Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!linus!philabs!cmcl2!harvard!seismo!hao!noao!terak!anasazi!steve
From: steve@anasazi.UUCP (Steve Villee)
Newsgroups: net.lang.c
Subject: Re: swap() macro
Message-ID: <370@anasazi.UUCP>
Date: Fri, 20-Jun-86 13:44:48 EDT
Article-I.D.: anasazi.370
Posted: Fri Jun 20 13:44:48 1986
Date-Received: Mon, 23-Jun-86 03:02:19 EDT
References: <1201@brl-smoke.ARPA>
Organization: Anasazi, Phoenix Az.
Lines: 41

> Can someone construct a version that makes
> 
>     int *a, *b;
>     swap (*a++,*b++);
> 
> work right?
> 
>           Paul
>           Schauble at MIT-Multics.arpa

--------------------------------

#define swap(x, y) \
  if (1) \
  { \
    register int *xp, *yp, t; \
    xp = &(x); \
    yp = &(y); \
    t = *xp; \
    *xp = *yp; \
    *yp = t; \
  } \
  else

--------------------------------

The "if (1) ... else" allows the user to put a semicolon after the macro
invocation, and makes code such as

  if (today == tuesday)
    swap(*a++, *b++);
  else
    swap(*c++, *d++);

work correctly.

--- Steve Villee (ihnp4!mot!anasazi!steve)
    International Anasazi, Inc.
    7500 North Dreamy Draw Drive, Suite 120
    Phoenix, Arizona 85020
    (602) 870-3330