"clear all" causes seg fault due to failure of calling a class destructor

Hello all,

Let me briefly describe my code. I made mex functions to access a C++ class. Based on my mex functions, I made an MATLAB class that mimics the original C++ class. Basically, the C++ class's constructor gets called in the MATLAB class's constructor, and likewise, the C++ class's destructor gets called in the MATLAB class's destructor, i.e. the delete() function. In the C++ class's constructor, I dynamically allocate some memory space and free the space in the C++ class's destructor.

My code worked fine, but I found it can cause seg fault at a particular case, which is the case that I run "clear all" in MATLAB. Specifically, I got a seg fault error when I run "clear classes." It seems to me at both cases the C++ class's destructor, which de-allocate memory, cannot be called. However, it does get called for "clear variables."

The MATLAB documentation says there are differences between "clear" and "delete," but I cannot find some answers to my problem. I wonder if there is a way to free memory space properly by calling the destructor for "clear all" and "clear classes." Look forward to hearing some advice.

K. Lee.

Answer 1

[Daniel Shub]

The clear command does not delete an object. An object is only deleted if all references to the object are cleared from memory. Is it possible that you have a reference to the object someplace that is being cleared (possibly in the application data of a figure or a callback of a timer object). I would bet strange things will happen if you clear classes without all your instances of the class not being cleared.

[Kyunghoon Lee]

Daniel,

Thank you for the reply. My MATLAB class constructor stores a pointer to a created C++ object in "obj_id," which is unit64, however "clear obj_id" does not look like it frees memory space allocated when the C++ object created. I wonder if there is a way to call delete() when "clear" is called.

K. Lee.

[James Tursa]

Are you using a mexAtExit function?

[Daniel Shub]

You really do not want to call delete when clear is called. This would screw up anything that depends on a "saved" handle to the object.

Answer 2

[Daniel Shub]

Are you defining your delete method in the a methods block in the classdef file or in a separate file within the @foo directory (where foo is the name of your class)? I have had problems getting the overloaded delete method to be called when I define it is a separate file. It seems to help if I add a methods block with the footprint of the delete function into the classdef file.

methods
  delete(Obj);
end

[Kyunghoon]

I have the delete function defined in the classdef file. I wonder if I can overload "clear" so that when "clear myobj" is called, I can invoke the delete method.