CMake Notes

Configure Clangd

CompileFlags:
  CompilationDatabase: ../build/

cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=YES ...

Public VS Private VS Interface

Some target properties

• SOURCES, INTERFACE_SOURCES;
• LINK_LIBRARIES, INTERFACE_LINK_LIBRARIES;
• COMPILE_DEFINITIONS, INTERFACE_COMPILE_DEFINITIONS.

To diagnostics:

get_target_property(ARG1 Tutorial SOURCES)
get_target_property(ARG2 Tutorial INTERFACE_SOURCES)

get_target_property(ARG3 Tutorial INCLUDE_DIRECTORIES)
get_target_property(ARG4 Tutorial INTERFACE_INCLUDE_DIRECTORIES)

get_target_property(ARG5 Tutorial LINK_LIBRARIES)
get_target_property(ARG6 Tutorial INTERFACE_LINK_LIBRARIES)

get_target_property(ARG7 Tutorial COMPILE_DEFINITIONS)
get_target_property(ARG8 Tutorial INTERFACE_COMPILE_DEFINITIONS)
message(${ARG1}, ${ARG2},\n
  ${ARG3}, ${ARG4},\n
  ${ARG5}, ${ARG6},\n
  ${ARG7}, ${ARG8})

Pass CMake Properties into Header Files

// CMakeLists.txt
project(Tutorial VERSION 1.0)
configure_file(TutorialConfig.h.in TutorialConfig.h)

#define Tutorial_VERSION_MAJOR @Tutorial_VERSION_MAJOR@
#define Tutorial_VERSION_MINOR @Tutorial_VERSION_MINOR@

Add a Library / Module (And Add an OPTION to Switch)

# CMakeLists.txt
cmake_minimum_required(VERSION 3.30 FATAL_ERROR)

set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD "0e5b6991-d74f-4b3d-a41c-cf096e0b2508")
set(CMAKE_CXX_FLAGS "-stdlib=libc++")

project(Hello CXX)

set(CMAKE_CXX_STANDARD 23)
set(CMAKE_CXX_STANDARD_REQUIRED True)
set(CMAKE_EXPORT_COMPILE_COMMANDS True)
set(CMAKE_CXX_MODULE_STD True)

add_executable(Hello main.cpp)

option(USE_MODULE "Whether use the form of C++20's module" YES)

add_subdirectory(mylib)
if(NOT USE_MODULE)
  target_include_directories(Hello PRIVATE "${PROJECT_SOURCE_DIR}/mylib")
else()
  target_compile_definitions(Hello PRIVATE USE_MODULE)
endif()
target_link_libraries(Hello PRIVATE Mylib)

# mylib/CMakeLists.txt
add_library(Mylib SHARED)
if(USE_MODULE)
  target_compile_definitions(Mylib PRIVATE USE_MODULE)
  target_sources(Mylib PUBLIC FILE_SET CXX_MODULES FILES mylib.cpp)
else()
  target_sources(Mylib PRIVATE mylib.cpp)
endif()

// mylib/mylib.h
#pragma once
namespace mylib { void print(); }

// mylib/mylib.cpp
#ifdef USE_MODULE
export module mylib;
import std;
export
#else
#include "mylib.h"
#include <print>
#endif
    namespace mylib {
void print() {
#ifdef USE_MODULE
  std::println(" with C++ modules!");
#else
  std::println(" without C++ modules!");
#endif
}
} // namespace mylib

// main.cpp
#ifdef USE_MODULE
import mylib;
import std;
#else
#include "mylib.h"
#include <print>
#endif
int main() { std::print("Hello"), mylib::print(); }

// CMakePresets.json
{
  "version": 9,
  "configurePresets": [
    {
      "name": "default",
      "binaryDir": "${sourceDir}/build",
      "displayName": "Default Config",
      "description": "Default build using Ninja generator",
      "generator": "Ninja",
      "cacheVariables": {
        "CMAKE_CXX_COMPILER": "/usr/bin/clang++",
        "CMAKE_EXE_LINKER_FLAGS": "-fuse-ld=lld",
        "CMAKE_AR": "/usr/bin/llvm-ar",
        "CMAKE_RANLIB": "/usr/bin/llvm-ranlib"
      }
    }
  ]
}

To validate:

$ cmake --preset=default -DUSE_MODULE=NO -B ./build && cmake --build ./build && ./build/Hello

Reference

• CMake: Public VS Private VS Interface
• Examples of when PUBLIC/PRIVATE/INTERFACE should be used in cmake
• CMake Tutorial
• Math functions for graphics and geometric calculations