CMAKE---Multiple directories

Overview

CMake is a directory-based project management tool. If your project has multiple directories, more CMakeLists.txt files should be created in your project directories.

Situation

As the following directories, each directory is a standalone module. For example:

1. the root target has its own source file(s) in ${ROOT}/src directory.
2. hello_object_lib is a OBJECT target, and it has its own including paths. So we use a CMakeLists.txt file for target management.
3. hello_shared_lib is a SHARED library target, the root project will link this shared library or provide for other projects.
4. hello_static_lib is a STATIC library target, this target will generate a static library file for other projects.

tree
.
├── CMakeLists.txt
├── hello_object_lib
│   ├── CMakeLists.txt
│   ├── inc
│   └── src
│       └── main.cc
├── hello_shared_lib
│   ├── CMakeLists.txt
│   ├── include
│   │   └── hello
│   │       └── hello.hpp
│   └── src
│       ├── hello.cc
│       ├── internal.cc
│       └── internal.hpp
├── hello_static_lib
│   ├── CMakeLists.txt
│   ├── include
│   │   └── hello
│   │       └── hello.hpp
│   └── src
│       ├── hello.cc
│       ├── internal.cc
│       └── internal.hpp
└── src
    └── main.cc

The content of root CMakeLists.txt is as follows. Each sub-directory should be added in this CMakeLists.txt.

In this CMakeLists.txt, we define a executable target multiple_exec, all of the other targets will be linked to this executable target. There’s a difference should be noticed. OBJECT target cannot be linked into other targets using target_link_libraries command before CMake V3.12. So if you use the older CMake version, you should use the

cmake_minimum_required(VERSION 3.21)

project(multiple_dirs
        VERSION 1.0
        DESCRIPTION "Multiple directory project"
        LANGUAGES CXX
)

# Add subdirectories with examples.
add_subdirectory(hello_object_lib)
add_subdirectory(hello_shared_lib)
add_subdirectory(hello_static_lib)

# add an example executable
add_executable(multiple_exec)

# add sources to the example executable
target_sources(multiple_exec PRIVATE src/main.cc)
# link libraries
target_link_libraries(
        multiple_exec
        PRIVATE hello_object_target hello_shared_target hello_static_target)

References

• My-Advanced-CMake-Repo