C++ Everywhere: How to Write Code for Windows, Linux, and macOS at Once

Someday You'll Write Code That Runs Everywhere

Imagine: you create a cool project in C++, everything works perfectly on Windows. Your friend asks you to build a version for Linux. You sigh, dive into the Makefile, change paths, compilers, stumble upon #ifdef _WIN32, and three hours later you get a binary that still crashes with a segmentation fault. Sound familiar?

Cross-platform development in C++ is not magic, but a set of disciplines and tools. In this article, we'll break down how to write code that works on Windows, Linux, and macOS without tears, with real code examples and ready-made solutions. Let's go!

Why C++ is Ideal for Cross-Platform (And Why It's a Pain)

C++'s strengths — compilability, performance, and memory control — make it the king of system programming. But you have to pay for it: each OS has its own APIs, compilers (MSVC, GCC, Clang), and file system peculiarities.

The main pitfalls:

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• Different header files — windows.h vs unistd.h
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• Different macros — _WIN32, __linux__, __APPLE__
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• Different compilers — MSVC doesn't like GCC extensions
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• Different libraries — dynamic loading (DLL vs .so)
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But don't worry — all these problems are solvable. The main thing is to choose the right approach from the start.

Tool #1: CMake — Your Universal Builder

If you're writing a cross-platform application in C++, your best friend is CMake. It's not a build system like Make, but a build file generator: it creates Makefiles for Linux/macOS and .sln for Visual Studio on Windows.

Here's a minimal CMakeLists.txt that works everywhere:

cmake_minimum_required(VERSION 3.16)\nproject(CrossPlatformApp VERSION 1.0 LANGUAGES CXX)\n\nset(CMAKE_CXX_STANDARD 17)\nset(CMAKE_CXX_STANDARD_REQUIRED ON)\n\n# Add executable\nadd_executable(myapp main.cpp utils.cpp)\n\n# Cross-platform handling\nif(WIN32)\n    target_compile_definitions(myapp PRIVATE PLATFORM_WINDOWS)\n    target_link_libraries(myapp PRIVATE ws2_32)  # sockets on Windows\nelseif(APPLE)\n    target_compile_definitions(myapp PRIVATE PLATFORM_MACOS)\n    target_link_libraries(myapp PRIVATE "-framework CoreFoundation")\nelse()\n    target_compile_definitions(myapp PRIVATE PLATFORM_LINUX)\nendif()

As you can see, target_compile_definitions allows you to set macros for each platform. In code, you use them like this:

#ifdef PLATFORM_WINDOWS\n    #include <windows.h>\n    void sleep_ms(int ms) { Sleep(ms); }\n#else\n    #include <unistd.h>\n    void sleep_ms(int ms) { usleep(ms * 1000); }\n#endif

CMake is the de facto standard. If your project doesn't use it, it's time to change your approach.

Boost and Qt: Ready-Made Solutions for Complex Tasks

Writing everything from scratch is for heroes and masochists. For cross-platform development in C++, there are mature libraries that hide OS differences.

Boost — Swiss Army Knife

Boost.Asio — for network programming (works on both Windows and Linux). Boost.Filesystem — for file operations (replaces std::filesystem if you have an old compiler). Example of cross-platform directory reading:

#include <boost/filesystem.hpp>\nnamespace fs = boost::filesystem;\n\nvoid list_files(const std::string& path) {\n    for (const auto& entry : fs::directory_iterator(path)) {\n        std::cout << entry.path().string() << std::endl;\n    }\n}

This code will compile on any OS without a single #ifdef.

Qt — Full-Featured Framework

If you need a GUI, networking, databases, or multithreading — Qt is your choice. It provides a unified API for all platforms. When