:: html
  5. .. contents::
  6. Introduction
  7. ============
  8. Generator expressions are evaluated during build system generation to produce
  9. information specific to each build configuration.
  10. Generator expressions are allowed in the context of many target properties,
  11. such as :prop_tgt:`LINK_LIBRARIES`, :prop_tgt:`INCLUDE_DIRECTORIES`,
  12. :prop_tgt:`COMPILE_DEFINITIONS` and others. They may also be used when using
  13. commands to populate those properties, such as :command:`target_link_libraries`,
  14. :command:`target_include_directories`, :command:`target_compile_definitions`
  15. and others.
  16. They enable conditional linking, conditional definitions used when compiling,
  17. conditional include directories, and more. The conditions may be based on
  18. the build configuration, target properties, platform information or any other
  19. queryable information.
  20. Generator expressions have the form ``$<...>``. To avoid confusion, this page
  21. deviates from most of the CMake documentation in that it omits angular brackets
  22. ``<...>`` around placeholders like ``condition``, ``string``, ``target``,
  23. among others.
  24. Generator expressions can be nested, as shown in most of the examples below.
  25. .. _`Boolean Generator Expressions`:
  26. Boolean Generator Expressions
  27. =============================
  28. Boolean expressions evaluate to either ``0`` or ``1``.
  29. They are typically used to construct the condition in a :ref:`conditional
  30. generator expression<Conditional Generator Expressions>`.
  31. Available boolean expressions are:
  32. Logical Operators
  33. -----------------
  34. ``$<BOOL:string>``
  35. Converts ``string`` to ``0`` or ``1`` according to the rules of the
  36. :command:`if()` command. Evaluates to ``0`` if any of the following is true:
  37. * ``string`` is empty,
  38. * ``string`` is a case-insensitive equal of
  39. ``0``, ``FALSE``, ``OFF``, ``N``, ``NO``, ``IGNORE``, or ``NOTFOUND``, or
  40. * ``string`` ends in the suffix ``-NOTFOUND`` (case-sensitive).
  41. Otherwise evaluates to ``1``.
  42. ``$<AND:conditions>``
  43. where ``conditions`` is a comma-separated list of boolean expressions.
  44. Evaluates to ``1`` if all conditions are ``1``.
  45. Otherwise evaluates to ``0``.
  46. ``$<OR:conditions>``
  47. where ``conditions`` is a comma-separated list of boolean expressions.
  48. Evaluates to ``1`` if at least one of the conditions is ``1``.
  49. Otherwise evaluates to ``0``.
  50. ``$<NOT:condition>``
  51. ``0`` if ``condition`` is ``1``, else ``1``.
  52. String Comparisons
  53. ------------------
  54. ``$<STREQUAL:string1,string2>``
  55. ``1`` if ``string1`` and ``string2`` are equal, else ``0``.
  56. The comparison is case-sensitive. For a case-insensitive comparison,
  57. combine with a :ref:`string transforming generator expression
  58. <String Transforming Generator Expressions>`,
  59. .. code-block:: cmake
  60. $<STREQUAL:$<UPPER_CASE:${foo}>,"BAR"> # "1" if ${foo} is any of "BAR", "Bar", "bar", ...
  61. ``$<EQUAL:value1,value2>``
  62. ``1`` if ``value1`` and ``value2`` are numerically equal, else ``0``.
  63. ``$<IN_LIST:string,list>``
  64. ``1`` if ``string`` is member of the semicolon-separated ``list``, else ``0``.
  65. Uses case-sensitive comparisons.
  66. ``$<VERSION_LESS:v1,v2>``
  67. ``1`` if ``v1`` is a version less than ``v2``, else ``0``.
  68. ``$<VERSION_GREATER:v1,v2>``
  69. ``1`` if ``v1`` is a version greater than ``v2``, else ``0``.
  70. ``$<VERSION_EQUAL:v1,v2>``
  71. ``1`` if ``v1`` is the same version as ``v2``, else ``0``.
  72. ``$<VERSION_LESS_EQUAL:v1,v2>``
  73. ``1`` if ``v1`` is a version less than or equal to ``v2``, else ``0``.
  74. ``$<VERSION_GREATER_EQUAL:v1,v2>``
  75. ``1`` if ``v1`` is a version greater than or equal to ``v2``, else ``0``.
  76. Variable Queries
  77. ----------------
  78. ``$<TARGET_EXISTS:target>``
  79. ``1`` if ``target`` exists, else ``0``.
  80. ``$<CONFIG:cfg>``
  81. ``1`` if config is ``cfg``, else ``0``. This is a case-insensitive comparison.
  82. The mapping in :prop_tgt:`MAP_IMPORTED_CONFIG_<CONFIG>` is also considered by
  83. this expression when it is evaluated on a property on an :prop_tgt:`IMPORTED`
  84. target.
  85. ``$<PLATFORM_ID:platform_id>``
  86. ``1`` if the CMake-id of the platform matches ``platform_id``
  87. otherwise ``0``.
  88. See also the :variable:`CMAKE_SYSTEM_NAME` variable.
  89. ``$<C_COMPILER_ID:compiler_id>``
  90. ``1`` if the CMake-id of the C compiler matches ``compiler_id``,
  91. otherwise ``0``.
  92. See also the :variable:`CMAKE_<LANG>_COMPILER_ID` variable.
  93. ``$<CXX_COMPILER_ID:compiler_id>``
  94. ``1`` if the CMake-id of the CXX compiler matches ``compiler_id``,
  95. otherwise ``0``.
  96. ``$<CUDA_COMPILER_ID:compiler_id>``
  97. ``1`` if the CMake-id of the CUDA compiler matches ``compiler_id``,
  98. otherwise ``0``.
  99. See also the :variable:`CMAKE_<LANG>_COMPILER_ID` variable.
  100. ``$<Fortran_COMPILER_ID:compiler_id>``
  101. ``1`` if the CMake-id of the Fortran compiler matches ``compiler_id``,
  102. otherwise ``0``.
  103. See also the :variable:`CMAKE_<LANG>_COMPILER_ID` variable.
  104. ``$<C_COMPILER_VERSION:version>``
  105. ``1`` if the version of the C compiler matches ``version``, otherwise ``0``.
  106. See also the :variable:`CMAKE_<LANG>_COMPILER_VERSION` variable.
  107. ``$<CXX_COMPILER_VERSION:version>``
  108. ``1`` if the version of the CXX compiler matches ``version``, otherwise ``0``.
  109. See also the :variable:`CMAKE_<LANG>_COMPILER_VERSION` variable.
  110. ``$<CUDA_COMPILER_VERSION:version>``
  111. ``1`` if the version of the CXX compiler matches ``version``, otherwise ``0``.
  112. See also the :variable:`CMAKE_<LANG>_COMPILER_VERSION` variable.
  113. ``$<Fortran_COMPILER_VERSION:version>``
  114. ``1`` if the version of the Fortran compiler matches ``version``, otherwise ``0``.
  115. See also the :variable:`CMAKE_<LANG>_COMPILER_VERSION` variable.
  116. ``$<TARGET_POLICY:policy>``
  117. ``1`` if the ``policy`` was NEW when the 'head' target was created,
  118. else ``0``. If the ``policy`` was not set, the warning message for the policy
  119. will be emitted. This generator expression only works for a subset of
  120. policies.
  121. ``$<COMPILE_FEATURES:features>``
  122. where ``features`` is a comma-spearated list.
  123. Evaluates to ``1`` if all of the ``features`` are available for the 'head'
  124. target, and ``0`` otherwise. If this expression is used while evaluating
  125. the link implementation of a target and if any dependency transitively
  126. increases the required :prop_tgt:`C_STANDARD` or :prop_tgt:`CXX_STANDARD`
  127. for the 'head' target, an error is reported. See the
  128. :manual:`cmake-compile-features(7)` manual for information on
  129. compile features and a list of supported compilers.
  130. .. _`Boolean COMPILE_LANGUAGE Generator Expression`:
  131. ``$<COMPILE_LANGUAGE:language>``
  132. ``1`` when the language used for compilation unit matches ``language``,
  133. otherwise ``0``. This expression may be used to specify compile options,
  134. compile definitions, and include directories for source files of a
  135. particular language in a target. For example:
  136. .. code-block:: cmake
  137. add_executable(myapp main.cpp foo.c bar.cpp zot.cu)
  138. target_compile_options(myapp
  139. PRIVATE $<$<COMPILE_LANGUAGE:CXX>:-fno-exceptions>
  140. )
  141. target_compile_definitions(myapp
  142. PRIVATE $<$<COMPILE_LANGUAGE:CXX>:COMPILING_CXX>
  143. $<$<COMPILE_LANGUAGE:CUDA>:COMPILING_CUDA>
  144. )
  145. target_include_directories(myapp
  146. PRIVATE $<$<COMPILE_LANGUAGE:CXX>:/opt/foo/cxx_headers>
  147. )
  148. This specifies the use of the ``-fno-exceptions`` compile option,
  149. ``COMPILING_CXX`` compile definition, and ``cxx_headers`` include
  150. directory for C++ only (compiler id checks elided). It also specifies
  151. a ``COMPILING_CUDA`` compile definition for CUDA.
  152. Note that with :ref:`Visual Studio Generators` and :generator:`Xcode` there
  153. is no way to represent target-wide compile definitions or include directories
  154. separately for ``C`` and ``CXX`` languages.
  155. Also, with :ref:`Visual Studio Generators` there is no way to represent
  156. target-wide flags separately for ``C`` and ``CXX`` languages. Under these
  157. generators, expressions for both C and C++ sources will be evaluated
  158. using ``CXX`` if there are any C++ sources and otherwise using ``C``.
  159. A workaround is to create separate libraries for each source file language
  160. instead:
  161. .. code-block:: cmake
  162. add_library(myapp_c foo.c)
  163. add_library(myapp_cxx bar.cpp)
  164. target_compile_options(myapp_cxx PUBLIC -fno-exceptions)
  165. add_executable(myapp main.cpp)
  166. target_link_libraries(myapp myapp_c myapp_cxx)
  167. String-Valued Generator Expressions
  168. ===================================
  169. These expressions expand to some string.
  170. For example,
  171. .. code-block:: cmake
  172. include_directories(/usr/include/$<CXX_COMPILER_ID>/)
  173. expands to ``/usr/include/GNU/`` or ``/usr/include/Clang/`` etc, depending on
  174. the compiler identifier.
  175. String-valued expressions may also be combined with other expressions.
  176. Here an example for a string-valued expression within a boolean expressions
  177. within a conditional expression:
  178. .. code-block:: cmake
  179. $<$<VERSION_LESS:$<CXX_COMPILER_VERSION>,4.2.0>:OLD_COMPILER>
  180. expands to ``OLD_COMPILER`` if the
  181. :variable:`CMAKE_CXX_COMPILER_VERSION <CMAKE_<LANG>_COMPILER_VERSION>` is less
  182. than 4.2.0.
  183. And here two nested string-valued expressions:
  184. .. code-block:: cmake
  185. -I$<JOIN:$<TARGET_PROPERTY:INCLUDE_DIRECTORIES>, -I>
  186. generates a string of the entries in the :prop_tgt:`INCLUDE_DIRECTORIES` target
  187. property with each entry preceded by ``-I``.
  188. Expanding on the previous example, if one first wants to check if the
  189. ``INCLUDE_DIRECTORIES`` property is non-empty, then it is advisable to
  190. introduce a helper variable to keep the code readable:
  191. .. code-block:: cmake
  192. set(prop "$<TARGET_PROPERTY:INCLUDE_DIRECTORIES>") # helper variable
  193. $<$<BOOL:${prop}>:-I$<JOIN:${prop}, -I>>
  194. The following string-valued generator expressions are available:
  195. Escaped Characters
  196. ------------------
  197. String literals to escape the special meaning a character would otherwise have:
  198. ``$<ANGLE-R>``
  199. A literal ``>``. Used for example to compare strings that contain a ``>``.
  200. ``$<COMMA>``
  201. A literal ``,``. Used for example to compare strings which contain a ``,``.
  202. ``$<SEMICOLON>``
  203. A literal ``;``. Used to prevent list expansion on an argument with ``;``.
  204. .. _`Conditional Generator Expressions`:
  205. Conditional Expressions
  206. -----------------------
  207. Conditional generator expressions depend on a boolean condition
  208. that must be ``0`` or ``1``.
  209. ``$<condition:true_string>``
  210. Evaluates to ``true_string`` if ``condition`` is ``1``.
  211. Otherwise evaluates to the empty string.
  212. ``$<IF:condition,true_string,false_string>``
  213. Evaluates to ``true_string`` if ``condition`` is ``1``.
  214. Otherwise evaluates to ``false_string``.
  215. Typically, the ``condition`` is a :ref:`boolean generator expression
  216. <Boolean Generator Expressions>`. For instance,
  217. .. code-block:: cmake
  218. $<$<CONFIG:Debug>:DEBUG_MODE>
  219. expands to ``DEBUG_MODE`` when the ``Debug`` configuration is used, and
  220. otherwise expands to the empty string.
  221. .. _`String Transforming Generator Expressions`:
  222. String Transformations
  223. ----------------------
  224. ``$<JOIN:list,string>``
  225. Joins the list with the content of ``string``.
  226. ``$<REMOVE_DUPLICATES:list>``
  227. Removes duplicated items in the given ``list``.
  228. ``$<FILTER:list,INCLUDE|EXCLUDE,regex>``
  229. Includes or removes items from ``list`` that match the regular expression ``regex``.
  230. ``$<LOWER_CASE:string>``
  231. Content of ``string`` converted to lower case.
  232. ``$<UPPER_CASE:string>``
  233. Content of ``string`` converted to upper case.
  234. ``$<GENEX_EVAL:expr>``
  235. Content of ``expr`` evaluated as a generator expression in the current
  236. context. This enables consumption of generator expressions whose
  237. evaluation results itself in generator expressions.
  238. ``$<TARGET_GENEX_EVAL:tgt,expr>``
  239. Content of ``expr`` evaluated as a generator expression in the context of
  240. ``tgt`` target. This enables consumption of custom target properties that
  241. themselves contain generator expressions.
  242. Having the capability to evaluate generator expressions is very useful when
  243. you want to manage custom properties supporting generator expressions.
  244. For example:
  245. .. code-block:: cmake
  246. add_library(foo ...)
  247. set_property(TARGET foo PROPERTY
  248. CUSTOM_KEYS $<$<CONFIG:DEBUG>:FOO_EXTRA_THINGS>
  249. )
  250. add_custom_target(printFooKeys
  251. COMMAND ${CMAKE_COMMAND} -E echo $<TARGET_PROPERTY:foo,CUSTOM_KEYS>
  252. )
  253. This naive implementation of the ``printFooKeys`` custom command is wrong
  254. because ``CUSTOM_KEYS`` target property is not evaluated and the content
  255. is passed as is (i.e. ``$<$<CONFIG:DEBUG>:FOO_EXTRA_THINGS>``).
  256. To have the expected result (i.e. ``FOO_EXTRA_THINGS`` if config is
  257. ``Debug``), it is required to evaluate the output of
  258. ``$<TARGET_PROPERTY:foo,CUSTOM_KEYS>``:
  259. .. code-block:: cmake
  260. add_custom_target(printFooKeys
  261. COMMAND ${CMAKE_COMMAND} -E
  262. echo $<TARGET_GENEX_EVAL:foo,$<TARGET_PROPERTY:foo,CUSTOM_KEYS>>
  263. )
  264. Variable Queries
  265. ----------------
  266. ``$<CONFIG>``
  267. Configuration name.
  268. ``$<CONFIGURATION>``
  269. Configuration name. Deprecated since CMake 3.0. Use ``CONFIG`` instead.
  270. ``$<PLATFORM_ID>``
  271. The CMake-id of the platform.
  272. See also the :variable:`CMAKE_SYSTEM_NAME` variable.
  273. ``$<C_COMPILER_ID>``
  274. The CMake-id of the C compiler used.
  275. See also the :variable:`CMAKE_<LANG>_COMPILER_ID` variable.
  276. ``$<CXX_COMPILER_ID>``
  277. The CMake-id of the CXX compiler used.
  278. See also the :variable:`CMAKE_<LANG>_COMPILER_ID` variable.
  279. ``$<CUDA_COMPILER_ID>``
  280. The CMake-id of the CUDA compiler used.
  281. See also the :variable:`CMAKE_<LANG>_COMPILER_ID` variable.
  282. ``$<Fortran_COMPILER_ID>``
  283. The CMake-id of the Fortran compiler used.
  284. See also the :variable:`CMAKE_<LANG>_COMPILER_ID` variable.
  285. ``$<C_COMPILER_VERSION>``
  286. The version of the C compiler used.
  287. See also the :variable:`CMAKE_<LANG>_COMPILER_VERSION` variable.
  288. ``$<CXX_COMPILER_VERSION>``
  289. The version of the CXX compiler used.
  290. See also the :variable:`CMAKE_<LANG>_COMPILER_VERSION` variable.
  291. ``$<CUDA_COMPILER_VERSION>``
  292. The version of the CUDA compiler used.
  293. See also the :variable:`CMAKE_<LANG>_COMPILER_VERSION` variable.
  294. ``$<Fortran_COMPILER_VERSION>``
  295. The version of the Fortran compiler used.
  296. See also the :variable:`CMAKE_<LANG>_COMPILER_VERSION` variable.
  297. ``$<COMPILE_LANGUAGE>``
  298. The compile language of source files when evaluating compile options.
  299. See :ref:`the related boolean expression
  300. <Boolean COMPILE_LANGUAGE Generator Expression>`
  301. ``$<COMPILE_LANGUAGE:language>``
  302. for notes about the portability of this generator expression.
  303. Target-Dependent Queries
  304. ------------------------
  305. ``$<TARGET_NAME_IF_EXISTS:tgt>``
  306. Expands to the ``tgt`` if the given target exists, an empty string
  307. otherwise.
  308. ``$<TARGET_FILE:tgt>``
  309. Full path to main file (.exe, .so.1.2, .a) where ``tgt`` is the name of a
  310. target.
  311. ``$<TARGET_FILE_BASE_NAME:tgt>``
  312. Base name of main file where ``tgt`` is the name of a target.
  313. The base name corresponds to the target file name (see
  314. ``$<TARGET_FILE_NAME:tgt>``) without prefix and suffix. For example, if
  315. target file name is ``libbase.so``, the base name is ``base``.
  316. See also the :prop_tgt:`OUTPUT_NAME`, :prop_tgt:`ARCHIVE_OUTPUT_NAME`,
  317. :prop_tgt:`LIBRARY_OUTPUT_NAME` and :prop_tgt:`RUNTIME_OUTPUT_NAME`
  318. target properties and their configuration specific variants
  319. :prop_tgt:`OUTPUT_NAME_<CONFIG>`, :prop_tgt:`ARCHIVE_OUTPUT_NAME_<CONFIG>`,
  320. :prop_tgt:`LIBRARY_OUTPUT_NAME_<CONFIG>` and
  321. :prop_tgt:`RUNTIME_OUTPUT_NAME_<CONFIG>`.
  322. Note that ``tgt`` is not added as a dependency of the target this
  323. expression is evaluated on.
  324. ``$<TARGET_FILE_PREFIX:tgt>``
  325. Prefix of main file where ``tgt`` is the name of a target.
  326. Note that ``tgt`` is not added as a dependency of the target this
  327. expression is evaluated on.
  328. ``$<TARGET_FILE_SUFFIX:tgt>``
  329. Suffix of main file where ``tgt`` is the name of a target.
  330. Note that ``tgt`` is not added as a dependency of the target this
  331. expression is evaluated on.
  332. ``$<TARGET_FILE_NAME:tgt>``
  333. Name of main file (.exe, .so.1.2, .a).
  334. ``$<TARGET_FILE_DIR:tgt>``
  335. Directory of main file (.exe, .so.1.2, .a).
  336. ``$<TARGET_LINKER_FILE:tgt>``
  337. File used to link (.a, .lib, .so) where ``tgt`` is the name of a target.
  338. ``$<TARGET_LINKER_FILE_BASE_NAME:tgt>``
  339. Base name of file used to link where ``tgt`` is the name of a target.
  340. The base name corresponds to the target linker file name (see
  341. ``$<TARGET_LINKER_FILE_NAME:tgt>``) without prefix and suffix. For example,
  342. if target file name is ``libbase.a``, the base name is ``base``.
  343. See also the :prop_tgt:`OUTPUT_NAME`, :prop_tgt:`ARCHIVE_OUTPUT_NAME`,
  344. and :prop_tgt:`LIBRARY_OUTPUT_NAME` target properties and their configuration
  345. specific variants :prop_tgt:`OUTPUT_NAME_<CONFIG>`,
  346. :prop_tgt:`ARCHIVE_OUTPUT_NAME_<CONFIG>` and
  347. :prop_tgt:`LIBRARY_OUTPUT_NAME_<CONFIG>`.
  348. Note that ``tgt`` is not added as a dependency of the target this
  349. expression is evaluated on.
  350. ``$<TARGET_LINKER_FILE_PREFIX:tgt>``
  351. Prefix of file used to link where ``tgt`` is the name of a target.
  352. Note that ``tgt`` is not added as a dependency of the target this
  353. expression is evaluated on.
  354. ``$<TARGET_LINKER_FILE_SUFFIX:tgt>``
  355. Suffix of file used to link where ``tgt`` is the name of a target.
  356. Note that ``tgt`` is not added as a dependency of the target this
  357. expression is evaluated on.
  358. ``$<TARGET_LINKER_FILE_NAME:tgt>``
  359. Name of file used to link (.a, .lib, .so).
  360. ``$<TARGET_LINKER_FILE_DIR:tgt>``
  361. Directory of file used to link (.a, .lib, .so).
  362. ``$<TARGET_SONAME_FILE:tgt>``
  363. File with soname (.so.3) where ``tgt`` is the name of a target.
  364. ``$<TARGET_SONAME_FILE_NAME:tgt>``
  365. Name of file with soname (.so.3).
  366. ``$<TARGET_SONAME_FILE_DIR:tgt>``
  367. Directory of with soname (.so.3).
  368. ``$<TARGET_PDB_FILE:tgt>``
  369. Full path to the linker generated program database file (.pdb)
  370. where ``tgt`` is the name of a target.
  371. See also the :prop_tgt:`PDB_NAME` and :prop_tgt:`PDB_OUTPUT_DIRECTORY`
  372. target properties and their configuration specific variants
  373. :prop_tgt:`PDB_NAME_<CONFIG>` and :prop_tgt:`PDB_OUTPUT_DIRECTORY_<CONFIG>`.
  374. ``$<TARGET_PDB_FILE_BASE_NAME:tgt>``
  375. Base name of the linker generated program database file (.pdb)
  376. where ``tgt`` is the name of a target.
  377. The base name corresponds to the target PDB file name (see
  378. ``$<TARGET_PDB_FILE_NAME:tgt>``) without prefix and suffix. For example,
  379. if target file name is ``base.pdb``, the base name is ``base``.
  380. See also the :prop_tgt:`PDB_NAME` target property and its configuration
  381. specific variant :prop_tgt:`PDB_NAME_<CONFIG>`.
  382. Note that ``tgt`` is not added as a dependency of the target this
  383. expression is evaluated on.
  384. ``$<TARGET_PDB_FILE_NAME:tgt>``
  385. Name of the linker generated program database file (.pdb).
  386. ``$<TARGET_PDB_FILE_DIR:tgt>``
  387. Directory of the linker generated program database file (.pdb).
  388. ``$<TARGET_BUNDLE_DIR:tgt>``
  389. Full path to the bundle directory (``my.app``, ``my.framework``, or
  390. ``my.bundle``) where ``tgt`` is the name of a target.
  391. ``$<TARGET_BUNDLE_CONTENT_DIR:tgt>``
  392. Full path to the bundle content directory where ``tgt`` is the name of a
  393. target. For the macOS SDK it leads to ``my.app/Contents``, ``my.framework``,
  394. or ``my.bundle/Contents``. For all other SDKs (e.g. iOS) it leads to
  395. ``my.app``, ``my.framework``, or ``my.bundle`` due to the flat bundle
  396. structure.
  397. ``$<TARGET_PROPERTY:tgt,prop>``
  398. Value of the property ``prop`` on the target ``tgt``.
  399. Note that ``tgt`` is not added as a dependency of the target this
  400. expression is evaluated on.
  401. ``$<TARGET_PROPERTY:prop>``
  402. Value of the property ``prop`` on the target on which the generator
  403. expression is evaluated. Note that for generator expressions in
  404. :ref:`Target Usage Requirements` this is the value of the property
  405. on the consuming target rather than the target specifying the
  406. requirement.
  407. ``$<INSTALL_PREFIX>``
  408. Content of the install prefix when the target is exported via
  409. :command:`install(EXPORT)` and empty otherwise.
  410. Output-Related Expressions
  411. --------------------------
  412. ``$<TARGET_NAME:...>``
  413. Marks ``...`` as being the name of a target. This is required if exporting
  414. targets to multiple dependent export sets. The ``...`` must be a literal
  415. name of a target- it may not contain generator expressions.
  416. ``$<LINK_ONLY:...>``
  417. Content of ``...`` except when evaluated in a link interface while
  418. propagating :ref:`Target Usage Requirements`, in which case it is the
  419. empty string.
  420. Intended for use only in an :prop_tgt:`INTERFACE_LINK_LIBRARIES` target
  421. property, perhaps via the :command:`target_link_libraries` command,
  422. to specify private link dependencies without other usage requirements.
  423. ``$<INSTALL_INTERFACE:...>``
  424. Content of ``...`` when the property is exported using :command:`install(EXPORT)`,
  425. and empty otherwise.
  426. ``$<BUILD_INTERFACE:...>``
  427. Content of ``...`` when the property is exported using :command:`export`, or
  428. when the target is used by another target in the same buildsystem. Expands to
  429. the empty string otherwise.
  430. ``$<MAKE_C_IDENTIFIER:...>``
  431. Content of ``...`` converted to a C identifier. The conversion follows the
  432. same behavior as :command:`string(MAKE_C_IDENTIFIER)`.
  433. ``$<TARGET_OBJECTS:objLib>``
  434. List of objects resulting from build of ``objLib``. ``objLib`` must be an
  435. object of type ``OBJECT_LIBRARY``.
  436. ``$<SHELL_PATH:...>``
  437. Content of ``...`` converted to shell path style. For example, slashes are
  438. converted to backslashes in Windows shells and drive letters are converted
  439. to posix paths in MSYS shells. The ``...`` must be an absolute path.
  440. The ``...`` may be a :ref:`semicolon-separated list <CMake Language Lists>`
  441. of paths, in which case each path is converted individually and a result
  442. list is generated using the shell path separator (``:`` on POSIX and
  443. ``;`` on Windows). Be sure to enclose the argument containing this genex
  444. in double quotes in CMake source code so that ``;`` does not split arguments.
  445. Debugging
  446. =========
  447. Since generator expressions are evaluated during generation of the buildsystem,
  448. and not during processing of ``CMakeLists.txt`` files, it is not possible to
  449. inspect their result with the :command:`message()` command.
  450. One possible way to generate debug messages is to add a custom target,
  451. .. code-block:: cmake
  452. add_custom_target(genexdebug COMMAND ${CMAKE_COMMAND} -E echo "$<...>")
  453. The shell command ``make genexdebug`` (invoked after execution of ``cmake``)
  454. would then print the result of ``$<...>``.
  455. Another way is to write debug messages to a file:
  456. .. code-block:: cmake
  457. file(GENERATE OUTPUT filename CONTENT "$<...>")