CERT C++: OOP55-CPP

Do not use pointer-to-member operators to access nonexistent members

Since R2022a

Description

Rule Definition

Do not use pointer-to-member operators to access nonexistent members.¹

Polyspace Implementation

The rule checker checks for Pointer to member accessing non-existent class members

Examples

Pointer to Member Accessing Non-Existent Class Members

Issue

This issue occurs when you use of pointer-to-member operators in these instances:

• You cast a pointer-to-member type to another pointer-to-member type which does not contain the class member pointed to. For instance, in this code snippet, pointer-to-member ptrToMember is obtained from myObj::f but is then upcast to baseObj::* which does not contain a method f.

  class baseObj {
    public:
      virtual ~baseObj() = default;
  };
  
  class myObj : public baseObj {
    public:
      void f();
  };
  
  
  void func() {
      baseObj* foo = new baseObj();
      void (baseObj::*ptrToMember)() =
          static_cast<void (baseObj::*)()>(&myObj::f); //Noncompliant
      (foo->*ptrToMember)();
  }
  

  Polyspace^® does not flag the casting operation if the type being cast to inherits from the other type. For example, in the preceding code, if baseObj inherits from myObj.

• The second operand of the pointer-to-member operator is a null pointer. For instance, in this code snippet, ptrToMember is declared but not initialized and defaults to a null pointer.

  class baseObj {
    public:
      virtual ~baseObj() = default;
  };
  static void (baseObj::*ptrToMember)(); //Not initialized 
  
  void func() {
      baseObj* foo = new baseObj();
  
      (foo->*ptrToMember)(); //Noncompliant
  }
  

Risk

The use of pointer-to-member operators results in undefined behavior in these cases:

• The dynamic type of the first operand does not contain the member referred to by the second operand.

• The second operand pointer is null.

Fix

Do not cast a pointer-to-member to a type that does not contain the class member pointed to, and do not use a null pointer as the second operand of the pointer to member operator.

Example — Pointer-to-Member Accesses Non-Existent Class Member

class Base {
  public:
    void f() {
    }
};

class Derived : public Base {
  public:
    int myVar;
};

void func() {
    Base myObj;
    auto ptrToMethod =
        static_cast<void (Base::*)()>(&Derived::f); // Compliant
    auto ptrToMember =
        static_cast<int(Base::*)>(&Derived::myVar); // Noncompliant

    (myObj.*ptrToMethod)(); // OK, equivalent to myObj.f()
    myObj.*ptrToMember;     // Undefined behavior
}

In this example, Polyspace flags the casting of ptrToMember, which is obtained from Derived::myVar, to Base::* because this class does not contain a member myVar. If you execute the code, the call myObj.*ptrToMember; results in undefined behavior.

Polyspace does not flag the casting of ptrToMethod to Base::* because class Derived inherits method f from Base.

Correction — Use Correct Type for Underlying Object

class Base {
  public:
    void f() {
    }
};

class Derived : public Base {
  public:
    int myVar;
};

void func() {
    Derived myObj;
    auto ptrToMethod =
        static_cast<void (Base::*)()>(&Derived::f); // Compliant
    int (Derived::*ptrToMember) = &Derived::myVar; 

    (myObj.*ptrToMethod)(); // OK, equivalent to myObj.f()
    myObj.*ptrToMember; // Compliant  
}

One possible correction is to use the correct type for the object that you use as the first operator of the pointer-to-member operator. In the preceding code, myObj is of type Derived and the casting is no longer necessary in the declaration of ptrToMember.

Check Information

Group: Rule 09. Object Oriented Programming (OOP)

Version History

Introduced in R2022a