[Gdal-dev] Null-Pointer in GDALOpen?

[Mateusz Loskot]

Tom Kazimiers wrote:
> Mateusz Loskot schrieb:
>> Tom Kazimiers wrote:
>>> thanks for the replys.
>>> Sure I do test against null - the posted code was just an excerpt :) -
>>> thanks anyway.
>>> And yes, the crash occurs within GDALOpen() - I put a MessageBox before
>>> and after GDALOpen() - only the first one appeared, than the crash.
>>> The file handle explanation looked promising but before this line is
>>> arrived I still can open files plus after a restart it also does not work.
>> Tom,
>>
>> It sounds strange. Perhaps you could post complete snippet of code,
>> then it will be easier to investigate it.
> 
> Ok, here is a bigger part of it:
> 
> bool CGDALContainer::AddFile(const wchar_t * w_pszFileName)
> {   
>    
>     // Convert wchar_t to char
>     const int newsize = wcslen(w_pszFileName);
>     char    *pszFileName = (char *)malloc(newsize + 1);
>     int count = wcstombs(pszFileName, w_pszFileName, newsize);

Tom,

wcstombs will work only for ASCII subset of characters.
If w_pszFileName consists of non-ASCII characters, but some characters
from polish, french, czech languages, it will not translate the string
properly. You need to use codepage aware function, like
WideCharToMultiByte from Windows API.

>     if (count == 0 || count != newsize) {
>         FILE * pFile = _wfopen(L"PDAShpTool_ErrorLog.log",L"a");
>         fwprintf(pFile, L"Error: The Filename \"%s\" could not be
> converted to Const Char *!\n", w_pszFileName);
>         fwprintf(pFile, L"       Charactos before: %d Converted items:
> %d\n", newsize, count);
>         fclose(pFile);
>         return false;
>     }
>     pszFileName[newsize] = '\0'; // one never knows...
>     GDALDataset  *poDataset = NULL;
>    
>     GDALAllRegister();
> 
>     MessageBoxW(NULL, L"HA", L"DLL", MB_OK);
>     poDataset = (GDALDataset *) GDALOpen( "\a.tif" /*pszFileName*/,
> GA_ReadOnly );

Replace \a.tif with \\a.tif

>>> The path "a.tif" is the full path of the file as this image is stored in
>>> root directory of Windows CE 5.
>> Do you mean that using file name only works like full path to root
>> directory \, then it's wrong. It doesn't work this way under Windows CE.
>>
>> If you use only file name, it's assumed you open it from \My Documents,
>> which is a default data location under Windows CE.
>
> Thanks for this hint - strange enough that it worked until yesterday
> evening with only the filename for the root directory.
> One more thing is that if I put "a.tif" in to open it crashes - if I put
> "\a.tif" in it does not crash - it just returns NULL and I
> can handle this (besides that the null return is strange, also). The
> error returned by CPLGetLastError() is:
> CPLError: `.tif' does not exist in the file system

yes, because \a is escape sequence but not backslach + 'a' letter.
Use \\a to get string like "\a"

> This error was without convertig from wchar_t to char  - it was with
> "\a.tif" inserted directly. It seems as if the const char * is not
> received properly.

Because you don't get what you expected as filename.

> Like I said, I can not really imagine that the problem is really
> GDALOpen as it worked until yesterday and I did not change the dll.
> But the crash occurs there.

Perhaps you accidentally removed slash from correct sequence of \\

>>> The last thing I tryed was to put "GDALAllRegister();" right befor
>>> GDALOpen() - before this I did it in completely different function,
>>> which I think, should work, too.
>>> But also this change did it not...
>> Another thing I'd suggest to check is to see if you have built GDAL with
>>  GTiff driver, means check if the GTiff driver is properly registered
>> and available, in run-time.
>
> At least returns
> "GetGDALDriverManager()->GetDriverByName("GTiff")->GetDescription()":
> GTiff
> 
> So I think it gets registered properly.

Yes, it's OK.

Cheers
-- 
Mateusz Loskot
http://mateusz.loskot.net