Problem with STL regex

Question

Hi,

I am having trouble with the following regular expression in the C++ STL for Visual Studio 2022.

(?<=<abc>)(.|\n|\r\n)*?(?=</abc>)

This is intended to match everything between the tags <abc> and </abc> . I have checked several online regexp analysers, and they indicate that it's fine. The STL throws a cryptic exception when construting a regex object.

Can anyone spot the issue?

Thanks,

Stan

Answer 1

The “lookbehind” assertions (?<= and (?!< are not allowed in STL: https://learn.microsoft.com/en-us/cpp/standard-library/regular-expressions-cpp.

For simple cases, try an alternative:

string s = "... <abc>some text</abc> ...";

regex r( "(?:<abc>)((.|\\n|\\r\\n)*?)(?:</abc>)" );
smatch m;
        
if( regex_search( s, m, r ))
{
    string result = m[1];
    // . . .
}

Answer 2

The relevant lines are below. The regex line throws an exception. Does this suffice? Thanks

	auto r = regex("(?<=<xyzzy>)(.|\n|\r\n)*?(?=</xyzzy>)");
	s = regex_replace(s, r, "$1");

Answer 3

Hi Viorel,

Thanks. That's answered my question. Is there a reference for STL not having that construct?

What I am trying to do is extract everything between two tags:

blah blah.....***<abc>****This is the text I want</abc>***blah... blah

Regards,

Stan