MATLAB: How to pass NULL to a function that I call in a generic DLL

MATLAB

My DLL has a function that takes in a pointer, and I want to pass NULL to it.

Best Answer

There are four ways to send NULL to your function

1. Send a 0.

2. Send p after creating p in one of the following ways:

2a. p=libpointer()

2b. p=libpointer('string')

2c. p=libpointer('stringPtr')

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MATLAB: How to detect null pointers in Generic DLL return values

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

Best Answer

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