Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!mcgill-vision!bloom-beacon!mintaka!think!zaphod.mps.ohio-state.edu!brutus.cs.uiuc.edu!jarthur!aqdata!sullivan
From: sullivan@aqdata.uucp (Michael T. Sullivan)
Newsgroups: comp.lang.c
Subject: Multi-statement macros (again)
Message-ID: <1990Feb8.235051.21779@aqdata.uucp>
Date: 8 Feb 90 23:50:51 GMT
Organization: aQdata, Inc.  Western Region -- San Dimas, CA
Lines: 30

One of the packages we use has some macros for returning values
from a function.  You call these macros when you want to return
instead of calling return.  An example is:

#define	new_return(n)	s1; s2; return (something)

This just wouldn't do so I put braces around the statements.  Recent
discussion here led me to change this macro to:

#define	BEGIN_BLOCK	do {
#define	END_BLOCK	} while (0)
#define	new_return(n)	BEGIN_BLOCK s1; s2; return (something); END_BLOCK

Problem with this particular macro is that because it has a return in it,
we would get a "statement not reached" warning from the compiler.  I then
changed BEGIN_ and END_BLOCK to:

#define	BEGIN_BLOCK	do { if (1) {
#define	END_BLOCK	} } while (0)

This seems to make everything happy.  My question is, will this make other
machines happy?  We are using a 3B2/400 SVR3 and it didn't even complain
when just braces were used (resulting in "};").  Does this shut everything
up on YOUR machine?

P.S. That BEGIN_BLOCK/END_BLOCK stuff really DOES come in handy.
-- 
Michael Sullivan          uunet!jarthur!aqdata!sullivan
aQdata, Inc.              sullivan@aqdata.uucp
San Dimas, CA             +1 714 599 9992