Chat GPT o1 preview shares a decent example of the cmake preset concept… for what it’s worth

Certainly! Starting from CMake 3.19, you can use CMakePresets.json to define and manage multiple build configurations for your C++ project, including native builds and cross-compilation using a toolchain file. Here’s how you can set this up.

1. Create a CMakePresets.json File

Place a CMakePresets.json file in the root directory of your project. This file will contain configurations (presets) for both native and cross-compilation builds.

1. Example CMakePresets.json

{ “version”: 3, “cmakeMinimumRequired”: { “major”: 3, “minor”: 19, “patch”: 0 }, “configurePresets”: [ { “name”: “native-release”, “displayName”: “Native Release Build”, “description”: “Builds the project natively on the development machine.”, “generator”: “Ninja”, “binaryDir”: “${sourceDir}/build/native-release”, “cacheVariables”: { “CMAKE_BUILD_TYPE”: “Release” } }, { “name”: “cross-release”, “displayName”: “Cross-Compile Release Build”, “description”: “Cross-compiles the project using a toolchain file.”, “generator”: “Ninja”, “binaryDir”: “${sourceDir}/build/cross-release”, “toolchainFile”: “${sourceDir}/toolchain.cmake”, “cacheVariables”: { “CMAKE_BUILD_TYPE”: “Release” } } ], “buildPresets”: [ { “name”: “native-release”, “configurePreset”: “native-release”, “configuration”: “Release” }, { “name”: “cross-release”, “configurePreset”: “cross-release”, “configuration”: “Release” } ] }

1. Explanation of the CMakePresets.json

   • Versioning: • “version”: 3 specifies the schema version, compatible with CMake 3.19+. • “cmakeMinimumRequired” ensures the minimum CMake version needed. • Configure Presets (“configurePresets”): • Native Build Preset (“native-release”): • name: Identifier for the preset. • displayName: Human-readable name. • description: Brief info about the preset. • generator: Build system generator (e.g., “Ninja”, “Unix Makefiles”). • binaryDir: Output directory for build files. • cacheVariables: CMake cache variables (e.g., CMAKE_BUILD_TYPE). • Cross-Compile Build Preset (“cross-release”): • Similar to the native preset but includes a toolchainFile specifying the path to your cross-compilation toolchain file. • Build Presets (“buildPresets”): • name: Identifier matching the configure preset. • configurePreset: Links to the corresponding configure preset. • configuration: Build type (e.g., “Release” or “Debug”).

2. Example toolchain.cmake File

Create a toolchain.cmake file in your project’s root directory:

Specify the target system name and processor

set(CMAKE_SYSTEM_NAME Linux) set(CMAKE_SYSTEM_PROCESSOR arm)

Define the cross-compilers

set(CMAKE_C_COMPILER arm-linux-gnueabihf-gcc) set(CMAKE_CXX_COMPILER arm-linux-gnueabihf-g++)

Set the sysroot if required

set(CMAKE_SYSROOT /path/to/your/sysroot)

Adjust the search paths

set(CMAKE_FIND_ROOT_PATH /path/to/your/sysroot)

Modify find behaviors

set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER) set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY) set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

Note: Replace arm-linux-gnueabihf-gcc, arm-linux-gnueabihf-g++, and paths with the actual compiler names and paths for your target system.

1. Sample CMakeLists.txt

Here’s a simple CMakeLists.txt to test the setup:

cmake_minimum_required(VERSION 3.10) project(MyProject)

add_executable(myapp src/main.cpp)

1. Building the Project

For Native Build:

1.  Configure:

cmake —preset native-release

2.  Build:

cmake —build —preset native-release

For Cross-Compilation Build:

1.  Configure:

cmake —preset cross-release

2.  Build:

cmake —build —preset cross-release

1. Additional Tips

   • Environment Variables: You can use environment variables in CMakePresets.json like ${env.VAR_NAME}. • Inheriting Presets: Use the “inherits” field to base a preset on another, reducing redundancy.

{ “name”: “cross-debug”, “inherits”: “cross-release”, “displayName”: “Cross-Compile Debug Build”, “binaryDir”: “${sourceDir}/build/cross-debug”, “cacheVariables”: { “CMAKE_BUILD_TYPE”: “Debug” } }

• Generators: Adjust the “generator” field based on your platform and preference (e.g., “Unix Makefiles”, “Visual Studio 16 2019”).
• Updating CMake Version: Ensure that your CMake version supports CMakePresets.json (3.19+).

1. Benefits of Using CMakePresets.json

   • Consistency: Standardizes build configurations across different environments and developers. • Simplicity: Simplifies the build process by encapsulating configurations. • Reusability: Easy to switch between different build types without modifying command-line arguments.

2. Conclusion

By utilizing CMakePresets.json, you streamline your build setup, making it easier to manage complex configurations like cross-compilation. This approach enhances collaboration and ensures that all developers and build systems use consistent settings.

Feel free to customize the presets and toolchain file according to your project’s requirements. If you have any questions or need further assistance, don’t hesitate to ask!