Compiler optimization (was: 8086 (was Re: more talking to the

From: der Mouse <mouse_at_Rodents.Montreal.QC.CA>
Date: Sat Nov 15 02:59:43 2003

> struct foo a;
> struct foo b;

> b = a; /* Legal under ANSI C! */

> I could have done:

> memcpy(b,a,sizeof(struct foo));

Well, memcpy(&b,&a,sizeof(struct foo)), actually.

> I like the first sequence though, since the intent is a bit more
> clear.

It also lets the compiler copy less than the whole struct in some
circumstances - for example, if the struct has holes:

        struct foo { char c; int i; };

The compiler would be free to generate the equivalent of
        b.c=a.c; b.i=a.i;
rather than the memcpy. Or for

        struct foo { int i; char c; };

the compiler might well do the equivalent of memcpy(&b,&a,5) rather
than ...,8 (assuming, for brevity, today's usual 32-bit-cpu sizes, and
the obvious struct-packing conventions).

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Received on Sat Nov 15 2003 - 02:59:43 GMT