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# target_include_directories

Add include directories to a target.

    target_include_directories(<target> [SYSTEM] [BEFORE]
      <INTERFACE|PUBLIC|PRIVATE> [items1...]
      [<INTERFACE|PUBLIC|PRIVATE> [items2...] ...])

Specify include directories to use when compiling a given target. The named `<target>` must have been created by a command such as `add_executable()` or `add_library()` and must not be an `IMPORTED` target.

If `BEFORE` is specified, the content will be prepended to the property instead of being appended.

The `INTERFACE`, `PUBLIC` and `PRIVATE` keywords are required to specify the scope of the following arguments. `PRIVATE` and `PUBLIC` items will populate the `INCLUDE_DIRECTORIES` property of `<target>`. `PUBLIC` and `INTERFACE` items will populate the `INTERFACE_INCLUDE_DIRECTORIES` property of `<target>`. The following arguments specify include directories.

Specified include directories may be absolute paths or relative paths. Repeated calls for the same <target> append items in the order called. If `SYSTEM` is specified, the compiler will be told the directories are meant as system include directories on some platforms (signalling this setting might achieve effects such as the compiler skipping warnings, or these fixed-install system files not being considered in dependency calculations - see compiler docs). If `SYSTEM` is used together with `PUBLIC` or `INTERFACE`, the `INTERFACE_SYSTEM_INCLUDE_DIRECTORIES` target property will be populated with the specified directories.

Arguments to `target_include_directories` 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.

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:

    target_include_directories(mylib PUBLIC
      $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/mylib>
      $<INSTALL_INTERFACE:include/mylib>  # <prefix>/include/mylib
    )

Note that it is not advisable to populate the `INSTALL_INTERFACE` of the `INTERFACE_INCLUDE_DIRECTORIES` of a target with paths for dependencies. That would hard-code into installed packages the include directory paths for dependencies as found on the machine the package was made on.

The `INSTALL_INTERFACE` of the `INTERFACE_INCLUDE_DIRECTORIES` is only suitable for specifying the required include directories of the target itself, not its dependencies.

That is, code like this is incorrect for targets which will be used to generate `cmake-packages(7)`:

    target_include_directories(mylib INTERFACE
      $<INSTALL_INTERFACE:${Boost_INCLUDE_DIRS};${OtherDep_INCLUDE_DIRS}>
    )

Dependencies must provide their own IMPORTED targets which have their own `INTERFACE_INCLUDE_DIRECTORIES` populated appropriately. Those IMPORTED targets may then be used with the `target_link_libraries()` command for `mylib`.

That way, when a consumer uses the installed package, the consumer will run the appropriate `find_package()` command to find the dependencies on their own machine and populate the IMPORTED targets with appropriate paths. See Creating Packages for more. Note that many modules currently shipped with CMake do not currently provide IMPORTED targets.

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