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From: gds@atticus.Sun.COM (Greg Schechter)
Newsgroups: comp.lang.c
Subject: Portability of TypeCasting LHS's in C
Keywords: LHS, typecast
Message-ID: <130175@sun.Eng.Sun.COM>
Date: 12 Jan 90 18:21:02 GMT
Sender: news@sun.Eng.Sun.COM
Reply-To: gds@sun.UUCP (Greg Schechter)
Organization: Sun Microsystems - Graphics Standards Group - Mountain View, CA
Lines: 47


 
    Does anyone know the validity of typecasting an LHS in C.  For
example, I have the following:

    char *ptr;
    
    ((long *)ptr)++;

That is, ptr is a pointer to a 1 byte entity and I want to increment
that pointer by the sizeof(long), so typecasting it to a (long *) and
incrementing it does work on those compilers that can handle such a beast.

     My question is: Is this portable C, K&R C, ANSI C, or none of
the above??  Please respond directly to gds@Sun.COM.


     Below is a program which demonstrates this:
     
------------

#include <stdio.h>

main()
{
    char *begin = (char *)malloc(40);
    char *end = begin + 40;
    char *charptr;
    int   i;

    /* count through 40 bytes one char at a time */    
    for (i = 0, charptr = begin; charptr < end; charptr++, i++)
        printf("%d\t0x%x\n", i, charptr);

    /* count through 40 bytes one long at a time */
    for (i = 0, charptr = begin; charptr < end; ((long *)charptr)++, i++)
        printf("%d\t0x%x\n", i, charptr);

}

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

Thanks in advance,

Greg Schechter
Graphics Standards Software
Sun Microsystems