Fundamental types

 

C++

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Technical specifications

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C++ language

General topics
Preprocessor Comments	Keywords Escape sequences
Flow control
Conditional execution statements
if	switch
Iteration statements (loops)
for range-for (C++11)	while do-while
Jump statements
continue - break	goto - return
Functions
Function declaration
Lambda function expression
inline specifier
Dynamic exception specifications (until C++20)
noexcept specifier (C++11)
Exceptions
throw-expression	try-catch block
Namespaces
Namespace declaration	Namespace aliases
Types
Fundamental types Enumeration types Function types	Class/struct types Union types
Specifiers
decltype (C++11) auto (C++11) alignas (C++11)	const/volatile constexpr (C++11)
Storage duration specifiers
Initialization
Default initialization Value initialization Zero initialization Copy initialization Direct initialization	Aggregate initialization List initialization (C++11) Constant initialization Reference initialization

Expressions
Value categories Order of evaluation	Operators Operator precedence
Alternative representations
Literals
Boolean - Integer - Floating-point
Character - String - nullptr (C++11)
User-defined (C++11)
Utilities
Attributes (C++11)
Types
typedef declaration
Type alias declaration (C++11)
Casts
Implicit conversions - Explicit conversions
static_cast - dynamic_cast
const_cast - reinterpret_cast
Memory allocation
new expression	delete expression
Classes
Class declaration Constructors this pointer	Access specifiers friend specifier
Class-specific function properties
Virtual function override specifier (C++11) final specifier (C++11)	explicit (C++11) static
Special member functions
Default constructor Copy constructor Move constructor (C++11)	Copy assignment Move assignment (C++11) Destructor
Templates
Class template Function template	Template specialization Parameter packs (C++11)
Miscellaneous
Inline assembly	History of C++

 

Basic Concepts

Language keywords

Character sets and encodings

Phases of translation

Comments

The main() function

Punctuation

Names and identifiers

Types

Fundamental types

Objects

Scope

Object lifetime

Storage duration and linkage

Definitions and ODR

Name lookup

Qualified name lookup

Unqualified name lookup

The as-if rule

Undefined behavior

Memory model

Modules (C++20)

 

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

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

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. Its values are null pointer constant (see NULL), and may be implicitly converted to any pointer and pointer to member type.

sizeof(std::nullptr_t) is equal to sizeof(void *).

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, macOS)

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, macOS)

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).

Signed and unsigned 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).

Modifiers

Modifies the basic 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.

Properties

The following table summarizes all available 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
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)

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.

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. 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). Required to be large enough to represent any supported character code point (until C++23). 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.

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.

Floating-point types

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

float - single precision floating-point type. Matches IEEE-754 binary32 format if supported.

double - double precision floating-point type. Matches IEEE-754 binary64 format if supported.

long double - extended precision floating-point type. Matches IEEE-754 binary128 format if supported, otherwise matches IEEE-754 binary64-extended format if supported, otherwise matches some non-IEEE-754 extended floating-point format as long as its precision is better than binary64 and range is at least as good as binary64, otherwise matches IEEE-754 binary64 format.

• binary128 format is used by some HP-UX, SPARC, MIPS, ARM64, and z/OS implementations.
• The most well known IEEE-754 binary64-extended format is 80-bit x87 extended precision format. It is used by many x86 and x86-64 implementations (a notable exception is MSVC, which implements long double in the same format as double, i.e. binary64).

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. 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 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.

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 CWG 1759), because a UTF-8 code unit of value 0x80 used in a UTF-8 string literal must be storable in a char element object.

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
binary 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
	80	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-16446 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.ffffffffffffffffffffffffffff p+16383

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.

Keywords

void, bool, true, false, char, wchar_t, char8_t, (since C++20) char16_t, char32_t, (since C++11) int, short, long, signed, unsigned, float, double

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 as no constraint
CWG 1759	C++11	char is not guaranteed to be able to represent UTF-8 code unit 0x80	guaranteed

See also

• the C++ type system overview
• const-volatility (cv) specifiers and qualifiers
• storage duration specifiers