fclose(NULL)
Chris Hills
Today I was asked what will fclose(NULL) do?
Microsoft Visual C/C++ V6 (used as a C compiler) generates an
exception (presumably because it tries to dereference the NULL
pointer)!
I think it should just return an error result (EOF, as defined in K & R
for errors during fclose() calls).
What do you think?
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Paul Jarc
> Today I was asked what will fclose(NULL) do?
n869 7.19.5.1p2:
# The fclose function causes the stream pointed to by stream to be
# flushed and the associated file to be closed.
No mention is made of what happens when `stream' doesn't point to a
stream, so I'd say it's implicitly undefined behavior.
paul
James Kuyper
>
> Hi all,
>
> Today I was asked what will fclose(NULL) do?
>
> exception (presumably because it tries to dereference the NULL
> pointer)!
>
> I think it should just return an error result (EOF, as defined in K & R
> for errors during fclose() calls).
>
> What do you think?
Section 7.1.4 p1 is an overview that applies to all the standard library
functions. It says that "If an argument to a function has an invalid
value (such as ... a null pointer) ... , the behavior is undefined."
Obviously, this doesn't apply to functions which have specifically
defined behavior for null pointers, but that's not the case with
fclose().
David R Tribble
It's interesting to note, however, that fflush(NULL) is defined and
causes all open streams to be flushed.
--
David R. Tribble, mailto:da...@tribble.com, http://david.tribble.com
James Kuyper
You're right. There's quite a few standard library routines with defined
behavior for a null pointer argument. In fact, there's too many to make
it worthwhile listing them. However, fclose() isn't one of them.