validating an object pointer returned by an exported function

[srilalpr]

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]

sr******@gmail. com wrote:

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 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]

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]

sr******@gmail. com skrev:

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

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

--
TB @ SWEDEN

[srilalpr]

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]

sr******@gmail. com skrev:

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.

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

--
TB @ SWEDEN

[srilalpr]

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:

sr******@gmail. com skrev:

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.

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

--
TB @ SWEDEN

[TB]

sr******@gmail. com skrev:

hi,

ok.
for me when i execute pMyClassCreate( );
i get an invalid pointer to MyClass object ie. pobjMyClassobj is
invalid.
pobjMyClassobj? Can't find that name in the source code you posted.

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

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

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

int != MyClass*
Thanks & Regards,
Srilal

TB wrote:

sr******@gmail. com skrev:

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.

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

--
TB @ SWEDEN

--
TB @ SWEDEN

[Rolf Magnus]

sr******@gmail. com wrote:

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.

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.