Hi
Are these the same?
if ($x eq undef) {print "hi"}
if (not defined $x) {print "hi}
If so, which is preferred?
Thank you
John
Note: I have tried posting to perl beginners (the obvious choice for a
simple question) but the posts do not appear.
"John"
news:6tOdnd0H26w1NATanZ2dnUVZ8rOdnZ2d@eclipse.net.uk:
> Hi
use strict;
use warnings;
> Are these the same?
No.
> if ($x eq undef) {print "hi"}
> if (not defined $x) {print "hi}
Can't find string terminator '"' anywhere before EOF at C:\Temp\t.pl
line 2.
> If so, which is preferred?
Testing equality with undef will generate a warning regardless of the
value of $x.
unless ( defined $x )
or
if ( not defined $x )
would not. They would also convey the intended meaning better.
> Note: I have tried posting to perl beginners (the obvious choice for a
> simple question) but the posts do not appear.
You can ask all Perl related questions here. However, you should read
and follow the posting guidelines to get the best help.
Sinan
--
A. Sinan Unur <1usa@llenroc.ude.invalid>
(remove .invalid and reverse each component for email address)
clpmisc guidelines:
John wrote:
>
> Are these the same?
>
> if ($x eq undef) {print "hi"}
> if (not defined $x) {print "hi}
No. ($x eq undef) has no valid meaning in perl.
> Note: I have tried posting to perl beginners (the obvious choice for a
> simple question) but the posts do not appear.
Have you subscribed?
http://lists.cpan.org/showlist.cgi?name=beginners
John
--
Perl isn't a toolbox, but a small machine shop where you
can special-order certain sorts of tools at low cost and
in short order. -- Larry Wall
In article <6tOdnd0H26w1NATanZ2dnUVZ8rOdnZ2d@eclipse.net.uk>, John
> Hi
>
> Are these the same?
>
> if ($x eq undef) {print "hi"}
> if (not defined $x) {print "hi}
>
> If so, which is preferred?
The trick is to show what you intend to do. Since there is a builtin to
check if something is defined, use the builtin. :)
Quoth "A. Sinan Unur" <1usa@llenroc.ude.invalid>:
> "John"
> news:6tOdnd0H26w1NATanZ2dnUVZ8rOdnZ2d@eclipse.net.uk:
>
> > if ($x eq undef) {print "hi"}
> > if (not defined $x) {print "hi}
>
> Testing equality with undef will generate a warning regardless of the
> value of $x.
More importantly, it doesn't test that $x is undef. ($x eq undef) is
equivalent to ($x eq ''), modulo warnings.
Ben
"brian d foy"
news:250120080534556664%brian.d.foy@gmail.com...
> In article <6tOdnd0H26w1NATanZ2dnUVZ8rOdnZ2d@eclipse.net.uk>, John
>
>
>> Hi
>>
>> Are these the same?
>>
>> if ($x eq undef) {print "hi"}
>> if (not defined $x) {print "hi}
>>
>> If so, which is preferred?
>
> The trick is to show what you intend to do. Since there is a builtin to
> check if something is defined, use the builtin. :)
Hi
OK since "eq undef" will generate warnings then "not defined" appears the
better choice.
And it's builtin.
Thanks
John
"John"
>Are these the same?
>
>if ($x eq undef) {print "hi"}
>if (not defined $x) {print "hi}
Try
my $x=''; #empty string
if ($x eq undef) {print "equal"}
and you will notice that the textual value of undef as used for the string
cmparison is the empty string. In other words: you are comparing $x with
the empty string, not with undef.
jue
>>>>> "J" == John
J> OK since "eq undef" will generate warnings then "not defined" appears the
J> better choice.
J> And it's builtin.
wrong. eq undef is a bad choice since it doesn't work. try it sometime
and see if you can tell if a var is undef or 0 or ''. it fails.
the rest of the reasons are gravy.
uri
--
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