# CMake Generators

**A generator is the backend build system CMake produces**. CMake reads `CMakeLists.txt` and generates build files for your chosen generator: Makefiles, Ninja, Visual Studio, Xcode, etc. Use `-G` to select:

```bash
cmake -G "Unix Makefiles" ..
cmake -G "Ninja" ..
cmake -G "Visual Studio 16 2019" ..
```

List available generators:

```bash
cmake --help       # shows all available generators
```

Common generators:

- **Unix Makefiles** — default on Linux/macOS, produces `Makefile`
- **Ninja** — fast, parallel-friendly, requires `ninja` installed
- **Visual Studio 16 2019** — Windows MSVC compiler
- **Xcode** — macOS, integrates with Xcode IDE
- **Ninja Multi-Config** — single build tree, multiple configurations

Single-config generators (one per build tree):

```bash
mkdir build-debug && cd build-debug
cmake -DCMAKE_BUILD_TYPE=Debug ..

mkdir build-release && cd build-release
cmake -DCMAKE_BUILD_TYPE=Release ..
```

Multi-config generators (all in one tree):

```bash
mkdir build && cd build
cmake -G "Ninja Multi-Config" ..
cmake --build . --config Debug
cmake --build . --config Release
```

Switching generators:

CMake caches the generator choice. To switch, delete `CMakeCache.txt` and `CMakeFiles/`:

```bash
rm -rf CMakeCache.txt CMakeFiles/
cmake -G "Ninja" ..
```

Or use a separate build directory for each generator.

Building with a specific generator:

```bash
cmake --build . -j 4        # use generator's parallel build
cmake --build . --verbose   # show compiler commands
cmake --build . --target myapp  # build specific target
```

Ninja is popular for speed (supports parallel builds by default). Visual Studio generators integrate with the IDE. Unix Makefiles are traditional and portable.

Choose a generator based on your platform and preferences. Most projects default to Unix Makefiles on Linux/macOS, Visual Studio on Windows. Ninja is preferred by many developers for faster iteration.