Fundamental types

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

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

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

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. 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). 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 integral types, but is a distinct type.

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 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:

| 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 |

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)

64 bit systems:

• LLP64 or 4/4/8 (int and long are 32-bit, pointer is 64-bit)

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

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.

Properties

Floating-point types may support special values:

• infinity (positive and negative), see INFINITY

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.

• min subnormal: ± 1.401,298,4 · 10-47

 64   IEEE-754   **± 1.7 · 10± 308**

(~15 digits)

• min subnormal: ± 4.940,656,458,412 · 10-324

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

| C documentation for arithmetic types |

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