Re: [Boost-users] [regex] problem w/ regex::extended

Subject: Re: [Boost-users] [regex] problem w/ regex::extended
From: Mark R Stallard (stallard_at_[hidden])
Date: 2015-02-13 09:03:23

U. Mutlu <for-gmane_at_[hidden]> wrote:

> the following regex expression works in perl-mode,
> but does not work in extented-mode.

It would help if you were more specific about what went wrong.
Did the constructor throw an exception?
Did the extended engine fail to match your input string?
If so, what input text are you using?

> I think I haven't used any perl-specific construct, or did I?
> Where?

I only use the Perl-compatible engine myself.  I check the POSIX
extended mode and did not see any obvious problems, though I did
wonder about this:

> #define WORD "[\\w\\-\\.~/]+"

I suspected that Perl would support the escape sequence \w
inside a [] character set, but POSIX extended might not.
The tests I ran affirmed those suspicions.

I tested this regex in a Perl one-liner and it matched the
input string "alpha only".  I tried the same regex in egrep
and it didn't work.  egrep did match that input string when
I replaced "\w" with "a-z".

I find it much easier to program with regular expressions if
I test them using a command-line tool first.

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From:	"U.Mutlu" <for-gmane_at_[hidden]>
To:	boost-users_at_[hidden]
Date:	02/12/2015 10:10 PM
Subject:	[Boost-users] [regex] problem w/ regex::extended
Sent by:	"Boost-users" <boost-users-bounces_at_[hidden]>

Hi,
the following regex expression works in perl-mode,
but does not work in extented-mode.
What's the reason?
I think I haven't used any perl-specific construct, or did I? Where?

...
#define NUM  "[+-]?(\\d+\\.?\\d*|\\.\\d+)([eE][+-]?\\d+)?"
#define WORD "[\\w\\-\\.~/]+"
#define EQU  "\\s*\\=\\s*"

const string sUserRE_VarAndVal = WORD EQU NUM;

#if 0
#define REGEX_ENGINE    boost::regex::extended
#else
#define REGEX_ENGINE    boost::regex::perl
#endif

regex reNum(sUserRE_VarAndVal, REGEX_ENGINE);
...

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