When you work on a C project, you need a way to transform your human-readable source code into an executable program. This process is managed by a build system. A build system automates the steps required to compile, link, and package your code, making sure everything is done in the right order and only when necessary. Some of the most common build systems are Make, Ninja, and Visual Studio.

Each build system has its own way of describing how files should be built. For example:

• Make uses Makefile scripts;
• Ninja uses its own fast, minimal build files;
• Visual Studio uses solution and project files.

Choosing the right build system can impact how quickly your project builds, how easy it is to debug, and which platforms you can support. If you want your project to be portable and easy to build on different machines, you need a way to generate the correct build files for each system.

This is where CMake becomes essential. CMake does not build your code directly. Instead, it takes your project's configuration and produces the necessary build files for your chosen build system. This process is handled by something called a generator.

When you run CMake, you specify which generator to use. The generator tells CMake what kind of build files to create. For instance, you might use the "Unix Makefiles" generator on Linux, the "Ninja" generator for fast incremental builds, or the "Visual Studio" generator on Windows. By choosing the right generator, you can target different development environments and toolchains without changing your project's source code.

CMake supports many generators out of the box. You can see the full list by running cmake --help in your terminal. When you invoke CMake, you can select a generator using the -G flag, like this:

cmake -G "Ninja" ..

This command tells CMake to generate build files suitable for the Ninja build system. If you do not specify a generator, CMake will choose a default based on your platform.