Path: utzoo!utgpu!attcan!uunet!husc6!ukma!mailrus!bbn!bbn.com!mesard
From: mesard@bbn.com (Wayne Mesard)
Newsgroups: comp.lang.c
Subject: Re: Passing types to a subroutine
Message-ID: <32119@bbn.COM>
Date: 10 Nov 88 15:17:54 GMT
References: <14461@mimsy.UUCP>
Sender: news@bbn.COM
Lines: 64

From article <14461@mimsy.UUCP>, by chris@mimsy.UUCP (Chris Torek):
> In article <14457@mimsy.UUCP> sjr@mimsy.UUCP (Stephen J. Roznowski) writes:
>>I'm in the process of developing a piece of code that needs
>>to be portable across several different machines.  What I
>>need to do is something of the following:
> [edited]
>>	subroutine(...., <float array>, ...);
>>	subroutine(...., <double array>, ...);
>
> The best approximation is something like this:
> 
> 	float a[100];
> 	subroutine(TYPE_FLOAT, a, (double *)NULL);
> 	...
> 
> 	double a[100];
> 	subroutine(TYPE_DOUBLE, (float *)NULL, a);
> 	...
> 
> 	subroutine(t, iffloat, ifdouble)
> 		enum whichtype t;
> 		float *iffloat;
> 		double *ifdouble;
[Rest deleted.]

Or, how 'bout using a good old union to get rid of the extra param:

   union ptr {
       float *f;
       double *d;
   };

   enum whichtype {TYPE_FLOAT, TYPE_DOUBLE};

   main()
   {
       void sub();
       float f[10];
       double d[10];

       f[1] = 1.234;
       d[1] = -5.432;
       sub(0, f);
       sub(1, d);
       printf("Incidently, the sizeof the union is %d\n", sizeof(union ptr));
   }


   void sub(t, p)
   enum whichtype t;
   union ptr p;
   {
       switch(t) {
	 case TYPE_DOUBLE:
	   printf("Itsa double, cell 1 is %g\n", p.d[1]);
	   break;
	 case TYPE_FLOAT:	
	   printf("Itsa float, cell 1 is %g\n", p.f[1]);
	   break;
       }
   }

-- 
void *Wayne_Mesard();         MESARD@BBN.COM         BBN, Cambridge, MA