Build Systems: CMake

After this lesson, you will be able to: Author a CMakeLists.txt for a multi-file C++ project; pull in dependencies with FetchContent or vcpkg.

CMake is the de facto C++ build system. Ugly, but every cross-platform C++ project uses it. Learn enough to build, link, and manage dependencies.

Prerequisites:Concurrency in C++

Why CMake won

C++ has no built-in build system. Every OS has different tooling (Visual Studio on Windows, Makefiles on Linux, Xcode on Mac). CMake generates the native build files for each. One CMakeLists.txt → all platforms. Alternatives (Bazel, Meson, Buck2) exist but CMake is what every library ships with.

Minimal CMakeLists.txt

Single-executable project.

tsx

cmake_minimum_required(VERSION 3.20)
project(myapp LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

# Add the executable
add_executable(myapp
    src/main.cpp
    src/user.cpp
)

target_include_directories(myapp PRIVATE include)
target_compile_options(myapp PRIVATE -Wall -Wextra -Wpedantic)

# Configure + build
# cmake -B build -DCMAKE_BUILD_TYPE=Release
# cmake --build build -j$(nproc)
# ./build/myapp

Library + dependencies via FetchContent

Pull a header-only or source dependency from GitHub.

tsx

include(FetchContent)

FetchContent_Declare(
    fmt
    GIT_REPOSITORY https://github.com/fmtlib/fmt.git
    GIT_TAG        10.1.1
)
FetchContent_MakeAvailable(fmt)

add_library(mylib STATIC src/mylib.cpp)
target_link_libraries(mylib PUBLIC fmt::fmt)

add_executable(myapp src/main.cpp)
target_link_libraries(myapp PRIVATE mylib)

vcpkg or Conan for big dependency graphs

Like npm for C++. vcpkg is the most-used in 2026.

json

# Install vcpkg (one-time)
# git clone https://github.com/microsoft/vcpkg
# ./vcpkg/bootstrap-vcpkg.sh

# Add a vcpkg.json manifest
{
  "name": "myapp",
  "version": "0.1.0",
  "dependencies": ["fmt", "boost", "sqlite3"]
}

# Configure with the vcpkg toolchain
# cmake -B build -DCMAKE_TOOLCHAIN_FILE=$VCPKG_ROOT/scripts/buildsystems/vcpkg.cmake

# In CMakeLists.txt:
# find_package(fmt CONFIG REQUIRED)
# target_link_libraries(myapp PRIVATE fmt::fmt)

Common mistakes

Global `include_directories()` / `link_directories()` (use target_* commands). Hardcoding compiler flags in CMakeLists (use presets + CMakePresets.json). Forgetting `find_package` REQUIRED, missing dep produces cryptic failure later. Skipping `CMAKE_BUILD_TYPE` (defaults to no optimization).

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