7 Standard conversions [conv]

7.11 Pointer conversions [conv.ptr]

A null pointer constant is an integer literal with value zero or a prvalue of type std​::​nullptr_­t.
A null pointer constant can be converted to a pointer type; the result is the null pointer value of that type and is distinguishable from every other value of object pointer or function pointer type.
Such a conversion is called a null pointer conversion.
Two null pointer values of the same type shall compare equal.
The conversion of a null pointer constant to a pointer to cv-qualified type is a single conversion, and not the sequence of a pointer conversion followed by a qualification conversion.
A null pointer constant of integral type can be converted to a prvalue of type std​::​nullptr_­t.
[Note
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The resulting prvalue is not a null pointer value.
end note
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A prvalue of type “pointer to cv T”, where T is an object type, can be converted to a prvalue of type “pointer to cv void.
The pointer value is unchanged by this conversion.
A prvalue of type “pointer to cv D”, where D is a class type, can be converted to a prvalue of type “pointer to cv B”, where B is a base class of D.
If B is an inaccessible or ambiguous base class of D, a program that necessitates this conversion is ill-formed.
The result of the conversion is a pointer to the base class subobject of the derived class object.
The null pointer value is converted to the null pointer value of the destination type.