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Are C# destructors the same as C++ destructors?

  Shared By: Ray Lawrence    Date: Dec 03    Category: C#    Views: 1019


No. They look the same but they are very different. The C# destructor syntax (with the familiar ~ character) is just syntactic sugar for an override of the System.Object Finalize method. This Finalize method is called by the garbage collector when it determines that an object is no longer referenced, before it frees the memory associated with the object. So far this sounds like a C++ destructor. The difference is that the garbage collector makes no guarantees about when this procedure happens. Indeed, the algorithm employed by the CLR garbage collector means that it may be a long time after the application has finished with the object. This lack of certainty is often termed 'non-deterministic finalization', and it means that C# destructors are not suitable for releasing scarce resources such as database connections, file handles etc.

To achieve deterministic destruction, a class must offer a method to be used for the purpose. The standard approach is for the class to implement the IDisposable interface. The user of the object must call the Dispose() method when it has finished with the object. C# offers the 'using' construct to make this easier.

Note that it's rarely necessary to define a destructor for a C# class - it only makes sense where the class holds direct references to unmanaged resources, which is very unusual. Implementing IDisposable is somewhat more commonly required, but still only necessary for a small minority of classes.


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