cmake(1)

PRIVATE / PUBLIC / INTERFACE

These modifier control where properties for a given target are visible.

• PRIVATE: Only for the target itself.
• INTERFACE: Only for anyone linking against the target.
• PUBLIC: For the target itself and anyone linking against it (effectively PRIVATE + INTERFACE).

The following gives an example for preprocessor definitions specified on a library target. This behaves in the same way for other properties like for example include directories.

# CMakeLists.txt

cmake_minimum_required(VERSION 3.14)
project(moose)

# -- LIBRARY
add_library(liba STATIC liba.cc)
target_compile_definitions(liba PUBLIC DEF_PUBLIC)
target_compile_definitions(liba PRIVATE DEF_PRIVATE)
target_compile_definitions(liba INTERFACE DEF_INTERFACE)

# -- APPLICATION
add_executable(main main.cc)
target_link_libraries(main liba)

> touch liba.cc; echo "int main() {}" > main.cc
> cmake -B build -S . -G Ninja
> ninja -C build -j1 --verbose
[1/4] /usr/bin/c++ -DDEF_PRIVATE -DDEF_PUBLIC  [..] .../liba.cc
[2/4] [..]
[3/4] /usr/bin/c++ -DDEF_INTERFACE -DDEF_PUBLIC [..] .../main.cc
[4/4] [..]