Boost REGEX regex_match grep option

[asmita]

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.

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");

Can any one help me to find whats wrong with my code?
Thanks in advance.

[Cubbi]

Nothing major wrong with the code, the regex simply doesn't match the string

The regex expects a string that consists of zero or more letters a, followed by exactly \n123, and the string "aaa" doesn't have those characters.

[asmita]

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.

[JLBorges]

> I am passing following parameters
> bool b = MatchWithGrep("(a)*\\n123", "aaa");

"newline separated" :

// bool b = MatchWithGrep("(a)*\\n123", "aaa");
bool b = MatchWithGrep( "a*\n123", "aaa" ) ;

[asmita]

JLBorges,

As i had mentioned above

(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).

Also i had tried "a*\n123", and i can see in watch window it takes value "a*n123" and also it does not work.

[JLBorges]

http://coliru.stacked-crooked.com/a/e417396b14695b59