[conv.ptr]

# 7 Expressions [[expr]](./#expr)

## 7.3 Standard conversions [[conv]](conv#ptr)

### 7.3.12 Pointer conversions [conv.ptr]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/expressions.tex#L1022)

A [*null pointer constant*](#def:constant,null_pointer "7.3.12 Pointer conversions [conv.ptr]") is an integer literal ([[lex.icon]](lex.icon "5.13.2 Integer literals")) with
value zero
or a prvalue of type std​::​nullptr_t[.](#1.sentence-1)

A null pointer constant can be
converted to a pointer type; the
result is the null pointer value of that type ([[basic.compound]](basic.compound "6.9.4 Compound types")) and is
distinguishable from every other value of
object pointer or function pointer
type[.](#1.sentence-2)

Such a conversion is called a [*null pointer conversion*](#def:conversion,null_pointer "7.3.12 Pointer conversions [conv.ptr]")[.](#1.sentence-3)

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 ([[conv.qual]](conv.qual "7.3.6 Qualification conversions"))[.](#1.sentence-4)

A null pointer constant of integral type
can be converted to a prvalue of type std​::​nullptr_t[.](#1.sentence-5)

[*Note [1](#note-1)*:

The resulting prvalue is not a null pointer value[.](#1.sentence-6)

— *end note*]

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/expressions.tex#L1045)

A prvalue of type “pointer to cv T”, where T is an object type, can be converted to a prvalue of type “pointer tocv void”[.](#2.sentence-1)

The pointer value ([[basic.compound]](basic.compound "6.9.4 Compound types")) is unchanged by this conversion[.](#2.sentence-2)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/expressions.tex#L1051)

A prvalue v of type “pointer to cv D”, where D is a complete class type, can be converted to a prvalue of type “pointer tocv B”, where B is a base class ([[class.derived]](class.derived "11.7 Derived classes"))
of D[.](#3.sentence-1)

If B is an
inaccessible ([[class.access]](class.access "11.8 Member access control")) or
ambiguous ([[class.member.lookup]](class.member.lookup "6.5.2 Member name lookup")) base class of D, a program
that necessitates this conversion is ill-formed[.](#3.sentence-2)

If v is a null pointer value,
the result is a null pointer value[.](#3.sentence-3)

Otherwise,
if B is a virtual base class of D andv does not point to an object
whose type is similar ([[conv.qual]](conv.qual "7.3.6 Qualification conversions")) to D and
that is
within its lifetime or
within its period of construction or destruction ([[class.cdtor]](class.cdtor "11.9.5 Construction and destruction")),
the behavior is undefined[.](#3.sentence-4)

Otherwise,
the result is a pointer to the base class subobject of
the derived class object[.](#3.sentence-5)