How and When Are Objects Destroyed in C ?

Object Destruction in C

In C , object destruction is a fundamental aspect of memory management. Understanding how objects are destroyed is crucial for writing robust and efficient code.

When Are Objects Destroyed?

Objects can be classified as either scoped or dynamic:

Scoped Objects:

• Their destruction time is determined statically by their enclosing scope.
• Examples include local variables, static objects at namespace scope, and local static objects.
• Scoped objects are destructed in reverse order of their definition within a block, after function execution, or after program termination.

Dynamic Objects:

• Their destruction time is under programmer control.
• Examples include objects created with new or dynamic arrays created with new[].
• Dynamic objects must be explicitly destroyed with delete or delete[] respectively to avoid memory leaks.

Stack Unwinding and Exceptions:

When an exception is thrown, stack unwinding occurs, which results in the destruction of all previously constructed scoped objects before the exception is propagated. However, destructors of these objects cannot throw exceptions, as that would lead to termination via std::terminate.

Destruction Order:

• For scoped objects, member subobjects and base class subobjects are destructed in reverse order of definition.
• For arrays, elements are destructed in descending order.
• For temporary objects, they are destructed when the full-expression containing the prvalue is completely evaluated.
• For dynamic objects, they are destructed when explicitly deleted.

Common Pitfalls:

• Forgetting to destroy dynamic objects can lead to memory leaks.
• Attempting to use deleted objects or destroy them multiple times results in undefined behavior.
• Ignoring exception safety in destructors can cause program termination via std::terminate.

In general, C provides a powerful approach to object management by offering both static and dynamic scope. Understanding the destruction semantics enables you to write code that effectively manages memory and avoids potential pitfalls.

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