Re: [Boost-users] Boost [Regex] (grep Falg) Why doesn't this pattern match?

Subject: Re: [Boost-users] Boost [Regex] (grep Falg) Why doesn't this pattern match?
From: Krzysztof Czainski (1czajnik_at_[hidden])
Date: 2013-12-27 11:03:59

2013/12/27 Asmita Gaikwad <asmita.gaikwad_at_[hidden]>

> Hi,
>
> Environment: Windows 7 (32 bit), Visual Studio 2010 (Visual C++)
>
> I am trying to use Boost REGEX regex_match algorithm.
> I am using its grep flag.
> My code is as follows and here (a)* matches string "aaa", but still b
> comes out to be false.
>
> 1
> 2
> 3
> 4
> 5
> 6
> 7
> 8
> 9
> 10
> 11
>
> *bool* MatchWithGrep(string& pattern, string& data)
>
> {
>
>
>
>         *const* boost::regex e(pattern.c_str(), boost::regex::grep);
>
>         *return* regex_match(data.c_str(), e);
>
>
>
> }
>
>
>
> I am passing following parameters
>
> *bool* b = MatchWithGrep("(a)*\\n123", "aaa");
>
I think your problem is "\\n". Shouldn't it be "\n"? (Not tested, reasoning
from the doc you qouted below)
HTH, Kris

 In Boost Help, following is documented.
>
>
> Link -
> http://www.boost.org/doc/libs/1_55_0/libs/regex/doc/html/boost_regex/syntax/basic_syntax.html
>
> When an expression is compiled with the flag grep set, then the expression
> is treated as a newline separated list of POSIX-Basic expressions, a match
> is found if any of the expressions in the list match, for example:
>
> boost::regex e("abc\ndef", boost::regex::grep);
>
> will match either of the POSIX-Basic expressions "abc" or "def".
>
> Considering this, in my example i have 2 basic expressions (a)* and 123.
> (Since its c++ string \\n will be taken as \n internally. I had debugged
> the code and i can see value of variable pattern as "(a)*\n123" in watch
> window).
> Presence of any should give me bool b as true. And my data is "aaa". So it
> should give true. But i am getting false.
>
>
>
> Can anyone help me to find what’s wrong with my code?
>
>
> Thanks & Regards,
>
> Asmita
>
>
>