std::numeric_limits

Defined in header <limits>
template< class T > class numeric_limits;

大numeric_limits类模板提供了一种标准的方法来查询算术类型%28的各种属性。类型的最大可能值。int是std::numeric_limits<int>::max()29%。

这些信息是通过numeric_limits模板。标准库为所有算术类型提供了可用的专门化：

Defined in header <limits>
template<> class numeric_limits<bool>; template<> class numeric_limits<char>; template<> class numeric_limits<signed char>; template<> class numeric_limits<unsigned char>; template<> class numeric_limits<wchar_t>; template<> class numeric_limits<char16_t>; // C++11 feature template<> class numeric_limits<char32_t>; // C++11 feature template<> class numeric_limits<short>; template<> class numeric_limits<unsigned short>; template<> class numeric_limits<int>; template<> class numeric_limits<unsigned int>; template<> class numeric_limits<long>; template<> class numeric_limits<unsigned long>; template<> class numeric_limits<long long>; template<> class numeric_limits<unsigned long long>; template<> class numeric_limits<float>; template<> class numeric_limits<double>; template<> class numeric_limits<long double>;

此外，每种算术类型的每个cv限定版本都存在一个专门化，与不合格的专门化相同。std::numeric_limits<const int>，，，std::numeric_limits<volatile int>，和std::numeric_limits<const volatile int>提供，并相当于std::numeric_limits<int>...

标准库类型，它是算术类型%28的别名，如std::size_t或std::streamsize5月29日%亦会与std::numeric_limits类型特征。

非算术标准类型，如std::complex<T>或std::nullptr_t，没有专门性。

实现可以提供以下方面的专门化：std::numeric_limits对于实现-特定类型：例如gcc提供std::numeric_limits<__int128>非标准图书馆可添加专门化为图书馆提供的类型，例如。OpenEXR提供std::numeric_limits<half>16位浮点类型。

模板参数

T	-	a type to retrieve numeric properties for

成员常数

is_specialized static	identifies types for which std::numeric_limits is specialized (public static member constant)
is_signed static	identifies signed types (public static member constant)
is_integer static	identifies integer types (public static member constant)
is_exact static	identifies exact types (public static member constant)
has_infinity static	identifies floating-point types that can represent the special value "positive infinity" (public static member constant)
has_quiet_NaN static	identifies floating-point types that can represent the special value "quiet not-a-number" (NaN) (public static member constant)
has_signaling_NaN static	identifies floating-point types that can represent the special value "signaling not-a-number" (NaN) (public static member constant)
has_denorm static	identifies the denormalization style used by the floating-point type (public static member constant)
has_denorm_loss static	identifies the floating-point types that detect loss of precision as denormalization loss rather than inexact result (public static member constant)
round_style static	identifies the rounding style used by the type (public static member constant)
is_iec559 static	identifies the IEC 559/IEEE 754 floating-point types (public static member constant)
is_bounded static	identifies types that represent a finite set of values (public static member constant)
is_modulo static	identifies types that handle overflows with modulo arithmetic (public static member constant)
digits static	number of radix digits that can be represented without change (public static member constant)
digits10 static	number of decimal digits that can be represented without change (public static member constant)
max_digits10 static	number of decimal digits necessary to differentiate all values of this type (public static member constant)
radix static	the radix or integer base used by the representation of the given type (public static member constant)
min_exponent static	one more than the smallest negative power of the radix that is a valid normalized floating-point value (public static member constant)
min_exponent10 static	the smallest negative power of ten that is a valid normalized floating-point value (public static member constant)
max_exponent static	one more than the largest integer power of the radix that is a valid finite floating-point value (public static member constant)
max_exponent10 static	the largest integer power of 10 that is a valid finite floating-point value (public static member constant)
traps static	identifies types which can cause arithmetic operations to trap (public static member constant)
tinyness_before static	identifies floating-point types that detect tinyness before rounding (public static member constant)

成员函数

min static	returns the smallest finite value of the given type (public static member function)
lowest static	returns the lowest finite value of the given type (public static member function)
max static	returns the largest finite value of the given type (public static member function)
epsilon static	returns the difference between 1.0 and the next representable value of the given floating-point type (public static member function)
round_error static	returns the maximum rounding error of the given floating-point type (public static member function)
infinity static	returns the positive infinity value of the given floating-point type (public static member function)
quiet_NaN static	returns a quiet NaN value of the given floating-point type (public static member function)
signaling_NaN static	returns a signaling NaN value of the given floating-point type (public static member function)
denorm_min static	returns the smallest positive subnormal value of the given floating-point type (public static member function)

帮助者类

float_round_style	indicates floating-point rounding modes (enum)
float_denorm_style	indicates floating-point denormalization modes (enum)

与C库宏常数的关系

Specialization	Members
min()	lowest()(C++11)	max()	epsilon()	digits	digits10	min_exponent	min_exponent10	max_exponent	max_exponent10	radix
numeric_limits< bool >											2
numeric_limits< char >	CHAR_MIN	CHAR_MIN	CHAR_MAX								2
numeric_limits< signed char >	SCHAR_MIN	SCHAR_MIN	SCHAR_MAX								2
numeric_limits< unsigned char >	0	0	UCHAR_MAX								2
numeric_limits< wchar_t >	WCHAR_MIN	WCHAR_MIN	WCHAR_MAX								2
numeric_limits< char16_t >	0	0	UINT_LEAST16_MAX								2
numeric_limits< char32_t >	0	0	UINT_LEAST32_MAX								2
numeric_limits< short >	SHRT_MIN	SHRT_MIN	SHRT_MAX								2
numeric_limits< signed short >
numeric_limits< unsigned short >	0	0	USHRT_MAX								2
numeric_limits< int >	INT_MIN	INT_MIN	INT_MAX								2
numeric_limits< signed int >
numeric_limits< unsigned int >	0	0	UINT_MAX								2
numeric_limits< long >	LONG_MIN	LONG_MIN	LONG_MAX								2
numeric_limits< signed long >
numeric_limits< unsigned long >	0	0	ULONG_MAX								2
numeric_limits< long long >	LLONG_MIN	LLONG_MIN	LLONG_MAX								2
numeric_limits< signed long long >
numeric_limits< unsigned long long >	0	0	ULLONG_MAX								2
numeric_limits< float >	FLT_MIN	-FLT_MAX	FLT_MAX	FLT_EPSILON	FLT_MANT_DIG	FLT_DIG	FLT_MIN_EXP	FLT_MIN_10_EXP	FLT_MAX_EXP	FLT_MAX_10_EXP	FLT_RADIX
numeric_limits< double >	DBL_MIN	-DBL_MAX	DBL_MAX	DBL_EPSILON	DBL_MANT_DIG	DBL_DIG	DBL_MIN_EXP	DBL_MIN_10_EXP	DBL_MAX_EXP	DBL_MAX_10_EXP	FLT_RADIX
numeric_limits< long double >	LDBL_MIN	-LDBL_MAX	LDBL_MAX	LDBL_EPSILON	LDBL_MANT_DIG	LDBL_DIG	LDBL_MIN_EXP	LDBL_MIN_10_EXP	LDBL_MAX_EXP	LDBL_MAX_10_EXP	FLT_RADIX

例

二次

#include <limits>
#include <iostream>
 
int main() 
{
    std::cout << "type\tlowest\thighest\n";
    std::cout << "int\t"
              << std::numeric_limits<int>::lowest() << '\t'
              << std::numeric_limits<int>::max() << '\n';
    std::cout << "float\t"
              << std::numeric_limits<float>::lowest() << '\t'
              << std::numeric_limits<float>::max() << '\n';
    std::cout << "double\t"
              << std::numeric_limits<double>::lowest() << '\t'
              << std::numeric_limits<double>::max() << '\n';
}

二次

可能的产出：

二次

type    lowest         highest
int     -2147483648    2147483647
float   -3.40282e+38   3.40282e+38
double  -1.79769e+308  1.79769e+308

二次

另见

固定宽度整数类型

算术类型

C++型系统概述

类型支持%28基本类型，RTTI，类型性状%29

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最后更新于：2017-12-18