Fundamental types - cppreference.com (original) (raw)

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

The following types are collectively called fundamental types :

Contents

[edit] void

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] Integral types

[edit] Standard 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 basic integer type. Can be mixed in any order. Only one of each group can be present in type name.

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

unsigned — target type will have unsigned representation

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 standard integer types and their properties in various common data models:

Type specifier Equivalent type Width in bits by data model
C++ standard LP32 ILP32 LLP64 LP64
signed char signed char at least 8 8 8 8 8
unsigned char unsigned char
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).

Extended integer types The extended integer types are implementation-defined. Note that fixed width integer types are typically aliases of the standard integer types. (since C++11)

[edit] Boolean type

bool — integer 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] Character types

Character types are integer types used for a character representation.

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. For every value of type unsigned char in range [​0​, 255], converting the value to char and then back to unsigned char produces the original value.(since C++11) 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). It has the same size, signedness, and alignment as one of the integer types, but is a distinct type. In practice, it is 32 bits and holds UTF-32 on Linux and many other non-Windows systems, but 16 bits and holds UTF-16 code units on Windows. The standard used to require wchar_t to be large enough to represent any supported character code point. However, such requirement cannot be fulfilled on Windows, and thus it is considered as a defect and removed.

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

[edit] Standard floating-point types

The following three types and their cv-qualified versions are collectively called standard floating-point types.

float — single precision floating-point type. Usually IEEE-754 binary32 format.

double — double precision floating-point type. Usually IEEE-754 binary64 format.

long double — extended precision floating-point type. Does not necessarily map to types mandated by IEEE-754.

[edit] Properties

Floating-point types may support special values:

Floating-point numbers may be used with arithmetic operators +, -, /, and * as well as various mathematical functions from . 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. Standard C++ does not restrict the accuracy of floating-point operations.

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 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 \(\scriptsize -(2^{N-1}-1)\)-(2N-1
-1) to \(\scriptsize +2^{N-1}-1\)+2N-1
-1 (e.g. −127 to 127 for a signed 8-bit type), which corresponds to the limits of ones' 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 \(\scriptsize -2^{N-1}\)-2N-1
to \(\scriptsize +2^{N-1}-1\)+2N-1
-1 (e.g. −128 to 127 for a signed 8-bit type).

8-bit ones' complement and sign-and-magnitude representations for char have been disallowed since C++11 (via the resolution of CWG issue 1759), because a UTF-8 code unit of value 0x80 used in a UTF-8 string literal must be storable in a char type object.

The range for a floating-point type T is defined as follows:

Since negative and positive infinity are representable in ISO/IEC/IEEE 60559 formats, all real numbers lie within the range of representable values of a floating-point type adhering to ISO/IEC/IEEE 60559.

Type Size in bits Format Value range
Approximate Exact
character 8 signed −128 to 127
unsigned 0 to 255
16 UTF-16 0 to 65535
32 UTF-32 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
binaryfloating-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
80[note 1] x86 min subnormal:± 3.645,199,531,882,474,602,528 · 10−4951 min normal:± 3.362,103,143,112,093,506,263 · 10−4932 max:± 1.189,731,495,357,231,765,021 · 104932 min subnormal:±0x1p−16445 min normal:±0x1p−16382 max:±0x1.fffffffffffffffep+16383
128 IEEE-754 min subnormal:± 6.475,175,119,438,025,110,924,438,958,227,646,552,5 · 10−4966 min normal:± 3.362,103,143,112,093,506,262,677,817,321,752,602,6 · 10−4932 max:± 1.189,731,495,357,231,765,085,759,326,628,007,016,2 · 104932 min subnormal:±0x1p−16494 min normal:±0x1p−16382 max:±0x1.ffffffffffffffffffffffffffffp+16383
  1. ↑ The object representation usually occupies 96/128 bits on 32/64-bit platforms respectively.

Note: actual (as opposed to guaranteed minimal) limits on the values representable by these types are available in C numeric limits interface and std::numeric_limits.

[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:

64 bit systems:

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] Notes

Feature-test macro Value Std Feature
__cpp_unicode_characters 200704L (C++11) New character types (char16_t and char32_t)
__cpp_char8_t 201811L (C++20) char8_t
202207L (C++23) char8_t compatibility and portability fix (allow initialization of (unsigned) char arrays from UTF-8 string literals)

[edit] Keywords

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

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
CWG 238 C++98 the constraints placed on a floating-point implementation was unspecified specified asno constraint
CWG 1759 C++11 char is not guaranteed to be able to represent UTF-8 code unit 0x80 guaranteed
CWG 2689 C++11 cv-qualified std::nullptr_t was not a fundemental type it is
CWG 2723 C++98 the ranges of representable values for floating-point types were not specified specified
P2460R2 C++98 wchar_t was required to be able to represent distinct codes for all membersof the largest extended character set specified among the supported locales not required

[edit] References

[edit] See also