Re: testing `this' against 0 in non-static member function

From:

"Balog Pal" <pasa@lib.hu>

Newsgroups:

comp.lang.c++

Date:

Mon, 20 Jun 2011 09:26:18 +0200

Message-ID:

<itmsmq$2p5g$1@news.ett.com.ua>

"Shen Weihui" <swlsww@gmail.com>

Is it valid that testing `this` against 0 in a non-static member function?

Yes, it is legal. But pointless.

Since I found that this kind of construction was totally
eliminated by the compiler in the release build.

Well done. That's what I was telling many years ago with little effect, as
compilers had tendency to leave it at the time. this can not be 0 through
any mandated behavior. To make it 0 you must dereference a 0 pointer
upstream, that is undefined behavior. This gives the compiler the licence to
eliminate the redundant check.

In N3126 (9.3.2/1), it says, 'In the body of a non-static (9.3) member
function, the keyword this is a prvalue expression whose value is the
address of the object for which the function is called.'

So I guess that the compiler assumes that the address of the object
cannot be 0, so it's safe to optimize away the if expression.

Yes. Current standard has tifferent wording but that means the same.