John Maddock wrote:

Mihaly Zachar wrote:

...

I'm using libboost-regex1.34.1 from gutsy.

here is a sample for my problem:

------- CUT ------- #include <boost/regex.hpp> #include <string> #include <iostream>

using namespace std; using namespace boost;

int main() { string input = "1111"; string a = "(.*)"; string b = "0$1";

regex reg (a, regex::perl);

string out = regex_replace(input, reg, b);

cout << out << endl;

return 0; }

------- CUT -------

the expected result would be "01111" but it gives "011110"... why does it work like this ?

By design: Perl does the same thing, after the first match against "1111" there is a second match against the empty string at the end of the text.

...

if I use anchors (^ and $) it works well, but the problem is I will not get anchors from the other applications :(

the problem is that I get regexes from different perl and php applications...

will the upgrade to 1.35 solve my problem ?

Nope, and as I say, Perl does the same thing. You could set the match flag match_not_null as the last argument to regex_replace, but that would disable matches against all zero-length strings which may not be what you want.

Was this a real use case, or just a "getting to know the library" test case?

unfortunately this is a real problem... I'm interworking with an existing perl system and it provides me rexes what I sohuld use. We should have the same result for the same regexes. mitya@stamford:~$ perl -e '$in = "1111"; $in =~ s/(.*)/0$1/; print $in."\n"' 01111 mitya@stamford:~$ to set match_not_null is not good for me :( for now I think I will put an anchor in a front of it in some cases, but that would be nice if there would be a "more official" way to do this... if you have any other ideas, please let me know. Thanks, Misi

Mihaly Zachar wrote:

unfortunately this is a real problem... I'm interworking with an existing perl system and it provides me rexes what I sohuld use.

We should have the same result for the same regexes.

mitya@stamford:~$ perl -e '$in = "1111"; $in =~ s/(.*)/0$1/; print $in."\n"' 01111 mitya@stamford:~$

to set match_not_null is not good for me :(

OK so the Perl code doesn't set the /g modifier so it only replaces the first match found: you can get the same behaviour in Boost.Regex by passing the format_first_only flag as the last argument to regex_replace. In other words the defaults are different: Boost.Regex defaults to "replace all occurences" but you can choose to replace just the first one if you want, and Perl is the other way around. HTH, John.