When is it valid to access a pointer to a “dead” object?

Question

First, to clarify, I am not talking about dereferencing invalid pointers!

Consider the following two examples.

Example 1

Answer 1

C++ discussion

Short answer: In C++, there is no such thing as accessing "reading" a class instance; you can only "read" non-class object, and this is done by a lvalue-to-rvalue conversion.

Detailed answer:

typedef struct { int *p; } T;

T designates an unnamed class. For the sake of the discussion let's name this class T:

struct T {
    int *p; 
};

Because you did not declare a copy constructor, the compiler implicitly declares one, so the class definition reads:

struct T {
    int *p; 
    T (const T&);
};

So we have:

T a;
T b = a;    // Access through a non-character type?

Yes, indeed; this is initialization by copy constructor, so the copy constructor definition will be generated by the compiler; the definition is equivalent with

inline T::T (const T& rhs) 
    : p(rhs.p) {
}

So you are accessing the value as a pointer, not a bunch of bytes.

If the pointer value is invalid (not initialized, freed), the behavior is not defined.