Re: [gdal-dev] OGRFree(pszSrcWKT) can crash Matlab

[jluis]

Quoting Chaitanya kumar CH <chaitanya...@gmail.com>:

Joaquim,

You did change pszSrcWkt (
http://code.google.com/p/mirone/source/browse/trunk/mex/gdalwarp_mex.cpp#385
).

You should remove line 385 and move the line 386 to 330.

Ok, thank you guys.

Joaquim

On Sat, Jan 23, 2010 at 11:17 PM, <jl...@ualg.pt> wrote:

Quoting Even Rouault <even.roua...@mines-paris.org>:

 Joaquim,

you don't provide enough code to really see what's wrong, but my guess is
that you misuse GDAL API.

Even

Quite possible the first and I was trying to summarize what happens

If you get pszSrcWKT, with

pszSrcWKT = GDALGetProjectionRef(hDS);

No, I got it from oSrcSRS.exportToWkt( &pszSrcWKT );

See lines 325 & 329 of

code.google.com/p/mirone/source/browse/trunk/mex/gdalwarp_mex.cpp

Joaquim

The pszSrcWKT string is owned by the hDS object, so as soon as you destroy
the hDS object with GDALClose(), the pointer becomes invalid and points to
arbitrary data.

For the same reason, you should never free the string returned by
GDALGetProjectionRef() with OGRFree() or any other free() call.

See http://gdal.org/classGDALDataset.html :

GDALDataset::GetProjectionRef() :

returns:
a pointer to an internal reference string. It should not be altered, freed
or expected to last for long.

Best regards,

Even

Le Saturday 23 January 2010 16:04:58 jl...@ualg.pt, vous avez écrit :

Hi,

I have a serious crash in one of my Matlab MEXs caused by a call to
OGRFree() with an argument of size one (possibly the  null terminator).
This happens on OSX SL (64 bits) but not on Windows (where I still
build at 32 bits)

Here is, as far as I could trace it, what is happening (SVN version of
the same age as GDAL1.7RC1)

mexPrintf("---- %s\n%s\n", pszSrcWKT,pszDstWKT);

That prints

---- GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS

84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],TOWGS84[0,0,0,0,0,0,0],

AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNI

T["degree",0.0174532925199433,AUTHORITY["EPSG","9108"]],AUTHORITY["EPSG","43
26"]] PROJCS["UTM Zone 29, Northern Hemisphere",GEOGCS["WGS
84",DATUM["WGS_1984",SPHEROID["WGS

84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],TOWGS84[0,0,0,0,0,0,0],

AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNI

T["degree",0.0174532925199433,AUTHORITY["EPSG","9108"]],AUTHORITY["EPSG","43

26"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PA

RAMETER["central_meridian",-9],PARAMETER["scale_factor",0.9996],PARAMETER["f
alse_easting",500000],PARAMETER["false_northing",0],UNIT["Meter",1]]


Next the code does:

       GDALClose( hSrcDS );
mexPrintf("---- %s\n%s\n", pszSrcWKT,pszDstWKT);

and now pszSrcWKT is empty. See

---- PROJCS["UTM Zone 29, Northern Hemisphere",GEOGCS["WGS
84",DATUM["WGS_1984",SPHEROID["WGS

84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],TOWGS84[0,0,0,0,0,0,0],

AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNI

T["degree",0.0174532925199433,AUTHORITY["EPSG","9108"]],AUTHORITY["EPSG","43

26"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PA

RAMETER["central_meridian",-9],PARAMETER["scale_factor",0.9996],PARAMETER["f
alse_easting",500000],PARAMETER["false_northing",0],UNIT["Meter",1]]

If I make it print the size of pszSrcWKT  with strlen(pszSrcWKT) the
answer is 1 and finally the MEX (and the entire MATLAB) crash on the
call

OGRFree(pszSrcWKT);


Joaquim Luis

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--
Best regards,
Chaitanya kumar CH.
/tʃaɪθənjə/ /kʊmɑr/
+91-9848167848
17.241582N 80.142635E

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