# 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
  - 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 in the current directory by a command such as `add_executable()` or `add_library()` and must not be an ALIAS target. Repeated calls for the same `<target>` append items in the order called. 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`).

- 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 Mac OSX 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.

  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.

- 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`).

- 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_FLAGS` target property to add link flags explicitly. The flags will then be placed at the toolchain-defined flag position in the link command.

- 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.

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`.

Arguments to `target_link_libraries` may use “generator expressions” with the syntax `$<...>`. Note however, that generator expressions will not be used in OLD handling of `CMP0003` or `CMP0004`. See the `cmake-generator-expressions(7)` manual for available expressions. 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

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.

## 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.