Re: GCC 3.4 Heads-up
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Date: 12/26/03
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Date: 26 Dec 2003 11:02:06 -0000 To: linux-kernel@vger.kernel.org, torvalds@osdl.org
> Similarly, what the _hell_ does the gcc extension
>
> int a;
>
> (char)a += b;
>
> really mean? The whole extension is just braindamaged,
It means a = (int)((char)a + b).
(Modulo the fact that the value of the expression is the sum of type
char and not the final value of type int.)
Applied to integer types, it *is* pretty brain damaged. But applied to
pointer types, it makes a lot more sense.
This is because "a += b" in C is actually "a += b * sizeof(*a)", and
sometimes you want a different *a.
In particular, 1 is a popular value.
Consider the common case of a structure which has a bunch of variable-sized
blocks with a standard header:
struct foo {
unsigned type, size;
...
} a;
Then you *do* have to write
a = (struct foo *)((char *)a + a->size);
and I might argue that
(char *)a += a->size;
is definitely cleaner.
Or consider the case when the structure doesn't have an explicit size
and you have a big case statement for parsing it:
switch (a->type) {
case BAR:
process_bar_chunk(((struct bar *)a)++);
break;
case BAZ:
process_baz_chunk(((struct baz *)a)++);
break;
...
};
Isn't that code a bit nicer looking? I put the redundant parens
in to remind people that I didn't mean to write "(struct bar *)(a++)"
(which also has its legitimate uses).
Necessary, no. But not "brain damaged", either.
It's well-defined and has legitimate uses.
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- Previous message: Nick Craig-Wood: "2.6.0 Huge pages not working as expected"
- Maybe in reply to: Chris Meadors: "GCC 3.4 Heads-up"
- Next in thread: Linus Torvalds: "Re: GCC 3.4 Heads-up"
- Reply: Linus Torvalds: "Re: GCC 3.4 Heads-up"
- Reply: Andreas Schwab: "Re: GCC 3.4 Heads-up"
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