Explanation, please!

[Jabir Hussain]

In article <9064 at pur-ee.UUCP> hankd at pur-ee.UUCP (Hank Dietz) writes:
>	struct t512 { int t[512]; };
>	struct t256 { int t[256]; };
[...]
>	if (n & 512) {
>		*((struct t512 *) q) = *((struct t512 *) p); q+=512; p+=512;
>	}
[...]
>	                      Unfortunately, the above code should have been
>	written as:
>
>	if (n & 512) {
>		*(((struct t512 *) q)++) = *(((struct t512 *) p)++);
>	}
>	...
>
>	but, for some unknown reason, the VAX C compiler didn't like that.


one portable way around that is to do something like:

	typedef char *caddr_t;
	typedef union {
	    struct { int t[512]; } t512;
	    struct { int t[256]; } t256;
	    caddr_t               caddr;
	} ustruct_t;

	{
	    register ustruct_t src,dst;

	    src.caddr = (caddr_t) p;
	    dst.caddr = (caddr_t) q;

	    if (n & 512) *dst.t512++ = *src.t512++;
	    ...
	}

jh