target_link_libraries¶
Specify libraries or flags to use when linking a given target and/or its dependents. Usage requirements from linked library targets will be propagated. Usage requirements of a target's dependencies affect compilation of its own sources.
Overview¶
This command has several signatures as detailed in subsections below. All of them have the general form
target_link_libraries(<target> ... <item>... ...)
The named <target>
must have been created by a command such as
add_executable()
or add_library()
and must not be an
ALIAS target. If policy CMP0079
is not
set to NEW
then the target must have been created in the current
directory. Repeated calls for the same <target>
append items in
the order called.
New in version 3.13: The <target>
doesn't have to be defined in the same directory as the
target_link_libraries
call.
Each <item>
may be:
A library target name: The generated link line will have the full path to the linkable library file associated with the target. The buildsystem will have a dependency to re-link
<target>
if the library file changes.The named target must be created by
add_library()
within the project or as an IMPORTED library. If it is created within the project an ordering dependency will automatically be added in the build system to make sure the named library target is up-to-date before the<target>
links.If an imported library has the
IMPORTED_NO_SONAME
target property set, CMake may ask the linker to search for the library instead of using the full path (e.g./usr/lib/libfoo.so
becomes-lfoo
).The full path to the target's artifact will be quoted/escaped for the shell automatically.
A full path to a library file: The generated link line will normally preserve the full path to the file. The buildsystem will have a dependency to re-link
<target>
if the library file changes.There are some cases where CMake may ask the linker to search for the library (e.g.
/usr/lib/libfoo.so
becomes-lfoo
), such as when a shared library is detected to have noSONAME
field. See policyCMP0060
for discussion of another case.If the library file is in a macOS framework, the
Headers
directory of the framework will also be processed as a usage requirement. This has the same effect as passing the framework directory as an include directory.New in version 3.8: On Visual Studio Generators for VS 2010 and above, library files ending in
.targets
will be treated as MSBuild targets files and imported into generated project files. This is not supported by other generators.The full path to the library file will be quoted/escaped for the shell automatically.
A plain library name: The generated link line will ask the linker to search for the library (e.g.
foo
becomes-lfoo
orfoo.lib
).The library name/flag is treated as a command-line string fragment and will be used with no extra quoting or escaping.
A link flag: Item names starting with
-
, but not-l
or-framework
, are treated as linker flags. Note that such flags will be treated like any other library link item for purposes of transitive dependencies, so they are generally safe to specify only as private link items that will not propagate to dependents.Link flags specified here are inserted into the link command in the same place as the link libraries. This might not be correct, depending on the linker. Use the
LINK_OPTIONS
target property ortarget_link_options()
command to add link flags explicitly. The flags will then be placed at the toolchain-defined flag position in the link command.New in version 3.13:
LINK_OPTIONS
target property andtarget_link_options()
command. For earlier versions of CMake, useLINK_FLAGS
property instead.The link flag is treated as a command-line string fragment and will be used with no extra quoting or escaping.
A generator expression: A
$<...>
generator expression
may evaluate to any of the above items or to a semicolon-separated list of them. If the...
contains any;
characters, e.g. after evaluation of a${list}
variable, be sure to use an explicitly quoted argument"$<...>"
so that this command receives it as a single<item>
.Additionally, a generator expression may be used as a fragment of any of the above items, e.g.
foo$<1:_d>
.Note that generator expressions will not be used in OLD handling of policy
CMP0003
or policyCMP0004
.A
debug
,optimized
, orgeneral
keyword immediately followed by another<item>
. The item following such a keyword will be used only for the corresponding build configuration. Thedebug
keyword corresponds to theDebug
configuration (or to configurations named in theDEBUG_CONFIGURATIONS
global property if it is set). Theoptimized
keyword corresponds to all other configurations. Thegeneral
keyword corresponds to all configurations, and is purely optional. Higher granularity may be achieved for per-configuration rules by creating and linking to IMPORTED library targets. These keywords are interpreted immediately by this command and therefore have no special meaning when produced by a generator expression.
Items containing ::
, such as Foo::Bar
, are assumed to be
IMPORTED or ALIAS library
target names and will cause an error if no such target exists.
See policy CMP0028
.
See the cmake-buildsystem(7)
manual for more on defining
buildsystem properties.
Libraries for a Target and/or its Dependents¶
target_link_libraries(<target>
<PRIVATE|PUBLIC|INTERFACE> <item>...
[<PRIVATE|PUBLIC|INTERFACE> <item>...]...)
The PUBLIC
, PRIVATE
and INTERFACE
scope keywords can be used to
specify both the link dependencies and the link interface in one command.
Libraries and targets following PUBLIC
are linked to, and are made
part of the link interface. Libraries and targets following PRIVATE
are linked to, but are not made part of the link interface. Libraries
following INTERFACE
are appended to the link interface and are not
used for linking <target>
.
Libraries for both a Target and its Dependents¶
target_link_libraries(<target> <item>...)
Library dependencies are transitive by default with this signature.
When this target is linked into another target then the libraries
linked to this target will appear on the link line for the other
target too. This transitive "link interface" is stored in the
INTERFACE_LINK_LIBRARIES
target property and may be overridden
by setting the property directly. When CMP0022
is not set to
NEW
, transitive linking is built in but may be overridden by the
LINK_INTERFACE_LIBRARIES
property. Calls to other signatures
of this command may set the property making any libraries linked
exclusively by this signature private.
Libraries for a Target and/or its Dependents (Legacy)¶
target_link_libraries(<target>
<LINK_PRIVATE|LINK_PUBLIC> <lib>...
[<LINK_PRIVATE|LINK_PUBLIC> <lib>...]...)
The LINK_PUBLIC
and LINK_PRIVATE
modes can be used to specify both
the link dependencies and the link interface in one command.
This signature is for compatibility only. Prefer the PUBLIC
or
PRIVATE
keywords instead.
Libraries and targets following LINK_PUBLIC
are linked to, and are
made part of the INTERFACE_LINK_LIBRARIES
. If policy
CMP0022
is not NEW
, they are also made part of the
LINK_INTERFACE_LIBRARIES
. Libraries and targets following
LINK_PRIVATE
are linked to, but are not made part of the
INTERFACE_LINK_LIBRARIES
(or LINK_INTERFACE_LIBRARIES
).
Libraries for Dependents Only (Legacy)¶
target_link_libraries(<target> LINK_INTERFACE_LIBRARIES <item>...)
The LINK_INTERFACE_LIBRARIES
mode appends the libraries to the
INTERFACE_LINK_LIBRARIES
target property instead of using them
for linking. If policy CMP0022
is not NEW
, then this mode
also appends libraries to the LINK_INTERFACE_LIBRARIES
and its
per-configuration equivalent.
This signature is for compatibility only. Prefer the INTERFACE
mode
instead.
Libraries specified as debug
are wrapped in a generator expression to
correspond to debug builds. If policy CMP0022
is
not NEW
, the libraries are also appended to the
LINK_INTERFACE_LIBRARIES_DEBUG
property (or to the properties corresponding to configurations listed in
the DEBUG_CONFIGURATIONS
global property if it is set).
Libraries specified as optimized
are appended to the
INTERFACE_LINK_LIBRARIES
property. If policy CMP0022
is not NEW
, they are also appended to the
LINK_INTERFACE_LIBRARIES
property. Libraries specified as
general
(or without any keyword) are treated as if specified for both
debug
and optimized
.
Linking Object Libraries¶
New in version 3.12.
Object Libraries may be used as the <target>
(first) argument
of target_link_libraries
to specify dependencies of their sources
on other libraries. For example, the code
add_library(A SHARED a.c)
target_compile_definitions(A PUBLIC A)
add_library(obj OBJECT obj.c)
target_compile_definitions(obj PUBLIC OBJ)
target_link_libraries(obj PUBLIC A)
compiles obj.c
with -DA -DOBJ
and establishes usage requirements
for obj
that propagate to its dependents.
Normal libraries and executables may link to Object Libraries to get their objects and usage requirements. Continuing the above example, the code
add_library(B SHARED b.c)
target_link_libraries(B PUBLIC obj)
compiles b.c
with -DA -DOBJ
, creates shared library B
with object files from b.c
and obj.c
, and links B
to A
.
Furthermore, the code
add_executable(main main.c)
target_link_libraries(main B)
compiles main.c
with -DA -DOBJ
and links executable main
to B
and A
. The object library's usage requirements are
propagated transitively through B
, but its object files are not.
Object Libraries may "link" to other object libraries to get usage requirements, but since they do not have a link step nothing is done with their object files. Continuing from the above example, the code:
add_library(obj2 OBJECT obj2.c)
target_link_libraries(obj2 PUBLIC obj)
add_executable(main2 main2.c)
target_link_libraries(main2 obj2)
compiles obj2.c
with -DA -DOBJ
, creates executable main2
with object files from main2.c
and obj2.c
, and links main2
to A
.
In other words, when Object Libraries appear in a target's
INTERFACE_LINK_LIBRARIES
property they will be
treated as Interface Libraries, but when they appear in
a target's LINK_LIBRARIES
property their object files
will be included in the link too.
Linking Object Libraries via $<TARGET_OBJECTS>
¶
New in version 3.21.
The object files associated with an object library may be referenced
by the $<TARGET_OBJECTS>
generator expression. Such object
files are placed on the link line before all libraries, regardless
of their relative order. Additionally, an ordering dependency will be
added to the build system to make sure the object library is up-to-date
before the dependent target links. For example, the code
add_library(obj3 OBJECT obj3.c)
target_compile_definitions(obj3 PUBLIC OBJ3)
add_executable(main3 main3.c)
target_link_libraries(main3 PRIVATE a3 $<TARGET_OBJECTS:obj3> b3)
links executable main3
with object files from main3.c
and obj3.c
followed by the a3
and b3
libraries.
main3.c
is not compiled with usage requirements from obj3
,
such as -DOBJ3
.
This approach can be used to achieve transitive inclusion of object files in link lines as usage requirements. Continuing the above example, the code
add_library(iface_obj3 INTERFACE)
target_link_libraries(iface_obj3 INTERFACE obj3 $<TARGET_OBJECTS:obj3>)
creates an interface library iface_obj3
that forwards the obj3
usage requirements and adds the obj3
object files to dependents'
link lines. The code
add_executable(use_obj3 use_obj3.c)
target_link_libraries(use_obj3 PRIVATE iface_obj3)
compiles use_obj3.c
with -DOBJ3
and links executable use_obj3
with object files from use_obj3.c
and obj3.c
.
This also works transitively through a static library. Since a static library does not link, it does not consume the object files from object libraries referenced this way. Instead, the object files become transitive link dependencies of the static library. Continuing the above example, the code
add_library(static3 STATIC static3.c)
target_link_libraries(static3 PRIVATE iface_obj3)
add_executable(use_static3 use_static3.c)
target_link_libraries(use_static3 PRIVATE static3)
compiles static3.c
with -DOBJ3
and creates libstatic3.a
using only its own object file. use_static3.c
is compiled without
-DOBJ3
because the usage requirement is not transitive through
the private dependency of static3
. However, the link dependencies
of static3
are propagated, including the iface_obj3
reference
to $<TARGET_OBJECTS:obj3>
. The use_static3
executable is
created with object files from use_static3.c
and obj3.c
, and
linked to library libstatic3.a
.
When using this approach, it is the project's responsibility to avoid
linking multiple dependent binaries to iface_obj3
, because they will
all get the obj3
object files on their link lines.
Note
Referencing $<TARGET_OBJECTS>
in target_link_libraries
calls worked in versions of CMake prior to 3.21 for some cases,
but was not fully supported:
It did not place the object files before libraries on link lines.
It did not add an ordering dependency on the object library.
It did not work in Xcode with multiple architectures.
Cyclic Dependencies of Static Libraries¶
The library dependency graph is normally acyclic (a DAG), but in the case
of mutually-dependent STATIC
libraries CMake allows the graph to
contain cycles (strongly connected components). When another target links
to one of the libraries, CMake repeats the entire connected component.
For example, the code
add_library(A STATIC a.c)
add_library(B STATIC b.c)
target_link_libraries(A B)
target_link_libraries(B A)
add_executable(main main.c)
target_link_libraries(main A)
links main
to A B A B
. While one repetition is usually
sufficient, pathological object file and symbol arrangements can require
more. One may handle such cases by using the
LINK_INTERFACE_MULTIPLICITY
target property or by manually
repeating the component in the last target_link_libraries
call.
However, if two archives are really so interdependent they should probably
be combined into a single archive, perhaps by using Object Libraries.
Creating Relocatable Packages¶
Note that it is not advisable to populate the
INTERFACE_LINK_LIBRARIES
of a target with absolute paths to dependencies.
That would hard-code into installed packages the library file paths
for dependencies as found on the machine the package was made on.
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.