Unsolved QT3D how to get the mesh from QCuboidMesh？

[jimfar]

for (auto &a : m3dentity->components())
{
auto b1 = dynamic_cast< Qt3DRender::QGeometryRenderer*>(a);
if (b1)
{
Qt3DExtras::QCuboidMesh b = (Qt3DExtras::QCuboidMesh)b1;
auto c=b->geometry();
for (auto d : c->attributes())
{
QString str = d->name();
if (str == Qt3DRender::QAttribute::defaultPositionAttributeName()) {
num = d->count();
auto buf = d->buffer();
buf->setAccessType(buf->ReadWrite);
auto ba = buf->data();

				break;
				 
			}
		 }
		 
	}

}
but ba is valid