c++_std-numeric_limits极值接口

言者无罪，闻者足戒。 --诗经·大序

std::numeric_limits

在C/C++11中，std::numeric_limits为模板类，在库编译平台提供基础算术类型的极值等属性信息。

用于取代和,浮点常数定义于和。

新的极值概念有两个优点，

• 一是提供了更好的类型安全性，

• 二是程序员可借此写出一些template以核定这些极值。

member

member	type	property
is_specialized	bool	true for all arithmetic types (i.e., those for which numeric_limits is specialized). false for all other types.
min()	T	Minimum finite value. For floating types with denormalization (variable number of exponent bits): minimum positive normalized value. Equivalent to CHAR_MIN, SCHAR_MIN, SHRT_MIN, INT_MIN, LONG_MIN, LLONG_MIN, FLT_MIN, DBL_MIN, LDBL_MIN or 0, depending on type.
max()	T	Maximum finite value. Equivalent to CHAR_MAX, SCHAR_MAX, UCHAR_MAX, SHRT_MAX, USHRT_MAX, INT_MAX, UINT_MAX, LONG_MAX, ULONG_MAX, LLONG_MAX, ULLONG_MAX, UINT_LEAST16_MAX, UINT_LEAST32_MAX, FLT_MAX, DBL_MAX or LDBL_MAX, depending on type.
lowest()	T	Minimum finite value. (since C++11) For integral types: the same as min(). For floating-point types: implementation-dependent; generally, the negative of max().
digits	int	For integer types: number of non-sign bits (radix base digits) in the representation. For floating types: number of digits (in radix base) in the mantissa (equivalent to FLT_MANT_DIG, DBL_MANT_DIG or LDBL_MANT_DIG).
digits10	int	Number of digits (in decimal base) that can be represented without change. Equivalent to FLT_DIG, DBL_DIG or LDBL_DIG for floating types.
max_digits10	int	Number of digits (in decimal base) required to ensure that values that differ are always differentiated.
is_signed	bool	true if type is signed.
is_integer	bool	测试目标类型是不是可以用整型来表示（比如char是1，float是0
is_exact	bool	true if type uses exact representations.
radix	int	For integer types: base of the representation. For floating types: base of the exponent of the representation (equivalent to FLT_RADIX).
epsilon()	T	返回目标数据类型能表示的最逼近1的正数和1的差的绝对值
round_error()	T	Measure of the maximum rounding error.
min_exponent	int	Minimum negative integer value such that radix raised to (min_exponent-1) generates a normalized floating-point number. Equivalent to FLT_MIN_EXP, DBL_MIN_EXP or LDBL_MIN_EXP for floating types.
min_exponent10	int	Minimum negative integer value such that 10 raised to that power generates a normalized floating-point number. Equivalent to FLT_MIN_10_EXP, DBL_MIN_10_EXP or LDBL_MIN_10_EXP for floating types.
max_exponent	int	Maximum integer value such that radix raised to (max_exponent-1) generates a representable finite floating-point number. Equivalent to FLT_MAX_EXP, DBL_MAX_EXP or LDBL_MAX_EXP for floating types.
max_exponent10	int	Maximum integer value such that 10 raised to that power generates a normalized finite floating-point number. Equivalent to FLT_MAX_10_EXP, DBL_MAX_10_EXP or LDBL_MAX_10_EXP for floating types.
has_infinity	bool	true if the type has a representation for positive infinity.
has_quiet_NaN	bool	true if the type has a representation for a quiet (non-signaling) "Not-a-Number".
has_signaling_NaN	bool	true if the type has a representation for a signaling "Not-a-Number".
has_denorm	float_denorm_style	测试目标类型是不是可以非规范化表示
has_denorm_loss	bool	测试所有类型是不是能测出因为非规范化而造成的精度损失（不是因为结果本身的不精确）
infinity()	T	检查目标类型的无限类型（如果支持无限表示）
quiet_NaN()	T	Representation of quiet (non-signaling) "Not-a-Number", if available.
signaling_NaN()	T	Representation of signaling "Not-a-Number", if available.
denorm_min()	T	Minimum positive denormalized value. For types not allowing denormalized values: same as min().
is_iec559	bool	测试目标类型是不是符合IEC559标准
is_bounded	bool	检查目标类型的取值是否有限
is_modulo	bool	true if the type is modulo. A type is modulo if it is possible to add two positive numbers and have a result that wraps around to a third number that is less.
traps	bool	true if trapping is implemented for the type.
tinyness_before	bool	true if tinyness is detected before rounding.
round_style	float_round_style	Rounding style. A type may have any of the following enum values: round_toward_zero, if it rounds toward zero. round_to_nearest, if it rounds to the nearest representable value. round_toward_infinity, if it rounds toward infinity. round_toward_neg_infinity, if it rounds toward negative infinity. round_indeterminate, if the rounding style is indeterminable at compile time.

sample code

#include
 
 
include
 
 
include
 
 
​
 using namespace std;
 int main(){
 cout<<"numeric_limits::min()= "<::min()< cout<<"numeric_limits::max()= "<::max()< cout<<"numeric_limits::min()= "<::min()< cout<<"numeric_limits::max()= "<::max()< cout<<"numeric_limits::min()= "<::min()< cout<<"numeric_limits::max()= "<::max()< ​
 cout<<"numeric_limits::is_signed()= "<::is_signed< cout<<"numeric_limits::is_specialized()= "<::is_specialized<< endl;//是否定义了数值极限
 system("pause");
 return 0;
 } 

参考链接

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