Including CMake Project Libraries

Question

I'm in the process of putting together a small c++ project using CMake for the first time. My current project structure is

├── bch
│   ├── CMakeLists.txt
│   ├── gf
│   │   ├── CMakeLists.txt
│   │   ├── include
│   │   │   └── gf.h
│   │   └── src
│   │       └── gf.cpp
│   ├── include
│   │   └── bch.h
│   └── src
│       └── bch.cpp
├── bsc
│   ├── CMakeLists.txt
│   ├── include
│   │   └── bsc.h
│   └── src
│       └── bsc.cpp
├── CMakeLists.txt
├── .gitignore
└── main.cpp

Currently I have gf as a subdirectory of bch. The contents of bch/CMakeLists is

cmake_minimum_required(VERSION 3.17)
project(bch VERSION 0.1.0)

# Targets
add_library(bch STATIC src/bch.cpp)

# Dependant
add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/gf)
target_link_libraries(bch PUBLIC gf)

# Export to dependants
target_include_directories(bch PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include)

I would like to take the gf CMake project and place outside of the directory path of bch. This doesn't seem to be a supported structure when using the add_subdirectory command unless I'm missing something. Generally, what would be the current "Best Practice" for accomplishing my goal of decoupling the directory structure from the dependency tree?

"I would like to take the `gf` CMake project and place outside of the directory path of `bch`. This doesn't seem to be a supported structure when using the `add_subdirectory` command" - **Why** do you think it is not supported? If you get an error `add_subdirectory not given a binary directory`, then see [that question](https://stackoverflow.com/q/50408169/3440745) and the answer about the way to resolve it. — Tsyvarev, Jul 19 '20 at 18:36
That's the current configuration that I've opted for until I can get around to packaging the `gf` library into a module. I'm using the `bch/build` directory for the `gf` binaries which seems to work. The various blog posts I was reading seemed to imply that `add_subdirectory` is recommended for tightly coupled projects in-tree. — ytgsyk4h, Jul 19 '20 at 19:12

b00rt00s · Accepted Answer · 2020-07-19T18:54:28.723

If you want to decouple the project from dependencies, then I would suggest splitting cmake project into two separate, exporting the dependent target and then importing it with 'find_package'. Here is quick google find for that topic: https://visualgdb.com/tutorials/linux/cmake/find_package

[edit]

For a more general approach I suggest cmake documentation:

https://cmake.org/cmake/help/latest/command/find_package.html#command:find_package

https://cmake.org/cmake/help/latest/module/CMakePackageConfigHelpers.html

https://cmake.org/cmake/help/v3.18/command/install.html#export

The idea is:

In a dependency project to generate a '*ConfigVersion.cmake' file, install all needed files (headers, binaries and *ConfigVersion.cmake) using the 'EXPORT' in parameter the 'install' command.
In a final project use 'find_package' to import the dependency.

For bigger library projects I also suggest using namespaces to allow importing only selected parts of the library.

Thanks for the link, though the walkthrough is pretty tightly coupled to VS environment. The issue I see with find_package() functionality is all the additional cruft necessary to cleanly package up the project. Even with the added complexity, it may end up being the way to go. I found [this](https://stackoverflow.com/questions/33534115/preferred-cmake-project-structure) while searching for some answers. — ytgsyk4h, Jul 19 '20 at 18:26
I've updated the answer with a more general description. I hope it will help You. — b00rt00s, Jul 19 '20 at 18:55

Including CMake Project Libraries

1 Answers1