C++ Programming

Should you explicitly call a destructor in C programming?

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2012-07-19 14:05:13
2012-07-19 14:05:13

Not to be pedantic, but you cannot call a destructor explicitly. Destructors are implicitly called when an object falls from scope or when you delete a pointer to an object.

Any object created dynamically (with the new keyword) must be deleted as soon as you are finished with it, and before the pointer falls from scope. In this sense, you are explicitly calling the object's destructor, however it's really being called implicitly by you deleting the pointer. It's also good practice to explicitly NULL your pointer immediately after deleting the object it pointed to.

An object reference is destroyed automatically when the reference falls from scope. If you have a pointer to that reference, do not delete the pointer, but do assign it to NULL as soon as possible to prevent any access to the deleted object. If you do delete a pointer to a reference that's still in scope, you will render the reference NULL and a NULL reference will render your program invalid.

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It is used in combination with pointers that point to a base class. When the pointer points to a base class, but is assigned to derived object, then a destructor called by the pointer needs to be the correct one. It needs to call the destructor of the derived object, so in this case, the base class destructor needs to be virtual to let the compiler know to call the destructor of the derived object.


Destructor usually called when programs exists. You can call destructor during execution of your program to free memory. If destructor is not called you get what is called memory leak. And if you operate with large volume of data in no time you can run out of memory.


until the object goes out of scope. or until u call a destructor


If a destructor throws an exception, the instance is left in an invalid state. When an exception is thrown, the destructor automatically terminates at the point of the throw, unwinding the call stack until an exception handler is found (if one is provided). However, any resources yet to be released by the destructor, including all the instance's base classes, cannot be destroyed. When writing your own destructors, it is important to never throw an exception. If an exception could be thrown from within your destructor, you must catch it and handle it within the same destructor -- you must not rethrow the exception.


There is no such thing as a pure-virtual destructor. Classes can declare destructors to be virtual to ensure base class destructors call their derived class destructors first, but they cannot be declared pure virtual. This would imply the class is abstract and that the destructor must be overridden by all derived classes. But class destructors cannot be overridden. Every class, including an abstract class, must handle its own destruction. The only reason to declare a virtual destructor (but not a pure-virtual destructor) is when the class has one or more virtual methods besides the destructor.


The term "destructor" made me believe this question is related to .Net languages. A destructor is to destroy an instance of object. If it is available at static/class level, what is it going to destroy? The entire class, so the class no longer available? Thus, semantically, destructor should be an instance method. Constructor is on the opposite end of the life cycle of an instance. However, in .NET, a static constructor is allowed. Personally, I call this static constructor as a class initialization method. This method will be invoked by the .net framework only once when the class is loaded into the application domain. With the similar concept, there should be a "finalizer" of the class when the class is unloaded out of the application domain. But wait, does a class ever go out of the application domain once it's loaded? Yes, only at the termination of the application! Currently a class cannot be unloaded explicitly in codes and thus no point to have a static finalizer.


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Using the super keyword. If you call super() from within your constructor, it will explicitly invoke the superclass version of the constructor.


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Sure you can, but it's never a good idea. You must never allow an exception to escape from a destructor. To do so would terminate the destructor prematurely, unwinding the call stack in search of an exception handler. This means that any remaining resources consumed by the instance, including its base classes, would be left in an invalid state with no possible way to recover those resources besides terminating the program. Any object that has the potential to throw an exception during its own destruction should always be treated with suspicion; it is a major design flaw.


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Nothing, you misread something. In C, when you call a function, parameters passed by-value.


You cannot call a destructor directly. They are called automatically when an object falls from scope.delete is used in conjunction with the newoperator (similar to the way free is used in conjunction with malloc, calloc and realloc). When deleting an object instantiated with the new operator, the object's destructor is called automatically. Object references are deleted when they fall from scope (references can never be NULL while they are still in scope, and therefore cannot be deleted while in scope).


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