CertC++-EXP51ΒΆ

Do not delete an array through a pointer of the incorrect type

Required inputs: IR, StaticSemanticAnalysis

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 array object through a static pointer type that differs from the dynamic pointer type of the object. Deleting an array through a pointer to the incorrect type results in  undefined behavior.

Noncompliant Code Example

In this noncompliant code example, an array of  Derived objects is created and the pointer is stored in a  Base *. Despite  Base::~Base() being declared virtual, it still results in undefined behavior. Further, attempting to perform pointer arithmetic on the static type  Base * violates CTR56-CPP. Do not use pointer arithmetic on polymorphic objects. 

struct Base {
  virtual ~Base() = default;
};

struct Derived final : Base {};

void f() {
   Base *b = new Derived[10];
   // ...
   delete [] b;
}
Compliant Solution

In this compliant solution, the static type of  b is  Derived *, which removes the  undefined behavior when indexing into the array as well as when deleting the pointer. 

struct Base {
  virtual ~Base() = default;
};

struct Derived final : Base {};

void f() {
   Derived *b = new Derived[10];
   // ...
   delete [] b;
}
Risk Assessment

Attempting to destroy an array of polymorphic objects through the incorrect static type is undefined behavior. In practice, potential consequences include abnormal program execution and memory leaks.

Rule Severity Likelihood Remediation Cost Priority Level
EXP51-CPP Low Unlikely Medium P2 L3
Related Guidelines
SEI CERT C++ Coding Standard

CTR56-CPP. Do not use pointer arithmetic on polymorphic objects

OOP52-CPP. Do not delete a polymorphic object without a virtual destructor
Bibliography
[ ISO/IEC 14882-2014] Subclause 5.3.5, "Delete"
Excerpt from SEI CERT C++ Coding Standard [https://cmu-sei.github.io/secure-coding-standards/sei-cert-cpp-coding-standard/rules/expressions-exp/exp51-cpp], Copyright (C) 1995-2026 Carnegie Mellon University. See section 9.4. "3rd-Party Licenses" in the documentation for full details.

Possible Messages

Key

Text

Severity

Disabled

bad_array_delete

Do not delete an array through a pointer of the incorrect type.

None

False

Options