From: Clint Adams <clint@zsh.org>
To: Bart Schaefer <schaefer@candle.brasslantern.com>
Cc: zsh-workers@sunsite.dk
Subject: Re: pcre_study
Date: Tue, 3 Jul 2001 12:40:26 -0400 [thread overview]
Message-ID: <20010703124026.C4396@dman.com> (raw)
In-Reply-To: <1010703162628.ZM14584@candle.brasslantern.com>; from schaefer@candle.brasslantern.com on Tue, Jul 03, 2001 at 04:26:28PM +0000
> Does `study' mean something completely different in PCRE than in Perl?
Yes, though I'd be happy if we could rename the builtin to something less
confusing.
> In Perl, `study' means to examine the *string that is to be searched* to
> increase the speed of matching. It has no effect at all on the pattern
> that was compiled. Hence in Perl, a `study' at the point where zpgrep
> calls `pcre_study' would be completely useless as no input has been read
> yet. (And calling `study' on every line would be a waste anyway.)
This is from Philip Hazel's PCRE library v3:
STUDYING A PATTERN
When a pattern is going to be used several times, it is
worth spending more time analyzing it in order to speed up
the time taken for matching. The function pcre_study()
takes a pointer to a compiled pattern as its first argu
ment, and returns a pointer to a pcre_extra block (another
void typedef) containing additional information about the
pattern; this can be passed to pcre_exec(). If no addi
tional information is available, NULL is returned.
The second argument contains option bits. At present, no
options are defined for pcre_study(), and this argument
should always be zero.
The third argument for pcre_study() is a pointer to an
error message. If studying succeeds (even if no data is
returned), the variable it points to is set to NULL. Oth
erwise it points to a textual error message.
At present, studying a pattern is useful only for non-
anchored patterns that do not have a single fixed starting
character. A bitmap of possible starting characters is
created.
prev parent reply other threads:[~2001-07-03 16:40 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-07-03 16:26 pcre_study Bart Schaefer
2001-07-03 16:40 ` Clint Adams [this message]
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