Error: no matching function for call to 'QSqlQuery::addBindValue(std::string&)'

[Amarda_4]

I have this code

@
include <iostream>
include<QSqlDatabase>
include<QSqlQuery>
#include <hyrje.h>
using namespace std;
class Votuesi
{
private:
string v_id,emeri,mbiemer,atesia,qarkui,passi;
public:
bool lidhDatabase();
void identifikohu();
Votuesi(string ,string ,string );
void publiko(){
cout<<v_id<<qarkui<<passi;}};
Votuesi::Votuesi(string a,string b,string c){
emeri=a;
qarkui=b;
passi=c;}
//Metode e cila ben te mundur lidhjen e programit me database-in
bool lidhDatabase(){
QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
db.setHostName("localhost");
db.setDatabaseName("evoting");
db.setUserName("root");
db.setPassword("");
if (!db.open())
return cout<<"Lidhja me database-in nuk mund te behet "; }
return cout<<"Lidhja me database-in u krye me sukses";}
//Metode e cila ben te mundur identifikimin e numrit te identitetit te votuesit
void Votuesi::identifikohu(){
QSqlQuery query;
query.prepare("SELECT * FROM evoting WHERE emer = ? and qyteti = ? and pass = ?");
query.addBindValue(this->emeri);
query.addBindValue(this->qarkui);
query.addBindValue(this->passi);
query.exec();
if(query.size()> 0){
query.next();{
else{
cout<<"Te dhenat qe ju vendoset nuk jane te sakta";}}
int main(){
Votuesi votues("Amarda","Tirane","amarda");
votues.lidhDatabase();
votues.publiko();
votues.identifikohu();}@

what should I do to give the query my values of constructor ?

[leon.anavi]

"QSqlQuery::addBindValue":http://qt-project.org/doc/qt-5.0/qtsql/qsqlquery.html#addBindValue expects a valid Qt data type such as QString but you are providing STD string instead.