main.cpp

#include <cstddef>
#include <filesystem>
#include <iostream>
#include <memory>
#include <Shlobj.h>
#include <string>
#include <winver.h>
#include <wil/resource.h>

#include "version.hpp"

std::pair<std::unique_ptr<std::byte[]>, HRESULT> LoadFileVersionInfo(const std::filesystem::path& file, DWORD flags = 0)
{
	const DWORD size = GetFileVersionInfoSizeEx(flags, file.c_str(), nullptr);
	if (!size)
	{
		return { nullptr, HRESULT_FROM_WIN32(GetLastError()) };
	}

	auto data = std::make_unique<std::byte[]>(size);
	if (!GetFileVersionInfoEx(flags, file.c_str(), 0, size, data.get()))
	{
		return { nullptr, HRESULT_FROM_WIN32(GetLastError()) };
	}

	return { std::move(data), S_OK };
}

std::pair<Version, HRESULT> GetFixedFileVersion(const std::filesystem::path &file)
{
	const auto [data, hr] = LoadFileVersionInfo(file, FILE_VER_GET_NEUTRAL);
	if (FAILED(hr))
	{
		return { { }, hr };
	}

	VS_FIXEDFILEINFO *fixedFileInfo;
	unsigned int length;
	if (!VerQueryValue(data.get(), L"\\", reinterpret_cast<void **>(&fixedFileInfo), &length))
	{
		return { { }, HRESULT_FROM_WIN32(GetLastError()) };
	}

	return { Version::FromHighLow(fixedFileInfo->dwProductVersionMS, fixedFileInfo->dwProductVersionLS), S_OK };
}

std::pair<std::wstring, HRESULT> GetWindowsBuild()
{
	// Microsoft recommends this themselves
	// https://docs.microsoft.com/en-us/windows/desktop/SysInfo/getting-the-system-version
	wil::unique_cotaskmem_string system32;
	const HRESULT hr = SHGetKnownFolderPath(FOLDERID_System, KF_FLAG_DEFAULT, nullptr, system32.put());
	if (FAILED(hr))
	{
		return { { }, hr };
	}

	std::filesystem::path user32 = system32.get();
	user32 /= L"user32.dll";

	const auto [version, hr2] = GetFixedFileVersion(user32);
	if (SUCCEEDED(hr2))
	{
		return { version.ToString(), S_OK };
	}
	else
	{
		return { { }, hr2 };
	}
}

int main()
{
	const auto [build, hr] = GetWindowsBuild();
	if (SUCCEEDED(hr))
	{
		std::wcout << build << std:endl;
	}
}

version.hpp

#pragma once
#include <cstdint>
#include <fmt/format.h>
#include <string>
#include <Windows.h>
#include <winrt/Windows.ApplicationModel.h>

struct Version {
	uint16_t Major;
	uint16_t Minor;
	uint16_t Build;
	uint16_t Revision;

	inline std::wstring ToString() const
	{
		return fmt::format(fmt(L"{}.{}.{}.{}"), Major, Minor, Build, Revision);
	}

	inline static Version FromHighLow(DWORD high, DWORD low)
	{
		return { HIWORD(high), LOWORD(high), HIWORD(low), LOWORD(low) };
	}

	inline static Version FromPackageVersion(winrt::Windows::ApplicationModel::PackageVersion version)
	{
		return { version.Major, version.Minor, version.Build, version.Revision };
	}
};