Cmake tutorial Step3 (requirements for adding libraries)

CMake Official documents

Refer to the official cmake3.24 Course translation
https://cmake.org/cmake/help/v3.24/guide/tutorial/index.html
https://gitlab.kitware.com/cmake/cmake/-/tree/master/Help/guide/tutorial
step3
https://cmake.org/cmake/help/v3.24/guide/tutorial/Adding%20Usage%20Requirements%20for%20a%20Library.html
My warehouse :
https://github.com/FRBoiling/cmake-tutorial.git

The use requirements of the library allow better control over the links and included lines of the library or executable , At the same time, it can better control CMake The transfer attribute of the target in .

The main command

• target_compile_definitions()
• target_compile_options()
• target_include_directories()
• target_link_libraries()

Refactoring project

Let's base ourselves on CMake course Step2 Refactoring the project in (Step3), To meet modern CMake Requirements for use in .
Let's first state , library MathFunctions Any links to , except MathFunctions Beyond itself , All need to include the current source directory .
therefore , This may become an interface usage requirement .
remember INTERFACE It means what consumers need but producers don't need . stay MathFunctions/CMakeLists.txt The changes are as follows ：

add_library(MathFunctions mysqrt.cxx)

# state that anybody linking to us needs to include the current source dir to find MathFunctions.h, while we don't.
target_include_directories(MathFunctions
          INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}
          )

Now we have designated MathFunctions Requirements for use of .
Safely from the top CMakeLists.txt Delete in EXTRA_INCLUDES Use of variables , Find the following location to change :

...
# add the MathFunctions library
if(USE_MYMATH)
  add_subdirectory(MathFunctions)
  list(APPEND EXTRA_LIBS MathFunctions)
  # list(APPEND EXTRA_INCLUDES "${PROJECT_SOURCE_DIR}/MathFunctions")
endif()

...
# add the binary tree to the search path for include files so that we will find TutorialConfig.h
target_include_directories(Tutorial PUBLIC
                           "${PROJECT_BINARY_DIR}"
                          #  ${EXTRA_INCLUDES}
                           )

Once that is done , function cmake Executable or cmake-gui To configure the project , Then use the build tool of your choice or use cmake——build Build it . From build directory .
After refactoring , Complete top-level directory CMakeLists.txt The contents are as follows

cmake_minimum_required(VERSION 3.10)

# set the project name and version
project(Tutorial VERSION 1.0)

# specify the C++ standard
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED True)

# should we use our own math functions
option(USE_MYMATH "Use tutorial provided math implementation" ON)

# configure a header file to pass some of the CMake settings
# to the source code
configure_file(TutorialConfig.h.in TutorialConfig.h)

# add the MathFunctions library
if(USE_MYMATH)
  add_subdirectory(MathFunctions)
  list(APPEND EXTRA_LIBS MathFunctions)
endif()

# add the executable
add_executable(Tutorial tutorial.cxx)

target_link_libraries(Tutorial PUBLIC ${EXTRA_LIBS})

# add the binary tree to the search path for include files
# so that we will find TutorialConfig.h
target_include_directories(Tutorial PUBLIC
                           "${PROJECT_BINARY_DIR}"
                           )

test

Now let's update USE_MYMATH Value .
The simplest way is to use it in the terminal cmake-gui or ccmake.
You can also modify this option from the command line , as follows
cmake …/Step3 -DUSE_MYMATH=ON
perhaps
cmake …/Step3 -DUSE_MYMATH=OFF

cd Step3_build
cmake ../Step3 -DUSE_MYMATH=ON
cmake --build .