[gdal-dev] Under what (if any) conditions would GDALWriteBlock modify data buffer?

[Andrew C Aitchison]

On Mon, 18 Dec 2023, Even Rouault via gdal-dev wrote:

> Hi,
>
> interesting question. No easy answer as it is highly driver dependent. I 
> believe that all drivers make sure that the content of the buffer before and 
> after the call is the same, but some drivers might temporarily modify it, to 
> do byte swapping. For example the HFA driver does that when run on big-endian 
> hosts for non-Byte data type. I wouldn't exclude that for formats with 
> MSB-byte ordering, a similar situation would happen for little endian hosts. 
> So it is definitely not safe to use WriteBlock() with a buffer that would 
> come from a read-only section of the calling program. Doc updated to reflect 
> that in 
> https://github.com/OSGeo/gdal/commit/ea321723dfc69ef3a422b1e3fe4dc9ee0832861d

Did you mean to say
   Note that even with eRWFlag==GF_Write, the content of the buffer
   might be temporarily modified during the execution of this method
   (and eventually restored back to its original content), so it is not
   safe to use a buffer stored in a read-only section of the calling
   program.

or
 	Note that even with eRWFlag==GF_Read,  ...

-- 
Andrew C. Aitchison                      Kendal, UK
                    andrew at aitchison.me.uk