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Brief CMake Tutorial

February 21, 2021

1. CMake is a build system

A build system is a tool that specifies which files need to be compiled for which executable and specifies their dependencies. A build system specifies which files need to be compiled to which executables. It configures the build process.

For example, a project may need to output:

  • Library A (libA.cpp, libA.h)
  • Executable A (execA.cpp, execA.h)
  • Library B (libB.cpp, libB.h)

Such that:

  • Executable A depends on Library A
  • Library B depends on Library A

We can define these files, outputs and dependencies in a build system. Then, the build system will produce the correct outputs.

Essentially, a build system configures the build process.

2. Targets and Linking

A target is an output: either a library or an executable. A library is an output that cannot be executed.

Targets can be libraries or executables. Dependencies are defined between targets. Files are attached to targets.

2.1 Define Targets

We can define a target by using the add_executable or add_library command:

add_executable(name_of_exec_target
    execA.cpp
    otherFile.cpp
    ...
)

add_library(name_of_library_target
    libA.cpp
    otherFile.cpp
)

2.2 Add header files to targets

In addition to the .cpp files added to the target, you can add an include directory to the target using target_include_directories . This will allow you to #include <...>.

Consider:

/
    /src
        main.cpp
    /include
        a.h
        b.h
    CMakeLists.txt

main.cpp:

#include <a.h>
#include <b.h>
// ...

CMakeLists.txt

cmake_minimum_required(VERSION 2.8.11)
project(my_project_name)

add_executable(my_program
    src/main.cpp
)

target_include_directories(my_program
    include
)

2.3 Specify dependencies between targets

We can specify dependencies of libraries of executables with target_link_libraries . Note that executables cannot be dependencies of other executables.

Consider:

/
    lib/
        myLib/
            include/
            src/
                myLib.cpp
    include/
    src/
        main.cpp
    CMakeLists.txt

CMakeLists.txt

cmake_minimum_required(VERSION 2.8.11)
project(my_project_name)

# Define library target "my_lib_name"
add_library(my_lib_name
    lib/myLib/src/myLib.cpp
)
target_include_directories(my_lib_name
    lib/myLib/include
)

# Define library target "my_program"
add_executable(my_program
    src/main.cpp
)
target_include_directories(my_program
    include
)

# Define dependency of my_program on my_lib_name
target_link_libraries(my_program
    my_lib_name
)

Written by Joel Tio who develops anything he finds interesting and tries to fit math into them. Check out the home page or his GitHub!

© 2021, Joel Tio