Hi i'm trying to convert a Qstring to double but i only receive a zero.

Qt Code: 
  1. std::string message(usb_data.constData(), 60); //usb_data.length()
  2.         QString qmessage = QString::fromStdString(message);
  3.         QString latitude = qmessage.mid(0,21);
  4.         QString longitude = qmessage.mid(23,25);
  5.         QString height = qmessage.mid(50);
  6.  
  7.         QString lat_mid = qmessage.mid(0,18);
  8.         QString lon_mid = qmessage.mid(23,21);
  9.  
  10.  
  11.  
  12.  
  13.         double lat =  lat_mid.toDouble();
  14.         double lon =  lon_mid.toDouble();
  15.  
  16.         qDebug() << lat << latitude;
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my output is 0 "4