Fundamental types

Fundamental types

• void type
• boolean type
• character types
• integer types
  • Modifiers
    • signedness
    • size
• Properties
• Data Models
• Floating-point types
• Floating-point properties

###Void type `void`-type with an empty set of values.There are no arrays of void,nor references to void.However,pointers to void and function returning type void are permitted. `std::nullptr_t` ###Boolean type `bool`-type,capable of holding one of the tow values:`true` or `false` ###Character types `signed char` `unsigned char` `char` `wchar_t` `char16_t` `char32_t` ###Integer types `int` - basic integer type.The keyword `int` may omitted if any of the modifiers listed below are used. If no length [modifiers](#modifiers) present,it's guaranteed to have a width of at least 16 bits.However,on 32/64 bit system is is almost exclusively guaranteed to have width of at least 32 bits. ####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 16bits `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**)

即int为integer type的基本类型，通过添加修饰符(modifiers)signedor unsigned 和short or long or long long来实现存储空间位数的大小,C++保证每一个类型的最小位数

###Properties **LP=Long Point** **LLP=Long Long Point** The following table summarizes all available integer types and their properties:

Type Specifier	Equivalent Type	C++Standard	LP32	ILP32	LLP64	LP64
short	short int	at least 16	16	16	16	16
short int	short int	at least 16	16	16	16	16
signed int	short int	at least 16	16	16	16	16
signed short int	short int	at least 16	16	16	16	16
unsigned short	unsigned short int	at least 16	16	16	16	16
unsigned short int	unsigned short int	at least 16	16	16	16	16
int	int	at least 16	16	32	32	32
signed	int	at least 16	16	32	32	32
signed int	int	at least 16	16	32	32	32
unsigned	unsigned int	at least 16	16	32	32	32
unsigned int	unsigned int	at least 16	16	32	32	32
long	long int	at least 32	32	32	32	64
signed long	long int	at least 32	32	32	32	64
signed long int	long int	at least 32	32	32	32	64
unsigned long	unsigned long int	at least 32	32	32	32	64
unsigned long int	unsigned long int	at least 32	32	32	32	64
long long	long long int	at least 32	64	64	64	64
long long int	long long int	at least 32	64	64	64	64
signed long long	long long int	at least 32	64	64	64	64
signed long long int	long long int	at least 32	64	64	64	64
unsigned long long	long long int	at least 32	64	64	64	64
unsigned long long	unsigned long long int since C++11	at least 32	64	64	64	64
unsigned long long int	unsigned long long int since C++11	at least 32	64	64	64	64

Besides the minimal bit counts,the C++ Standard guaranteed that
1 == sizeof(char) <= sizeof(short) <= sizeof(int) <= sizeof(long) <= sizeof(long long)

Note:integer arithmetic is defined differently for signed and unsigned integer types.See arithmetic operators,in particular integer overflows

Win64 is a LLP64 platform, while Solaris and Linux are LP64 platforms. Thus the only safe way to store pointers in integer types is either always use uintptr_t (defined in stdint.h not included at least with MSVC2003 and earlier), or always use long long fields.

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)
  • Win16API
    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)
    

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

Floating-point properties

Floating-point types may support special values:

• infinity (positive and negative)
• 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).

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.

浮点数的精度表示FLT_EVAL_METHOD和精收缩问题#pragma STDC FP_CONTRACT
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.

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.

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