target_link_libraries

Contents

• target_link_libraries

  • Overview

  • Libraries for a Target and/or its Dependents

  • Libraries for both a Target and its Dependents

  • Libraries for a Target and/or its Dependents (Legacy)

  • Libraries for Dependents Only (Legacy)

  • Linking Object Libraries

    • Linking Object Libraries via $<TARGET_OBJECTS>

  • Cyclic Dependencies of Static Libraries

  • Creating Relocatable Packages

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 no SONAME field. See policy CMP0060 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 or foo.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 or target_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 and target_link_options() command. For earlier versions of CMake, use LINK_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 policy CMP0004.

• A debug, optimized, or general keyword immediately followed by another <item>. The item following such a keyword will be used only for the corresponding build configuration. The debug keyword corresponds to the Debug configuration (or to configurations named in the DEBUG_CONFIGURATIONS global property if it is set). The optimized keyword corresponds to all other configurations. The general 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 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.