Le 18/12/2023 à 16:18, Andrew C Aitchison via gdal-dev a écrit :
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.
Yes I meant that. I've less evidence in the RasterIO(GF_Write, ...) case
than in the WriteBlock() case, but without checking all drivers, it is
more prudent to assume that the buffer might be touched during
RasterIO(GF_Write) by some drivers.
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