[Help]progress bar with loading data

Does anyone know how to make progress bar? I have made a progress bar gui but, the problem is when i loading data the progress bar won't show up only show up when loading is done, i mean how to make progress bar and loading data at same time?

When you loading something you usually stop rendering so nothing is updated, so you should callOgre::Root::getSingleton().renderOneFrame();every time when you updating progress and want to see result.