Is Deleting a `void*` Pointer with `delete[]` Safe in C ?

Deleting Void Pointers: A Safety Assessment

Consider the following code snippet:

void* my_alloc(size_t size) {
  return new char[size];
}

void my_free(void* ptr) {
  delete[] ptr;
}

Is it safe to delete a pointer allocated as a void* using the delete[] operator?

Answer:

Deleting a pointer via a void* is explicitly undefined by the C Standard. Section 5.3.5/3 states:

In the first alternative (delete object), if the static type of the operand is different from its dynamic type, the static type shall be a base class of the operand's dynamic type and the static type shall have a virtual destructor or the behavior is undefined. In the second alternative (delete array), if the dynamic type of the object to be deleted differs from its static type, the behavior is undefined.

Additionally, the footnote notes:

This implies that an object cannot be deleted using a pointer of type void* because there are no objects of type void.

Conclusion:

It is unsafe to delete a pointer allocated as a void* using the delete[] operator. Always cast the pointer to its original type before deletion.

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