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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: size of |
| Date | 2013-08-17 13:35 -0700 |
| Organization | None to speak of |
| Message-ID | <lnbo4wjbsp.fsf@nuthaus.mib.org> (permalink) |
| References | <kuduo2$a74$1@speranza.aioe.org> <kudutp$g64$1@dont-email.me> <kum7po$g06$1@speranza.aioe.org> <kumnja$nir$1@dont-email.me> <43986715-639e-4a1a-84c0-a6b0bcf686e5@googlegroups.com> |
Malcolm McLean <malcolm.mclean5@btinternet.com> writes:
> On Saturday, August 17, 2013 3:36:27 AM UTC+1, Eric Sosman wrote:
>> int *ptr = malloc(42 * sizeof *ptr);
>>
>> - The fourth is an example of the allocation pattern favored by
>> thoughtful C programmers, but it *relies* on `*ptr' not being
>> evaluated by `sizeof'. (If `*ptr' were evaluated at that moment,
>> before it had been initialized, the effect of trying to
>> dereference the garbage pointer would be undefined).
>>
> No, that's how a geek writes an allocation call.
Yes, it is.
Unless you meant "geek" to be a derogatory term, in which case you're
spewing nonsense.
> What he's thinking is that if ptr is changed to a long *, the code
> won't break. And he's right. It is a genuine advantage. But the price
> is a construct which is meaningless to human reader, unless he's very
> familiar with C. As you say it looks like *ptr should yield
> something, but ptr is currently wild. Then we've got another use of
> the * operator. Finally, it's not obvious that sizeof is not an
> identifier, it's not clear what its scope is. Could sizeof * be
> sizeof a wildcard, which is somehow applied to ptr?
>
> ptr = malloc(42 * sizeof(int));
>
> is far more readable. Everyone can see that we're allocating a space for 42
> ints.
So we should write fragile code so that readers who are unfamiliar with
the language can read it a little more easily? But you're assuming they
know what "malloc" means, and that "=" means assignment and "*" means
multiplication.
The solution to not understanding what
int *ptr = malloc(42 * sizeof *ptr);
means is to *learn* what
int *ptr = malloc(42 * sizeof *ptr);
means. You apparently understand it yourself. Why do you want to
impose limits on others?
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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