Scott Lurndal wrote:
>if((fd = open(_PATH_UTMP , O_RDONLY)) < 0)
The open system call is defined to return '-1' on failure, not any
negative number. So the above check is incorrect. This can
cause problems with mmap, lseek and other system calls whose return
values, if declared or cast as signed, while legal are negative.
mmap() should always be checked against MAP_FAILED, and lseek return
should always be compared with the expected value (i.e. the offset
arg for SEEK_SET, and the expected offset for the other SEEK_* variants).
Would it also cause a problem if your file descriptors go "around the horn", and
exceed some platform-specific limit, such as 0x80000000? They would "go
negative" when expressed as signed integers...
It's good practice to always test for the defined return code
(which in most cases is -1, not < 0).
Does some relatively standard .h file define a good constant there?
--
Phlip
Aug 7 '08
40  2494 
On Aug 7, 3:00 pm, Phlip <phlip2...@gmai l.comwrote:
CBFalconer wrote:
Please don't delete attributions for quoted material.
If they are not important to understand one post, alone, they are still
accessible in modern newsreaders' threading systems. Nobody is stealing anyone's
verbiage.
Just don't remove them. Not removing something takes less time than
removing something.
Phlip wrote:
vi******@gmail. com wrote:
>Also note that _PATH_UTMP is an invalid identifier in standard C,
since it's reserved for the implementation.
Yet open() _is_ the implementation. It's just not (apparently) in
the narrowest C Standard.
No, open() is not in ANY C implementation.
Some useful references about C:
<http://www.ungerhu.com/jxh/clc.welcome.txt >
<http://c-faq.com/ (C-faq)
<http://benpfaff.org/writings/clc/off-topic.html>
<http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf(C99)
<http://cbfalconer.home .att.net/download/n869_txt.bz2(C9 9, txt)
<http://www.dinkumware. com/c99.aspx (C-library}
<http://gcc.gnu.org/onlinedocs/ (GNU docs)
<http://clc-wiki.net/wiki/C_community:com p.lang.c:Introd uction>
--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.
Phlip wrote:
CBFalconer wrote:
>Please don't delete attributions for quoted material.
If they are not important to understand one post, alone, they
are still accessible in modern newsreaders' threading systems.
Nobody is stealing anyone's verbiage.
Among other things, they identify the writer. This enables the
reader to evaluate the accuracy. It is also easier to leave them
than to remove them.
--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section. vi******@gmail. com writes:
On Aug 7, 3:00 pm, Phlip <phlip2...@gmai l.comwrote:
>CBFalconer wrote:
Please don't delete attributions for quoted material.
If they are not important to understand one post, alone, they are still
accessible in modern newsreaders' threading systems. Nobody is stealing anyone's
verbiage.
Just don't remove them. Not removing something takes less time than
removing something.
And wading through unnecessary lengthy repetition to find the new
comments can take more time. Use some common sense. If you dont have a
threaded news reader then get one.
Phlip <ph*******@gmai l.comwrites:
CBFalconer wrote:
>Please don't delete attributions for quoted material.
If they are not important to understand one post, alone, they are
still accessible in modern newsreaders' threading systems. Nobody is
stealing anyone's verbiage.
Please leave the attribution lines alone anyway. I use a threaded
newsreader, but it's much easier to see the attribution line in the
article itself than to traverse up to the parent article (*if* it's
still on the server) and then figure out how to get back to the
article I was reading (non-trivial, since there can be multiple
responses).
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
CBFalconer <cb********@yah oo.comwrites:
Phlip wrote:
>vi******@gmail. com wrote:
>>Also note that _PATH_UTMP is an invalid identifier in standard C,
since it's reserved for the implementation.
Yet open() _is_ the implementation. It's just not (apparently) in
the narrowest C Standard.
No, open() is not in ANY C implementation.
[...]
Yes, it certainly is in many C implementations . It's not defined by
the C standard, but it's allowed as an extension.
C99 4p6:
A conforming implementation may have extensions (including
additional library functions), provided they do not alter the
behavior of any strictly conforming program.
open() is one of these "additional library functions".
Your apparent belief that anything not defined by the ISO C standard
is not C is clearly contradicted by the ISO C standard itself.
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
In article <ln************ @nuthaus.mib.or g>,
Keith Thompson <ks***@mib.orgw rote:
>CBFalconer <cb********@yah oo.comwrites:
>Phlip wrote:
>>vi******@gmail. com wrote:
Also note that _PATH_UTMP is an invalid identifier in standard C,
since it's reserved for the implementation.
Yet open() _is_ the implementation. It's just not (apparently) in
the narrowest C Standard.
No, open() is not in ANY C implementation.
[...]
Yes, it certainly is in many C implementations . It's not defined by
the C standard, but it's allowed as an extension.
In the minds of the purists, no, open() is not C and code that uses it
is not C. They often refer to these as "C-like languages".
In a group that is so tightly controlled by dogma, I think it is
imporant for you guys to get together and agree on such things, so as to
be able to present a united front to us peons.
On 7 Aug 2008 at 3:08, Phlip wrote:
Scott Lurndal wrote:
>>if((fd = open(_PATH_UTMP , O_RDONLY)) < 0)
>It's good practice to always test for the defined return code
(which in most cases is -1, not < 0).
Does some relatively standard .h file define a good constant there?
No.
Many, many standard functions - everything from readdir() to socket() to
fcntl() - follow the convention that on error they return -1 and set
errno appropriately. This isn't going to change any time soon. Checking
against -1 is therefore completely idiomatic, and a special constant
would be quite unnecessary.
Keith Thompson wrote:
CBFalconer <cb********@yah oo.comwrites:
>Phlip wrote:
>>vi******@gmail. com wrote:
Also note that _PATH_UTMP is an invalid identifier in standard C,
since it's reserved for the implementation.
Yet open() _is_ the implementation. It's just not (apparently) in
the narrowest C Standard.
No, open() is not in ANY C implementation.
[...]
Yes, it certainly is in many C implementations . It's not defined by
the C standard, but it's allowed as an extension.
Why does everyone misinterpret my concern here? It must be what I
wrote. At any point, my point is that there is usually NO reason
to use open, when fopen is guaranteed to be documented and
available.
--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.
CBFalconer <cb********@yah oo.comwrites:
Keith Thompson wrote:
>CBFalconer <cb********@yah oo.comwrites:
>>Phlip wrote:
vi******@gmail. com wrote:
Also note that _PATH_UTMP is an invalid identifier in standard C,
since it's reserved for the implementation.
Yet open() _is_ the implementation. It's just not (apparently) in
the narrowest C Standard.
No, open() is not in ANY C implementation.
[...]
Yes, it certainly is in many C implementations . It's not defined by
the C standard, but it's allowed as an extension.
Why does everyone misinterpret my concern here? It must be what I
wrote. At any point, my point is that there is usually NO reason
to use open, when fopen is guaranteed to be documented and
available.
You said that "open() is not in ANY C implementation" . That is simply
not true, as I explained. It's a common extension. It's not topical,
but that doesn't make it nonexistent or non-C.
<OT>
And there *are* sometimes valid reasons to use open(), which (assuming
we're talking about the POSIX open() function) has some features that
fopen() does not. With your qualification that there's *usually* no
reason to use open, you're probably right, but of course that's
off-topic.
</OT>
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
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