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From: worley@compass.com (Dale Worley)
Newsgroups: comp.lang.c
Subject: Re: casting ints and floats to char*
Message-ID: <WORLEY.91Apr25104733@sn1987a.compass.com>
Date: 25 Apr 91 14:47:33 GMT
References: <6185@mahendo.Jpl.Nasa.Gov>
Sender: root@compass.com
Organization: Compass, Inc., Wakefield, MA, U.S.A.
Lines: 38
In-reply-to: robert@nereid.jpl.nasa.gov's message of 25 Apr 91 00:10:47 GMT

In article <6185@mahendo.Jpl.Nasa.Gov> robert@nereid.jpl.nasa.gov (Robert Angelino) writes:

   void has_to_be_done_this_way()
   {
   char *ptr[12];
   int  i;
   long j;
   double p;

   ptr[0] = &i;
   ptr[1] = &j;
   ptr[2] = &p;

   sscanf(buf,"%2d %5ld %15lf",&(*ptr[0]),&(*ptr[1]),&(*ptr[2]));
   }

Better would be to define ptr as an array of void *, since that's
the new convention for "generic pointer".  (char * will also work, and
you have to use it if your compiler doesn't support void *, but it
doesn't protect you from accidentally dereferencing the pointer.)

Second, &(*ptr[0]) is equivalent to ptr[0].

But you don't want to say that, because sscanf wants three pointer
arguments: int *, long *, and double *, each of which may be
represented in a different manner than char * or void *.  What you
want to say is:

   sscanf(..., (int *)ptr[0], (long *)ptr[1], (double *)ptr[2]);

Always cast your generic pointers back to the right types before using
them to access data.

Dale

Dale Worley		Compass, Inc.			worley@compass.com
--
"Bob" sold it.  I bought it.  That settles it. -- <_Jym_R_Dobbs_>