Re: [Boost-Users] Unexpected result in parsing a regular expression

From: John Maddock (john_maddock_at_[hidden])
Date: 2002-10-27 07:10:31

> I recently downloaded the boost regex library and am trying to use
> the search and replace (regex_merge) API. But I am not getting the
> expected result.
>
> Here is what I am trying to do. I am trying to replace a single
> quoted string with something. But, the catch here is that the string
> in single quotes can have zero or many 2 consecutive single quotes.
> For example:
>
> Input (Ignore the angle brackets>:
> <foo='string with '' consecutive '' single ''quotes' bar='string
> with no single quotes'>
> To be replaced by 'XXX'. So the output that I want:
> <foo=XXX bar=XXX>
>
> Here is the regular expression that I wrote in Perl:
> /(\'[^']*(\'\')*[^']*\')/
>
> I get the expected result in Perl.

Actually are you really sure that this works in perl: IMO it shouldn't,
since it can never match a string with more than *one* '' embedded in it, I
think you should be using:

/((?:\'[^']*\')+)/

John Maddock
http://ourworld.compuserve.com/homepages/john_maddock/index.htm

> So, to test this with regex library I wrote a sample program to use
> the regex_merge API and try the replace functionality.
> ---------------------------replace.cc--------------------------------
> #include <boost/regex.hpp>
> #include <string>
> #include <iostream>
> #include <sstream>
> #include <iterator>
>
> using namespace std;
> using namespace boost;
>
> const std::string formatstr("XXX");
>
> std::string processexp(string resp)
> {
>    regex expression("(\'[^']*(\'\')*[^']*\')");
>    std::string result;
>    std::ostringstream t;
>    std::ostream_iterator<char, char> oi(t);
>    cout << "Response:" << resp << endl;
>    result = boost::regex_merge(resp, expression, formatstr,
> boost::format_all);
>    return result;
> }
>
> int main(int argc)
> {
>    std::string res;
>
>    res = processexp("foo='string with '' consecutive ''
> single ''quotes' bar='string with no single quotes'");
>    cout << "results=" << res << endl;
>    return 0;
> }
> ---------------------------------------------------------------------
> The output I get is:
> foo=REPLACEDREPLACED bar=REPLACED
>
> I tried several ways, but couldn't get the regular expression to
> work to return the expected result.
>
> I WOULD really appreciate if someone could help me.
>
> Thanks in advance,
>
> Sameer
>
>
>
>
>
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