# add_library

Contents

- add_library

  - Normal Libraries

  - Imported Libraries

  - Object Libraries

  - Alias Libraries

  - Interface Libraries

Add a library to the project using the specified source files.

## Normal Libraries

    add_library(<name> [STATIC | SHARED | MODULE]
                [EXCLUDE_FROM_ALL]
                [source1] [source2 ...])

Adds a library target called `<name>` to be built from the source files listed in the command invocation. (The source files can be omitted here if they are added later using `target_sources()`.) The `<name>` corresponds to the logical target name and must be globally unique within a project. The actual file name of the library built is constructed based on conventions of the native platform (such as `lib<name>.a` or `<name>.lib`).

`STATIC`, `SHARED`, or `MODULE` may be given to specify the type of library to be created. `STATIC` libraries are archives of object files for use when linking other targets. `SHARED` libraries are linked dynamically and loaded at runtime. `MODULE` libraries are plugins that are not linked into other targets but may be loaded dynamically at runtime using dlopen-like functionality. If no type is given explicitly the type is `STATIC` or `SHARED` based on whether the current value of the variable `BUILD_SHARED_LIBS` is `ON`. For `SHARED` and `MODULE` libraries the `POSITION_INDEPENDENT_CODE` target property is set to `ON` automatically. A `SHARED` or `STATIC` library may be marked with the `FRAMEWORK` target property to create an macOS Framework.

If a library does not export any symbols, it must not be declared as a `SHARED` library. For example, a Windows resource DLL or a managed C++/CLI DLL that exports no unmanaged symbols would need to be a `MODULE` library. This is because CMake expects a `SHARED` library to always have an associated import library on Windows.

By default the library file will be created in the build tree directory corresponding to the source tree directory in which the command was invoked. See documentation of the `ARCHIVE_OUTPUT_DIRECTORY`, `LIBRARY_OUTPUT_DIRECTORY`, and `RUNTIME_OUTPUT_DIRECTORY` target properties to change this location. See documentation of the `OUTPUT_NAME` target property to change the `<name>` part of the final file name.

If `EXCLUDE_FROM_ALL` is given the corresponding property will be set on the created target. See documentation of the `EXCLUDE_FROM_ALL` target property for details.

Source arguments to `add_library` may use “generator expressions” with the syntax `$<...>`. See the `cmake-generator-expressions(7)` manual for available expressions. See the `cmake-buildsystem(7)` manual for more on defining buildsystem properties.

See also `HEADER_FILE_ONLY` on what to do if some sources are pre-processed, and you want to have the original sources reachable from within IDE.

## Imported Libraries

    add_library(<name> <SHARED|STATIC|MODULE|OBJECT|UNKNOWN> IMPORTED
                [GLOBAL])

An IMPORTED library target references a library file located outside the project. No rules are generated to build it, and the `IMPORTED` target property is `True`. The target name has scope in the directory in which it is created and below, but the `GLOBAL` option extends visibility. It may be referenced like any target built within the project. `IMPORTED` libraries are useful for convenient reference from commands like `target_link_libraries()`. Details about the imported library are specified by setting properties whose names begin in `IMPORTED_` and `INTERFACE_`.

The most important properties are:

- `IMPORTED_LOCATION` (and its per-configuration variant `IMPORTED_LOCATION_<CONFIG>`) which specifies the location of the main library file on disk.

- `IMPORTED_OBJECTS` (and `IMPORTED_OBJECTS_<CONFIG>`) for object libraries, specifies the locations of object files on disk.

- `PUBLIC_HEADER` files to be installed during `install()` invocation

See documentation of the `IMPORTED_*` and `INTERFACE_*` properties for more information.

An `UNKNOWN` library type is typically only used in the implementation of Find Modules. It allows the path to an imported library (often found using the `find_library()` command) to be used without having to know what type of library it is. This is especially useful on Windows where a static library and a DLL’s import library both have the same file extension.

## Object Libraries

    add_library(<name> OBJECT <src>...)

Creates an Object Library. An object library compiles source files but does not archive or link their object files into a library. Instead other targets created by `add_library()` or `add_executable()` may reference the objects using an expression of the form `$<TARGET_OBJECTS:objlib>` as a source, where `objlib` is the object library name. For example:

    add_library(... $<TARGET_OBJECTS:objlib> ...)
    add_executable(... $<TARGET_OBJECTS:objlib> ...)

will include objlib’s object files in a library and an executable along with those compiled from their own sources. Object libraries may contain only sources that compile, header files, and other files that would not affect linking of a normal library (e.g. `.txt`). They may contain custom commands generating such sources, but not `PRE_BUILD`, `PRE_LINK`, or `POST_BUILD` commands. Some native build systems (such as Xcode) may not like targets that have only object files, so consider adding at least one real source file to any target that references `$<TARGET_OBJECTS:objlib>`.

## Alias Libraries

    add_library(<name> ALIAS <target>)

Creates an Alias Target, such that `<name>` can be used to refer to `<target>` in subsequent commands. The `<name>` does not appear in the generated buildsystem as a make target. The `<target>` may not be an `ALIAS`.

An `ALIAS` to a non-`GLOBAL` Imported Target has scope in the directory in which the alias is created and below. The `ALIAS_GLOBAL` target property can be used to check if the alias is global or not.

`ALIAS` targets can be used as linkable targets and as targets to read properties from. They can also be tested for existence with the regular `if(TARGET)` subcommand. The `<name>` may not be used to modify properties of `<target>`, that is, it may not be used as the operand of `set_property()`, `set_target_properties()`, `target_link_libraries()` etc. An `ALIAS` target may not be installed or exported.

## Interface Libraries

    add_library(<name> INTERFACE [IMPORTED [GLOBAL]])

Creates an Interface Library. An `INTERFACE` library target does not directly create build output, though it may have properties set on it and it may be installed, exported and imported. Typically the `INTERFACE_*` properties are populated on the interface target using the commands:

- `set_property()`,

- `target_link_libraries(INTERFACE)`,

- `target_link_options(INTERFACE)`,

- `target_include_directories(INTERFACE)`,

- `target_compile_options(INTERFACE)`,

- `target_compile_definitions(INTERFACE)`, and

- `target_sources(INTERFACE)`,

and then it is used as an argument to `target_link_libraries()` like any other target.

An `INTERFACE` Imported Target may also be created with this signature. An `IMPORTED` library target references a library defined outside the project. The target name has scope in the directory in which it is created and below, but the `GLOBAL` option extends visibility. It may be referenced like any target built within the project. `IMPORTED` libraries are useful for convenient reference from commands like `target_link_libraries()`.