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bingfeng
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 Posted: Wed Jul 27, 2005 3:34 pm Post subject: why regex "^$" or "^s*$" cannot match "" line? |
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{Moderator's note: although I think that Boost specific questions are
off-topic in comp.lang.c++.moderated, I let this article pass because
TR1 includes regular expressions which are pretty close, if not identical,
to Boost::Regex. -mod/dk}
I use boost:regex in my project. I find regex "^$" or "^s*$" cannot
match "" line, but perl do. the match_flag_type is match_default and
some other reg express can do.
Can someone give me some hints? thks
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Pete Becker
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| Posted: Wed Jul 27, 2005 5:37 pm Post subject: Re: why regex "^$" or "^s*$" cannot match "" line? |
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bingfeng wrote:
| Quote: | {Moderator's note: although I think that Boost specific questions are
off-topic in comp.lang.c++.moderated, I let this article pass because
TR1 includes regular expressions which are pretty close, if not identical,
to Boost::Regex. -mod/dk}
I use boost:regex in my project. I find regex "^$" or "^s*$" cannot
match "" line, but perl do. the match_flag_type is match_default and
some other reg express can do.
Can someone give me some hints? thks
|
Sounds like a bug in the boost version. In our not-yet-available
implementation of TR1 both of those searches succeed.
--
Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Thomas Maeder
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| Posted: Wed Jul 27, 2005 6:40 pm Post subject: Re: why regex "^$" or "^s*$" cannot match "" line? |
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"bingfeng" <bfzhao (AT) gmail (DOT) com> writes:
| Quote: | I use boost:regex in my project. I find regex "^$" or "^s*$" cannot
match "" line, but perl do. the match_flag_type is match_default and
some other reg express can do.
Can someone give me some hints? thks
|
The second expression looks wrong. Did you mean to write "^\s*$"?
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bingfeng
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| Posted: Thu Jul 28, 2005 11:50 am Post subject: Re: why regex "^$" or "^s*$" cannot match "" line? |
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Yeah, It's "^\s*$"! I allow user enter a regex, than I match all text.
I use the one user entered.
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kanze@gabi-soft.fr
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| Posted: Thu Jul 28, 2005 12:32 pm Post subject: Re: why regex "^$" or "^s*$" cannot match "" line? |
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bingfeng wrote:
| Quote: | I use boost:regex in my project. I find regex "^$" or "^s*$" cannot
match "" line, but perl do. the match_flag_type is match_default and
some other reg express can do.
Can someone give me some hints? thks
|
Where do you get the line from? If the 'n' is still there,
then "^$" shouldn't match, and of course, in "^s*$", there's
undefined behavior, because you have an undefined escape
sequence in the string -- you probably want "^\s*$", so that
the regex parser sees the ''.
--
James Kanze GABI Software
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34
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Pete Becker
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| Posted: Thu Jul 28, 2005 3:07 pm Post subject: Re: why regex "^$" or "^s*$" cannot match "" line? |
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[email]kanze (AT) gabi-soft (DOT) fr[/email] wrote:
| Quote: |
Where do you get the line from? If the 'n' is still there,
then "^$" shouldn't match,
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His line was "", which should match "^$". In addition, by default the
various regex matching functions treat their input sequence as a
complete line. So "n" won't exactly match "^$", i.e. regex_match will
return false, but its head matches the pattern, so regex_search will
succeed, and find the "first" line, consisting of just the newline
character. At least, that's my interpretation of the ECMAScript rules,
and it's what our implementation does.
--
Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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