validating an object pointer returned by an exported function

[srilalpr@gmail.com]

Hi,

I have a dll and one of its exported function is suppossed to return a
pointer to an object.
How can i check whether the exported function is of the same prototype
i want.


Please comment


Thanks & Regards
Srilal

[benben]

Re: validating an object pointer returned by an exported function

srilalpr@gmail. com wrote:[color=blue]
> Hi,
>
> I have a dll and one of its exported function is suppossed to return a
> pointer to an object.
> How can i check whether the exported function is of the same prototype
> i want.[/color]

Please be noted that the concept of DLL may be implemented differently
across platforms and such a concept is not a concern of the C++ standard
and is generally off-topic in this newsgroup. You may therefore consult
platform specific documentation on DLL's or ask in a more suitable
newsgroup.

That said, I think the C++ name mangling would do the trick, although in
some systems it is mandated exported functions must be extern "C" and
therefore cannot be mangled.

Regards,
Ben

[srilalpr@gmail.com]

Re: validating an object pointer returned by an exported function

hi,
actually what i meant was, if i am executing the exported function
then how can i test if the returned values is a valid pointer to the
expected object.

Thanks & Regards,
Srilal

[TB]

Re: validating an object pointer returned by an exported function

srilalpr@gmail. com skrev:[color=blue]
> hi,
> actually what i meant was, if i am executing the exported function
> then how can i test if the returned values is a valid pointer to the
> expected object.
>
> Thanks & Regards,
> Srilal
>[/color]

If the function does not guarantee that a returned non-null pointer
is valid, then don't use the function.

--
TB @ SWEDEN

[srilalpr@gmail.com]

Re: validating an object pointer returned by an exported function

Hi,

here is the code snippent of my application

HINSTANCE hHandle = LoadLibrary ("UserDLL.dll") ;

//If the dll handle returns is null then trow exception.
if (!hHandle)
{ throw Exception; }

//Else get call the exported function pointer for creating the
object
typedef MyClass* (*pMyClass) ();

pMyClass pMyClassCreate= (pMyClass) GetProcAddress( hHandle,
"ExportedFuncti on");

if (!pMyClassCreat e)
{
if (hHandle)
{
FreeLibrary (hHandle);
}

throw Exception
}

MyClass * pMyClassobj;
try
{
pMyClassobj = pMyClassCreate( );
}
catch(...)
{
throw Exception;
}

try
{
pMyClass->MyFunction() ;
}
catch(...)
{
}

now my question is what if the ExportedFunctio n does not return the
pointer to MyClass
then executing pMyClass->MyFunction is giving access violations.

Thanks & Regards,
Srilal

[TB]

Re: validating an object pointer returned by an exported function

srilalpr@gmail. com skrev:[color=blue]
> Hi,
>
> here is the code snippent of my application
>
> HINSTANCE hHandle = LoadLibrary ("UserDLL.dll") ;
>
> //If the dll handle returns is null then trow exception.
> if (!hHandle)
> { throw Exception; }
>
> //Else get call the exported function pointer for creating the
> object
> typedef MyClass* (*pMyClass) ();
>
> pMyClass pMyClassCreate= (pMyClass) GetProcAddress( hHandle,
> "ExportedFuncti on");
>
> if (!pMyClassCreat e)
> {
> if (hHandle)
> {
> FreeLibrary (hHandle);
> }
>
> throw Exception
> }
>
> MyClass * pMyClassobj;
> try
> {
> pMyClassobj = pMyClassCreate( );
> }
> catch(...)
> {
> throw Exception;
> }
>
> try
> {
> pMyClass->MyFunction() ;
> }
> catch(...)
> {
> }
>
> now my question is what if the ExportedFunctio n does not return the
> pointer to MyClass
> then executing pMyClass->MyFunction is giving access violations.
>[/color]

if(pMyClassobj) {
pMyClassobj->MyFunction() ;
}

--
TB @ SWEDEN

[srilalpr@gmail.com]

Re: validating an object pointer returned by an exported function

hi,

ok.
for me when i execute pMyClassCreate( );
i get an invalid pointer to MyClass object ie. pobjMyClassobj is
invalid.

e.g if the ExportedFunctio n has the prototype int Function(int,in t)
then executing it will give me int instead of MyClass*

so is there a way to check whether the returned pointer is of a valid
object because else executing MyFunction will give access violation.

Thanks & Regards,
Srilal

TB wrote:
[color=blue]
> srilalpr@gmail. com skrev:[color=green]
> > Hi,
> >
> > here is the code snippent of my application
> >
> > HINSTANCE hHandle = LoadLibrary ("UserDLL.dll") ;
> >
> > //If the dll handle returns is null then trow exception.
> > if (!hHandle)
> > { throw Exception; }
> >
> > //Else get call the exported function pointer for creating the
> > object
> > typedef MyClass* (*pMyClass) ();
> >
> > pMyClass pMyClassCreate= (pMyClass) GetProcAddress( hHandle,
> > "ExportedFuncti on");
> >
> > if (!pMyClassCreat e)
> > {
> > if (hHandle)
> > {
> > FreeLibrary (hHandle);
> > }
> >
> > throw Exception
> > }
> >
> > MyClass * pMyClassobj;
> > try
> > {
> > pMyClassobj = pMyClassCreate( );
> > }
> > catch(...)
> > {
> > throw Exception;
> > }
> >
> > try
> > {
> > pMyClass->MyFunction() ;
> > }
> > catch(...)
> > {
> > }
> >
> > now my question is what if the ExportedFunctio n does not return the
> > pointer to MyClass
> > then executing pMyClass->MyFunction is giving access violations.
> >[/color]
>
> if(pMyClassobj) {
> pMyClassobj->MyFunction() ;
> }
>
> --
> TB @ SWEDEN[/color]

[TB]

Re: validating an object pointer returned by an exported function

srilalpr@gmail. com skrev:[color=blue]
> hi,
>
> ok.
> for me when i execute pMyClassCreate( );
> i get an invalid pointer to MyClass object ie. pobjMyClassobj is
> invalid.[/color]

pobjMyClassobj? Can't find that name in the source code you posted.
[color=blue]
>
> e.g if the ExportedFunctio n has the prototype int Function(int,in t)
> then executing it will give me int instead of MyClass*[/color]

Yes, of course it does.
[color=blue]
>
> so is there a way to check whether the returned pointer is of a valid
> object because else executing MyFunction will give access violation.
>[/color]

Which pointer, it apparently returns an 'int', not a pointer
to an object of MyClass.

int != MyClass*
[color=blue]
> Thanks & Regards,
> Srilal
>
> TB wrote:
>[color=green]
>> srilalpr@gmail. com skrev:[color=darkred]
>>> Hi,
>>>
>>> here is the code snippent of my application
>>>
>>> HINSTANCE hHandle = LoadLibrary ("UserDLL.dll") ;
>>>
>>> //If the dll handle returns is null then trow exception.
>>> if (!hHandle)
>>> { throw Exception; }
>>>
>>> //Else get call the exported function pointer for creating the
>>> object
>>> typedef MyClass* (*pMyClass) ();
>>>
>>> pMyClass pMyClassCreate= (pMyClass) GetProcAddress( hHandle,
>>> "ExportedFuncti on");
>>>
>>> if (!pMyClassCreat e)
>>> {
>>> if (hHandle)
>>> {
>>> FreeLibrary (hHandle);
>>> }
>>>
>>> throw Exception
>>> }
>>>
>>> MyClass * pMyClassobj;
>>> try
>>> {
>>> pMyClassobj = pMyClassCreate( );
>>> }
>>> catch(...)
>>> {
>>> throw Exception;
>>> }
>>>
>>> try
>>> {
>>> pMyClass->MyFunction() ;
>>> }
>>> catch(...)
>>> {
>>> }
>>>
>>> now my question is what if the ExportedFunctio n does not return the
>>> pointer to MyClass
>>> then executing pMyClass->MyFunction is giving access violations.
>>>[/color]
>> if(pMyClassobj) {
>> pMyClassobj->MyFunction() ;
>> }
>>
>> --
>> TB @ SWEDEN[/color]
>[/color]

--
TB @ SWEDEN

[Rolf Magnus]

Re: validating an object pointer returned by an exported function

srilalpr@gmail. com wrote:
[color=blue]
> hi,
>
> ok.
> for me when i execute pMyClassCreate( );
> i get an invalid pointer to MyClass object ie. pobjMyClassobj is
> invalid.
>
> e.g if the ExportedFunctio n has the prototype int Function(int,in t)
> then executing it will give me int instead of MyClass*
>
> so is there a way to check whether the returned pointer is of a valid
> object because else executing MyFunction will give access violation.[/color]

I would simply do that like you do it with every other library function.
Make a header that belongs to the library and declare the prototype in that
header.