path_combine.cpp

#include <windows.h>
#include <pathcch.h>
#include <string>

#pragma comment(lib, "pathcch")

namespace impl
{
    void check(HRESULT const result)
    {
        if (result != S_OK)
        {
            throw result;
        }
    }

    void path_append(std::wstring & path, wchar_t const * const more, size_t const size)
    {
        path.resize(path.size() + 5 + size); // \\?\path\more

        check(PathCchAppendEx(&path[0],
                              path.size() + 1,
                              more,
                              PATHCCH_ALLOW_LONG_PATHS));

        path.resize(wcslen(path.c_str()));
    }

    void path_append(std::wstring & path, wchar_t const * const more)
    {
        path_append(path, more, wcslen(more));
    }

    void path_append(std::wstring & path, std::wstring const & more)
    {
        path_append(path, more.c_str(), more.size());
    }

    void path_combine(std::wstring & path) {}

    template <typename First, typename ... Rest>
    void path_combine(std::wstring & path, First const & first, Rest const & ... rest)
    {
        path_append(path, first);
        path_combine(path, rest ...);
    }
}

template <typename ... T>
std::wstring path_combine(T const & ... paths)
{
    std::wstring path;
    impl::path_combine(path, paths ...);
    return path;
}

int main()
{
    std::wstring path = path_combine(L"C:\\root", L"one", L"two", L"three", L"four");

    printf("%ls\n", path.c_str());
}