Link CMake subprojects with one another - c++

Question

I would like to link projects that are added via add_subproject with one another. Suppose i have a project structure like this:
(root)
I--exec
I--"some source files"
I--CMakeLists.txt
I--lib
I--"some source files"
I--CMakeLists.txt
I--CMakeLists.txt
Is there some way i can have my root level CMakeLists.txt just sort-of as a workspace file? So it behaves like a .sln from Visual Studio?
I tried this, to give you an idea of what i mean:
cmake_minimum_required(VERSION 2.8)
project(test)
add_subdirectory(exec)
add_subdirectory(lib)
target_link_libraries(exec lib)
target_include_directories(exec lib/include)
Obviously, it threw a config error at the second last line, stating that i cannot do that because exec is not built by this file (the current CMakeLists.txt?). Is there some way to achive what i want to do?

Answer 1

For CMake >= 2.8.10, the usage of target_link_libraries and target_include_directories is incorrect.
They should specify the target SYSTEM|BEFORE|PUBLIC|INTERFACE|PRIVATE; prefixed by LINK_ on target_link_libraries.
As a side-note, just for clear dependency management (IMHO):
In your root CMakeLists.txt there should be no target_link_libraries nor target_include_directories, they should be in the subproject. So your root CMakeLists, for example, should be:
cmake_minimum_required(VERSION 2.8)
project(test)
add_subdirectory(lib)
add_subdirectory(exec)
In your exec/CMakeLists.txt:
add_executable (exec main.cpp)
target_link_libraries (exec LINK_PUBLIC lib)
target_include_directories (exec PUBLIC ${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_CURRENT_SOURCE_DIR}/../lib)
In your lib/CMakeLists.txt:
add_library (lib libmain.cpp)
target_include_directories (lib PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
I'm not sure if it makes a difference, but I use the add_subdirectory for the library before the executable.