Fundamental types
(See also type for type system overview and the list of type-related utilities that are provided by the C++ library)
Contents |
[edit] 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 ofvoid
, nor references tovoid
. However, pointers tovoid
and functions returning typevoid
(procedures in other languages) are permitted.
[edit] std::nullptr_t
[edit] Boolean type
- bool - type, capable of holding one of the two values: true or false.
[edit] Character types
- signed char - type for signed character representation.
- unsigned char - type for unsigned character representation.
- char - type for character representation which can be most efficiently processed on the target system (equivalent to either signed char or unsigned char, but still different type).
- wchar_t - type for wide character representation
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(since C++11) |
[edit] Integer types
- int - basic integer type. Can be omitted if any of the modifiers are present. If no length modifiers are present, guaranteed to have 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 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.
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(since C++11) |
[edit] Properties
The following table summarizes all available integer types and their properties:
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
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signed short
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signed short int
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unsigned short
|
unsigned short int | |||||
unsigned short int
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int
|
int | at least 16 |
16 | 32 | 32 | 32 |
signed
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signed int
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unsigned
|
unsigned int | |||||
unsigned int
|
||||||
long
|
long int | at least 32 |
32 | 32 | 32 | 64 |
long int
|
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signed long
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signed long int
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unsigned long
|
unsigned long int | |||||
unsigned long int
|
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long long
|
long long int (C++11) |
at least 64 |
64 | 64 | 64 | 64 |
long long int
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signed long long
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signed long long int
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unsigned long long
|
unsigned long long int (C++11) |
|||||
unsigned long long int
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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.
[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:
-
- 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).
[edit] 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.
[edit] 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.
Type | Size in bits | Format | Value range | |
---|---|---|---|---|
Approximate | Exact | |||
character | 8 | signed (one's complement) | -127 to 127(until C++14) | |
signed (two's complement) | -128 to 127 | |||
unsigned | 0 to 255 | |||
integral | 16 | signed (one's complement) | ± 3.27 · 104 | -32767 to 32767 |
signed (two's complement) | -32768 to 32767 | |||
unsigned | 0 to 6.55 · 104 | 0 to 65535 | ||
32 | signed (one's complement) | ± 2.14 · 109 | -2,147,483,647 to 2,147,483,647 | |
signed (two's complement) | -2,147,483,648 to 2,147,483,647 | |||
unsigned | 0 to 4.29 · 109 | 0 to 4,294,967,295 | ||
64 | signed (one's complement) | ± 9.22 · 1018 | -9,223,372,036,854,775,807 to 9,223,372,036,854,775,807 | |
signed (two's complement) | -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 | ||
floating point |
32 | IEEE-754 | ± 3.4 · 10± 38 (~7 digits) |
|
64 | IEEE-754 | ± 1.7 · 10± 308 (~15 digits) |
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[edit] Keywords
bool, true, false, char, wchar_t, char16_t, char32_t, int, short, long, signed, unsigned, float, double