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.

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. The character types are large enough to represent 256 different values (in order to be suitable for storing UTF-8 encoded data) (since C++14)

wchar_t - type for wide character representation (see wide strings). Required to be large enough to represent any supported character code unit (32 bits on systems that support Unicode. A notable exception is Windows, where wchar_t is 16 bits) It has the same size, signedness, and alignment as one of the integral types, but is a distinct type.

Integer types

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.

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:

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

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.

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.

1. As of C++14, char must represent 256 distinct values, bijectively convertible to the values 0..255 of unsigned char, which may require a wider range of values.

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

Keywords

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

See also

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