std::vector<QString> mXmlFiles

void foo()
{
   ...
   QString file = mXmlFiles[ui->reportTypeComboBox->currentIndex()];
   std::string str = "db/class/" + file.toStdString(); // 4 строка
   QString outFile = "out/reports/report_" + ui->reportTypeComboBox->currentText();
   QDateTime dt = QDateTime::currentDateTime();
   outFile.append(dt.toString("_yyyy.MM.dd_hh:mm:ss") + ".html");
   std::string str2 = "temp/" + outFile.toStdString(); // 8 строка
   ...
}