### [basic.fundamental]3.9.1 Fundamental types

1 Objects declared as characters (`char`

) shall be large enough to
store any member of the implementation’s basic character set. If a
character from this set is stored in a character object, the integral
value of that character object is equal to the value of the single
character literal form of that character. It is implementation-defined
whether a `char`

object can hold negative values.
Characters can be explicitly declared `unsigned`

or
`signed`

.
Plain `char`

, `signed char`

, and `unsigned char`

are
three distinct types, collectively called narrow character types.
A `char`

, a `signed char`

, and an
`unsigned char`

occupy the same amount of storage and have the
same alignment requirements (3.11); that is, they have the
same object representation. For character types, all bits of the object
representation participate in the value representation. For unsigned narrow
character types, each possible bit pattern of the value representation
represents a distict number. These requirements do not hold for other types. In
any particular implementation, a plain `char`

object can take on
either the same values as a `signed char`

or an ```
unsigned
char
```

; which one is implementation-defined..
For each value `i` of type `unsigned char`

in the range
0 to 255 inclusive, there exists a value `j` of type
`char`

such that the result of an integral
conversion (4.7) from `i` to `char`

is
`j`, and the result of an integral conversion from
`j` to `unsigned char`

is `i`.

2
There are five
standard signed integer types:
“`signed char`

”, “`short int`

”, “`int`

”,
“`long int`

”, and “`long long int`

”. In
this list, each type provides at least as much storage as those
preceding it in the list.
There may also be
implementation-defined
extended signed
integer types. The standard and
extended signed integer types are collectively called
signed integer types.
Plain
`int`

s have the natural size suggested by the architecture of the
execution environment^{46};
the other signed integer types are provided to meet special needs.

3
For each of the standard signed integer types,
there exists a corresponding (but different)
standard unsigned integer type:
“`unsigned char`

”, “`unsigned short int`

”,
“`unsigned int`

”, “`unsigned long int`

”, and
“`unsigned long long int`

”, each of
which occupies the same amount of storage and has the same alignment
requirements (3.11) as the corresponding signed integer
type^{47};
that is, each signed integer type has the same object representation as
its corresponding unsigned integer type.
Likewise, for each of the extended signed integer types there exists a
corresponding
extended unsigned integer type with the same amount of storage and alignment
requirements. The standard and extended unsigned integer types are
collectively called
unsigned integer types. The range of non-negative
values of a signed integer type is a subrange of the corresponding
unsigned integer type, and the value
representation of each corresponding signed/unsigned type shall be the
same.
The standard signed integer ntypes and standard unsigned integer types
are collectively called the
standard integer types,
and the extended
signed integer types and extended
unsigned integer types are collectively called the
extended integer types.
The signed and unsigned integer types shall satisfy
the constraints given in the C standard, section 5.2.4.2.1.

4
Unsigned integers shall obey the laws of arithmetic modulo 2^{n} where `n` is
the number of bits in the value representation of that particular size of
integer.^{48}

5
Type `wchar_t`

is a distinct type whose values can represent
distinct codes for all members of the largest extended character set
specified among the supported locales (22.3.1). Type
`wchar_t`

shall have the same size, signedness, and alignment
requirements (3.11) as one of the other integral types,
called its underlying type. Types `char16_t`

and
`char32_t`

denote distinct types with the same size, signedness,
and alignment as `uint_least16_t`

and `uint_least32_t`

,
respectively, in `<stdint.h>`

, called the underlying types.

6
Values of type `bool`

are either `true`

or
`false`

.^{49}
[ *Note:* There are no `signed`

, `unsigned`

, `short`

,
or `long`

`bool`

types or values. — *end note* ] Values of type
`bool`

participate in integral promotions (4.5).

7 Types `bool`

, `char`

, `char16_t`

, `char32_t`

,
`wchar_t`

, and the signed and unsigned integer types are
collectively called
integral typess.^{50}
A synonym for integral type is
integer type. The representations of integral types shall
define values by use of a pure binary numeration system.^{51}
[ *Example:* this International Standard permits 2’s complement, 1’s
complement and signed magnitude representations for integral types. — *end example* ]

8 There are three
floating point types:
`float`

,
`double`

,
and
`long double`

. The type `double`

provides at least as much
precision as `float`

, and the type `long double`

provides at
least as much precision as `double`

. The set of values of the type
`float`

is a subset of the set of values of the type
`double`

; the set of values of the type `double`

is a subset
of the set of values of the type `long double`

. The value
representation of floating-point types is implementation-defined.
Integral and floating types are collectively
called arithmetic types.
Specializations of the standard template
`std::numeric_limits`

(18.3) shall specify the
maximum and minimum values of each arithmetic type for an
implementation.

9
The `void`

type has an empty set of values. The `void`

type
is an incomplete type that cannot be completed. It is used as the return
type for functions that do not return a value. Any expression can be
explicitly converted to type `cv`
`void`

(5.4). An expression of type `void`

shall
be used only as an expression statement (6.2), as an operand
of a comma expression (5.19), as a second or third operand
of `?:`

(5.16), as the operand of
`typeid`

, `noexcept`

, or `decltype`

, as
the expression in a return statement (6.6.3) for a function
with the return type `void`

, or as the operand of an explicit conversion
to type `cv` `void`

.

10
A value of type `std::nullptr_t`

is a null pointer
constant (4.10). Such values participate in the pointer and the
pointer to member conversions (4.10, 4.11).
`sizeof(std::nullptr_t)`

shall be equal to `sizeof(void*)`

.

11 [ *Note:* Even if the implementation defines two or more basic types to have the
same value representation, they are nevertheless different types. — *end note* ]

46) that is, large enough to contain any value in the range of
`INT_MIN`

and `INT_MAX`

, as defined in the header
`<climits>`

.

47) See 7.1.6.2 regarding the correspondence between types and
the sequences of *type-specifier*s that designate them.

48) This implies that unsigned arithmetic does not overflow because a result that cannot be represented by the resulting unsigned integer type is reduced modulo the number that is one greater than the largest value that can be represented by the resulting unsigned integer type.

49) Using a `bool`

value in ways described by this International
Standard as “undefined”, such as by examining the value of an
uninitialized automatic object, might cause it to behave as if it is
neither `true`

nor `false`

.

50) Therefore, enumerations (7.2) are not integral; however, enumerations can be promoted to integral types as specified in 4.5.

51) A positional representation for integers that uses the binary digits 0 and 1, in which the values represented by successive bits are additive, begin with 1, and are multiplied by successive integral power of 2, except perhaps for the bit with the highest position. (Adapted from the American National Dictionary for Information Processing Systems.)