List of public include directories requirements for a library.

Targets may populate this property to publish the include directories required to compile against the headers for the target. The target_include_directories() command populates this property with values given to the PUBLIC and INTERFACE keywords. Projects may also get and set the property directly.

When target dependencies are specified using target_link_libraries(), CMake will read this property from all target dependencies to determine the build properties of the consumer.

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:

target_include_directories(mylib INTERFACE
  $<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

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.