search and replace using regex_replace

Question

I have a string to be searched

QString sObjectName = "looolok"

The regex_search for ".?o" results in 3 matched texts which I push to a vector matchedText

"lo" "oo" "lo"

Now I my replace text is "o" So I would expect the str to be changed to

oook

I am using boost xpressive regex_replace for this operation . This is my code

std::vector<QString>::iterator it = matchedText.begin();
wsregex regExp;
std::string strOut;
std::string::iterator itStr = strOut.begin(); ;
for( ; it != matchedText.end(); ++it )
 {
     regExp = wsregex::compile( (*it).toStdWString() );
     boost::xpressive::regex_replace( itStr, sObjectName.begin(), sObjectName.end(), regExp, qReplaceBy.toStdString(), regex_constants::format_perl );
 }

However the strOut contains ooook. What am I missing ?