[32190] in Perl-Users-Digest
Perl-Users Digest, Issue: 3455 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Wed Jul 27 11:09:28 2011
Date: Wed, 27 Jul 2011 08:09:07 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Wed, 27 Jul 2011 Volume: 11 Number: 3455
Today's topics:
Posting Guidelines for comp.lang.perl.misc ($Revision: tadmc@seesig.invalid
saml sso and perl <mir@miras.org>
Re: saml sso and perl <glex_no-spam@qwest-spam-no.invalid>
Re: saml sso and perl <mir@miras.org>
Re: stuck in regex sln@netherlands.com
Re: why won't perl say which value was uninitialized? <hjp-usenet2@hjp.at>
Re: why won't perl say which value was uninitialized? <bart.lateur@telenet.be>
Re: why won't perl say which value was uninitialized? <rweikusat@mssgmbh.com>
Re: why won't perl say which value was uninitialized? <rweikusat@mssgmbh.com>
Re: why won't perl say which value was uninitialized? <jidanni@jidanni.org>
Re: why won't perl say which value was uninitialized? <kst-u@mib.org>
Re: why won't perl say which value was uninitialized? <willem@toad.stack.nl>
Re: why won't perl say which value was uninitialized? <hjp-usenet2@hjp.at>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Tue, 26 Jul 2011 02:17:30 -0500
From: tadmc@seesig.invalid
Subject: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.9 $)
Message-Id: <n7OdndBR4uyX97PTnZ2dnUVZ5j6dnZ2d@giganews.com>
Outline
Before posting to comp.lang.perl.misc
Must
- Check the Perl Frequently Asked Questions (FAQ)
- Check the other standard Perl docs (*.pod)
Really Really Should
- Lurk for a while before posting
- Search a Usenet archive
If You Like
- Check Other Resources
Posting to comp.lang.perl.misc
Is there a better place to ask your question?
- Question should be about Perl, not about the application area
How to participate (post) in the clpmisc community
- Carefully choose the contents of your Subject header
- Use an effective followup style
- Speak Perl rather than English, when possible
- Ask perl to help you
- Do not re-type Perl code
- Provide enough information
- Do not provide too much information
- Do not post binaries, HTML, or MIME
Social faux pas to avoid
- Asking a Frequently Asked Question
- Asking a question easily answered by a cursory doc search
- Asking for emailed answers
- Beware of saying "doesn't work"
- Sending a "stealth" Cc copy
Be extra cautious when you get upset
- Count to ten before composing a followup when you are upset
- Count to ten after composing and before posting when you are upset
-----------------------------------------------------------------
Posting Guidelines for comp.lang.perl.misc ($Revision: 1.9 $)
This newsgroup, commonly called clpmisc, is a technical newsgroup
intended to be used for discussion of Perl related issues (except job
postings), whether it be comments or questions.
As you would expect, clpmisc discussions are usually very technical in
nature and there are conventions for conduct in technical newsgroups
going somewhat beyond those in non-technical newsgroups.
The article at:
http://www.catb.org/~esr/faqs/smart-questions.html
describes how to get answers from technical people in general.
This article describes things that you should, and should not, do to
increase your chances of getting an answer to your Perl question. It is
available in POD, HTML and plain text formats at:
http://www.rehabitation.com/clpmisc.shtml
For more information about netiquette in general, see the "Netiquette
Guidelines" at:
http://andrew2.andrew.cmu.edu/rfc/rfc1855.html
A note to newsgroup "regulars":
Do not use these guidelines as a "license to flame" or other
meanness. It is possible that a poster is unaware of things
discussed here. Give them the benefit of the doubt, and just
help them learn how to post, rather than assume that they do
know and are being the "bad kind" of Lazy.
A note about technical terms used here:
In this document, we use words like "must" and "should" as
they're used in technical conversation (such as you will
encounter in this newsgroup). When we say that you *must* do
something, we mean that if you don't do that something, then
it's unlikely that you will benefit much from this group.
We're not bossing you around; we're making the point without
lots of words.
Do *NOT* send email to the maintainer of these guidelines. It will be
discarded unread. The guidelines belong to the newsgroup so all
discussion should appear in the newsgroup. I am just the secretary that
writes down the consensus of the group.
Before posting to comp.lang.perl.misc
Must
This section describes things that you *must* do before posting to
clpmisc, in order to maximize your chances of getting meaningful replies
to your inquiry and to avoid getting flamed for being lazy and trying to
have others do your work.
The perl distribution includes documentation that is copied to your hard
drive when you install perl. Also installed is a program for looking
things up in that (and other) documentation named 'perldoc'.
You should either find out where the docs got installed on your system,
or use perldoc to find them for you. Type "perldoc perldoc" to learn how
to use perldoc itself. Type "perldoc perl" to start reading Perl's
standard documentation.
Check the Perl Frequently Asked Questions (FAQ)
Checking the FAQ before posting is required in Big 8 newsgroups in
general, there is nothing clpmisc-specific about this requirement.
You are expected to do this in nearly all newsgroups.
You can use the "-q" switch with perldoc to do a word search of the
questions in the Perl FAQs.
Check the other standard Perl docs (*.pod)
The perl distribution comes with much more documentation than is
available for most other newsgroups, so in clpmisc you should also
see if you can find an answer in the other (non-FAQ) standard docs
before posting.
It is *not* required, or even expected, that you actually *read* all of
Perl's standard docs, only that you spend a few minutes searching them
before posting.
Try doing a word-search in the standard docs for some words/phrases
taken from your problem statement or from your very carefully worded
"Subject:" header.
Really Really Should
This section describes things that you *really should* do before posting
to clpmisc.
Lurk for a while before posting
This is very important and expected in all newsgroups. Lurking means
to monitor a newsgroup for a period to become familiar with local
customs. Each newsgroup has specific customs and rituals. Knowing
these before you participate will help avoid embarrassing social
situations. Consider yourself to be a foreigner at first!
Search a Usenet archive
There are tens of thousands of Perl programmers. It is very likely
that your question has already been asked (and answered). See if you
can find where it has already been answered.
One such searchable archive is:
http://groups.google.com/advanced_search
If You Like
This section describes things that you *can* do before posting to
clpmisc.
Check Other Resources
You may want to check in books or on web sites to see if you can
find the answer to your question.
But you need to consider the source of such information: there are a
lot of very poor Perl books and web sites, and several good ones
too, of course.
Posting to comp.lang.perl.misc
There can be 200 messages in clpmisc in a single day. Nobody is going to
read every article. They must decide somehow which articles they are
going to read, and which they will skip.
Your post is in competition with 199 other posts. You need to "win"
before a person who can help you will even read your question.
These sections describe how you can help keep your article from being
one of the "skipped" ones.
Is there a better place to ask your question?
Question should be about Perl, not about the application area
It can be difficult to separate out where your problem really is,
but you should make a conscious effort to post to the most
applicable newsgroup. That is, after all, where you are the most
likely to find the people who know how to answer your question.
Being able to "partition" a problem is an essential skill for
effectively troubleshooting programming problems. If you don't get
that right, you end up looking for answers in the wrong places.
It should be understood that you may not know that the root of your
problem is not Perl-related (the two most frequent ones are CGI and
Operating System related), so off-topic postings will happen from
time to time. Be gracious when someone helps you find a better place
to ask your question by pointing you to a more applicable newsgroup.
How to participate (post) in the clpmisc community
Carefully choose the contents of your Subject header
You have 40 precious characters of Subject to win out and be one of
the posts that gets read. Don't waste them. Take care while
composing them, they are the key that opens the door to getting an
answer.
Spend them indicating what aspect of Perl others will find if they
should decide to read your article.
Do not spend them indicating "experience level" (guru, newbie...).
Do not spend them pleading (please read, urgent, help!...).
Do not spend them on non-Subjects (Perl question, one-word
Subject...)
For more information on choosing a Subject see "Choosing Good
Subject Lines":
http://www.cpan.org/authors/id/D/DM/DMR/subjects.post
Part of the beauty of newsgroup dynamics, is that you can contribute
to the community with your very first post! If your choice of
Subject leads a fellow Perler to find the thread you are starting,
then even asking a question helps us all.
Use an effective followup style
When composing a followup, quote only enough text to establish the
context for the comments that you will add. Always indicate who
wrote the quoted material. Never quote an entire article. Never
quote a .signature (unless that is what you are commenting on).
Intersperse your comments *following* each section of quoted text to
which they relate. Unappreciated followup styles are referred to as
"top-posting", "Jeopardy" (because the answer comes before the
question), or "TOFU" (Text Over, Fullquote Under).
Reversing the chronology of the dialog makes it much harder to
understand (some folks won't even read it if written in that style).
For more information on quoting style, see:
http://web.presby.edu/~nnqadmin/nnq/nquote.html
Speak Perl rather than English, when possible
Perl is much more precise than natural language. Saying it in Perl
instead will avoid misunderstanding your question or problem.
Do not say: I have variable with "foo\tbar" in it.
Instead say: I have $var = "foo\tbar", or I have $var = 'foo\tbar',
or I have $var = <DATA> (and show the data line).
Ask perl to help you
You can ask perl itself to help you find common programming mistakes
by doing two things: enable warnings (perldoc warnings) and enable
"strict"ures (perldoc strict).
You should not bother the hundreds/thousands of readers of the
newsgroup without first seeing if a machine can help you find your
problem. It is demeaning to be asked to do the work of a machine. It
will annoy the readers of your article.
You can look up any of the messages that perl might issue to find
out what the message means and how to resolve the potential mistake
(perldoc perldiag). If you would like perl to look them up for you,
you can put "use diagnostics;" near the top of your program.
Do not re-type Perl code
Use copy/paste or your editor's "import" function rather than
attempting to type in your code. If you make a typo you will get
followups about your typos instead of about the question you are
trying to get answered.
Provide enough information
If you do the things in this item, you will have an Extremely Good
chance of getting people to try and help you with your problem!
These features are a really big bonus toward your question winning
out over all of the other posts that you are competing with.
First make a short (less than 20-30 lines) and *complete* program
that illustrates the problem you are having. People should be able
to run your program by copy/pasting the code from your article. (You
will find that doing this step very often reveals your problem
directly. Leading to an answer much more quickly and reliably than
posting to Usenet.)
Describe *precisely* the input to your program. Also provide example
input data for your program. If you need to show file input, use the
__DATA__ token (perldata.pod) to provide the file contents inside of
your Perl program.
Show the output (including the verbatim text of any messages) of
your program.
Describe how you want the output to be different from what you are
getting.
If you have no idea at all of how to code up your situation, be sure
to at least describe the 2 things that you *do* know: input and
desired output.
Do not provide too much information
Do not just post your entire program for debugging. Most especially
do not post someone *else's* entire program.
Do not post binaries, HTML, or MIME
clpmisc is a text only newsgroup. If you have images or binaries
that explain your question, put them in a publically accessible
place (like a Web server) and provide a pointer to that location. If
you include code, cut and paste it directly in the message body.
Don't attach anything to the message. Don't post vcards or HTML.
Many people (and even some Usenet servers) will automatically filter
out such messages. Many people will not be able to easily read your
post. Plain text is something everyone can read.
Social faux pas to avoid
The first two below are symptoms of lots of FAQ asking here in clpmisc.
It happens so often that folks will assume that it is happening yet
again. If you have looked but not found, or found but didn't understand
the docs, say so in your article.
Asking a Frequently Asked Question
It should be understood that you may have missed the applicable FAQ
when you checked, which is not a big deal. But if the Frequently
Asked Question is worded similar to your question, folks will assume
that you did not look at all. Don't become indignant at pointers to
the FAQ, particularly if it solves your problem.
Asking a question easily answered by a cursory doc search
If folks think you have not even tried the obvious step of reading
the docs applicable to your problem, they are likely to become
annoyed.
If you are flamed for not checking when you *did* check, then just
shrug it off (and take the answer that you got).
Asking for emailed answers
Emailed answers benefit one person. Posted answers benefit the
entire community. If folks can take the time to answer your
question, then you can take the time to go get the answer in the
same place where you asked the question.
It is OK to ask for a *copy* of the answer to be emailed, but many
will ignore such requests anyway. If you munge your address, you
should never expect (or ask) to get email in response to a Usenet
post.
Ask the question here, get the answer here (maybe).
Beware of saying "doesn't work"
This is a "red flag" phrase. If you find yourself writing that,
pause and see if you can't describe what is not working without
saying "doesn't work". That is, describe how it is not what you
want.
Sending a "stealth" Cc copy
A "stealth Cc" is when you both email and post a reply without
indicating *in the body* that you are doing so.
Be extra cautious when you get upset
Count to ten before composing a followup when you are upset
This is recommended in all Usenet newsgroups. Here in clpmisc, most
flaming sub-threads are not about any feature of Perl at all! They
are most often for what was seen as a breach of netiquette. If you
have lurked for a bit, then you will know what is expected and won't
make such posts in the first place.
But if you get upset, wait a while before writing your followup. I
recommend waiting at least 30 minutes.
Count to ten after composing and before posting when you are upset
After you have written your followup, wait *another* 30 minutes
before committing yourself by posting it. You cannot take it back
once it has been said.
AUTHOR
Tad McClellan and many others on the comp.lang.perl.misc newsgroup.
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.liamg\100cm.j.dat/"
The above message is a Usenet post.
I don't recall having given anyone permission to use it on a Web site.
------------------------------
Date: Tue, 26 Jul 2011 00:37:27 +0200
From: Michael Rasmussen <mir@miras.org>
Subject: saml sso and perl
Message-Id: <20110726003727.3f76e5fe@sleipner.datanom.net>
Hi list,
Anybody here who can give me directions to examples or documentation
for implementing sso with saml in a perl application?
--
Hilsen/Regards
Michael Rasmussen
http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xE3E80917
A computer is like air conditioning: it becomes useless when you open
windows.
------------------------------
Date: Tue, 26 Jul 2011 15:10:08 +0000
From: "J. Gleixner" <glex_no-spam@qwest-spam-no.invalid>
Subject: Re: saml sso and perl
Message-Id: <4e2ed8d0$0$63194$815e3792@news.qwest.net>
On 07/25/11 22:37, Michael Rasmussen wrote:
> Hi list,
>
> Anybody here who can give me directions to examples or documentation
> for implementing sso with saml in a perl application?
>
Try using your favorite search engine and searching on 'sso saml perl',
or try http://search.cpan.org/
Doing those simple things showed a possible starting point and it took
all of 5-seconds.
Net::SAML
Perl extension for using SAML SSO
------------------------------
Date: Tue, 26 Jul 2011 20:43:29 +0200
From: Michael Rasmussen <mir@miras.org>
Subject: Re: saml sso and perl
Message-Id: <20110726204329.3dc82f92@sleipner.datanom.net>
On Tue, 26 Jul 2011 15:10:08 +0000
"J. Gleixner" <glex_no-spam@qwest-spam-no.invalid> wrote:
> Doing those simple things showed a possible starting point and it took all of 5-seconds.
>
> Net::SAML
> Perl extension for using SAML SSO
I did try that but Net::SAML is in a bad shape - only builds with
GCC-3.x and since GCC on my dist is GCC-4.6 then this is not an option.
Apart from the above the build system is terrible!
--
Hilsen/Regards
Michael Rasmussen
http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xE3E80917
A computer is like air conditioning: it becomes useless when you open
windows.
------------------------------
Date: Mon, 25 Jul 2011 17:30:28 -0700
From: sln@netherlands.com
Subject: Re: stuck in regex
Message-Id: <rn1s27t8d2t4bld0ls8vphvkj9fq45dpbu@4ax.com>
On Mon, 25 Jul 2011 13:00:30 -0700, sln@netherlands.com wrote:
>On Sun, 24 Jul 2011 21:00:45 -0600, elliot <elliot@example.net> wrote:
>
>>On 07/24/2011 12:13 PM, sln@netherlands.com wrote:
>>
>>> That script produces this output:
[...]
>>> Doesen't make a lot of sence.
>>
>>What input files were you using?
>>
>>$ cat cfile3.c
>> 1 #include <stdio.h>
[...]
>> 23 }
>>
>>
>>// gcc -c -Wall -Wextra cfile2.c -o testc.o
>>
>>Something like this?
>
>The line numbering wasn't apparent (to me) as being the thing you
>wanted stripped. Why not just use a copy of the original?
>
>But, if that's the case, its easy to strip.
>Below is what you would do to preserve the original source formatting
>(incase of a compile error that you might need a reference back to).
>
I'm not going to try to read your mind but some things.
The regex becomes much more complicated, depending on how
(or what) generated the line numbered source file.
For example, maybe a generator did this:
9 a+=4;
10 a &= 65535;
as part of its self formatting.
Or, there might be other hidden 'formatting' peculiarities/issue's,
even some that might be C-parsing knowledge related. Some editors are
famous for that. Or, there could be cutn'paste issue's.
Some of the above-mentioned issues could affect the compilers interpretation
of the source, significantly different from what you might expect.
So, be forewarned.
-sln
------------------------------
Date: Tue, 26 Jul 2011 18:07:56 +0200
From: "Peter J. Holzer" <hjp-usenet2@hjp.at>
Subject: Re: why won't perl say which value was uninitialized?
Message-Id: <slrnj2tpis.voi.hjp-usenet2@hrunkner.hjp.at>
On 2011-07-25 17:25, Rainer Weikusat <rweikusat@mssgmbh.com> wrote:
> "Peter J. Holzer" <hjp-usenet2@hjp.at> writes:
>> On 2011-07-25 14:08, Tad McClellan <tadmc@seesig.invalid> wrote:
>>> jidanni@jidanni.org <jidanni@jidanni.org> wrote:
>>>> I don't see why messages like
>>>> Use of uninitialized value in print at bla.pl line 44
>>>> can't say which value was it that was uninitialized.
[...]
>>>> It knows exactly which of the say 50 variables had the problem,
>>>
>>> What if it was not a variable at all?
>>>
>>> print give_undef(), "\n";
>>> sub give_undef { return undef }
>>>
>>> What should it say in that case?
>>
>> Use of uninitialized value in argument 1 of print.
>
> Why should it say anything,
Because I have requested that particular warning.
> given that there isn't even an lvalue involved here?
Irrelevant. The message is misleading (I even noted that in a
parenthetical remark, but you chose to delete that so that you could
rant on your favourite topic), it isn't about whether the the value is
initialized but about whether it is undef (which is also immediately
apparent to any Perl programmer).
I want that warning for the same reason I want a C program to throw a
segmentation fault if I dereference NULL: I don't do that on purpose, so
if it happens it is a bug. There have been C implementations where
dereferencing NULL gave a predictable, even useful result (Ultrix on VAX
returned 0, I think SunOS at the time did the same thing. Not sure about
Minix/8086), but very few programs which did that on purpose and lots of
programs where segfaulting uncovered a hidden bug - so most programmers
thought that segfaulting on null pointer access was a good thing even
though in some rare cases it made code a bit more complex.
hp
------------------------------
Date: Tue, 26 Jul 2011 19:00:09 +0200
From: Bart Lateur <bart.lateur@telenet.be>
Subject: Re: why won't perl say which value was uninitialized?
Message-Id: <7fst27dhhbfc5r3ci7ilamklgil0karh60@4ax.com>
Tad McClellan wrote:
>What if it was not a variable at all?
>
> print give_undef(), "\n";
> sub give_undef { return undef }
>
>What should it say in that case?
Perl could count the items and say at what position an item was
undefined. In case of interpolation of strings, perl treats that as a
concatenation of items and again, perl might tell which items in the
concatenation list were undefined.
--
Bart.
------------------------------
Date: Tue, 26 Jul 2011 23:14:43 +0100
From: Rainer Weikusat <rweikusat@mssgmbh.com>
Subject: Re: why won't perl say which value was uninitialized?
Message-Id: <87pqkw7kq4.fsf@sapphire.mobileactivedefense.com>
"Peter J. Holzer" <hjp-usenet2@hjp.at> writes:
[...]
> I want that warning for the same reason I want a C program to throw a
> segmentation fault if I dereference NULL: I don't do that on purpose, so
> if it happens it is a bug.
Derefencing a null pointer is undefined behaviour in C. As opposed to
that, the return value of undef is a scalar named PL_sv_undef and
since this is just a scalar, it is a valid to use it in exactly the
same ways as any other scalar. In particular, it stringifies to a
well-defined value (an empty string) and it has the same numerical
value all non-numerical scalars have (0).
Your C lore doesn't cut it here "Perl programmer".
------------------------------
Date: Tue, 26 Jul 2011 23:25:58 +0100
From: Rainer Weikusat <rweikusat@mssgmbh.com>
Subject: Re: why won't perl say which value was uninitialized?
Message-Id: <87ipqo7k7d.fsf@sapphire.mobileactivedefense.com>
Keith Thompson <kst-u@mib.org> writes:
> Rainer Weikusat <rweikusat@mssgmbh.com> writes:
[...]
>>>> Why is this to be sacrificed on an altar dediciated to someone who did
>>>> a half-assed implementation of a warning for situation which is
>>>> perfectly legal because of a bad hangover and inbred intolerance
>>>> for differences, no matter if they happen to be beneficial or not?
>>>
>>> Perfectly legal? Then what should print do with an undef argument?
>>
>> Well, what it is supposed to do: Print nothing aka 'an empty string'.
>
> What is the basis for your assertion that ``print undef'' is *supposed*
> to print an empty string?
What is the basis for your assertion that the scalar representing 'an
undefined value' is supposed to behave differently from all other Perl
scalars wrt to stringification and conversion to a numerical value,
especially given that it doesn't?
Note that since "undef" is a valid scalar, its presence
doesn't *necessarily* indicate an exceptional condition
That's from the documentation of the 'defined' function.
------------------------------
Date: Tue, 26 Jul 2011 17:58:26 -0700 (PDT)
From: jidanni <jidanni@jidanni.org>
Subject: Re: why won't perl say which value was uninitialized?
Message-Id: <87fd2cdd-75e4-46fe-b8ba-b8b7cde93026@glegroupsg2000goo.googlegroups.com>
Well there is no denying that perl could mention that it was $_ that was bothering it in
$ perl -we 'print $_ for undef'
Use of uninitialized value in print at -e line 1.
You could imagine the wild goose chase that could result if there were several other variables on that line.
Do submit a bug for me. I'm locked out for life from @perl.org mailing lists.
------------------------------
Date: Tue, 26 Jul 2011 20:34:47 -0700
From: Keith Thompson <kst-u@mib.org>
Subject: Re: why won't perl say which value was uninitialized?
Message-Id: <lnoc0ggzvs.fsf@nuthaus.mib.org>
Rainer Weikusat <rweikusat@mssgmbh.com> writes:
> Keith Thompson <kst-u@mib.org> writes:
>> Rainer Weikusat <rweikusat@mssgmbh.com> writes:
> [...]
>
>>>>> Why is this to be sacrificed on an altar dediciated to someone who did
>>>>> a half-assed implementation of a warning for situation which is
>>>>> perfectly legal because of a bad hangover and inbred intolerance
>>>>> for differences, no matter if they happen to be beneficial or not?
>>>>
>>>> Perfectly legal? Then what should print do with an undef argument?
>>>
>>> Well, what it is supposed to do: Print nothing aka 'an empty string'.
>>
>> What is the basis for your assertion that ``print undef'' is *supposed*
>> to print an empty string?
>
> What is the basis for your assertion that the scalar representing 'an
> undefined value' is supposed to behave differently from all other Perl
> scalars wrt to stringification and conversion to a numerical value,
> especially given that it doesn't?
Oh, but it does; see below.
> Note that since "undef" is a valid scalar, its presence
> doesn't *necessarily* indicate an exceptional condition
>
> That's from the documentation of the 'defined' function.
Did you notice the word "necessarily" there? It implies that the
presence of "undef" sometimes *does* indicate an exceptional condition.
If it didn't, the sentence would probably read:
Note that since "undef" is a valid scalar, its presence doesn't
indicate an exceptional condition.
But this:
print undef;
does in fact trigger a warning (if warnings are enabled).
So apparently an argument to print is one of the contexts where
the presence of "undef" indicates an exceptional condition.
I take it you think it shouldn't do so, and you're certainly entitled
to that opinion. But if you don't like the way Perl treats "undef",
I'm not the one you should be complaining to.
--
Keith Thompson (The_Other_Keith) kst-u@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"
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Date: Wed, 27 Jul 2011 08:50:11 +0000 (UTC)
From: Willem <willem@toad.stack.nl>
Subject: Re: why won't perl say which value was uninitialized?
Message-Id: <slrnj2vka3.26rp.willem@toad.stack.nl>
Keith Thompson wrote:
<snip>
) So apparently an argument to print is one of the contexts where
) the presence of "undef" indicates an exceptional condition.
)
) I take it you think it shouldn't do so, and you're certainly entitled
) to that opinion. But if you don't like the way Perl treats "undef",
) I'm not the one you should be complaining to.
no warnings 'uninitialized';
(Which, incidently, adorns most of my perl code, as I use a lot of autoviv)
SaSW, Willem
--
Disclaimer: I am in no way responsible for any of the statements
made in the above text. For all I know I might be
drugged or something..
No I'm not paranoid. You all think I'm paranoid, don't you !
#EOT
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Date: Wed, 27 Jul 2011 17:00:23 +0200
From: "Peter J. Holzer" <hjp-usenet2@hjp.at>
Subject: Re: why won't perl say which value was uninitialized?
Message-Id: <slrnj30a08.27v.hjp-usenet2@hrunkner.hjp.at>
On 2011-07-26 22:14, Rainer Weikusat <rweikusat@mssgmbh.com> wrote:
> "Peter J. Holzer" <hjp-usenet2@hjp.at> writes:
> [...]
>> I want that warning for the same reason I want a C program to throw a
>> segmentation fault if I dereference NULL: I don't do that on purpose, so
>> if it happens it is a bug.
>
> Derefencing a null pointer is undefined behaviour in C.
Yes, because the standards committee chose to make it undefined. They
could have mandated that a null pointer dereference must return 0 (which
was probably the most common behaviour at the time) or they could have
made it implementation defined. But they chose to put a big "Don't do
that" sign on it. For IMHO very similar reasons (I was neither a member of
the ANSI WG nor of P5P) the perl developers chose to warn about using an
undef scalar in a string or numeric context.
> As opposed to that, the return value of undef is a scalar named
> PL_sv_undef and since this is just a scalar,
A null pointer is just a pointer ...
> it is a valid to use it in exactly the same ways as any other scalar.
... but it isn't valid to use it the same way as a pointer which points
to an object.
> In particular, it stringifies to a well-defined value (an empty
> string) and it has the same numerical value all non-numerical scalars
> have (0).
It also has the well-defined behaviour of issuing a warning if that
particular warning has been enabled. If you don't like it, disable that
warning (I do so occasionally), but don't try to convince people that
this warning is generally bad - you won't succeed.
hp
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End of Perl-Users Digest V11 Issue 3455
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