here is my code, it dont seems enything wrong,

 QSqlDatabase db=QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName("thedata.sqlite");
db.open();

QSqlQuery quary;
quary.prepare("SELECT lastname FROM people where firstname='?' ");
quary.bindValue(0,lineEdit->text());

bool x=quary.exec();
if(x){
   //......
 }

 else {
   QSqlError err;
    err=quary.lastError();
    QMessageBox::about(this,"error",err.text()   );
    }

when the program is working always it gives the error parameter count mismatch im using qt 4.8 and its own headers for using sqlite.

I would be very thankful for eny advice, though I searched in google i see many posts in this issue but nothing helped me.

thank you.