04. CMake Flow

CMake Flow

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Prerequisites

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1. What is flow of CMake

CMake follows a structured three-step workflow: Configure → Build → Install Each step has a clear and distinct purpose.

2. Workflow

2-1. Project Structure

A typical CMake project contains:

• CMakeLists.txt
• Source files (.cpp)
• Header files (.h / .hpp)

CMake uses CMakeLists.txt as the main entry point.

2-2. Out-of-Source Build

Create a separate build directory to keep generated files isolated:

/build

This prevents mixing source files with build artifacts.

2-3. Configure Step

Run the following command:

cmake -S . -B build

What happens during configure:

• Parses CMakeLists.txt
• Detects and configures compiler

• Generates build system files:

  • Makefile
  • .sln (Visual Studio)
  • build.ninja

• Creates:

  • CMakeCache.txt
  • CMakeFiles/

⚠️ No compilation happens at this stage.

2-3 (Optional). Configure Step Using CMakePresets

Instead of writing long CLI commands, you can define presets in:

CMakePresets.json

Usually placed at the same level as CMakeLists.txt.

cmake --preset <preset-name>

Important:

• cmake -S -B and cmake --preset both perform configure
• You should use only one of them

Example (CLI):

cmake -S . -B build \
  -DCMAKE_BUILD_TYPE=Release \
  -DOpenCV_DIR=... \
  -G Ninja

Example (Preset):

cmake --preset <preset-name>

• CLI → manual input
• Preset → predefined configuration (JSON)

2-4 Build Step (Compile + Link)

cmake --build build

• .cpp → .o / .obj (compile)
• .o / .obj → executable / library (link)

Inside the build/ directory, you may see:

• Object files (.o, .obj)
• Executables (.exe, binary)
• Static libraries (.lib, .a)
• Shared libraries (.dll, .so)

2-5 Install Step

cmake --build build --target install

Install takes build outputs and organizes them based on rules defined in CMakeLists.txt. When we process install, it calls cmake_install.cmake files

Typical structure:

install/
 ├── bin/
 ├── lib/
 ├── include/

Install is NOT just “cleaning up”.

It is copying and organizing build outputs into a structured layout for distribution or reuse.

3. Summary

Configure → Build → Install
   ↓          ↓        ↓
Setup     Compile   Package/Deploy

• cmake -S -B and cmake --preset both perform configure
• Presets are just a way to store configuration
• Build step performs actual compilation
• Install step prepares a clean, usable structure