case-insensitive-env.cpp

#include <Windows.h>

#include <array>
#include <iostream>
#include <exception>

[[noreturn]] void throw_last_error() {
	throw std::system_error{static_cast<int>(GetLastError()), std::system_category()};
}

#define die (throw_last_error(), false)

int main()
{
	constexpr auto varName = L"USERNAME";
	constexpr auto altName = L"uSeRNaME"; // sO RaNDoM?~

	std::array<wchar_t, 1024> str;
	
	try
	{
		GetEnvironmentVariable(varName, str.data(), str.size()) || die;
		std::wcout << varName << ": " << str.data() << '\n';

		GetEnvironmentVariable(altName, str.data(), str.size()) || die;
		std::wcout << altName << ": " << str.data() << '\n';

		return 0;
	}
	catch (const std::exception& err)
	{
		std::cerr << err.what() << '\n';
		return -1;
	}
}