cmake-buildsystem(7) CMake cmake-buildsystem(7)
NAME
cmake-buildsystem - CMake Buildsystem Reference
INTRODUCTION
A CMake-based buildsystem is organized as a set of high-level logical
targets. Each target corresponds to an executable or library, or is a
custom target containing custom commands. Dependencies between the
targets are expressed in the buildsystem to determine the build order
and the rules for regeneration in response to change.
BINARY TARGETS
Executables and libraries are defined using the add_executable() and
add_library() commands. The resulting binary files have appropriate
PREFIX, SUFFIX and extensions for the platform targeted. Dependencies
between binary targets are expressed using the target_link_libraries()
command:
add_library(archive archive.cpp zip.cpp lzma.cpp)
add_executable(zipapp zipapp.cpp)
target_link_libraries(zipapp archive)
archive is defined as a STATIC library -- an archive containing objects
compiled from archive.cpp, zip.cpp, and lzma.cpp. zipapp is defined as
an executable formed by compiling and linking zipapp.cpp. When linking
the zipapp executable, the archive static library is linked in.
Binary Executables
The add_executable() command defines an executable target:
add_executable(mytool mytool.cpp)
Commands such as add_custom_command(), which generates rules to be run
at build time can transparently use an EXECUTABLE target as a COMMAND
executable. The buildsystem rules will ensure that the executable is
built before attempting to run the command.
Binary Library Types
Normal Libraries
By default, the add_library() command defines a STATIC library, unless
a type is specified. A type may be specified when using the command:
add_library(archive SHARED archive.cpp zip.cpp lzma.cpp)
add_library(archive STATIC archive.cpp zip.cpp lzma.cpp)
The BUILD_SHARED_LIBS variable may be enabled to change the behavior of
add_library() to build shared libraries by default.
In the context of the buildsystem definition as a whole, it is largely
irrelevant whether particular libraries are SHARED or STATIC -- the
commands, dependency specifications and other APIs work similarly
regardless of the library type. The MODULE library type is dissimilar
in that it is generally not linked to -- it is not used in the
right-hand-side of the target_link_libraries() command. It is a type
which is loaded as a plugin using runtime techniques. If the library
does not export any unmanaged symbols (e.g. Windows resource DLL,
C++/CLI DLL), it is required that the library not be a SHARED library
because CMake expects SHARED libraries to export at least one symbol.
add_library(archive MODULE 7z.cpp)
Apple Frameworks
A SHARED library may be marked with the FRAMEWORK target property to
create an macOS or iOS Framework Bundle. A library with the FRAMEWORK
target property should also set the FRAMEWORK_VERSION target property.
This property is typically set to the value of "A" by macOS
conventions. The MACOSX_FRAMEWORK_IDENTIFIER sets the
CFBundleIdentifier key and it uniquely identifies the bundle.
add_library(MyFramework SHARED MyFramework.cpp)
set_target_properties(MyFramework PROPERTIES
FRAMEWORK TRUE
FRAMEWORK_VERSION A # Version "A" is macOS convention
MACOSX_FRAMEWORK_IDENTIFIER org.cmake.MyFramework
)
Object Libraries
The OBJECT library type defines a non-archival collection of object
files resulting from compiling the given source files. The object
files collection may be used as source inputs to other targets by using
the syntax $<TARGET_OBJECTS:name>. This is a generator expression that
can be used to supply the OBJECT library content to other targets:
add_library(archive OBJECT archive.cpp zip.cpp lzma.cpp)
add_library(archiveExtras STATIC $<TARGET_OBJECTS:archive> extras.cpp)
add_executable(test_exe $<TARGET_OBJECTS:archive> test.cpp)
The link (or archiving) step of those other targets will use the object
files collection in addition to those from their own sources.
Alternatively, object libraries may be linked into other targets:
add_library(archive OBJECT archive.cpp zip.cpp lzma.cpp)
add_library(archiveExtras STATIC extras.cpp)
target_link_libraries(archiveExtras PUBLIC archive)
add_executable(test_exe test.cpp)
target_link_libraries(test_exe archive)
The link (or archiving) step of those other targets will use the object
files from OBJECT libraries that are directly linked. Additionally,
usage requirements of the OBJECT libraries will be honored when
compiling sources in those other targets. Furthermore, those usage
requirements will propagate transitively to dependents of those other
targets.
Object libraries may not be used as the TARGET in a use of the
add_custom_command(TARGET) command signature. However, the list of
objects can be used by add_custom_command(OUTPUT) or file(GENERATE) by
using $<TARGET_OBJECTS:objlib>.
BUILD SPECIFICATION AND USAGE REQUIREMENTS
Targets build according to their own build specification in combination
with usage requirements propagated from their link dependencies. Both
may be specified using target-specific commands.
For example:
add_library(archive SHARED archive.cpp zip.cpp)
if (LZMA_FOUND)
# Add a source implementing support for lzma.
target_sources(archive PRIVATE lzma.cpp)
# Compile the 'archive' library sources with '-DBUILDING_WITH_LZMA'.
target_compile_definitions(archive PRIVATE BUILDING_WITH_LZMA)
endif()
target_compile_definitions(archive INTERFACE USING_ARCHIVE_LIB)
add_executable(consumer consumer.cpp)
# Link 'consumer' to 'archive'. This also consumes its usage requirements,
# so 'consumer.cpp' is compiled with '-DUSING_ARCHIVE_LIB'.
target_link_libraries(consumer archive)
Target Commands
Target-specific commands populate the build specification of Binary
Targets and usage requirements of Binary Targets, Interface Libraries,
and Imported Targets.
Invocations must specify scope keywords, each affecting the visibility
of arguments following it. The scopes are:
PUBLIC Populates both properties for building and properties for using
a target.
PRIVATE
Populates only properties for building a target.
INTERFACE
Populates only properties for using a target.
The commands are:
target_compile_definitions()
Populates the COMPILE_DEFINITIONS build specification and
INTERFACE_COMPILE_DEFINITIONS usage requirement properties.
For example, the call
target_compile_definitions(archive
PRIVATE BUILDING_WITH_LZMA
INTERFACE USING_ARCHIVE_LIB
)
appends BUILDING_WITH_LZMA to the target's COMPILE_DEFINITIONS
property and appends USING_ARCHIVE_LIB to the target's
INTERFACE_COMPILE_DEFINITIONS property.
target_compile_options()
Populates the COMPILE_OPTIONS build specification and
INTERFACE_COMPILE_OPTIONS usage requirement properties.
target_compile_features()
Added in version 3.1.
Populates the COMPILE_FEATURES build specification and
INTERFACE_COMPILE_FEATURES usage requirement properties.
target_include_directories()
Populates the INCLUDE_DIRECTORIES build specification and
INTERFACE_INCLUDE_DIRECTORIES usage requirement properties.
With the SYSTEM option, it also populates the
INTERFACE_SYSTEM_INCLUDE_DIRECTORIES usage requirement.
For convenience, the CMAKE_INCLUDE_CURRENT_DIR variable may be
enabled to add the source directory and corresponding build
directory as INCLUDE_DIRECTORIES on all targets. Similarly, the
CMAKE_INCLUDE_CURRENT_DIR_IN_INTERFACE variable may be enabled
to add them as INTERFACE_INCLUDE_DIRECTORIES on all targets.
target_sources()
Added in version 3.1.
Populates the SOURCES build specification and INTERFACE_SOURCES
usage requirement properties.
It also supports specifying File Sets, which can add C++ module
sources and headers not listed in the SOURCES and
INTERFACE_SOURCES properties. File sets may also populate the
INCLUDE_DIRECTORIES build specification and
INTERFACE_INCLUDE_DIRECTORIES usage requirement properties with
the include directories containing the headers.
target_precompile_headers()
Added in version 3.16.
Populates the PRECOMPILE_HEADERS build specification and
INTERFACE_PRECOMPILE_HEADERS usage requirement properties.
target_link_libraries()
Populates the LINK_LIBRARIES build specification and
INTERFACE_LINK_LIBRARIES usage requirement properties.
This is the primary mechanism by which link dependencies and
their usage requirements are transitively propagated to affect
compilation and linking of a target.
target_link_directories()
Added in version 3.13.
Populates the LINK_DIRECTORIES build specification and
INTERFACE_LINK_DIRECTORIES usage requirement properties.
target_link_options()
Added in version 3.13.
Populates the LINK_OPTIONS build specification and
INTERFACE_LINK_OPTIONS usage requirement properties.
Target Build Specification
The build specification of Binary Targets is represented by target
properties. For each of the following compile and link properties,
compilation and linking of the target is affected both by its own value
and by the corresponding usage requirement property, named with an
INTERFACE_ prefix, collected from the transitive closure of link
dependencies.
Target Compile Properties
These represent the build specification for compiling a target.
COMPILE_DEFINITIONS
List of compile definitions for compiling sources in the target.
These are passed to the compiler with -D flags, or equivalent,
in an unspecified order.
The DEFINE_SYMBOL target property is also used as a compile
definition as a special convenience case for SHARED and MODULE
library targets.
COMPILE_OPTIONS
List of compile options for compiling sources in the target.
These are passed to the compiler as flags, in the order of
appearance.
Compile options are automatically escaped for the shell.
Some compile options are best specified via dedicated settings,
such as the POSITION_INDEPENDENT_CODE target property.
COMPILE_FEATURES
Added in version 3.1.
List of compile features needed for compiling sources in the
target. Typically these ensure the target's sources are
compiled using a sufficient language standard level.
INCLUDE_DIRECTORIES
List of include directories for compiling sources in the target.
These are passed to the compiler with -I or -isystem flags, or
equivalent, in the order of appearance.
For convenience, the CMAKE_INCLUDE_CURRENT_DIR variable may be
enabled to add the source directory and corresponding build
directory as INCLUDE_DIRECTORIES on all targets.
SOURCES
List of source files associated with the target. This includes
sources specified when the target was created by the
add_executable(), add_library(), or add_custom_target() command.
It also includes sources added by the target_sources() command,
but does not include File Sets.
PRECOMPILE_HEADERS
Added in version 3.16.
List of header files to precompile and include when compiling
sources in the target.
AUTOMOC_MACRO_NAMES
Added in version 3.10.
List of macro names used by AUTOMOC to determine if a C++ source
in the target needs to be processed by moc.
AUTOUIC_OPTIONS
Added in version 3.0.
List of options used by AUTOUIC when invoking uic for the
target.
Target Link Properties
These represent the build specification for linking a target.
LINK_LIBRARIES
List of link libraries for linking the target, if it is an
executable, shared library, or module library. Entries for
Normal Libraries are passed to the linker either via paths to
their link artifacts, or with -l flags or equivalent. Entries
for Object Libraries are passed to the linker via paths to their
object files.
Additionally, for compiling and linking the target itself, usage
requirements are propagated from LINK_LIBRARIES entries naming
Normal Libraries, Interface Libraries, Object Libraries, and
Imported Targets, collected over the transitive closure of their
INTERFACE_LINK_LIBRARIES properties.
LINK_DIRECTORIES
Added in version 3.13.
List of link directories for linking the target, if it is an
executable, shared library, or module library. The directories
are passed to the linker with -L flags, or equivalent.
LINK_OPTIONS
Added in version 3.13.
List of link options for linking the target, if it is an
executable, shared library, or module library. The options are
passed to the linker as flags, in the order of appearance.
Link options are automatically escaped for the shell.
LINK_DEPENDS
List of files on which linking the target depends, if it is an
executable, shared library, or module library. For example,
linker scripts specified via LINK_OPTIONS may be listed here
such that changing them causes binaries to be linked again.
Target Usage Requirements
The usage requirements of a target are settings that propagate to
consumers, which link to the target via target_link_libraries(), in
order to correctly compile and link with it. They are represented by
transitive compile and link properties.
Note that usage requirements are not designed as a way to make
downstreams use particular COMPILE_OPTIONS, COMPILE_DEFINITIONS, etc.
for convenience only. The contents of the properties must be
requirements, not merely recommendations.
See the Creating Relocatable Packages section of the cmake-packages(7)
manual for discussion of additional care that must be taken when
specifying usage requirements while creating packages for
redistribution.
The usage requirements of a target can transitively propagate to the
dependents. The target_link_libraries() command has PRIVATE, INTERFACE
and PUBLIC keywords to control the propagation.
add_library(archive archive.cpp)
target_compile_definitions(archive INTERFACE USING_ARCHIVE_LIB)
add_library(serialization serialization.cpp)
target_compile_definitions(serialization INTERFACE USING_SERIALIZATION_LIB)
add_library(archiveExtras extras.cpp)
target_link_libraries(archiveExtras PUBLIC archive)
target_link_libraries(archiveExtras PRIVATE serialization)
# archiveExtras is compiled with -DUSING_ARCHIVE_LIB
# and -DUSING_SERIALIZATION_LIB
add_executable(consumer consumer.cpp)
# consumer is compiled with -DUSING_ARCHIVE_LIB
target_link_libraries(consumer archiveExtras)
Because the archive is a PUBLIC dependency of archiveExtras, the usage
requirements of it are propagated to consumer too.
Because serialization is a PRIVATE dependency of archiveExtras, the
usage requirements of it are not propagated to consumer.
Generally, a dependency should be specified in a use of
target_link_libraries() with the PRIVATE keyword if it is used by only
the implementation of a library, and not in the header files. If a
dependency is additionally used in the header files of a library (e.g.
for class inheritance), then it should be specified as a PUBLIC
dependency. A dependency which is not used by the implementation of a
library, but only by its headers should be specified as an INTERFACE
dependency. The target_link_libraries() command may be invoked with
multiple uses of each keyword:
target_link_libraries(archiveExtras
PUBLIC archive
PRIVATE serialization
)
Usage requirements are propagated by reading the INTERFACE_ variants of
target properties from dependencies and appending the values to the
non-INTERFACE_ variants of the operand. For example, the
INTERFACE_INCLUDE_DIRECTORIES of dependencies is read and appended to
the INCLUDE_DIRECTORIES of the operand. In cases where order is
relevant and maintained, and the order resulting from the
target_link_libraries() calls does not allow correct compilation, use
of an appropriate command to set the property directly may update the
order.
For example, if the linked libraries for a target must be specified in
the order lib1 lib2 lib3 , but the include directories must be
specified in the order lib3 lib1 lib2:
target_link_libraries(myExe lib1 lib2 lib3)
target_include_directories(myExe
PRIVATE $<TARGET_PROPERTY:lib3,INTERFACE_INCLUDE_DIRECTORIES>)
Note that care must be taken when specifying usage requirements for
targets which will be exported for installation using the
install(EXPORT) command. See Creating Packages for more.
Transitive Compile Properties
These represent usage requirements for compiling consumers.
INTERFACE_COMPILE_DEFINITIONS
List of compile definitions for compiling sources in the
target's consumers. Typically these are used by the target's
header files.
INTERFACE_COMPILE_OPTIONS
List of compile options for compiling sources in the target's
consumers.
INTERFACE_COMPILE_FEATURES
Added in version 3.1.
List of compile features needed for compiling sources in the
target's consumers. Typically these ensure the target's header
files are processed when compiling consumers using a sufficient
language standard level.
INTERFACE_INCLUDE_DIRECTORIES
List of include directories for compiling sources in the
target's consumers. Typically these are the locations of the
target's header files.
INTERFACE_SYSTEM_INCLUDE_DIRECTORIES
List of directories that, when specified as include directories,
e.g., by INCLUDE_DIRECTORIES or INTERFACE_INCLUDE_DIRECTORIES,
should be treated as "system" include directories when compiling
sources in the target's consumers.
INTERFACE_SOURCES
List of source files to associate with the target's consumers.
INTERFACE_PRECOMPILE_HEADERS
Added in version 3.16.
List of header files to precompile and include when compiling
sources in the target's consumers.
INTERFACE_AUTOMOC_MACRO_NAMES
Added in version 3.27.
List of macro names used by AUTOMOC to determine if a C++ source
in the target's consumers needs to be processed by moc.
INTERFACE_AUTOUIC_OPTIONS
Added in version 3.0.
List of options used by AUTOUIC when invoking uic for the
target's consumers.
Transitive Link Properties
These represent usage requirements for linking consumers.
INTERFACE_LINK_LIBRARIES
List of link libraries for linking the target's consumers, for
those that are executables, shared libraries, or module
libraries. These are the transitive dependencies of the target.
Additionally, for compiling and linking the target's consumers,
usage requirements are collected from the transitive closure of
INTERFACE_LINK_LIBRARIES entries naming Normal Libraries,
Interface Libraries, Object Libraries, and Imported Targets,
INTERFACE_LINK_DIRECTORIES
Added in version 3.13.
List of link directories for linking the target's consumers, for
those that are executables, shared libraries, or module
libraries.
INTERFACE_LINK_OPTIONS
Added in version 3.13.
List of link options for linking the target's consumers, for
those that are executables, shared libraries, or module
libraries.
INTERFACE_LINK_DEPENDS
Added in version 3.13.
List of files on which linking the target's consumers depends,
for those that are executables, shared libraries, or module
libraries.
Custom Transitive Properties
Added in version 3.30.
The TARGET_PROPERTY generator expression evaluates the above build
specification and usage requirement properties as builtin transitive
properties. It also supports custom transitive properties defined by
the TRANSITIVE_COMPILE_PROPERTIES and TRANSITIVE_LINK_PROPERTIES
properties on the target and its link dependencies.
For example:
add_library(example INTERFACE)
set_target_properties(example PROPERTIES
TRANSITIVE_COMPILE_PROPERTIES "CUSTOM_C"
TRANSITIVE_LINK_PROPERTIES "CUSTOM_L"
INTERFACE_CUSTOM_C "EXAMPLE_CUSTOM_C"
INTERFACE_CUSTOM_L "EXAMPLE_CUSTOM_L"
)
add_library(mylib STATIC mylib.c)
target_link_libraries(mylib PRIVATE example)
set_target_properties(mylib PROPERTIES
CUSTOM_C "MYLIB_PRIVATE_CUSTOM_C"
CUSTOM_L "MYLIB_PRIVATE_CUSTOM_L"
INTERFACE_CUSTOM_C "MYLIB_IFACE_CUSTOM_C"
INTERFACE_CUSTOM_L "MYLIB_IFACE_CUSTOM_L"
)
add_executable(myexe myexe.c)
target_link_libraries(myexe PRIVATE mylib)
set_target_properties(myexe PROPERTIES
CUSTOM_C "MYEXE_CUSTOM_C"
CUSTOM_L "MYEXE_CUSTOM_L"
)
add_custom_target(print ALL VERBATIM
COMMAND ${CMAKE_COMMAND} -E echo
# Prints "MYLIB_PRIVATE_CUSTOM_C;EXAMPLE_CUSTOM_C"
"$<TARGET_PROPERTY:mylib,CUSTOM_C>"
# Prints "MYLIB_PRIVATE_CUSTOM_L;EXAMPLE_CUSTOM_L"
"$<TARGET_PROPERTY:mylib,CUSTOM_L>"
# Prints "MYEXE_CUSTOM_C"
"$<TARGET_PROPERTY:myexe,CUSTOM_C>"
# Prints "MYEXE_CUSTOM_L;MYLIB_IFACE_CUSTOM_L;EXAMPLE_CUSTOM_L"
"$<TARGET_PROPERTY:myexe,CUSTOM_L>"
)
Compatible Interface Properties
Some target properties are required to be compatible between a target
and the interface of each dependency. For example, the
POSITION_INDEPENDENT_CODE target property may specify a boolean value
of whether a target should be compiled as position-independent-code,
which has platform-specific consequences. A target may also specify
the usage requirement INTERFACE_POSITION_INDEPENDENT_CODE to
communicate that consumers must be compiled as
position-independent-code.
add_executable(exe1 exe1.cpp)
set_property(TARGET exe1 PROPERTY POSITION_INDEPENDENT_CODE ON)
add_library(lib1 SHARED lib1.cpp)
set_property(TARGET lib1 PROPERTY INTERFACE_POSITION_INDEPENDENT_CODE ON)
add_executable(exe2 exe2.cpp)
target_link_libraries(exe2 lib1)
Here, both exe1 and exe2 will be compiled as position-independent-code.
lib1 will also be compiled as position-independent-code because that is
the default setting for SHARED libraries. If dependencies have
conflicting, non-compatible requirements cmake(1) issues a diagnostic:
add_library(lib1 SHARED lib1.cpp)
set_property(TARGET lib1 PROPERTY INTERFACE_POSITION_INDEPENDENT_CODE ON)
add_library(lib2 SHARED lib2.cpp)
set_property(TARGET lib2 PROPERTY INTERFACE_POSITION_INDEPENDENT_CODE OFF)
add_executable(exe1 exe1.cpp)
target_link_libraries(exe1 lib1)
set_property(TARGET exe1 PROPERTY POSITION_INDEPENDENT_CODE OFF)
add_executable(exe2 exe2.cpp)
target_link_libraries(exe2 lib1 lib2)
The lib1 requirement INTERFACE_POSITION_INDEPENDENT_CODE is not
"compatible" with the POSITION_INDEPENDENT_CODE property of the exe1
target. The library requires that consumers are built as
position-independent-code, while the executable specifies to not built
as position-independent-code, so a diagnostic is issued.
The lib1 and lib2 requirements are not "compatible". One of them
requires that consumers are built as position-independent-code, while
the other requires that consumers are not built as
position-independent-code. Because exe2 links to both and they are in
conflict, a CMake error message is issued:
CMake Error: The INTERFACE_POSITION_INDEPENDENT_CODE property of "lib2" does
not agree with the value of POSITION_INDEPENDENT_CODE already determined
for "exe2".
To be "compatible", the POSITION_INDEPENDENT_CODE property, if set must
be either the same, in a boolean sense, as the
INTERFACE_POSITION_INDEPENDENT_CODE property of all transitively
specified dependencies on which that property is set.
This property of "compatible interface requirement" may be extended to
other properties by specifying the property in the content of the
COMPATIBLE_INTERFACE_BOOL target property. Each specified property
must be compatible between the consuming target and the corresponding
property with an INTERFACE_ prefix from each dependency:
add_library(lib1Version2 SHARED lib1_v2.cpp)
set_property(TARGET lib1Version2 PROPERTY INTERFACE_CUSTOM_PROP ON)
set_property(TARGET lib1Version2 APPEND PROPERTY
COMPATIBLE_INTERFACE_BOOL CUSTOM_PROP
)
add_library(lib1Version3 SHARED lib1_v3.cpp)
set_property(TARGET lib1Version3 PROPERTY INTERFACE_CUSTOM_PROP OFF)
add_executable(exe1 exe1.cpp)
target_link_libraries(exe1 lib1Version2) # CUSTOM_PROP will be ON
add_executable(exe2 exe2.cpp)
target_link_libraries(exe2 lib1Version2 lib1Version3) # Diagnostic
Non-boolean properties may also participate in "compatible interface"
computations. Properties specified in the COMPATIBLE_INTERFACE_STRING
property must be either unspecified or compare to the same string among
all transitively specified dependencies. This can be useful to ensure
that multiple incompatible versions of a library are not linked
together through transitive requirements of a target:
add_library(lib1Version2 SHARED lib1_v2.cpp)
set_property(TARGET lib1Version2 PROPERTY INTERFACE_LIB_VERSION 2)
set_property(TARGET lib1Version2 APPEND PROPERTY
COMPATIBLE_INTERFACE_STRING LIB_VERSION
)
add_library(lib1Version3 SHARED lib1_v3.cpp)
set_property(TARGET lib1Version3 PROPERTY INTERFACE_LIB_VERSION 3)
add_executable(exe1 exe1.cpp)
target_link_libraries(exe1 lib1Version2) # LIB_VERSION will be "2"
add_executable(exe2 exe2.cpp)
target_link_libraries(exe2 lib1Version2 lib1Version3) # Diagnostic
The COMPATIBLE_INTERFACE_NUMBER_MAX target property specifies that
content will be evaluated numerically and the maximum number among all
specified will be calculated:
add_library(lib1Version2 SHARED lib1_v2.cpp)
set_property(TARGET lib1Version2 PROPERTY INTERFACE_CONTAINER_SIZE_REQUIRED 200)
set_property(TARGET lib1Version2 APPEND PROPERTY
COMPATIBLE_INTERFACE_NUMBER_MAX CONTAINER_SIZE_REQUIRED
)
add_library(lib1Version3 SHARED lib1_v3.cpp)
set_property(TARGET lib1Version3 PROPERTY INTERFACE_CONTAINER_SIZE_REQUIRED 1000)
add_executable(exe1 exe1.cpp)
# CONTAINER_SIZE_REQUIRED will be "200"
target_link_libraries(exe1 lib1Version2)
add_executable(exe2 exe2.cpp)
# CONTAINER_SIZE_REQUIRED will be "1000"
target_link_libraries(exe2 lib1Version2 lib1Version3)
Similarly, the COMPATIBLE_INTERFACE_NUMBER_MIN may be used to calculate
the numeric minimum value for a property from dependencies.
Each calculated "compatible" property value may be read in the consumer
at generate-time using generator expressions.
Note that for each dependee, the set of properties specified in each
compatible interface property must not intersect with the set specified
in any of the other properties.
Property Origin Debugging
Because build specifications can be determined by dependencies, the
lack of locality of code which creates a target and code which is
responsible for setting build specifications may make the code more
difficult to reason about. cmake(1) provides a debugging facility to
print the origin of the contents of properties which may be determined
by dependencies. The properties which can be debugged are listed in
the CMAKE_DEBUG_TARGET_PROPERTIES variable documentation:
set(CMAKE_DEBUG_TARGET_PROPERTIES
INCLUDE_DIRECTORIES
COMPILE_DEFINITIONS
POSITION_INDEPENDENT_CODE
CONTAINER_SIZE_REQUIRED
LIB_VERSION
)
add_executable(exe1 exe1.cpp)
In the case of properties listed in COMPATIBLE_INTERFACE_BOOL or
COMPATIBLE_INTERFACE_STRING, the debug output shows which target was
responsible for setting the property, and which other dependencies also
defined the property. In the case of COMPATIBLE_INTERFACE_NUMBER_MAX
and COMPATIBLE_INTERFACE_NUMBER_MIN, the debug output shows the value
of the property from each dependency, and whether the value determines
the new extreme.
Build Specification with Generator Expressions
Build specifications may use generator expressions containing content
which may be conditional or known only at generate-time. For example,
the calculated "compatible" value of a property may be read with the
TARGET_PROPERTY expression:
add_library(lib1Version2 SHARED lib1_v2.cpp)
set_property(TARGET lib1Version2 PROPERTY
INTERFACE_CONTAINER_SIZE_REQUIRED 200)
set_property(TARGET lib1Version2 APPEND PROPERTY
COMPATIBLE_INTERFACE_NUMBER_MAX CONTAINER_SIZE_REQUIRED
)
add_executable(exe1 exe1.cpp)
target_link_libraries(exe1 lib1Version2)
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.
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:
add_library(lib1 lib1.cpp)
target_compile_definitions(lib1 INTERFACE
$<$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 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 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 install(EXPORT) command:
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
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:
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 cmake-packages(7) manual.
Include Directories and Usage Requirements
Include directories require some special consideration when specified
as usage requirements and when used with generator expressions. The
target_include_directories() command accepts both relative and absolute
include directories:
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
INTERFACE_INCLUDE_DIRECTORIES of 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:
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 CMAKE_INCLUDE_CURRENT_DIR_IN_INTERFACE variable may
be enabled, with an equivalent effect to:
set_property(TARGET tgt APPEND PROPERTY INTERFACE_INCLUDE_DIRECTORIES
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR};${CMAKE_CURRENT_BINARY_DIR}>
)
for each target affected. The convenience for installed targets is an
INCLUDES DESTINATION component with the install(TARGETS) command:
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
INTERFACE_INCLUDE_DIRECTORIES of each of the installed IMPORTED targets
when generated by install(EXPORT).
When the INTERFACE_INCLUDE_DIRECTORIES of an imported target is
consumed, the entries in the property may be treated as system include
directories. The effects of that are toolchain-dependent, but one
common effect is to omit compiler warnings for headers found in those
directories. The SYSTEM property of the installed target determines
this behavior (see the EXPORT_NO_SYSTEM property for how to modify the
installed value for a target). It is also possible to change how
consumers interpret the system behavior of consumed imported targets by
setting the NO_SYSTEM_FROM_IMPORTED target property on the consumer.
If a binary target is linked transitively to a macOS 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, 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:
add_library(lib1 lib1.cpp)
add_library(lib2 lib2.cpp)
target_link_libraries(lib1 PUBLIC
$<$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 POSITION_INDEPENDENT_CODE
property, the dependency graph above contains a cycle. cmake(1) issues
an error message.
Output Artifacts
The buildsystem targets created by the add_library() and
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.
There are three kinds of output artifacts that may be build by targets
as detailed in the following sections. Their classification differs
between DLL platforms and non-DLL platforms. All Windows-based systems
including Cygwin are DLL platforms.
Runtime Output Artifacts
A runtime output artifact of a buildsystem target may be:
o The executable file (e.g. .exe) of an executable target created by
the add_executable() command.
o On DLL platforms: the executable file (e.g. .dll) of a shared library
target created by the add_library() command with the SHARED option.
The RUNTIME_OUTPUT_DIRECTORY and RUNTIME_OUTPUT_NAME target properties
may be used to control runtime output artifact locations and names in
the build tree.
Library Output Artifacts
A library output artifact of a buildsystem target may be:
o The loadable module file (e.g. .dll or .so) of a module library
target created by the add_library() command with the MODULE option.
o On non-DLL platforms: the shared library file (e.g. .so or .dylib) of
a shared library target created by the add_library() command with the
SHARED option.
The LIBRARY_OUTPUT_DIRECTORY and LIBRARY_OUTPUT_NAME target properties
may be used to control library output artifact locations and names in
the build tree.
Archive Output Artifacts
An archive output artifact of a buildsystem target may be:
o The static library file (e.g. .lib or .a) of a static library target
created by the add_library() command with the STATIC option.
o On DLL platforms: the import library file (e.g. .lib) of a shared
library target created by the add_library() command with the SHARED
option. This file is only guaranteed to exist if the library exports
at least one unmanaged symbol.
o On DLL platforms: the import library file (e.g. .lib) of an
executable target created by the add_executable() command when its
ENABLE_EXPORTS target property is set.
o On AIX: the linker import file (e.g. .imp) of an executable target
created by the add_executable() command when its ENABLE_EXPORTS
target property is set.
o On macOS: the linker import file (e.g. .tbd) of a shared library
target created by the add_library() command with the SHARED option
and when its ENABLE_EXPORTS target property is set.
The ARCHIVE_OUTPUT_DIRECTORY and ARCHIVE_OUTPUT_NAME target properties
may be used to control archive output artifact locations and names in
the build tree.
Directory-Scoped Commands
The target_include_directories(), target_compile_definitions() and
target_compile_options() commands have an effect on only one target at
a time. The commands add_compile_definitions(), add_compile_options()
and include_directories() have a similar function, but operate at
directory scope instead of target scope for convenience.
BUILD CONFIGURATIONS
Configurations determine specifications for a certain type of build,
such as Release or Debug. The way this is specified depends on the
type of generator being used. For single configuration generators like
Makefile Generators and Ninja, the configuration is specified at
configure time by the CMAKE_BUILD_TYPE variable. For
multi-configuration generators like Visual Studio, Xcode, and Ninja
Multi-Config, the configuration is chosen by the user at build time and
CMAKE_BUILD_TYPE is ignored. In the multi-configuration case, the set
of available configurations is specified at configure time by the
CMAKE_CONFIGURATION_TYPES variable, but the actual configuration used
cannot be known until the build stage. This difference is often
misunderstood, leading to problematic code like the following:
# WARNING: This is wrong for multi-config generators because they don't use
# and typically don't even set CMAKE_BUILD_TYPE
string(TOLOWER ${CMAKE_BUILD_TYPE} build_type)
if (build_type STREQUAL debug)
target_compile_definitions(exe1 PRIVATE DEBUG_BUILD)
endif()
Generator expressions should be used instead to handle
configuration-specific logic correctly, regardless of the generator
used. For example:
# Works correctly for both single and multi-config generators
target_compile_definitions(exe1 PRIVATE
$<$IMPORTED targets, the content of
MAP_IMPORTED_CONFIG_DEBUG is also accounted for by the above
$<CONFIG:Debug> expression.
Case Sensitivity
CMAKE_BUILD_TYPE and CMAKE_CONFIGURATION_TYPES are just like other
variables in that any string comparisons made with their values will be
case-sensitive. The $<CONFIG> generator expression also preserves the
casing of the configuration as set by the user or CMake defaults. For
example:
# NOTE: Don't use these patterns, they are for illustration purposes only.
set(CMAKE_BUILD_TYPE Debug)
if(CMAKE_BUILD_TYPE STREQUAL DEBUG)
# ... will never get here, "Debug" != "DEBUG"
endif()
add_custom_target(print_config ALL
# Prints "Config is Debug" in this single-config case
COMMAND ${CMAKE_COMMAND} -E echo "Config is $<CONFIG>"
VERBATIM
)
set(CMAKE_CONFIGURATION_TYPES Debug Release)
if(DEBUG IN_LIST CMAKE_CONFIGURATION_TYPES)
# ... will never get here, "Debug" != "DEBUG"
endif()
In contrast, CMake treats the configuration type case-insensitively
when using it internally in places that modify behavior based on the
configuration. For example, the $<CONFIG:Debug> generator expression
will evaluate to 1 for a configuration of not only Debug, but also
DEBUG, debug or even DeBuG. Therefore, you can specify configuration
types in CMAKE_BUILD_TYPE and CMAKE_CONFIGURATION_TYPES with any
mixture of upper and lowercase, although there are strong conventions
(see the next section). If you must test the value in string
comparisons, always convert the value to upper or lowercase first and
adjust the test accordingly.
Default And Custom Configurations
By default, CMake defines a number of standard configurations:
o Debug
o Release
o RelWithDebInfo
o MinSizeRel
In multi-config generators, the CMAKE_CONFIGURATION_TYPES variable will
be populated with (potentially a subset of) the above list by default,
unless overridden by the project or user. The actual configuration
used is selected by the user at build time.
For single-config generators, the configuration is specified with the
CMAKE_BUILD_TYPE variable at configure time and cannot be changed at
build time. The default value will often be none of the above standard
configurations and will instead be an empty string. A common
misunderstanding is that this is the same as Debug, but that is not the
case. Users should always explicitly specify the build type instead to
avoid this common problem.
The above standard configuration types provide reasonable behavior on
most platforms, but they can be extended to provide other types. Each
configuration defines a set of compiler and linker flag variables for
the language in use. These variables follow the convention
CMAKE_<LANG>_FLAGS_<CONFIG>, where <CONFIG> is always the uppercase
configuration name. When defining a custom configuration type, make
sure these variables are set appropriately, typically as cache
variables.
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
An IMPORTED target represents a pre-existing dependency. Usually such
targets are defined by an upstream package and should be treated as
immutable. After declaring an IMPORTED target one can adjust its target
properties by using the customary commands such as
target_compile_definitions(), target_include_directories(),
target_compile_options() or target_link_libraries() just like with any
other regular target.
IMPORTED targets may have the same usage requirement properties
populated as binary targets, such as INTERFACE_INCLUDE_DIRECTORIES,
INTERFACE_COMPILE_DEFINITIONS, INTERFACE_COMPILE_OPTIONS,
INTERFACE_LINK_LIBRARIES, and INTERFACE_POSITION_INDEPENDENT_CODE.
The LOCATION may also be read from an IMPORTED target, though there is
rarely reason to do so. Commands such as add_custom_command() can
transparently use an IMPORTED EXECUTABLE target as a COMMAND
executable.
The scope of the definition of an 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 IMPORTED target which is
accessible globally in the buildsystem.
See the cmake-packages(7) manual for more on creating packages with
IMPORTED targets.
Alias Targets
An ALIAS target is a name which may be used interchangeably 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.
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 IMPORTED target from a package, or an ALIAS
target if built as part of the same buildsystem.
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 ALIASED_TARGET property
from it:
get_target_property(_aliased Upstream::lib1 ALIASED_TARGET)
if(_aliased)
message(STATUS "The name Upstream::lib1 is an ALIAS for ${_aliased}.")
endif()
Interface Libraries
An INTERFACE library target does not compile sources and does not
produce a library artifact on disk, so it has no LOCATION.
It may specify usage requirements such as
INTERFACE_INCLUDE_DIRECTORIES, INTERFACE_COMPILE_DEFINITIONS,
INTERFACE_COMPILE_OPTIONS, INTERFACE_LINK_LIBRARIES, INTERFACE_SOURCES,
and INTERFACE_POSITION_INDEPENDENT_CODE. Only the INTERFACE modes of
the target_include_directories(), target_compile_definitions(),
target_compile_options(), target_sources(), and target_link_libraries()
commands may be used with INTERFACE libraries.
Since CMake 3.19, an INTERFACE library target may optionally contain
source files. An interface library that contains source files will be
included as a build target in the generated buildsystem. It does not
compile sources, but may contain custom commands to generate other
sources. Additionally, IDEs will show the source files as part of the
target for interactive reading and editing.
A primary use-case for INTERFACE libraries is header-only libraries.
Since CMake 3.23, header files may be associated with a library by
adding them to a header set using the target_sources() command:
add_library(Eigen INTERFACE)
target_sources(Eigen PUBLIC
FILE_SET HEADERS
BASE_DIRS src
FILES src/eigen.h src/vector.h src/matrix.h
)
add_executable(exe1 exe1.cpp)
target_link_libraries(exe1 Eigen)
When we specify the FILE_SET here, the BASE_DIRS we define
automatically become include directories in the usage requirements for
the target Eigen. The usage requirements from the target are consumed
and used when compiling, but have no effect on linking.
Another use-case is to employ an entirely target-focussed design for
usage requirements:
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
$<$exe1 is expressed entirely as
linked targets, and the complexity of compiler-specific flags is
encapsulated in an INTERFACE library target.
INTERFACE libraries may be installed and exported. We can install the
default header set along with the target:
add_library(Eigen INTERFACE)
target_sources(Eigen INTERFACE
FILE_SET HEADERS
BASE_DIRS src
FILES src/eigen.h src/vector.h src/matrix.h
)
install(TARGETS Eigen EXPORT eigenExport
FILE_SET HEADERS DESTINATION include/Eigen)
install(EXPORT eigenExport NAMESPACE Upstream::
DESTINATION lib/cmake/Eigen
)
Here, the headers defined in the header set are installed to
include/Eigen. The install destination automatically becomes an
include directory that is a usage requirement for consumers.
COPYRIGHT
2000-2024 Kitware, Inc. and Contributors
3.31.2 December 20, 2024 cmake-buildsystem(7)
cmake 3.31.2 - Generated Sat Dec 21 07:41:16 CST 2024