How to Effectively Manage Dependencies in CMake: A Guide to Local Dependencies, Library Targets, and Project Structure?

Dependencies Management in CMake: Source, Library, and CMakeLists.txt

In CMake, managing dependencies between source files, libraries, and CMakeLists.txt ensures a well-structured and efficient project. This article explores strategies to effectively handle dependencies in a complex project involving multiple libraries and executables.

Local Dependencies: An Advantage

Setting up local dependencies simplifies dependency management by specifying dependencies at the source and link levels within each subdirectory's CMakeLists.txt. This approach provides a clear hierarchy and avoids unnecessary bloating by excluding irrelevant dependencies.

Example Project Structure and CMakeLists.txt

Consider a project with interconnected libraries and an executable:

Lib
  - LibA
    - CMakeLists.txt
    - Src
      - a.cc
    - Inc
      - a.h
  - LibB
    - CMakeLists.txt
    - Src
      - b.cc
    - Inc
      - b.h
  - LibC
    - CMakeLists.txt
    - Src
      - c.cc
    - Inc
      - c.h

App1
  - CMakeLists.txt
  - Src
    - main.cc

Library CMakeLists.txt (LibA, LibB, LibC)

include_directories(Inc ../LibC/Inc)
add_subdirectory(../LibC LibC)
add_library(LibA Src/a.cc Inc/a.h)
target_link_libraries(LibA LibC)

include_directories(Inc)
add_library(LibB Src/b.cc Inc/b.h)

include_directories(Inc ../LibB/Inc)
add_subdirectory(../LibB LibB)
add_library(LibC Src/c.cc Inc/c.h)
target_link_libraries(LibC LibB)

App1 CMakeLists.txt

cmake_minimum_required(VERSION 2.8)
project(App1 CXX)

file(WRITE "Src/main.cc" "#include \"a.h\"\n#include \"b.h\"\nint main()\n{\na();\nb();\nreturn 0;\n}")
...
include_directories(../Lib/LibA/Inc ../Lib/LibB/Inc)
add_subdirectory(../Lib/LibA LibA)
add_subdirectory(../Lib/LibB LibB)
add_executable(App1 Src/main.cc)
target_link_libraries(App1 LibA LibB)

Library Dependency Graph

The dependency graph for this project: App1 -> LibA -> LibC -> LibB App1 -> LibB

Strategies for Managing Multiple Dependencies

Several approaches exist for managing multiple dependencies:

1. Build Libraries in the Same Project:
   This approach consolidates libraries and the executable within the same project, facilitating dependency resolution.
2. Build Libraries in Separate Projects:
   For static, infrequently modified libraries, this strategy may be preferred to avoid cluttering the main project.

Best Practices

• Create full-featured library targets that include header and library paths.
• Use PUBLIC/PRIVATE modifiers in target_link_libraries to control header inclusion visibility.
• Utilize the find_package command to manage dependencies with external, pre-built libraries.

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