i have made out a thread for data processing，

I want to read a series data (QPointF) from local harddisk，once a new data comes then tell the main thread to draw the new point,
signal:
newDataCome(QPointF newpoint);

there are nothing like QMutex, QReadWriteLock, QWaitCondition in the qthread ,

than a made a extern object of thread

extern ProcessThread processthread;

but after building there is a error by this row:
connect(&processthread, SIGNAL(newDataCome(QPointF)), this, SLOT(paintNewPoint(QPoint)));

and the error code is:
undefined reference to `_processthread`

i don`t unterstand what is a _processthread？

thanks for your help!!