[gdal-dev] NODATA value in an array from RasterIO

[Limei Ran]

Hi:

I am reading a region out from a band using RaterIO into an array.  
What are NODATA cell values in the array?  Are they 0 or something 
else?  Can I modify the array and write back to the image.  How do I 
keep NODATA values in the array to be on the image after writing?

Thanks,

Limei