Question

I found this source code:

inline GUID& WString2Guid(wstring src)
{
    static GUID result;
    HRESULT hr = ::CLSIDFromString(W2OLE(const_cast<WCHAR*>(src.c_str())), &result);
    if (FAILED(hr)) {
        //ERROR: The string '%s' is not formatted as a GUID!
        throw(E_INVALIDARG);
    }
    return result;
}

What’s the use of returning a reference here? The calling code cannot get a reference anyway because the variable would have left its scope by then. So does this little & sign make any difference?

To clarify/extend the question: In the same example program, the function is called as

GUID guid = WString2Guid(id); // way 1

If I wanted to make use of the reference, wouldn’t I have to call

GUID& guid = WString2Guid(id); // way 2

instead?

And another question; why is the CLSIDFromString function called with the :: scope operator before? This would only make any sense if there was another local function declared with the same name, wouldn’t it?

Answer 1

No. result is a static local variable, so it will exist even after the function exit. Don’t confuse this with non-static local variable.

:: in ::CLSIDFromString tells the compiler to choose CLSIDFromString from the global namespace, in case if there are many definition of CLSIDFromString defined in other namespace(s), visible at the call-site.