Delete_exception

[myron]

This is defined at STDAFX.h

#define DELETE_EXCEPTION(e) do { e->Delete(); } while (0)

Can there anyone explain why they need a do-while loop here?

[humptydumpty]

MFC does not rely on auto-delete semantics of the TRY/CATCH macros, therefore those
macros are mapped to something closer to the native C++ exception handling mechanism
when building MFC itself."

The stdafx.h used to build MFC contains its own entirely different definitions for TRY, CATCH,
and so on; ones that map more or less directly to try/catch (with some ASSERTs thrown in
for good measure). Since these internal TRY/CATCH implementations don't have the magic
delete code, DELETE_EXCEPTION is required to manually call e->Delete.
So there are three possible implementations of TRY/CATCH: the "normal" implementation
you get without doing anything (with all the magic auto-delete stuff using
AFX_EXCEPTION_LINK); the "old" backward-compatible setjmp/longjmp implementation you
get when you #define _AFX_OLD_EXCEPTIONS; and the implementation MFC uses
internally, which requires DELETE_EXCEPTION to delete the exceptions. If all this makes
you want to throw up your hands and pull out your hair, I can sympathize. It would be nice
if the folks in Redmond rationalized their exception handling to map TRY/CATCH directly to
try/catch, but I don't think it will happen since that might break lots of existing code.
So what should you do? If you call an MFC function that can throw an exception, you have
no choice but to try to catch it. If you have old code that already uses TRY/CATCH, it
probably works fine and you shouldn't do anything. But if you're writing new code, I would
avoid TRY/CATCH entirely and stick with try/catch. Why? Three reasons: first, try/catch
produces smaller code than the MFC macros (no hidden local objects with
constructor/destructor calls); second, CATCH limits you to catching CException-derived
exceptions; and finally, it just plain looks better to use real C++. TRY/CATCH was always a
temporary kludge, so the sooner you forget it, the better. The only catch is, if you use
try/catch, you have to remember to delete your exception object!

 try{
   CallSomeMFCFunction();
 } catch( CException*e) {
 // recover
 e->Delete();
 }

[Paul McKenzie]

This is defined at STDAFX.h

#define DELETE_EXCEPTION(e) do { e->Delete(); } while (0)

Can there anyone explain why they need a do-while loop here?

It is used to enclose the macro in a block so that a semicolon at the end of the macro invocation doesn't cause a syntax error:

DELETE_EXCEPTION(whatever);

Regards,

Paul McKenzie