How can I detect null pointers in Generic DLL return values?

I am using the Generic DLL interface with a library that may return null pointers as expected results. I would like to check for null values in my LIBPOINTER results in MATLAB.

Answer 1

[MathWorks Support Team]

Starting MATLAB 7.6(R2008a), you can use the function 'IsNull' to verify if a LIBPOINTER is pointing to a null reference.

For previous product releases, read below for any possible workarounds:

The ability to check directly whether a LIBPOINTER is null is not available in MATLAB 7.4 (R2007a) and previous releases. To work around this issue, try to retrieve the pointer's target in a TRY-CATCH block.

Attempting to dereference a null pointer will cause a MATLAB error of type "MATLAB:libpointer:ValueNotDefined". This error usually indicates a null pointer. You can use the following code to check for null pointers:

p = libpointer() % Create a null pointer for testing

try

      setdatatype(p, 'int8Ptr', 1, 80) % Use actual expected type and size

      get(p) % Try to display data

catch

      e = lasterror

      if strcmp(e.identifier, 'MATLAB:libpointer:ValueNotDefined')

          disp('Null pointer.')

          % React to null pointer result

      end

end

get(p)  % Show pointer target