re question

[=?ISO-8859-1?Q?Sch=FCle_Daniel?=]

Hello all,

I didn't found more appropriate news group for
this question, please let me know if there is ng with
regular expression as its main topic

I am trying to construct a case where a greedy and
non greedy operation produce different result.
I dont see the difference between 'a??b' and 'a?b'
As far I understand is that ? will first try to match a
(it's greedy) and only if it fails then it step back
and lets a unmatched. The other doesn't match a at first,
only if the pattern fails to match it steps back and match a.

But don't they do eventually the same thing?
Can someone provide an example where 2 patterns yield
different results.

Regards, Daniel

 

[Steve Holden]

Hello all,

I didn't found more appropriate news group for
this question, please let me know if there is ng with
regular expression as its main topic

I am trying to construct a case where a greedy and
non greedy operation produce different result.
I dont see the difference between 'a??b' and 'a?b'
As far I understand is that ? will first try to match a
(it's greedy) and only if it fails then it step back
and lets a unmatched. The other doesn't match a at first,
only if the pattern fails to match it steps back and match a.

But don't they do eventually the same thing?
Can someone provide an example where 2 patterns yield
different results.

regards
Steve

 

[attn.steven.kuo]

Schüle Daniel wrote:

(snipped)

I am trying to construct a case where a greedy and
non greedy operation produce different result.
I dont see the difference between 'a??b' and 'a?b'
As far I understand is that ? will first try to match a
(it's greedy) and only if it fails then it step back
and lets a unmatched. The other doesn't match a at first,
only if the pattern fails to match it steps back and match a.

But don't they do eventually the same thing?
Can someone provide an example where 2 patterns yield
different results.

Perhaps this sheds some light

Yields:

['a', 'a', 'ab', 'a', ''] ['', '', '', 'b', '', '']