Beefy Boxes and Bandwidth Generously Provided by pair Networks
laziness, impatience, and hubris
 
PerlMonks  

Re: pos()atively dangerous.

by dingus (Friar)
on Dec 16, 2002 at 12:06 UTC ( #220180=note: print w/replies, xml ) Need Help??


in reply to pos()atively mysterious.

BTW pos and regex m//g is very dangerous to use in a while loop if you do more regexes on the same string. For example the following code, similar to yours, loops once OK with the source string the same as yours. (The modification is search for a vowel. Search for the next 'x'. Search for next vowel if there is one)

However if we set $var = 'the quick brown fox jumped' then the same code gets into some endless loop whereas $var = 'The quick brown fox jump x' loops twice OK.

$var = 'the quick brown fox'; while( $var =~ m/([aeiou])/g ) { print "\n$var Matched '$1' \@ pos:", pos($var), "\n"; $var =~ m/x/g; print "$var : Matched X \@ pos:", pos($var), "\n"; }
I'm not quite sure whether this is defined behaviour but it caused me some head scratching when trying to parse some text into name/value bits. There are of course any number of work arounds, but its a bit of a surprise when misformed data causes your code to hang.

Dingus


Enter any 47-digit prime number to continue.

Replies are listed 'Best First'.
Re^2: pos()atively dangerous.
by diotalevi (Canon) on Dec 16, 2002 at 14:15 UTC

    If that matters to you then you just save a copy of the variable's pos value and restore it after stomping on it. This is partly why it's writable.

    $var = 'the quick brown fox'; while( $var =~ m/([aeiou])/g ) { # Save pos $pos = pos $var; # Do something to stomp on $var's pos value # Restore pos pos($var) = $pos; }

    Fun Fun Fun in the Fluffy Chair

Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?
Node Status?
node history
Node Type: note [id://220180]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others making s'mores by the fire in the courtyard of the Monastery: (3)
As of 2022-05-24 02:37 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    Do you prefer to work remotely?



    Results (82 votes). Check out past polls.

    Notices?