Hi,
size_t is an incorrect size for DataLength (if you run on 32 bit
architecture). You should use vsi_l_offset.
Besides that the following standalone inspired from your code works fine
for me:
#include <stdio.h>
#include "gdal_priv.h"
int main()
{
GDALAllRegister();
GDALDataset* Dataset
=GDALDataset::FromHandle(GDALOpenEx("poly.shp", GDAL_OF_VECTOR |
GDAL_OF_VERBOSE_ERROR, nullptr, nullptr, nullptr));
GDALDataset* Copy =
Dataset->GetDriver()->CreateCopy("/vsimem/foo.shp", Dataset, false,
nullptr, nullptr, nullptr); //appears to produce a valid Dataset
containing the same layers & features as its source.
GDALClose(Dataset);
GDALClose(Copy);
vsi_l_offset DataLength = 0;
GByte* Buffer = VSIGetMemFileBuffer("/vsimem/foo.shp", &DataLength,
true);
printf("%p %d\n", Buffer, int(DataLength)); // buffer not null and
DataLength > 0
CPLFree(Buffer);
VSIUnlink("/vsimem/foo.dbf");
VSIUnlink("/vsimem/foo.shx");
return 0;
}
Even
Le 04/10/2023 à 06:26, Soren Saville Scott via gdal-dev a écrit :
Hi,
I'm integrating GDAL in C++ with a system that defines its own asset
types stored on disk, and am writing a wrapper for datasets using this
asset system. To 'import' a dataset I call GDALOpenEx on it,
CreateCopy() it to some "/vsimem/foo.shp" path, GDALClose() the
datasets to flush it, and call VSIGetMemFileBuffer with
bUnlinkAndSeize=true to take ownership of the underlying memory buffer.
GDALDataset* Dataset = GDALOpenEx("foo.shp", GDAL_OF_VECTOR |
GDAL_OF_VERBOSE_ERROR, nullptr, nullptr, nullptr);
GDALDataset* Copy =
Dataset->GetDriver()->CreateCopy("/vsimem/foo.shp", Dataset, false,
nullptr, nullptr, nullptr); //appears to produce a valid Dataset
containing the same layers & features as its source.
GDALClose(Dataset);
GDALClose(Copy);
size_t DataLength;
GByte* Buffer = VSIGetMemFileBuffer("/vsimem/foo.shp", &DataLength,
true); //<-- returns NULL
For some reason VSIGetMemFileBuffer always fails, returning a nullptr.
This is basically identical to a similar problem I had, described
here: https://stackoverflow.com/questions/73644157/get-raw-buffer-for-in-memory-dataset-in-gdal-c-api
<https://stackoverflow.com/questions/73644157/get-raw-buffer-for-in-memory-dataset-in-gdal-c-api> which
I never really found a solution to. I have similar issues with other
VSI functions, e.g. calling GDALOpenEx on a path created by
VSIFileFromMemBuffer also fails.
Any idea as to what the problem is here?
Alternatively, maybe there's a better way to 'emplace' datasets inside
some other file?
Thanks,
Soren Saville Scott
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