[boost] regex: .*xxx.*

From: John Maddock (John_Maddock_at_[hidden])
Date: 2001-08-25 06:52:55

>This is most likely my error, but I am trying to do the following:

1)  A user types in a search string
2)  I add the prefix ".*" and suffix ".*" to the string

When I call regex_match, anything and everything matches, regardless of
what
the user typed.  I would like the following results, and am guessing I am
not using the correct regular expression syntax:

a)  User types "Test"
b)  Internally, I create the regular expression ".*Test.*"

Results (String : result)
"A Test" : true
"Testing 123" : false
"foo" : false

Using regex, regex_match is returning true for "foo".  I tried changing the
prefix to ".*?" to ensure a non-greedy search, but the results were the
same.
<

OK, first things first, heres the code I used to test this:

   boost::regex e(".*Test.*");
   boost::cmatch m;
   if(regex_match("A Test", m, e))
   {
      cout << "matched \"A Test\"" << endl;
   }
   if(regex_match("Testing 123", m, e))
   {
      cout << "matched \"Testing 123\"" << endl;
   }
   if(regex_match("foo", m, e))
   {
      cout << "matched \"foo\"" << endl;
   }

This gave the expected results:

"A Test": matched
"Testing 123": Matched
"foo": not matched

There is one possible source of error which may have confused you: if no
match is found then the regex_match structure is left unchanged - in other
words it may still contain a match from a previous invocation - you should
always check the return value from regex_match to see if a match occured,
and not the regex_match struct.

I would also suggest that rather than pre/post pending .*, that you use
regex_search instead - this is likely to be much more efficient.

Finally if you don't want to find the "Test" in "Testing", then prepend
with \< and append \> to ensure that only whole words are found.

- John Maddock
http://ourworld.compuserve.com/homepages/john_maddock/