Rule Definition
From a language point of view, the pointer 'p' is part of the class and then cannot be modified in a 'const' function. But the pointed-to value is not part of the class, and may be modified. However, from a design point of view, in this case the pointed to value is still logically part of the class, it should not be modified in a 'const' function, nor should a 'const' function allow its caller to modify it through a reference.

Remediation
To correct the violation, return a 'const' reference, or return by value.

Violation Code Sample

class A
{
public:
    A() : p(new int(0)) {}
    ~A() {delete p;}
    int &violation() const {return *p;} // Violation
    int *p;
};

void f(A const &a)
{
    a.violation() = 42;
}

Fixed Code Sample

class A
{
    //...
    int const &correct1() const {return *p;}
    int correct2() const {return *p;}
}

High Integrity C++ Coding Standard Manual