6 Basics [basic]

6.7 Types [basic.types]

6.7.1 Fundamental types [basic.fundamental]

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.
The range of representable values for a signed integer type is to (inclusive), where N is called the width of the type.
Note
:
Plain ints are intended to have the natural size suggested by the architecture of the execution environment; the other signed integer types are provided to meet special needs.
— end note
 ]
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.
Likewise, for each of the extended signed integer types, there exists a corresponding extended unsigned integer type.
The standard and extended unsigned integer types are collectively called unsigned integer types.
An unsigned integer type has the same width N as the corresponding signed integer type.
The range of representable values for the unsigned type is 0 to (inclusive); arithmetic for the unsigned type is performed modulo .
Note
:
Unsigned arithmetic does not overflow.
Overflow for signed arithmetic yields undefined behavior ([expr.pre]).
— end note
 ]
An unsigned integer type has the same object representation, value representation, and alignment requirements ([basic.align]) as the corresponding signed integer type.
For each value x of a signed integer type, the value of the corresponding unsigned integer type congruent to x modulo has the same value of corresponding bits in its value representation.41
Example
:
The value of a signed integer type has the same representation as the largest value of the corresponding unsigned type.
— end example
 ]
Table 10: Minimum width   [tab:basic.fundamental.width]
Type
Minimum width N
signed char
8
short
16
int
16
long
32
long long
64
The width of each signed integer type shall not be less than the values specified in Table 10.
The value representation of a signed or unsigned integer type comprises N bits, where N is the respective width.
Each set of values for any padding bits ([basic.types]) in the object representation are alternative representations of the value specified by the value representation.
Note
:
Padding bits have unspecified value, but do not cause traps.
See also ISO C 6.2.6.2.
— end note
 ]
Note
:
The signed and unsigned integer types satisfy the constraints given in ISO C 5.2.4.2.1.
— end note
 ]
Except as specified above, the width of a signed or unsigned integer type is implementation-defined.
Each value x of an unsigned integer type with width N has a unique representation , where each coefficient is either 0 or 1; this is called the base-2 representation of x.
The base-2 representation of a value of signed integer type is the base-2 representation of the congruent value of the corresponding unsigned integer type.
The standard signed integer types 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.
A fundamental type specified to have a signed or unsigned integer type as its underlying type has the same object representation, value representation, alignment requirements ([basic.align]), and range of representable values as the underlying type.
Further, each value has the same representation in both types.
Type char is a distinct type that has an implementation-defined choice of “signed char” or “unsigned char” as its underlying type.
The values of type char can represent distinct codes for all members of the implementation's basic character set.
The three types char, signed char, and unsigned char are collectively called ordinary character types.
The ordinary character types and char8_­t are collectively called narrow character types.
For narrow character types, each possible bit pattern of the object representation represents a distinct value.
Note
:
This requirement does not hold for other types.
— end note
 ]
Note
:
A bit-field of narrow character type whose width is larger than the width of that type has padding bits; see [basic.types].
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 ]
Type wchar_­t is a distinct type that has an implementation-defined signed or unsigned integer type as its underlying type.
The values of type wchar_­t can represent distinct codes for all members of the largest extended character set specified among the supported locales ([locale]).
Type char8_­t denotes a distinct type whose underlying type is unsigned char.
Types char16_­t and char32_­t denote distinct types whose underlying types are uint_­least16_­t and uint_­least32_­t, respectively, in <cstdint>.
Type bool is a distinct type that has the same object representation, value representation, and alignment requirements as an implementation-defined unsigned integer type.
The values of type bool are true and false.
Note
:
There are no signed, unsigned, short, or long bool types or values.
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 ]
Types bool, char, wchar_­t, char8_­t, char16_­t, char32_­t, and the signed and unsigned integer types are collectively called integral types.
A synonym for integral type is integer type.
Note
:
Enumerations ([dcl.enum]) are not integral; however, unscoped enumerations can be promoted to integral types as specified in [conv.prom].
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 ]
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.
Note
: This document imposes no requirements on the accuracy of floating-point operations; see also [support.limits]. — end note
 ]
Integral and floating-point types are collectively called arithmetic types.
Specializations of the standard library template std​::​numeric_­limits shall specify the maximum and minimum values of each arithmetic type for an implementation.
A type cv void is an incomplete type that cannot be completed; such a type has an empty set of values.
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 ([expr.cast]).
An expression of type cv void shall be used only as an expression statement, as an operand of a comma expression, as a second or third operand of ?: ([expr.cond]), as the operand of typeid, noexcept, or decltype, as the expression in a return statement for a function with the return type cv void, or as the operand of an explicit conversion to type cv void.
A value of type std​::​nullptr_­t is a null pointer constant.
Such values participate in the pointer and the pointer-to-member conversions ([conv.ptr], [conv.mem]).
sizeof(std​::​nullptr_­t) shall be equal to sizeof(void*).
The types described in this subclause are called fundamental types.
Note
:
Even if the implementation defines two or more fundamental types to have the same value representation, they are nevertheless different types.
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This is also known as two's complement representation.