When is Explicit Destructor Invocation Allowed in C ?

Explicit Destructor Invocation: Exceptions and Applications

In most instances, explicit destructor calls are discouraged due to undefined behavior. However, the C 11 Standard provides an exception in cases of template argument specification for destructors.

Consider the following code snippet:

template<class T> struct A {
    ~A();
}; 

void f(A<int>* p, A<int>* q) {
    p->A<int>::~A();      // OK: destructor call
    q->A<int>::~A<int>(); // OK: destructor call
}

In this example, explicit destructor calls are permitted because they pertain to objects of specialized class templates. The template arguments (in this case, int) can be explicitly provided in the destructor call syntax.

Beyond this exception, explicit destructor invocation can also be justified in the context of placement delete. This is because when memory is allocated using placement new, the destructor must be invoked explicitly to deallocate the memory.

While explicit destructor calls are generally not advisable for regular variables, they can be considered in the following scenarios:

1. Object Destruction after Placement New: To manually release memory allocated via placement new.
2. Trivial Destructors: Destructors with empty bodies can be safely called explicitly. However, this practice is usually unnecessary.

In summary, explicit destructor invocation is permissible in certain circumstances such as template argument specification or handling placement new. However, it remains crucial to exercise caution and avoid accessing destroyed objects to prevent undefined behavior.

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