Re: Logical Value Of A Pointer
On Feb 5, 11:39 pm, "Andrew Koenig" <a...@acm.org> wrote:
"James Kanze" <james.ka...@gmail.com> wrote in message
news:0611b478-c16a-4e5c-b0e4-cadddc316957@t26g2000prh.googlegroups.com...
Rather, I consider
if (p) { /* ... */ }
to be an abbreviation for
if (p != 0) { /* ... */ }
Why?
Because it's an idiom that has been in common usage for more
than 30 years.
In some circles. In others, no. In the groups I've worked
with, ``if (p)'' has never been used. Personally, I find it
confusing, and I have to stop and think about it each time I see
it. (And I've probably got almost as much experience in C and
C++ as you do:-).)
I understand that the standard doesn't describe it that
way, but that's just a matter of descriptive convenience,
and doesn't affect how I personally think about it.
I'm not sure I follow you: are you saying that anytime a
variable (pointer or arithmetic type) is used in a
condition, it should automatically be treated as if there
was a != 0 behind it? A sort of a short cut way of writing
it?
I'm saying that that's how people who have been programming in
C or C++ for a long time often think about it.
How some people think about it, perhaps. But it's certainly not
universal, and in itself, is confusing.
I find it easier to read
if (p && p->thing == "foo") { ... }
than to read
if (p != NULL && p->thing == "foo") { ... }
because the "!= NULL" in the second example is redundant and
makes me stop to think "Why did the author of that statement
put the redundant comparison in?"
Maybe because he wanted to make it clear to others what he was
testing?
I think that the widespread adoption STL iterator idiom makes
this even more important. I don't write:
if ( iter && iter->... )
, for the obvious reason that I can't. People expect to see a
comparison when an iterator is used, and this expectation
carries over to pointers. If we accept the ``if (p)'' idiom,
then logically, we should insist on the GoF pattern for
iterators, with an implicit conversion to bool, returning
!isDone.
While I prefer the GoF pattern myself (and use it at least as
often as the STL pattern, since I like filtering iterators and
such), I don't agree with the implicit conversion either. Say
whay you mean, and mean what you say---an iterator or a pointer
is not a bool, and I don't like to pretend it is.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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