[Insight-users] Cannot access LightObject functions in object instantiated in DLL

[Gao Han]

Dear Cory,

Thank you for your answer. I do think that function is correct, as in it
does not give the problems. I purposely added that function to show that the
problem was really in the itk::LightObject. The function was added *after* I
found the problem. 

Today, I spent the whole day on tracking down the cause of this problem, and
I think I found it. When I intantiate the filter, I used a common pointer.
If I would directly run the member function Register() the program crashed,
as Register() is a member function of LightObject. So I tried to instantiate
directly into a smart pointer, and also then I got a crash when running
member functions of LightObject. However, if I manually run Register() on
the smart pointer, directly after creating, everything works fine, but I do
have to run a UnRegister() when destroying the object, otherwise it will
result in a memory leak. Why it works this way is totally beyond me, but
then again, I do not have any experience with working with DLLs. If you have
any suggestions to what is going wrong, I would greatly appreciate to hear
this.

Thank you again for responding to my message.

Sincerely,

Gao Han 

For reference, I put the code in the form of a macro, which you can find it
below here:

// Macro for setting input. Arguments:
//          dataT       - Type of the data
//          dataE       - Enumeration label of the data
//          dataO       - The data object
//          typeI       - value keeping track of the current filter type
//          filterT     - Current filter type
//          filterO     - Filter Object
//          nextO       - Next filter in the chain
#define SET_INPUT( dataT , dataE , dataO, typeI , filterT , filterO, nextO )       
\
        {                                                                          
\
            MCAD::dataT * d = dynamic_cast<MCAD::dataT *>(dataO);                  
\
            if (d)                                                                 
\
            {                                                                      
\
                filterT * f = dynamic_cast<filterT *>(filterO.GetPointer());       
\
                if (!f)                                                            
\
                {                                                                  
\
                    filterT::Pointer nf = filterT::New();                          
\
                    nf->Register();                                                
\
                    f = nf.GetPointer();                                           
\
                    typeI = MCAD::dataE;                                           
\
                }                                                                  
\
                f->SetInput(d);                                                    
\
                nextO->SetInput(f->GetOutput());                                   
\
                filterO = f;                                                       
\
                return true;                                                       
\
            }                                                                      
\
        }



Cory Quammen wrote:
> 
> This line
> 
>>    std::cout << filt->tralalie() << "\n";           // Fine....
> 
> May be causing a problem.
> 
> In your function
> 
>>    char * tralalie() {return "In itkImageToVTKImageFilter.h";}
> 
> Here you are allocating a character array on the stack which is
> deallocated as soon as tralalie() returns. When you print out the
> return value from tralalie(), std::cout steps through the now-invalid
> memory. It probably works well enough to fool you into thinking it
> works, but it could be corrupting memory in a way that doesn't show up
> until you call
> 
> std::cout << filt->GetReferenceCount() << "\n";    // Crash with
> 
> Try removing the call to filt-tralalie() and see if that fixes your
> problem.
> 
> Hope that helps,
> Cory
> 
> -- 
> Cory Quammen
> Center for Computer Integrated Systems for Microscopy and Manipulation
> (CISMM)
> Department of Computer Science
> University of North Carolina at Chapel Hill
> http://www.cs.unc.edu/~cquammen
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