The C++ Standard, [expr.delete], paragraph 3 [ISO/IEC 14882-2014 ], states the following:
In the first alternative (delete object), if the static type of the object to be deleted is different from its dynamic type, the static type shall be a base class of the dynamic type of the object to be deleted 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.
Do not delete an object of derived class type through a pointer to its base class type that has a non-virtual
destructor. Instead, the base class should be defined with a virtual
destructor. Deleting an object through a pointer to a type without a virtual
destructor results in undefined behavior.
Noncompliant Code Example
In this noncompliant example, b
is a polymorphic pointer type whose static type is Base *
and whose dynamic type is Derived *
. When b
is deleted, it results in undefined behavior because Base
does not have a virtual
destructor. The C++ Standard, [class.dtor], paragraph 4 [ISO/IEC 14882-2014 ], states the following:
If a class has no user-declared destructor, a destructor is implicitly declared as defaulted. An implicitly declared destructor is an
inline public
member of its class.
The implicitly declared destructor is not declared as virtual
even in the presence of other virtual
functions.
struct Base { virtual void f(); }; struct Derived : Base {}; void f() { Base *b = new Derived(); // ... delete b; }
Noncompliant Code Example
In this noncompliant example, the explicit pointer operations have been replaced with a smart pointer object, demonstrating that smart pointers suffer from the same problem as other pointers. Because the default deleter for std::unique_ptr
calls delete
on the internal pointer value, the resulting behavior is identical to the previous noncompliant example.
#include <memory> struct Base { virtual void f(); }; struct Derived : Base {}; void f() { std::unique_ptr<Base> b = std::make_unique<Derived()>(); }
Compliant Solution
In this compliant solution, the destructor for Base
has an explicitly declared virtual
destructor, ensuring that the polymorphic delete operation results in well-defined behavior.
struct Base { virtual ~Base() = default; virtual void f(); }; struct Derived : Base {}; void f() { Base *b = new Derived(); // ... delete b; }
Risk Assessment
Attempting to destruct a polymorphic object that does not have a virtual
destructor declared results in undefined behavior. In practice, potential consequences include abnormal program termination and memory leaks.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
---|---|---|---|---|---|
OOP52-CPP | Low | Likely | Low | P9 | L2 |
Automated Detection
Tool | Version | Checker | Description |
---|---|---|---|
4.4 | 2116, 3403 | ||
Klocwork | 2023.3 | CL.MLK.VIRTUAL | |
Clang | 3.9 | -Wdelete-non-virtual-dtor | |
LDRA tool suite | 9.7.1
| 303 S | Partially implemented |
Parasoft C/C++test | 9.5 | OOP-22 | |
SonarQube C/C++ Plugin | 4.10 | S1235 |
Related Vulnerabilities
Search for other vulnerabilities resulting from the violation of this rule on the CERT website.
Related Guidelines
SEI CERT C++ Coding Standard | EXP51-CPP. Do not delete an array through a pointer of the incorrect type |
Bibliography
[ISO/IEC 14882-2014] | Subclause 5.3.5, "Delete" |
[Stroustrup 06] | "Why Are Destructors Not Virtual by Default?" |