Build an executable

The status quo "Hello world!" project for C and C++ looks something like this:

#include <stdio.h>
int main() {
  puts("Hello world!");
  return 0;
}

cc main.c -o my-app
./my-app
#=> Hello world!

Instead of running cc main.c -o app, a "Hello world!" CMake project is a bit more involved:

#include <stdio.h>
int main() {
  puts("Hello world!");
  return 0;
}

cmake_minimum_required(VERSION 3.28)
project(my-project)
add_executable(my-app main.c)

cmake -B build
cmake --build build
./build/my-app

cmake_minimum_required() will error early if the CMake version is too outdated. This helps prevent weird "not found" error messages that are hard to debug from popping up 5 minutes into a long compilation process. project() defines a project name for this particular collection of CMake scripts & targets. One project can have multiple libraries and binaries. add_executable() tells CMake to create an executable using the C/C++ compiler with the given files as inputs. In this example that's just main.c but it could include more .c files or additional .a static libraries or .o object files.

The cmake -B build command tells CMake to generate the actual native C/C++ toolchain build scripts and other resources (for Visual Studio, Ninja, Make, or others) into the build/ folder. That's what the -B flag does. If you just run cmake it will clutter your current directory with lots of generated toolchain files. The cmake --build build command tells CMake to execute the native toolchain (that's the --build flag) from the build/ folder. --build is a distinct and different flag from -B.

Option A

# Puts all the generated build tooling files somewhere else
cmake -B build
cmake --build build

Option B

# Clutters your current directory with all the build tooling files
cmake .
cmake --build .

What is a target?

Probably the most important item is targets. Targets represent executables, libraries, and utilities built by CMake. Every add_library, add_executable, and add_custom_target command creates a target. For example, the following command will create a target named "foo" that is a static library, with foo1.c and foo2.c as source files.

add_library(foo STATIC foo1.c foo2.c)

— Key Concepts | CMake