Shouldn't Gdiplus::Image::GetWidth() and a bunch of other getters be "const"?

Question

Why aren't they const?

I believe that's flawed API design. Or am I missing something?

UINT GetWidth();
UINT GetHeight();
...

vs.

UINT GetWidth() const;
UINT GetHeight() const;
...

Answer 1

Hard to say. I'd agree, but perhaps there is something in the implementation that prevents them from being const, and that they didn't want to add overhead to hide. Nowdays we have the mutable keyword, but I think that is younger than this API.

Or maybe the designers of the API belong to the (sometimes shockingly large, imo) bunch of C++ developers who are hostile towards the const keyword, feeling that only makes things harder to use. I'm no Windows historian, so I can't tell you. :)

Answer 2

Flawed API design? C-style C++ headers? From the teams who brought us CString? Nah, can't be...

Seriously, though, don't expect GoTW-level C++ usage in any Win32 API, or more than a basic wrapper around the C-style handles. Herb Sutter has been busy with .NET:ing C++ rather than improving Microsoft library design. The WTL is as close as I've seen Microsoft come to modern C++, and that has led a rather obscure existence.

Answer 3

Strictly speaking you are probably right - the variable should be const.

I'm assuming you are talking about the Gdiplus C++ native API. If you look into the implementation of this code and the Gdiplus classes you'll find that most of the code is a basic wrapper around the Gdiplus Flat API functions (http://msdn.microsoft.com/en-us/library/ms533969(VS.85).aspx). This might make it either difficult to make the code const-correct... or (as another hinted at) it's Microsoft being typically not-very-modern-C++.

EDIT: Looking at the code for Gdiplus::Image::GetWidth() (in GdiPlusBitmap.h), it would have been easy for MS to implement many of the functions with the const modifier. They've done it with Image::GetType() and the code inside is pretty much identical to Image::GetWidth(), Image::GetHeight().