Re: [PATCH] Documentation: Explain a second alternative for multi-linemacros.

From: Randy Dunlap
Date: Sun Dec 31 2006 - 23:47:38 EST

Segher Boessenkool wrote:
#define setcc(cc) ({ \
partial_status &= ~(SW_C0|SW_C1|SW_C2|SW_C3); \
partial_status |= (cc) & (SW_C0|SW_C1|SW_C2|SW_C3); })
This _does_ return a value though, bad example.

Where does it return a value?

partial_status |=

as I expected (or suspected).
I also suspect that it wasn't intended, but this is old code
and I wasn't around Linux when it was written, so I don't know
about it for sure.

I don't see any uses of it

Ah, that's a separate thing -- it returns a value, it's just
never used.


And with a small change to put it inside a do-while block
instead of ({ ... }), it at least builds cleanly.

Well please replace it then, statement expressions should be
avoided where possible (to start with, they don't have well-
defined semantics).

We should probably avoid gcc extensions when possible.

I'll send a separate email for the patch.

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