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INTRODUCTION

These are some notes extracted from to talks on CppCon2017 and BoostCon 2018. The purpose of these notes is to explain as short as possbile to the developer, what he or she has to do to provide an usable library. For more detailes information, please refer to the videos.

CMAKE BASICS

  • CMake is no build system.
  • Not a build system!
  • CMake is a "cross-plattform C++ build generator"
  • CMake is code, hence treate it accordingly, e.g. DRY

The following are from Pfeifer2017 [2] - 03:45 :

CMake Directories

  • Every directory, that contains CMakeLists.txt
  • Hence, directories added with add_subdirectory() must also contain a CMakeLists.txt

Scripts

  • has extension .cmake
  • can be excuted with cmake -P
  • Not all commands are supported
  • HelloWorld
    • create a file and name it hello.cmake
    • paste message("----- Hello World! Bests, CMake -----")
    • run with cmake -P hello.cmake

Module

  • scripts located in CMAKE_MODULE_PATH
  • can be loaded with include()

Targets

  • If you compare CMake usage to OOP (Pfeifer2017 - 17:20) then
    • Targets compare to objects
    • add_executable() and add_library() compare to thier respective constructors
    • properties compare to thier respective member variables
    • and e.g. target_link_library() compate to member functions

EXPORTING AND IMPORTING

FIND AND CONFIG

Find-Module:

  • Use when 3rd-Party-Libraries do not support CMake

Config-Module:

  • Provided by developer of library

KEYWORDS

e.g. for:

 targe_link_library(<target>
   <PRIVAT|PUBLIC|INTERFACE> <item>
 )

we should use the following keywords:

NEEDED BY ME NOT NEEDED BY ME
NEEDED BY DEPENDENCY PUBLIC INTERFACE
NOT NEEDED BY DEPENDENCY PRIVATE :-)
- Pusz2018 - 00:11:30

Alternative Explanation:

Keyword
Usage Requirement INTERFACE
Build Requirement PRIVATE
Build & Usage Requirement PUBLIC
- Bahadir2018 - 00:08:40

CMAKE APPLIED

In the following, some basic CMake concepts are applied to an upstream (provided) library 'Foo' and a downstream (consumed) app 'Bar'.

UPSTREAM LIBRARY

CMAKE STRUCTURE

This is an example for the structure of a CMakeLists.txt from Pfeifer2017 - 43:06

toplevel
|
|-- CMakeLists.txt
    |-- add_library and correponding install
    |-- install
    |   |-- FooConfig.cmake
    |   |-- FooConfigVersion.cmake
    |   |-- FooTargets.cmake
    |-- include
    |   |-- CMakePackageConfigHelpers
            |-- generates FooTargets.cmake

FooConfig.cmake - manually written and installed

FooTagets.cmake

  • generaed by cmake (Pfeifer2017 - 40:25) with install(EXPORT): The EXPORT form generates and installs a CMake file containing code to import targets from the installation tree into another project." - CMakeDocInstall

FOLDER STRUCTURE

|-- buil_helloCMake
└───helloCMake
    └───Foo
        ├───cmake
        └───src

INVOKING

cmake ..\helloCMake\Foo\ -DCMAKE_INSTALL_PREFIX="install"
cmake --build . --target install

DOWNSTREAM APP

YET TO COME

REFERENCES

NOT COVERED (YET)

  • generator expressions
  • macros and functions
  • cpack
  • ctest

CONAN AND CMAKE