Thanks a lot John for this, I changed my code to this and it worked..

    boost::smatch what;
    while (boost::regex_search(startOffset ,endOffset , what, expression))
    {
      int32 pos = what.position();
      int32 len = what.length();
    }

However, could you tell me how to do this if my input string is "Hello World, Hello".
that is the reason I am using a while loop instead of an if since my input string can contain more than 1 search string.

Subhash

On Tue, Mar 8, 2011 at 4:40 PM, John Maddock <boost.regex@virgin.net> wrote:
I am new to boost Libraries and I am trying to find a substring using
Boost::Regex

Lets say I want to find string "Hello" in "Hello world".

std::string completeStr = "Hello World";
std::string::const_iterator startOffset = completeStr.begin();
std::string::const_iterator endOffset = completeStr.end();

std::string searchWord= "Hello";
boost::regex expression(searchWord);

boost::match_flag_type flags = boost::match_any;
while(boost::regex_search(startOffset, endOffset, what, expression, flags))
{
 int32 position = what.position(1);
 int32 len = what[1].length();
}

but value of this position and length value is coming out to be -1.
It is not able to find this substring, Could anyone tell me what I am doing
wrong ?

First off, you don't need to use "match_any" unless it's what you really mean.

You're then accessing *marked subexpression 1* inside the loop, but the regular expression *does not contain any marked subexpressions*.

Use what.position() and what.length() to access the position and length info of the match as a whole.

HTH, John.
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