OBJ02-A. Ensure the proper destructor is calledfor polymorphic objects

Calling the destructor of a derived class in an inheritance hierarchy invokes the destructors of that class and all of its parent classes. However, if the derived class is referenced by a pointer of a type higher up the hierarchy, then the destructor of the pointer's type will be called rather than the destructor of the object being pointed to, causing the object to be improperly destroyed. To correct this situation, the parent class should be defined with a virtual destructor.

Non-Compliant Code Example

In this non-compliant example, a reference to the parent class Base is used to instantiate a Derived object. When b is deleted, the destructor for Base is invoked rather than the destructor for Derived. As a result, the object b refers to will not be properly destroyed.

class Base {
public:
   Base() {
      // Build Base object
   }
   ~Base() {
      // Destroy Base object
   }
};

class Derived : public Base {
public:
   Derived() {
      // Build Derived object
   }
   ~Derived() {
      // Destroy Derived object
   }
};

void function(void) {
   Base *b = new Derived();
   // ...
   delete b;
}

Compliant Solution

To correct this example, the destructor for Base should be declared virtual. This ensures that the object b refers to will be correctly evaluated at runtime thus, deleting b will call the destructor for class Derived.

class Base {
public:
   Base() {
      // Build Base object
   }
   virtual ~Base() {
      // Destroy Base object
   }
};

class Derived : public Base {
public:
   Derived() {
      // Build Derived object
   }
   ~Derived() {
      // Destroy Derived object
   }
};

void function(void) {
   Base *b = new Derived();
   // ...
   delete b;
}

Risk Assessment

Calling the wrong destructor for a polymorphic object may lead to resource mismanagement and possibly unintended program behavior.

References