How to compile all the libraries as static but one as shared? - cmake

Question

My folder structure is like that:
├── SubLibA
│   ├── CMakeLists.txt
│   ├── include
│   │   └── SubLibA.h
│   └── SubLibA.cpp
├── SubLibB
│   ├── CMakeLists.txt
│   ├── include
│   │   └── structs.h
│   └── SubLibB.cpp
└── SharedLib
├── CMakeLists.txt
├── include
│   └── SharedLib.h
├── SharedLib.cpp
└── SharedLib.h
My global CMakeLists.txt looks like this:
add_subdirectory(SubLibA)
add_subdirectory(SubLibB)
add_subdirectory(SharedLib)
They all compile as static by default.
SharedLib depends on SubLibB that depends on SubLibA.
The dependent libraries SharedLib and SubLibB have:
#SubLibB
target_link_libraries(${PROJECT_NAME}
SubLibA::SubLibA
)
#SharedLib
target_link_libraries(${PROJECT_NAME}
SubLibB::SubLibB
)
Running cmake .. -DBUILD_SHARED_LIBS=ON compiles all the three libs as shared library...
Since they are tightly dependent, I'd like to keep them in the same repository with a unique CMakeLists.txt that compiles them all at once. I want to use the power of Modern CMake with the least hard-coded file and custom files as possible to keep a straightforward maintenance.

Answer 1

Try setting the variable within cmake:
set(BUILD_SHARED_LIBS OFF)
add_subdirectory(SubLibA)
add_subdirectory(SubLibB)
set(BUILD_SHARED_LIBS ON)
add_subdirectory(SharedLib)
set(BUILD_SHARED_LIBS OFF)

Answer 2

If you want SubLibA and SubLibB always be static libraries you can use the STATIC keyword on the add_library command, e.g. add_library(SubLibA STATIC ${SOURCES}) By omitting the keyword for SharedLib you are still free to build it as static or shared lib by setting -DBUILD_SHARED_LIBS=ON on the CMake command line.