CMake target_include_directories meaning of scope

Question

What is the meaning of the keyword PUBLIC, PRIVATE, and INTERFACE related to CMake\'s target_include_directories?

Answer 1

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.

From the documentation: http://www.cmake.org/cmake/help/v3.0/command/target_include_directories.html

To rephrase the documentation with my own words:

• you want to add a directory to list of include directory for a target
• with PRIVATE the directory is added to the target's include directories
• with INTERFACE the target is not modified, but the INTERFACE_INCLUDE_DIRECTORIES is extended by the directory. The variable is a list of public include directories for a library.
• with PUBLIC both actions from PRIVATE and INTERFACE are performed.