# INTERFACE_INCLUDE_DIRECTORIES

Added in version 4.4.

List of public include directories requirements for a file set.

File sets may populate this property to publish the include directories required to compile the sources for the target. The `set_property(FILE_SET)` command populates this property.

When target dependencies are specified using `target_link_libraries()`, CMake will read this property from file sets of all target dependencies to determine the build properties of the consumer. These build properties are only applied to the sources of the file sets. The other sources of the consumer are unaffected.

Contents of `INTERFACE_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:

    set_property(FILE_SET myfile_set TARGET mylib PROPERTY INTERFACE_INCLUDE_DIRECTORIES
      $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/mylib>
      $<INSTALL_INTERFACE:include/mylib>  # <prefix>/include/mylib
    )

Related properties:

- Use `INTERFACE_COMPILE_DEFINITIONS` to pass additional preprocessor definitions.

- Use `INTERFACE_COMPILE_OPTIONS` to pass additional compile flags.

## Creating Relocatable Packages

Note that it is not advisable to populate the `INSTALL_INTERFACE` of the `INTERFACE_INCLUDE_DIRECTORIES` of a target with absolute paths to the include directories of 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 for headers provided with the target itself, not those provided by the transitive dependencies listed in its `INTERFACE_LINK_LIBRARIES` target property. Those dependencies should themselves be targets that specify their own header locations in `INTERFACE_INCLUDE_DIRECTORIES`.

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.