Win32FileHandle.cpp

#include <memory>
#include <cassert>
#include <Windows.h>

struct FileHandle
{
    ::HANDLE fileHandle;

    //implicit
    FileHandle(::HANDLE h) noexcept
        : fileHandle{h}
    {}

    //implicit
    FileHandle(std::nullptr_t = nullptr) noexcept
        : FileHandle{ INVALID_HANDLE_VALUE }
    {}

    operator ::HANDLE() noexcept { return fileHandle; }

    explicit operator bool() noexcept { return fileHandle != INVALID_HANDLE_VALUE; }
};

bool operator== (FileHandle lhs, FileHandle rhs) noexcept
{
    return lhs.fileHandle == rhs.fileHandle;
}

bool operator!= (FileHandle lhs, FileHandle rhs) noexcept
{
    return !(lhs == rhs);
}

struct FileCloser
{
    using pointer = FileHandle;

    void operator()(pointer p) const noexcept
    {
        (void)::CloseHandle(p.fileHandle);
    }
};

using UniqueFile = std::unique_ptr<void, FileCloser>;

struct LocalMemoryDeleter
{
    void operator()(void* p) const noexcept
    {
        (void)::LocalFree(p);
    }
};

using UniqueLocalMemory = std::unique_ptr<void, LocalMemoryDeleter>;

int main()
{
    {
        UniqueFile f;
        assert(f.get().fileHandle == INVALID_HANDLE_VALUE);
        f.reset(::CreateFile(LR"(.\Bar.txt)", GENERIC_WRITE, {}, {}, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, {}));
        if (f)
        {
            const unsigned char buffer[] = "hello";
            ::WriteFile(f.get(), buffer, sizeof(buffer), {}, {});
        }
       
    }

    {
        const auto h = UniqueLocalMemory{ ::LocalAlloc(LMEM_FIXED, 20) };
        *static_cast<int*>(h.get()) = 233;
    }
}