The 3ds Max API provides a method used to allocate memory when a new instance of a plug-in class is required. It also provides several different ways to deallocate this memory depending on the plug-in type. In the most common case, these methods are ClassDesc::Create() and Animatable::DeleteThis().

Note: While the Create() method is a member of ClassDesc, developers should use ClassDesc2 which inherits from ClassDesc.

When 3ds Max needs to create a new instance of a plug-in class, it calls the Create() method of the class descriptor. This method returns a new instance of the plug-in class. The memory for the class may be allocated by using the new operator as shown below:

void* Create(BOOL loading = FALSE) { return new MyObject; }

For example, when 3ds Max loads a file from disk it needs to create instances of the plug-ins that are used (the geometric objects, lights, cameras, materials, controllers, etc.). It does this by calling ClassDesc::Create().

The memory must be freed when 3ds Max is done with the item. Usually a method named DeleteThis() is called. This method is called to free the memory associated with the plug-in class. Since the memory was allocated with the new operator, it must be de-allocated using the delete operator as shown below:

void DeleteThis() { deletethis; }

For plug-ins that are part of the Animatable class hierarchy, DeleteThis() is a method of Animatable. For plug-ins that are not derived from Animatable there may be a non-inherited DeleteThis() method. For example, the UtilityObj class used to create Utility plug-ins is not derived from Animatable and has its own DeleteThis().

The DeleteThis() method also gives the developer control over deleting. For example, a Utility plug-in object may be statically declared and not actually declared in the heap. A utility plug-in such as\MAXSDK\SAMPLES\RETIRED\ASCIIOUT.CPP would implement DeleteThis() to do nothing since there is no heap memory to free. Fore example:

void DeleteThis() {}

A few plug-in types have no DeleteThis() method at all -- 3ds Max deletes the memory directly. The Image Filter and Compositor plug-in types are derived from ImageFilter. They are allocated by system using ClassDesc::Create() but have no DeleteThis() method to override. The system just calls the operatordelete() operator on the object instance.