Fundamental types

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

Void type

std::nullptr_t

typedef decltype(nullptr) nullptr_t;

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

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.

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:

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).

Boolean type

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). 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 by P2460R2.

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.

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.

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.

See also

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