Rule Definition
Casting from pointer to base class to pointer to derived class should usually be done through 'dynamic_cast'. See rule #8060 for more information. In performances-constrained situations, and if you know through another mean that the 'dynamic_cast' will succeed, you can instead call 'static_cast', which will be slightly more efficient. In this case, it is advised to write code that will check in debug builds that the assumption is true. In any case, a C-style cast is unsafe to use, because it will be considered as a 'reinterpret_cast' if the classes are not related, and will do the wrong thing.

Remediation
Use 'dynamic_cast' or 'static_cast' to cast pointers to base class to pointer to derived class. See remediation example for more details.

Violation Code Sample

class A
{
};

class B : public A
{
};

void f(A *p)
{
    B* pb = (B*)p; // Violation
    // Use pb
}

Fixed Code Sample

void f(A *p)
{
    B* pb = dynamic_cast<B*>(p);
    if (!pb)
    {
        // Not the expected type, handle the error 
    }
    else
    {
        // Use pb
    }
}

In circumstances where the @dynamic_cast@ has been measured to cause unacceptable delay, a @static_cast@ could be used instead, but would benefit from being written this way:

template<class To, class From> To checked_cast(From* p)
{
    assert(dynamic_cast<To>(p) == static_cast<To>(p) && "Error: Check cast failed");
    return static_cast<To>(p);
}

void f(A *p)
{
    B* pb = checked_cast<B*>(p);
    // Use pb
}

MISRA C++ C++ Coding Standard (Sutter/Alexandrescu) Item 93, http://www.gotw.ca/publications/c++cs.htm