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The pointer-to-member operators .* and ->* are used to obtain an object or a function as though it were a member of an underlying object. For instance, the following are functionally equivalent ways to call the member function f() on the object o:

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The C++ Standard, [expr.mptr.oper], paragraph 4 , states [ISO/IEC 14882-2014], states :

Abbreviating pm-expression.*cast-expression as E1.*E2, E1 is called the object expression. If the dynamic type of E1 does not contain the member to which E2 refers, the behavior is undefined.

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Further, the C++ Standard, [expr.mptr.oper], paragraph 6, states, in part:

If the second operand is the null pointer to member value, the behavior is undefined.

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In this noncompliant code example, a pointer-to-member object is obtained from D::g, but upcast to be a B::*. When called on an object whose dynamic type is D, the pointer-to-member call is well - defined. However, in this noncompliant code example, the dynamic type of the underlying object is B, resulting in undefined behavior:

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

struct D : B {
  virtual ~D() = default;
  virtual void g() { /* ... */ }
};

void f() {
  B *b = new B;
 
  // ...
 
  void (B::*gptr)() = static_cast<void(B::*)()>(&D::g);
  (b->*gptr)();
  delete b;
}

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In this compliant solution, the upcast is removed, rendering the initial code ill-formed . This emphasizes and emphasizing the underlying problem: that B::g() does not exist. This compliant solution assumed assumes the programmer intent was to use the correct dynamic type for the underlying object:

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In this noncompliant code example, a null pointer-to-member value is passed as the second operand to a pointer-to-member expression, resulting in undefined behavior:

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

struct D : B {
  virtual ~D() = default;
  virtual void g() { /* ... */ }
};
 
static void (D::*gptr)();
void call_memptr(D *ptr) {
  (ptr->*gptr)();
}
 
void f() {
  D *d = new D;
  call_memptr(d);
  delete d;
}

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In this compliant solution, gptr is properly initialized to a valid pointer-to-member value , instead of to the default value of nullptr:

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Search for other vulnerabilities resulting from the violation of this rule on the CERT website.

Related Guidelines

Bibliography

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OOP54-CPP. Gracefully handle self-assignment      Image Removed         Image Added