[Boost-users] [Regex] Search Substring

Hi, 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 ? Subhash