QSqlDatabase db;

    db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName("D:/Programiranje/c++ projects/Skolski projekti/School_student_managment_system/school.db");
    if (db.open())
    {
        QSqlQuery query;
        query.prepare("select * from accounts where username='"+username+"' and password='"+password+"'");
        if(query.exec()){
            int count;
            while(query.next()){
                count++;
            }
            if(count==1){
                QMessageBox::information(this, "warning", "Access granted.");
            }
            else{
                QMessageBox::information(this, "warning", "Access denied.");
            }
        }
    }