Irrlicht Engine

I have tried scene::IMesh* buffer = terrain->getMesh(); video::S3DVertex2TCoords* data = (video::S3DVertex2TCoords*)buffer->getMeshBuffer(0)->getVertices(); Every time I do my program does not work with that in it any suggestions? It is specifically that code right there too because everything stops...

Is there anyway I can access height map data. The tutorial doesn't go into any detail on how to change the data. I have looked around the forum and all I see is how to get the data and not change it.