890 lines
34 KiB
ReStructuredText
890 lines
34 KiB
ReStructuredText
.. cmake-manual-description: CMake Buildsystem Reference
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cmake-buildsystem(7)
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********************
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.. only:: html or latex
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.. contents::
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Introduction
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============
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A CMake-based buildsystem is organized as a set of high-level logical
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targets. Each target corresponds to an executable or library, or
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is a custom target containing custom commands. Dependencies between the
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targets are expressed in the buildsystem to determine the build order
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and the rules for regeneration in response to change.
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Binary Targets
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==============
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Executables and libraries are defined using the :command:`add_executable`
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and :command:`add_library` commands. The resulting binary files have
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appropriate prefixes, suffixes and extensions for the platform targeted.
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Dependencies between binary targets are expressed using the
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:command:`target_link_libraries` command:
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.. code-block:: cmake
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add_library(archive archive.cpp zip.cpp lzma.cpp)
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add_executable(zipapp zipapp.cpp)
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target_link_libraries(zipapp archive)
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``archive`` is defined as a static library -- an archive containing objects
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compiled from ``archive.cpp``, ``zip.cpp``, and ``lzma.cpp``. ``zipapp``
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is defined as an executable formed by compiling and linking ``zipapp.cpp``.
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When linking the ``zipapp`` executable, the ``archive`` static library is
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linked in.
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Binary Executables
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------------------
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The :command:`add_executable` command defines an executable target:
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.. code-block:: cmake
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add_executable(mytool mytool.cpp)
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Commands such as :command:`add_custom_command`, which generates rules to be
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run at build time can transparently use an :prop_tgt:`EXECUTABLE <TYPE>`
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target as a ``COMMAND`` executable. The buildsystem rules will ensure that
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the executable is built before attempting to run the command.
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Binary Library Types
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--------------------
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.. _`Normal Libraries`:
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Normal Libraries
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^^^^^^^^^^^^^^^^
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By default, the :command:`add_library` command defines a static library,
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unless a type is specified. A type may be specified when using the command:
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.. code-block:: cmake
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add_library(archive SHARED archive.cpp zip.cpp lzma.cpp)
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.. code-block:: cmake
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add_library(archive STATIC archive.cpp zip.cpp lzma.cpp)
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The :variable:`BUILD_SHARED_LIBS` variable may be enabled to change the
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behavior of :command:`add_library` to build shared libraries by default.
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In the context of the buildsystem definition as a whole, it is largely
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irrelevant whether particular libraries are ``SHARED`` or ``STATIC`` --
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the commands, dependency specifications and other APIs work similarly
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regardless of the library type. The ``MODULE`` library type is
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dissimilar in that it is generally not linked to -- it is not used in
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the right-hand-side of the :command:`target_link_libraries` command.
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It is a type which is loaded as a plugin using runtime techniques.
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.. code-block:: cmake
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add_library(archive MODULE 7z.cpp)
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.. _`Object Libraries`:
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Object Libraries
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^^^^^^^^^^^^^^^^
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The ``OBJECT`` library type is also not linked to. It defines a non-archival
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collection of object files resulting from compiling the given source files.
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The object files collection can be used as source inputs to other targets:
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.. code-block:: cmake
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add_library(archive OBJECT archive.cpp zip.cpp lzma.cpp)
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add_library(archiveExtras STATIC $<TARGET_OBJECTS:archive> extras.cpp)
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add_executable(test_exe $<TARGET_OBJECTS:archive> test.cpp)
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``OBJECT`` libraries may only be used locally as sources in a buildsystem --
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they may not be installed, exported, or used in the right hand side of
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:command:`target_link_libraries`. They also may not be used as the ``TARGET``
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in a use of the :command:`add_custom_command(TARGET)` command signature.
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Although object libraries may not be named directly in calls to
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the :command:`target_link_libraries` command, they can be "linked"
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indirectly by using an :ref:`Interface Library <Interface Libraries>`
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whose :prop_tgt:`INTERFACE_SOURCES` target property is set to name
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``$<TARGET_OBJECTS:objlib>``.
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Build Specification and Usage Requirements
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==========================================
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The :command:`target_include_directories`, :command:`target_compile_definitions`
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and :command:`target_compile_options` commands specify the build specifications
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and the usage requirements of binary targets. The commands populate the
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:prop_tgt:`INCLUDE_DIRECTORIES`, :prop_tgt:`COMPILE_DEFINITIONS` and
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:prop_tgt:`COMPILE_OPTIONS` target properties respectively, and/or the
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:prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES`, :prop_tgt:`INTERFACE_COMPILE_DEFINITIONS`
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and :prop_tgt:`INTERFACE_COMPILE_OPTIONS` target properties.
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Each of the commands has a ``PRIVATE``, ``PUBLIC`` and ``INTERFACE`` mode. The
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``PRIVATE`` mode populates only the non-``INTERFACE_`` variant of the target
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property and the ``INTERFACE`` mode populates only the ``INTERFACE_`` variants.
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The ``PUBLIC`` mode populates both variants of the repective target property.
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Each command may be invoked with multiple uses of each keyword:
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.. code-block:: cmake
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target_compile_definitions(archive
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PRIVATE BUILDING_WITH_LZMA
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INTERFACE USING_ARCHIVE_LIB
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)
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Note that usage requirements are not designed as a way to make downstreams
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use particular :prop_tgt:`COMPILE_OPTIONS` or
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:prop_tgt:`COMPILE_DEFINITIONS` etc for convenience only. The contents of
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the properties must be **requirements**, not merely recommendations or
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convenience.
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Target Properties
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-----------------
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The contents of the :prop_tgt:`INCLUDE_DIRECTORIES`,
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:prop_tgt:`COMPILE_DEFINITIONS` and :prop_tgt:`COMPILE_OPTIONS` target
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properties are used appropriately when compiling the source files of a
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binary target.
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Entries in the :prop_tgt:`INCLUDE_DIRECTORIES` are added to the compile line
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with ``-I`` or ``-isystem`` prefixes and in the order of appearance in the
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property value.
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Entries in the :prop_tgt:`COMPILE_DEFINITIONS` are prefixed with ``-D`` or
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``/D`` and added to the compile line in an unspecified order. The
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:prop_tgt:`DEFINE_SYMBOL` target property is also added as a compile
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definition as a special convenience case for ``SHARED`` and ``MODULE``
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library targets.
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Entries in the :prop_tgt:`COMPILE_OPTIONS` are escaped for the shell and added
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in the order of appearance in the property value. Several compile options have
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special separate handling, such as :prop_tgt:`POSITION_INDEPENDENT_CODE`.
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The contents of the :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES`,
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:prop_tgt:`INTERFACE_COMPILE_DEFINITIONS` and
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:prop_tgt:`INTERFACE_COMPILE_OPTIONS` target properties are
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*Usage Requirements* -- they specify content which consumers
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must use to correctly compile and link with the target they appear on.
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For any binary target, the contents of each ``INTERFACE_`` property on
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each target specified in a :command:`target_link_libraries` command is
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consumed:
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.. code-block:: cmake
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set(srcs archive.cpp zip.cpp)
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if (LZMA_FOUND)
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list(APPEND srcs lzma.cpp)
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endif()
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add_library(archive SHARED ${srcs})
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if (LZMA_FOUND)
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# The archive library sources are compiled with -DBUILDING_WITH_LZMA
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target_compile_definitions(archive PRIVATE BUILDING_WITH_LZMA)
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endif()
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target_compile_definitions(archive INTERFACE USING_ARCHIVE_LIB)
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add_executable(consumer)
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# Link consumer to archive and consume its usage requirements. The consumer
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# executable sources are compiled with -DUSING_ARCHIVE_LIB.
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target_link_libraries(consumer archive)
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Because it is common to require that the source directory and corresponding
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build directory are added to the :prop_tgt:`INCLUDE_DIRECTORIES`, the
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:variable:`CMAKE_INCLUDE_CURRENT_DIR` variable can be enabled to conveniently
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add the corresponding directories to the :prop_tgt:`INCLUDE_DIRECTORIES` of
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all targets. The variable :variable:`CMAKE_INCLUDE_CURRENT_DIR_IN_INTERFACE`
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can be enabled to add the corresponding directories to the
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:prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` of all targets. This makes use of
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targets in multiple different directories convenient through use of the
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:command:`target_link_libraries` command.
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.. _`Target Usage Requirements`:
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Transitive Usage Requirements
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-----------------------------
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The usage requirements of a target can transitively propagate to dependents.
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The :command:`target_link_libraries` command has ``PRIVATE``,
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``INTERFACE`` and ``PUBLIC`` keywords to control the propagation.
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.. code-block:: cmake
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add_library(archive archive.cpp)
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target_compile_definitions(archive INTERFACE USING_ARCHIVE_LIB)
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add_library(serialization serialization.cpp)
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target_compile_definitions(serialization INTERFACE USING_SERIALIZATION_LIB)
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add_library(archiveExtras extras.cpp)
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target_link_libraries(archiveExtras PUBLIC archive)
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target_link_libraries(archiveExtras PRIVATE serialization)
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# archiveExtras is compiled with -DUSING_ARCHIVE_LIB
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# and -DUSING_SERIALIZATION_LIB
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add_executable(consumer consumer.cpp)
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# consumer is compiled with -DUSING_ARCHIVE_LIB
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target_link_libraries(consumer archiveExtras)
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Because ``archive`` is a ``PUBLIC`` dependency of ``archiveExtras``, the
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usage requirements of it are propagated to ``consumer`` too. Because
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``serialization`` is a ``PRIVATE`` dependency of ``archive``, the usage
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requirements of it are not propagated to ``consumer``.
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Generally, a dependency should be specified in a use of
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:command:`target_link_libraries` with the ``PRIVATE`` keyword if it is used by
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only the implementation of a library, and not in the header files. If a
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dependency is additionally used in the header files of a library (e.g. for
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class inheritance), then it should be specified as a ``PUBLIC`` dependency.
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A dependency which is not used by the implementation of a library, but only by
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its headers should be specified as an ``INTERFACE`` dependency. The
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:command:`target_link_libraries` command may be invoked with multiple uses of
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each keyword:
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.. code-block:: cmake
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target_link_libraries(archiveExtras
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PUBLIC archive
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PRIVATE serialization
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)
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Usage requirements are propagated by reading the ``INTERFACE_`` variants
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of target properties from dependencies and appending the values to the
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non-``INTERFACE_`` variants of the operand. For example, the
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:prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` of dependencies is read and
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appended to the :prop_tgt:`INCLUDE_DIRECTORIES` of the operand. In cases
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where order is relevant and maintained, and the order resulting from the
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:command:`target_link_libraries` calls does not allow correct compilation,
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use of an appropriate command to set the property directly may update the
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order.
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For example, if the linked libraries for a target must be specified
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in the order ``lib1`` ``lib2`` ``lib3`` , but the include directories must
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be specified in the order ``lib3`` ``lib1`` ``lib2``:
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.. code-block:: cmake
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target_link_libraries(myExe lib1 lib2 lib3)
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target_include_directories(myExe
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PRIVATE $<TARGET_PROPERTY:INTERFACE_INCLUDE_DIRECTORIES:lib3>)
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.. _`Compatible Interface Properties`:
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Compatible Interface Properties
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-------------------------------
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Some target properties are required to be compatible between a target and
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the interface of each dependency. For example, the
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:prop_tgt:`POSITION_INDEPENDENT_CODE` target property may specify a
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boolean value of whether a target should be compiled as
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position-independent-code, which has platform-specific consequences.
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A target may also specify the usage requirement
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:prop_tgt:`INTERFACE_POSITION_INDEPENDENT_CODE` to communicate that
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consumers must be compiled as position-independent-code.
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.. code-block:: cmake
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add_executable(exe1 exe1.cpp)
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set_property(TARGET exe1 PROPERTY POSITION_INDEPENDENT_CODE ON)
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add_library(lib1 SHARED lib1.cpp)
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set_property(TARGET lib1 PROPERTY INTERFACE_POSITION_INDEPENDENT_CODE ON)
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add_executable(exe2 exe2.cpp)
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target_link_libraries(exe2 lib1)
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Here, both ``exe1`` and ``exe2`` will be compiled as position-independent-code.
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``lib1`` will also be compiled as position-independent-code because that is the
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default setting for ``SHARED`` libraries. If dependencies have conflicting,
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non-compatible requirements :manual:`cmake(1)` issues a diagnostic:
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.. code-block:: cmake
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add_library(lib1 SHARED lib1.cpp)
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set_property(TARGET lib1 PROPERTY INTERFACE_POSITION_INDEPENDENT_CODE ON)
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add_library(lib2 SHARED lib2.cpp)
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set_property(TARGET lib2 PROPERTY INTERFACE_POSITION_INDEPENDENT_CODE OFF)
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add_executable(exe1 exe1.cpp)
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target_link_libraries(exe1 lib1)
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set_property(TARGET exe1 PROPERTY POSITION_INDEPENDENT_CODE OFF)
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add_executable(exe2 exe2.cpp)
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target_link_libraries(exe2 lib1 lib2)
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The ``lib1`` requirement ``INTERFACE_POSITION_INDEPENDENT_CODE`` is not
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"compatible" with the ``POSITION_INDEPENDENT_CODE`` property of the ``exe1``
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target. The library requires that consumers are built as
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position-independent-code, while the executable specifies to not built as
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position-independent-code, so a diagnostic is issued.
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The ``lib1`` and ``lib2`` requirements are not "compatible". One of them
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requires that consumers are built as position-independent-code, while
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the other requires that consumers are not built as position-independent-code.
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Because ``exe2`` links to both and they are in conflict, a diagnostic is
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issued.
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To be "compatible", the :prop_tgt:`POSITION_INDEPENDENT_CODE` property,
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if set must be either the same, in a boolean sense, as the
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:prop_tgt:`INTERFACE_POSITION_INDEPENDENT_CODE` property of all transitively
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specified dependencies on which that property is set.
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This property of "compatible interface requirement" may be extended to other
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properties by specifying the property in the content of the
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:prop_tgt:`COMPATIBLE_INTERFACE_BOOL` target property. Each specified property
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must be compatible between the consuming target and the corresponding property
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with an ``INTERFACE_`` prefix from each dependency:
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.. code-block:: cmake
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add_library(lib1Version2 SHARED lib1_v2.cpp)
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set_property(TARGET lib1Version2 PROPERTY INTERFACE_CUSTOM_PROP ON)
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set_property(TARGET lib1Version2 APPEND PROPERTY
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COMPATIBLE_INTERFACE_BOOL CUSTOM_PROP
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)
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add_library(lib1Version3 SHARED lib1_v3.cpp)
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set_property(TARGET lib1Version3 PROPERTY INTERFACE_CUSTOM_PROP OFF)
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add_executable(exe1 exe1.cpp)
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target_link_libraries(exe1 lib1Version2) # CUSTOM_PROP will be ON
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add_executable(exe2 exe2.cpp)
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target_link_libraries(exe2 lib1Version2 lib1Version3) # Diagnostic
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Non-boolean properties may also participate in "compatible interface"
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computations. Properties specified in the
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:prop_tgt:`COMPATIBLE_INTERFACE_STRING`
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property must be either unspecified or compare to the same string among
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all transitively specified dependencies. This can be useful to ensure
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that multiple incompatible versions of a library are not linked together
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through transitive requirements of a target:
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.. code-block:: cmake
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add_library(lib1Version2 SHARED lib1_v2.cpp)
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set_property(TARGET lib1Version2 PROPERTY INTERFACE_LIB_VERSION 2)
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set_property(TARGET lib1Version2 APPEND PROPERTY
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COMPATIBLE_INTERFACE_STRING LIB_VERSION
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)
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add_library(lib1Version3 SHARED lib1_v3.cpp)
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set_property(TARGET lib1Version3 PROPERTY INTERFACE_LIB_VERSION 3)
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add_executable(exe1 exe1.cpp)
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target_link_libraries(exe1 lib1Version2) # LIB_VERSION will be "2"
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add_executable(exe2 exe2.cpp)
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target_link_libraries(exe2 lib1Version2 lib1Version3) # Diagnostic
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The :prop_tgt:`COMPATIBLE_INTERFACE_NUMBER_MAX` target property specifies
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that content will be evaluated numerically and the maximum number among all
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specified will be calculated:
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.. code-block:: cmake
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add_library(lib1Version2 SHARED lib1_v2.cpp)
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set_property(TARGET lib1Version2 PROPERTY INTERFACE_CONTAINER_SIZE_REQUIRED 200)
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set_property(TARGET lib1Version2 APPEND PROPERTY
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COMPATIBLE_INTERFACE_NUMBER_MAX CONTAINER_SIZE_REQUIRED
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)
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add_library(lib1Version3 SHARED lib1_v3.cpp)
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set_property(TARGET lib1Version2 PROPERTY INTERFACE_CONTAINER_SIZE_REQUIRED 1000)
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add_executable(exe1 exe1.cpp)
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# CONTAINER_SIZE_REQUIRED will be "200"
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target_link_libraries(exe1 lib1Version2)
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add_executable(exe2 exe2.cpp)
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# CONTAINER_SIZE_REQUIRED will be "1000"
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target_link_libraries(exe2 lib1Version2 lib1Version3)
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Similarly, the :prop_tgt:`COMPATIBLE_INTERFACE_NUMBER_MIN` may be used to
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calculate the numeric minimum value for a property from dependencies.
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Each calculated "compatible" property value may be read in the consumer at
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generate-time using generator expressions.
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Note that for each dependee, the set of properties specified in each
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compatible interface property must not intersect with the set specified in
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any of the other properties.
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Property Origin Debugging
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-------------------------
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Because build specifications can be determined by dependencies, the lack of
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locality of code which creates a target and code which is responsible for
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setting build specifications may make the code more difficult to reason about.
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:manual:`cmake(1)` provides a debugging facility to print the origin of the
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contents of properties which may be determined by dependencies. The properties
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which can be debugged are listed in the
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:variable:`CMAKE_DEBUG_TARGET_PROPERTIES` variable documentation:
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.. code-block:: cmake
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set(CMAKE_DEBUG_TARGET_PROPERTIES
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INCLUDE_DIRECTORIES
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COMPILE_DEFINITIONS
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POSITION_INDEPENDENT_CODE
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CONTAINER_SIZE_REQUIRED
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LIB_VERSION
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)
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add_executable(exe1 exe1.cpp)
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In the case of properties listed in :prop_tgt:`COMPATIBLE_INTERFACE_BOOL` or
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:prop_tgt:`COMPATIBLE_INTERFACE_STRING`, the debug output shows which target
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was responsible for setting the property, and which other dependencies also
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defined the property. In the case of
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:prop_tgt:`COMPATIBLE_INTERFACE_NUMBER_MAX` and
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:prop_tgt:`COMPATIBLE_INTERFACE_NUMBER_MIN`, the debug output shows the
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value of the property from each dependency, and whether the value determines
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the new extreme.
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Build Specification with Generator Expressions
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----------------------------------------------
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Build specifications may use
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|
:manual:`generator expressions <cmake-generator-expressions(7)>` containing
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content which may be conditional or known only at generate-time. For example,
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the calculated "compatible" value of a property may be read with the
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``TARGET_PROPERTY`` expression:
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.. code-block:: cmake
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add_library(lib1Version2 SHARED lib1_v2.cpp)
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set_property(TARGET lib1Version2 PROPERTY
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INTERFACE_CONTAINER_SIZE_REQUIRED 200)
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set_property(TARGET lib1Version2 APPEND PROPERTY
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COMPATIBLE_INTERFACE_NUMBER_MAX CONTAINER_SIZE_REQUIRED
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)
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add_executable(exe1 exe1.cpp)
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target_link_libraries(exe1 lib1Version2)
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|
target_compile_definitions(exe1 PRIVATE
|
|
CONTAINER_SIZE=$<TARGET_PROPERTY:CONTAINER_SIZE_REQUIRED>
|
|
)
|
|
|
|
In this case, the ``exe1`` source files will be compiled with
|
|
``-DCONTAINER_SIZE=200``.
|
|
|
|
Configuration determined build specifications may be conveniently set using
|
|
the ``CONFIG`` generator expression.
|
|
|
|
.. code-block:: cmake
|
|
|
|
target_compile_definitions(exe1 PRIVATE
|
|
$<$<CONFIG:Debug>:DEBUG_BUILD>
|
|
)
|
|
|
|
The ``CONFIG`` parameter is compared case-insensitively with the configuration
|
|
being built. In the presence of :prop_tgt:`IMPORTED` targets, the content of
|
|
:prop_tgt:`MAP_IMPORTED_CONFIG_DEBUG <MAP_IMPORTED_CONFIG_<CONFIG>>` is also
|
|
accounted for by this expression.
|
|
|
|
Some buildsystems generated by :manual:`cmake(1)` have a predetermined
|
|
build-configuration set in the :variable:`CMAKE_BUILD_TYPE` variable. The
|
|
buildsystem for the IDEs such as Visual Studio and Xcode are generated
|
|
independent of the build-configuration, and the actual build configuration
|
|
is not known until build-time. Therefore, code such as
|
|
|
|
.. code-block:: cmake
|
|
|
|
string(TOLOWER ${CMAKE_BUILD_TYPE} _type)
|
|
if (_type STREQUAL debug)
|
|
target_compile_definitions(exe1 PRIVATE DEBUG_BUILD)
|
|
endif()
|
|
|
|
may appear to work for ``Makefile`` based and ``Ninja`` generators, but is not
|
|
portable to IDE generators. Additionally, the :prop_tgt:`IMPORTED`
|
|
configuration-mappings are not accounted for with code like this, so it should
|
|
be avoided.
|
|
|
|
The unary ``TARGET_PROPERTY`` generator expression and the ``TARGET_POLICY``
|
|
generator expression are evaluated with the consuming target context. This
|
|
means that a usage requirement specification may be evaluated differently based
|
|
on the consumer:
|
|
|
|
.. code-block:: cmake
|
|
|
|
add_library(lib1 lib1.cpp)
|
|
target_compile_definitions(lib1 INTERFACE
|
|
$<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,EXECUTABLE>:LIB1_WITH_EXE>
|
|
$<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>:LIB1_WITH_SHARED_LIB>
|
|
$<$<TARGET_POLICY:CMP0041>:CONSUMER_CMP0041_NEW>
|
|
)
|
|
|
|
add_executable(exe1 exe1.cpp)
|
|
target_link_libraries(exe1 lib1)
|
|
|
|
cmake_policy(SET CMP0041 NEW)
|
|
|
|
add_library(shared_lib shared_lib.cpp)
|
|
target_link_libraries(shared_lib lib1)
|
|
|
|
The ``exe1`` executable will be compiled with ``-DLIB1_WITH_EXE``, while the
|
|
``shared_lib`` shared library will be compiled with ``-DLIB1_WITH_SHARED_LIB``
|
|
and ``-DCONSUMER_CMP0041_NEW``, because policy :policy:`CMP0041` is
|
|
``NEW`` at the point where the ``shared_lib`` target is created.
|
|
|
|
The ``BUILD_INTERFACE`` expression wraps requirements which are only used when
|
|
consumed from a target in the same buildsystem, or when consumed from a target
|
|
exported to the build directory using the :command:`export` command. The
|
|
``INSTALL_INTERFACE`` expression wraps requirements which are only used when
|
|
consumed from a target which has been installed and exported with the
|
|
:command:`install(EXPORT)` command:
|
|
|
|
.. code-block:: cmake
|
|
|
|
add_library(ClimbingStats climbingstats.cpp)
|
|
target_compile_definitions(ClimbingStats INTERFACE
|
|
$<BUILD_INTERFACE:ClimbingStats_FROM_BUILD_LOCATION>
|
|
$<INSTALL_INTERFACE:ClimbingStats_FROM_INSTALLED_LOCATION>
|
|
)
|
|
install(TARGETS ClimbingStats EXPORT libExport ${InstallArgs})
|
|
install(EXPORT libExport NAMESPACE Upstream::
|
|
DESTINATION lib/cmake/ClimbingStats)
|
|
export(EXPORT libExport NAMESPACE Upstream::)
|
|
|
|
add_executable(exe1 exe1.cpp)
|
|
target_link_libraries(exe1 ClimbingStats)
|
|
|
|
In this case, the ``exe1`` executable will be compiled with
|
|
``-DClimbingStats_FROM_BUILD_LOCATION``. The exporting commands generate
|
|
:prop_tgt:`IMPORTED` targets with either the ``INSTALL_INTERFACE`` or the
|
|
``BUILD_INTERFACE`` omitted, and the ``*_INTERFACE`` marker stripped away.
|
|
A separate project consuming the ``ClimbingStats`` package would contain:
|
|
|
|
.. code-block:: cmake
|
|
|
|
find_package(ClimbingStats REQUIRED)
|
|
|
|
add_executable(Downstream main.cpp)
|
|
target_link_libraries(Downstream Upstream::ClimbingStats)
|
|
|
|
Depending on whether the ``ClimbingStats`` package was used from the build
|
|
location or the install location, the ``Downstream`` target would be compiled
|
|
with either ``-DClimbingStats_FROM_BUILD_LOCATION`` or
|
|
``-DClimbingStats_FROM_INSTALL_LOCATION``. For more about packages and
|
|
exporting see the :manual:`cmake-packages(7)` manual.
|
|
|
|
.. _`Include Directories and Usage Requirements`:
|
|
|
|
Include Directories and Usage Requirements
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
Include directories require some special consideration when specified as usage
|
|
requirements and when used with generator expressions. The
|
|
:command:`target_include_directories` command accepts both relative and
|
|
absolute include directories:
|
|
|
|
.. code-block:: cmake
|
|
|
|
add_library(lib1 lib1.cpp)
|
|
target_include_directories(lib1 PRIVATE
|
|
/absolute/path
|
|
relative/path
|
|
)
|
|
|
|
Relative paths are interpreted relative to the source directory where the
|
|
command appears. Relative paths are not allowed in the
|
|
:prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` of :prop_tgt:`IMPORTED` targets.
|
|
|
|
In cases where a non-trivial generator expression is used, the
|
|
``INSTALL_PREFIX`` expression may be used within the argument of an
|
|
``INSTALL_INTERFACE`` expression. It is a replacement marker which
|
|
expands to the installation prefix when imported by a consuming project.
|
|
|
|
Include directories usage requirements commonly differ between the build-tree
|
|
and the install-tree. The ``BUILD_INTERFACE`` and ``INSTALL_INTERFACE``
|
|
generator expressions can be used to describe separate usage requirements
|
|
based on the usage location. Relative paths are allowed within the
|
|
``INSTALL_INTERFACE`` expression and are interpreted relative to the
|
|
installation prefix. For example:
|
|
|
|
.. code-block:: cmake
|
|
|
|
add_library(ClimbingStats climbingstats.cpp)
|
|
target_include_directories(ClimbingStats INTERFACE
|
|
$<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}/generated>
|
|
$<INSTALL_INTERFACE:/absolute/path>
|
|
$<INSTALL_INTERFACE:relative/path>
|
|
$<INSTALL_INTERFACE:$<INSTALL_PREFIX>/$<CONFIG>/generated>
|
|
)
|
|
|
|
Two convenience APIs are provided relating to include directories usage
|
|
requirements. The :variable:`CMAKE_INCLUDE_CURRENT_DIR_IN_INTERFACE` variable
|
|
may be enabled, with an equivalent effect to:
|
|
|
|
.. code-block:: cmake
|
|
|
|
set_property(TARGET tgt APPEND PROPERTY
|
|
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR};${CMAKE_CURRENT_BINARY_DIR}>
|
|
)
|
|
|
|
for each target affected. The convenience for installed targets is
|
|
an ``INCLUDES DESTINATION`` component with the :command:`install(TARGETS)`
|
|
command:
|
|
|
|
.. code-block:: cmake
|
|
|
|
install(TARGETS foo bar bat EXPORT tgts ${dest_args}
|
|
INCLUDES DESTINATION include
|
|
)
|
|
install(EXPORT tgts ${other_args})
|
|
install(FILES ${headers} DESTINATION include)
|
|
|
|
This is equivalent to appending ``${CMAKE_INSTALL_PREFIX}/include`` to the
|
|
:prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` of each of the installed
|
|
:prop_tgt:`IMPORTED` targets when generated by :command:`install(EXPORT)`.
|
|
|
|
When the :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` of an
|
|
:ref:`imported target <Imported targets>` is consumed, the entries in the
|
|
property are treated as ``SYSTEM`` include directories, as if they were
|
|
listed in the :prop_tgt:`INTERFACE_SYSTEM_INCLUDE_DIRECTORIES` of the
|
|
dependency. This can result in omission of compiler warnings for headers
|
|
found in those directories. This behavior for :ref:`imported targets` may
|
|
be controlled with the :prop_tgt:`NO_SYSTEM_FROM_IMPORTED` target property.
|
|
|
|
If a binary target is linked transitively to a Mac OX framework, the
|
|
``Headers`` directory of the framework is also treated as a usage requirement.
|
|
This has the same effect as passing the framework directory as an include
|
|
directory.
|
|
|
|
Link Libraries and Generator Expressions
|
|
----------------------------------------
|
|
|
|
Like build specifications, :prop_tgt:`link libraries <LINK_LIBRARIES>` may be
|
|
specified with generator expression conditions. However, as consumption of
|
|
usage requirements is based on collection from linked dependencies, there is
|
|
an additional limitation that the link dependencies must form a "directed
|
|
acyclic graph". That is, if linking to a target is dependent on the value of
|
|
a target property, that target property may not be dependent on the linked
|
|
dependencies:
|
|
|
|
.. code-block:: cmake
|
|
|
|
add_library(lib1 lib1.cpp)
|
|
add_library(lib2 lib2.cpp)
|
|
target_link_libraries(lib1 PUBLIC
|
|
$<$<TARGET_PROPERTY:POSITION_INDEPENDENT_CODE>:lib2>
|
|
)
|
|
add_library(lib3 lib3.cpp)
|
|
set_property(TARGET lib3 PROPERTY INTERFACE_POSITION_INDEPENDENT_CODE ON)
|
|
|
|
add_executable(exe1 exe1.cpp)
|
|
target_link_libraries(exe1 lib1 lib3)
|
|
|
|
As the value of the :prop_tgt:`POSITION_INDEPENDENT_CODE` property of
|
|
the ``exe1`` target is dependent on the linked libraries (``lib3``), and the
|
|
edge of linking ``exe1`` is determined by the same
|
|
:prop_tgt:`POSITION_INDEPENDENT_CODE` property, the dependency graph above
|
|
contains a cycle. :manual:`cmake(1)` issues a diagnostic in this case.
|
|
|
|
Output Files
|
|
------------
|
|
|
|
The buildsystem targets created by the :command:`add_library` and
|
|
:command:`add_executable` commands create rules to create binary outputs.
|
|
The exact output location of the binaries can only be determined at
|
|
generate-time because it can depend on the build-configuration and the
|
|
link-language of linked dependencies etc. ``TARGET_FILE``,
|
|
``TARGET_LINKER_FILE`` and related expressions can be used to access the
|
|
name and location of generated binaries. These expressions do not work
|
|
for ``OBJECT`` libraries however, as there is no single file generated
|
|
by such libraries which is relevant to the expressions.
|
|
|
|
Directory-Scoped Commands
|
|
-------------------------
|
|
|
|
The :command:`target_include_directories`,
|
|
:command:`target_compile_definitions` and
|
|
:command:`target_compile_options` commands have an effect on only one
|
|
target at a time. The commands :command:`add_definitions`,
|
|
:command:`add_compile_options` and :command:`include_directories` have
|
|
a similar function, but operate at directory scope instead of target
|
|
scope for convenience.
|
|
|
|
Pseudo Targets
|
|
==============
|
|
|
|
Some target types do not represent outputs of the buildsystem, but only inputs
|
|
such as external dependencies, aliases or other non-build artifacts. Pseudo
|
|
targets are not represented in the generated buildsystem.
|
|
|
|
.. _`Imported Targets`:
|
|
|
|
Imported Targets
|
|
----------------
|
|
|
|
An :prop_tgt:`IMPORTED` target represents a pre-existing dependency. Usually
|
|
such targets are defined by an upstream package and should be treated as
|
|
immutable. It is not possible to use an :prop_tgt:`IMPORTED` target in the
|
|
left-hand-side of the :command:`target_compile_definitions`,
|
|
:command:`target_include_directories`, :command:`target_compile_options` or
|
|
:command:`target_link_libraries` commands, as that would be an attempt to
|
|
modify it. :prop_tgt:`IMPORTED` targets are designed to be used only in the
|
|
right-hand-side of those commands.
|
|
|
|
:prop_tgt:`IMPORTED` targets may have the same usage requirement properties
|
|
populated as binary targets, such as
|
|
:prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES`,
|
|
:prop_tgt:`INTERFACE_COMPILE_DEFINITIONS`,
|
|
:prop_tgt:`INTERFACE_COMPILE_OPTIONS`,
|
|
:prop_tgt:`INTERFACE_LINK_LIBRARIES`, and
|
|
:prop_tgt:`INTERFACE_POSITION_INDEPENDENT_CODE`.
|
|
|
|
The :prop_tgt:`LOCATION` may also be read from an IMPORTED target, though there
|
|
is rarely reason to do so. Commands such as :command:`add_custom_command` can
|
|
transparently use an :prop_tgt:`IMPORTED` :prop_tgt:`EXECUTABLE <TYPE>` target
|
|
as a ``COMMAND`` executable.
|
|
|
|
The scope of the definition of an :prop_tgt:`IMPORTED` target is the directory
|
|
where it was defined. It may be accessed and used from subdirectories, but
|
|
not from parent directories or sibling directories. The scope is similar to
|
|
the scope of a cmake variable.
|
|
|
|
It is also possible to define a ``GLOBAL`` :prop_tgt:`IMPORTED` target which is
|
|
accessible globally in the buildsystem.
|
|
|
|
See the :manual:`cmake-packages(7)` manual for more on creating packages
|
|
with :prop_tgt:`IMPORTED` targets.
|
|
|
|
.. _`Alias Targets`:
|
|
|
|
Alias Targets
|
|
-------------
|
|
|
|
An ``ALIAS`` target is a name which may be used interchangably with
|
|
a binary target name in read-only contexts. A primary use-case for ``ALIAS``
|
|
targets is for example or unit test executables accompanying a library, which
|
|
may be part of the same buildsystem or built separately based on user
|
|
configuration.
|
|
|
|
.. code-block:: cmake
|
|
|
|
add_library(lib1 lib1.cpp)
|
|
install(TARGETS lib1 EXPORT lib1Export ${dest_args})
|
|
install(EXPORT lib1Export NAMESPACE Upstream:: ${other_args})
|
|
|
|
add_library(Upstream::lib1 ALIAS lib1)
|
|
|
|
In another directory, we can link unconditionally to the ``Upstream::lib1``
|
|
target, which may be an :prop_tgt:`IMPORTED` target from a package, or an
|
|
``ALIAS`` target if built as part of the same buildsystem.
|
|
|
|
.. code-block:: cmake
|
|
|
|
if (NOT TARGET Upstream::lib1)
|
|
find_package(lib1 REQUIRED)
|
|
endif()
|
|
add_executable(exe1 exe1.cpp)
|
|
target_link_libraries(exe1 Upstream::lib1)
|
|
|
|
``ALIAS`` targets are not mutable, installable or exportable. They are
|
|
entirely local to the buildsystem description. A name can be tested for
|
|
whether it is an ``ALIAS`` name by reading the :prop_tgt:`ALIASED_TARGET`
|
|
property from it:
|
|
|
|
.. code-block:: cmake
|
|
|
|
get_target_property(_aliased Upstream::lib1 ALIASED_TARGET)
|
|
if(_aliased)
|
|
message(STATUS "The name Upstream::lib1 is an ALIAS for ${_aliased}.")
|
|
endif()
|
|
|
|
.. _`Interface Libraries`:
|
|
|
|
Interface Libraries
|
|
-------------------
|
|
|
|
An ``INTERFACE`` target has no :prop_tgt:`LOCATION` and is mutable, but is
|
|
otherwise similar to an :prop_tgt:`IMPORTED` target.
|
|
|
|
It may specify usage requirements such as
|
|
:prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES`,
|
|
:prop_tgt:`INTERFACE_COMPILE_DEFINITIONS`,
|
|
:prop_tgt:`INTERFACE_COMPILE_OPTIONS`,
|
|
:prop_tgt:`INTERFACE_LINK_LIBRARIES`, and
|
|
:prop_tgt:`INTERFACE_SOURCES`,
|
|
:prop_tgt:`INTERFACE_POSITION_INDEPENDENT_CODE`.
|
|
Only the ``INTERFACE`` modes of the :command:`target_include_directories`,
|
|
:command:`target_compile_definitions`, :command:`target_compile_options`,
|
|
:command:`target_sources`, and :command:`target_link_libraries` commands
|
|
may be used with ``INTERFACE`` libraries.
|
|
|
|
A primary use-case for ``INTERFACE`` libraries is header-only libraries.
|
|
|
|
.. code-block:: cmake
|
|
|
|
add_library(Eigen INTERFACE)
|
|
target_include_directories(Eigen INTERFACE
|
|
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
|
|
$<INSTALL_INTERFACE:include/Eigen>
|
|
)
|
|
|
|
add_executable(exe1 exe1.cpp)
|
|
target_link_libraries(exe1 Eigen)
|
|
|
|
Here, the usage requirements from the ``Eigen`` target are consumed and used
|
|
when compiling, but it has no effect on linking.
|
|
|
|
Another use-case is to employ an entirely target-focussed design for usage
|
|
requirements:
|
|
|
|
.. code-block:: cmake
|
|
|
|
add_library(pic_on INTERFACE)
|
|
set_property(TARGET pic_on PROPERTY INTERFACE_POSITION_INDEPENDENT_CODE ON)
|
|
add_library(pic_off INTERFACE)
|
|
set_property(TARGET pic_off PROPERTY INTERFACE_POSITION_INDEPENDENT_CODE OFF)
|
|
|
|
add_library(enable_rtti INTERFACE)
|
|
target_compile_options(enable_rtti INTERFACE
|
|
$<$<OR:$<COMPILER_ID:GNU>,$<COMPILER_ID:Clang>>:-rtti>
|
|
)
|
|
|
|
add_executable(exe1 exe1.cpp)
|
|
target_link_libraries(exe1 pic_on enable_rtti)
|
|
|
|
This way, the build specification of ``exe1`` is expressed entirely as linked
|
|
targets, and the complexity of compiler-specific flags is encapsulated in an
|
|
``INTERFACE`` library target.
|
|
|
|
The properties permitted to be set on or read from an ``INTERFACE`` library
|
|
are:
|
|
|
|
* Properties matching ``INTERFACE_*``
|
|
* Built-in properties matching ``COMPATIBLE_INTERFACE_*``
|
|
* ``EXPORT_NAME``
|
|
* ``IMPORTED``
|
|
* ``NAME``
|
|
* Properties matching ``MAP_IMPORTED_CONFIG_*``
|
|
|
|
``INTERFACE`` libraries may be installed and exported. Any content they refer
|
|
to must be installed separately:
|
|
|
|
.. code-block:: cmake
|
|
|
|
add_library(Eigen INTERFACE)
|
|
target_include_directories(Eigen INTERFACE
|
|
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
|
|
$<INSTALL_INTERFACE:include/Eigen>
|
|
)
|
|
|
|
install(TARGETS Eigen EXPORT eigenExport)
|
|
install(EXPORT eigenExport NAMESPACE Upstream::
|
|
DESTINATION lib/cmake/Eigen
|
|
)
|
|
install(FILES
|
|
${CMAKE_CURRENT_SOURCE_DIR}/src/eigen.h
|
|
${CMAKE_CURRENT_SOURCE_DIR}/src/vector.h
|
|
${CMAKE_CURRENT_SOURCE_DIR}/src/matrix.h
|
|
DESTINATION include/Eigen
|
|
)
|