Casey Carter wrote:
> I've never touched the preprocessor, but I can't imagine it would be
> challenging to duplicate the implementation of #error and tweak it to emit a
> warning instead of an error. I see no particular reason why MSVC would
> oppose #warning. I suspect the reason we don't support it now is that
> #pragma message is superior since it accepts a string literal message instead of
> a sequence of preprocessing tokens.

And maybe because #pragma message was standard, whereas #warning was
not.