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Fundamental types

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Revision as of 04:25, 8 July 2014 by D41D8CD98F (Talk | contribs)

(See also type for type system overview and the list of type-related utilities that are provided by the C++ library)

Contents

Void type

void - type with an empty set of values. It is an incomplete type that cannot be completed (consequently, objects of type void are disallowed). There are no arrays of void, nor references to void. However, pointers to void and functions returning type void (procedures in other languages) are permitted.

std::nullptr_t

Boolean type

bool - type, capable of holding one of the two values: true or false.

Character types

signed char - type for signed character representation.
unsigned char - type for unsigned character representation.
char - type for character representation which can be most efficiently processed on the target system (equivalent to either signed char or unsigned char, but still different type).
wchar_t - type for wide character representation
char16_t - type for UTF-16 character representation
char32_t - type for UTF-32 character representation
(since C++11)

Integer types

int - basic integer type. Can be omitted if any of the modifiers are present. If no length modifiers are present, guaranteed to have width of at least 16 bits. However, on 32/64 bit systems it is almost exclusively guaranteed to have width of at least 32 bits (see below).

Modifiers

Modifies the integer type. Can be mixed in any order. Only one of each group can be present in type name.

Signedness

signed - target type will have signed representation (this is the default if omitted)
unsigned - target type will have unsigned representation

Size

short - target type will be optimized for space and will have width of at least 16 bits.
long - target type will have width of at least 32 bits.
long long - target type will have width of at least 64 bits.
(since C++11)

Properties

The following table summarizes all available integer types and their properties:

Type specifier Equivalent type Width in bits by data model
C++ standard LP32 ILP32 LLP64 LP64
short
short int at least
16
16 16 16 16
short int
signed short
signed short int
unsigned short
unsigned short int
unsigned short int
int
int at least
16
16 32 32 32
signed
signed int
unsigned
unsigned int
unsigned int
long
long int at least
32
32 32 32 64
long int
signed long
signed long int
unsigned long
unsigned long int
unsigned long int
long long
long long int
(C++11)
at least
64
64 64 64 64
long long int
signed long long
signed long long int
unsigned long long
unsigned long long int
(C++11)
unsigned long long int

Besides the minimal bit counts, the C++ Standard guarantees that

1 == sizeof(char) <= sizeof(short) <= sizeof(int) <= sizeof(long) <= sizeof(long long).

Note: this allows the extreme case in which bytes are sized 64 bits, all types (including char) are 64 bits wide, and sizeof returns 1 for every type.

Note: integer arithmetic is defined differently for the signed and unsigned integer types. See arithmetic operators, in particular integer overflows.

Data models

The choices made by each implementation about the sizes of the fundamental types are collectively known as data model. Four data models found wide acceptance:

32 bit systems:

  • LP32 or 2/4/4 (int is 16-bit, long and pointer are 32-bit)
  • Win16 API
  • ILP32 or 4/4/4 (int, long, and pointer are 32-bit);
  • Win32 API
  • Unix and Unix-like systems (Linux, Mac OS X)

64 bit systems:

  • LLP64 or 4/4/8 (int and long are 32-bit, pointer is 64-bit)
  • Win64 API
  • LP64 or 4/8/8 (int is 32-bit, long and pointer are 64-bit)
  • Unix and Unix-like systems (Linux, Mac OS X)

Other models are very rare. For example, ILP64 (8/8/8: int, long, and pointer are 64-bit) only appeared in some early 64-bit Unix systems (e.g. Unicos on Cray).

Floating point types

float - single precision floating point type. Usually IEEE-754 32 bit floating point type
double - double precision floating point type. Usually IEEE-754 64 bit floating point type
long double - extended precision floating point type. Does not necessarily map to types mandated by IEEE-754. Usually 80-bit x87 floating point type on x86 and x86-64 architectures.

Range of values

The following table provides a reference for the limits of common numeric representations. As the C++ Standard allows any signed integer representation, the table gives both the minimum guaranteed requirements (which correspond to the limits of one's complement or sign-and-magnitude) and the limits of the most commonly used implementation, two's complement. All popular data models (including all of ILP32, LP32, LP64, LLP64) use two's complement representation, though.

Type Size in bits Format Value range
Approximate Exact
character 8 signed (one's complement) -127 to 127(until C++14)
signed (two's complement) -128 to 127
unsigned 0 to 255
integral 16 signed (one's complement) ± 3.27 · 104 -32767 to 32767
signed (two's complement) -32768 to 32767
unsigned 0 to 6.55 · 104 0 to 65535
32 signed (one's complement) ± 2.14 · 109 -2,147,483,647 to 2,147,483,647
signed (two's complement) -2,147,483,648 to 2,147,483,647
unsigned 0 to 4.29 · 109 0 to 4,294,967,295
64 signed (one's complement) ± 9.22 · 1018 -9,223,372,036,854,775,807 to 9,223,372,036,854,775,807
signed (two's complement) -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
unsigned 0 to 1.84 · 1019 0 to 18,446,744,073,709,551,615
floating
point
32 IEEE-754 ± 3.4 · 10± 38
(~7 digits)
  • min subnormal: ± 1.401,298,4 · 10-47
  • min normal: ± 1.175,494,3 · 10-38
  • max: ± 3.402,823,4 · 1038
64 IEEE-754 ± 1.7 · 10± 308
(~15 digits)
  • min subnormal: ± 4.940,656,458,412 · 10-324
  • min normal: ± 2.225,073,858,507,201,4 · 10-308
  • max: ± 1.797,693,134,862,315,7 · 10308

Keywords

bool, true, false, char, wchar_t, char16_t, char32_t, int, short, long, signed, unsigned, float, double

See also