Namespaces
Variants
Views
Actions

Fundamental types

From cppreference.com
< cpp‎ | language
 
C++
 
C++ language
 
Basic Concepts
 

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

Contents

[edit] 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.

[edit] std::nullptr_t

Defined in header <cstddef>
typedef decltype(nullptr) nullptr_t;
 (since C++11)

std::nullptr_t is the type of the null pointer literal, nullptr. It is a distinct type that is not itself a pointer type or a pointer to member type.

[edit] Boolean type

bool - type, capable of holding one of the two values: true or false. The value of sizeof(bool) is implementation defined and might differ from 1.

[edit] Integer types

int - basic integer type. The keyword int may be omitted if any of the modifiers listed below are used. If no length modifiers are present, it's guaranteed to have a 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).

[edit] 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)

Note: as with all type specifiers, any order is permitted: unsigned long long int and long int unsigned long name the same type.

[edit] 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

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

std::size_t is the unsigned integer type of the result of the sizeof operator as well as the sizeof... operator and the alignof operator (since C++11).

See also Fixed width integer types. (since C++11)

[edit] 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).

[edit] Character types

signed char - type for signed character representation.
unsigned char - type for unsigned character representation. Also used to inspect object representations (raw memory).
char - type for character representation which can be most efficiently processed on the target system (has the same representation and alignment as either signed char or unsigned char, but is always a distinct type). Multibyte characters strings use this type to represent code units. The character types are large enough to represent any UTF-8 eight-bit code unit (since C++14). The signedness of char depends on the compiler and the target platform: the defaults for ARM and PowerPC are typically unsigned, the defaults for x86 and x64 are typically signed.
wchar_t - type for wide character representation (see wide strings). Required to be large enough to represent any supported character code point (32 bits on systems that support Unicode. A notable exception is Windows, where wchar_t is 16 bits and holds UTF-16 code units) It has the same size, signedness, and alignment as one of the integer types, but is a distinct type.
char16_t - type for UTF-16 character representation, required to be large enough to represent any UTF-16 code unit (16 bits). It has the same size, signedness, and alignment as std::uint_least16_t, but is a distinct type.
char32_t - type for UTF-32 character representation, required to be large enough to represent any UTF-32 code unit (32 bits). It has the same size, signedness, and alignment as std::uint_least32_t, but is a distinct type.
(since C++11)
char8_t - type for UTF-8 character representation, required to be large enough to represent any UTF-8 code unit (8 bits). It has the same size, signedness, and alignment as unsigned char (and. therefore, the same size and alignment as char and signed char), but is a distinct type.
(since C++20)

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.

[edit] 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.

[edit] Properties

Floating-point types may support special values:

  • infinity (positive and negative), see INFINITY
  • the negative zero, -0.0. It compares equal to the positive zero, but is meaningful in some arithmetic operations, e.g. 1.0/0.0 == INFINITY, but 1.0/-0.0 == -INFINITY), and for some mathematical functions, e.g. sqrt(std::complex)
  • not-a-number (NaN), which does not compare equal with anything (including itself). Multiple bit patterns represent NaNs, see std::nan, NAN. Note that C++ takes no special notice of signalling NaNs other than detecting their support by std::numeric_limits::has_signaling_NaN, and treats all NaNs as quiet.

Real floating-point numbers may be used with arithmetic operators + - / * and various mathematical functions from cmath. Both built-in operators and library functions may raise floating-point exceptions and set errno as described in math_errhandling

Floating-point expressions may have greater range and precision than indicated by their types, see FLT_EVAL_METHOD. Floating-point expressions may also be contracted, that is, calculated as if all intermediate values have infinite range and precision, see #pragma STDC FP_CONTRACT.

Some operations on floating-point numbers are affected by and modify the state of the floating-point environment (most notably, the rounding direction)

Implicit conversions are defined between real floating types and integer types.

See Limits of floating point types and std::numeric_limits for additional details, limits, and properties of the floating-point types.

[edit] Range of values

The following table provides a reference for the limits of common numeric representations.

Prior to C++20, the C++ Standard allowed any signed integer representation, and the minimum guaranteed range of N-bit signed integers was from -(2N-1
-1) to +2N-1
-1 (e.g. -127 to 127 for a signed 8-bit type), which corresponds to the limits of one's complement or sign-and-magnitude.

However, all C++ compilers use two's complement representation, and as of C++20, it is the only representation allowed by the standard, with the guaranteed range from -2N-1
 to +2N-1
-1 (e.g. -128 to 127 for a signed 8-bit type).

Type Size in bits Format Value range
Approximate Exact
character 8 signed -128 to 127
unsigned 0 to 255
16 unsigned 0 to 65535
32 unsigned 0 to 1114111 (0x10ffff)
integer 16 signed ± 3.27 · 104 -32768 to 32767
unsigned 0 to 6.55 · 104 0 to 65535
32 signed ± 2.14 · 109 -2,147,483,648 to 2,147,483,647
unsigned 0 to 4.29 · 109 0 to 4,294,967,295
64 signed ± 9.22 · 1018 -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
  • min subnormal:
    ± 1.401,298,4 · 10-45
  • min normal:
    ± 1.175,494,3 · 10-38
  • max:
    ± 3.402,823,4 · 1038
  • min subnormal:
    ±0x1p-149
  • min normal:
    ±0x1p-126
  • max:
    ±0x1.fffffep+127
64 IEEE-754
  • 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
  • min subnormal:
    ±0x1p-1074
  • min normal:
    ±0x1p-1022
  • max:
    ±0x1.fffffffffffffp+1023


Note: actual (as opposed to guaranteed minimal) limits on the values representable by these types are available in <climits>, <cfloat> and std::numeric_limits

[edit] Keywords

void, bool, true, false, char, wchar_t, char8_t, char16_t, char32_t, int, short, long, signed, unsigned, float, double

[edit] See also

C documentation for arithmetic types
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/language/types&oldid=108124"