C++ standard question

should the following result in undefined behavior?

should value of pointer2 be NULL?

double *pointer = 0;
doubl开发者_StackOverflow中文版e &value = *pointer;
double *pointer2 = &value;

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Yes.

double *pointer = 0;    // init `pointer` to a NULL pointer value
double &value = *pointer; // dereference it

The standard specifically speaks to this situation - from 8.3.2/4 "References":

A reference shall be initialized to refer to a valid object or function. [Note: in particular, a null reference cannot exist in a well-defined program, because the only way to create such a reference would be to bind it to the “object” obtained by dereferencing a null pointer, which causes undefined behavior. As described in 9.6, a reference cannot be bound directly to a bit-field. ]

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Yes, you're dereferencing a null pointer when you do *pointer in line 2.