Re: Printing Enum Variable Re: Linux World

[Florian Weimer <fw@cygnus.stuttgart.netsurf.de>]

Samuel Mize <smize@imagin.net> writes:

>   /* one of these must be right, the other wrong */
>   SetWindow (W1, color, attribs);
>   SetWindow (W1, attribs, color);

This reminds me of another C problem which is related to some point.
For example, there once was a function called ReleaseDC(HWND hwnd,
HDC hdc) on Microsoft Windows (don't know if still exists), which had
to be called to release one of the five system-wide per-window drawing
contexts.  Of course, the `types' HWND and HDC were defined like this:

typedef unsigned int HWND;
typedef unsigned int HDC;

Nothing prevented you from calling ReleaseDC(hdc, hwnd), thus not
releasing the drawing context.  This was especially annoying during
software development---the machine froze if no more drawing contexts
where available.  But I've seen software which had this drawing context
leak and was delivered, too.

In the final days of Win16, Microsoft used the following trick to make
HWND and HDC (and the other handle types) distinct types:

struct tagHWND { int dummy; };
struct tagHDC { int dummy; };

typedef struct tagHWND *HWND;
typedef struct tagHDC *HDC;

Of course, this extremely ugly and platform dependent, but in fact,
it's quite helpful if you are programming with C (and not Ada ;).
AFAIK it is still used with Win32.