Can I add a library from the folder above? - cmake

Question

I can't add my static library to my project.
I have the following project structure:
+ root/
+ CmakeLists.txt // Include all projects
+ Base/
| + foo.cpp
| + CmakeLists.txt
+ App1/
| + app1.cpp
| + CmakeLists.txt // Requires Base lib
+ App2/
| + app2.cpp
| + CmakeLists.txt // Requires Base lib
I try to do it in the following way:
Base CmakeLists.txt:
cmake_minimum_required(VERSION 3.10.2)
add_library(Base STATIC foo.cpp)
App1 CmakeLists.txt:
cmake_minimum_required(VERSION 3.10.2)
project(App1)
add_executable(${CMAKE_PROJECT_NAME} app1.cpp)
include(../Base/CMakeLists.txt)
But I have the following error:
CMake Error at C:/DPA/Base/CMakeLists.txt:3 (add_library):
Cannot find source file:
foo.cpp
How I can properly setup library to include in all projects?

Answer 1

That's not how you use such a directory structure. Instead, in App1/CmakeLists.txt, go with
add_executable(App1 app1.cpp)
target_link_libraries(App1 Base)
This declares that App1 depends on Base and shall be linked against that library. "Linking" means not only passing the correct arguments to your linker, it also propagates include flags and other options to the compiler when building App1 sources.
If you intend to build only parts of your project, you can use an additional argument to add_executable, i.e.
add_executable(App1 EXCLUDE_FROM_ALL app1.cpp)
This way, when you build the default target, App1 won't be part of the build. You can still build it manually/upon request, e.g. when working with makefiles,
make App1
will build the executable App1 and everything that's required for it.