[Boost-users] [Xpressive] Baffled about results of search

From: Lynn Allan (l_d_allan_at_[hidden])
Date: 2006-04-12 01:54:00

<alert comment="xpressive newbie">

vc7.1
xpressive from "vault" as of today (April 11)

With the statements below (more or less based on Example 1 and Example 
2 in the sample code provided with xpressive), I'm attempting to 
detect which "group" of subexpressions matched, and getting results 
that I don't understand (not unexpected for a newbie <g>).

std::string altDow( "Alternate days of the week are Tue and Thursday 
and Sat and Monday." );

sregex rex = sregex::compile( "((Sunday|Sun)"
      "|(Monday|Mon)"
      "|(Tuesday|Tue)"
      "|(Wednesday|Wed)"
      "|(Thursday|Thu)"
      "|(Friday|Fri)"
      "|(Saturday|Sat))" );

The first regex_search sort of works, but I'm unclear what field in 
the smatch:what variable to use to tell what matched, and some 
oddities are happening.
regex_search( altDow, what, rex )

Length(0): 3
Position(0): 31
what[0]: Tue
what[1]: Tue
what[2]:
what[3]:
what[4]: Tue

The subsequent searches give valid information about the length and 
position, but other fields in the smatch:what variable seem invalid.
regex_search( altDow.substr(32), what, rex)
regex_search( altDow.substr(45), what, rex)

Regardless, I'm unclear how to tell which of the "groups" of 
subexpressions was "hit". With boost::regex there was a way to loop 
thru the boolean field:
what[i].matched
and see what "hit", but I am not seeing a comparable accessor.

Am I doing something wrong, leaving something out, completely clueless 
on using xpressive, or is xpressive not intended for this kind of 
usage?

(and if xpressive is appropriate, what statements will provide the 
intended information?)

The intention is to be able to to replace/encode the altDay string to 
be:
Alternate days of the week are <dow=2>Tue</dow>
 and <dow=4>Thursday</dow>
 and <dow=6>Sat</dow>
 and <dow=1>Monday</dow>." );

If it will help, here is a link to the vc7.1 project.
http://cleanspeech.sf.net/misc/DayOfWeekTest.zip

</alert>