Advanced CMake Features

Introduction

CMake has several advanced features that can make your build system more powerful and flexible. In this lesson, we’ll cover:

  • Generator Expressions: Dynamic expressions evaluated at build time.
  • Toolchain Files: Customize the build for different compilers or platforms.
  • Exporting and Importing Targets: Share targets between projects.

Key Concepts

  • Generator Expressions: Allow you to write dynamic CMake code that adapts to the build configuration.
  • Toolchain Files: Specify compilers, flags, and paths for cross-platform development.
  • Exporting Targets: Share targets between projects using export() and install(EXPORT).

Code Sample

  1. Update your CMakeLists.txt:
cmake_minimum_required(VERSION 3.10)
project(GeneratorExpressionsDemo)

# Add an executable
add_executable(HelloWorld main.cpp)

# Conditionally add a compile definition for Debug builds
target_compile_definitions(HelloWorld PRIVATE
    $<$<CONFIG:Debug>:DEBUG_MODE>  # Define DEBUG_MODE only in Debug builds
)

# Conditionally add a compiler flag for Debug builds
target_compile_options(HelloWorld PRIVATE
    $<$<CONFIG:Debug>:-O0>  # Disable optimizations in Debug builds
)
  1. Write main.cpp:
#include <iostream>

int main() {
#ifdef DEBUG_MODE
    std::cout << "Hello World from Debug mode!" << std::endl;
#else
    std::cout << "Hello World from Release mode!" << std::endl;
#endif
    return 0;
}
  1. Build in Debug and Release modes:
mkdir build-debug
cd build-debug
cmake .. -DCMAKE_BUILD_TYPE=Debug
cmake --build .
./HelloWorld

cd ..
mkdir build-release
cd build-release
cmake .. -DCMAKE_BUILD_TYPE=Release
cmake --build .
./HelloWorld
  1. Output (Debug):
Hello World from Debug mode!
  1. Output (Release):
Hello World from Release mode!

Quiz

What is the purpose of generator expressions?

Generator expressions allow you to write dynamic CMake code that adapts to the build configuration.

How do you conditionally add a compiler flag for Debug builds?

You can conditionally add a compiler flag using target_compile_options(MyTarget PRIVATE $<$<CONFIG:Debug>:-O0>).

What does $<CONFIG:Debug> evaluate to in Release mode?

$<CONFIG:Debug> evaluates to 0 (false) in Release mode.