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std::numeric_limits::signaling_NaN

提供: cppreference.com

 
 
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static T signaling_NaN()
(C + + 11時まで)
static constexpr T signaling_NaN()
(C + + 11以来)
浮動小数点型の非数値によって表されるように特別な値 "シグナリングはT"を返します。 std::numeric_limits<T>::has_signaling_NaN == true場合のみ意味。 IEEE 754では、浮動小数点数の最も一般的なバイナリ表現では、すべての指数セットのビットと分数のセットの少なくとも1つのビットを持つ任意の値はNaNを表します。これは、分数の値は静かまたはシグナリングNaNを表す実装定義され、符号ビットは意味があるかどうか.
Original:
Returns the special value "signaling 非数値", as represented by the floating-point type T. Only meaningful if std::numeric_limits<T>::has_signaling_NaN == true. In IEEE 754, the most common binary representation of floating-point numbers, any value with all bits of the exponent set and at least one bit of the fraction set represents a NaN. It is implementation-defined which values of the fraction represent quiet or signaling NaNs, and whether the sign bit is meaningful.
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目次

[編集] 値を返します

T std::numeric_limits<T>::quiet_NaN()
/* non-specialized */ T();
bool false
char 0
signed char 0
unsigned char 0
wchar_t 0
char16_t 0
char32_t 0
short 0
unsigned short 0
int 0
unsigned int 0
long 0
unsigned long 0
long long 0
unsigned long long 0
float
実装定義である
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implementation-defined
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double
実装定義である
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implementation-defined
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long double
実装定義である
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implementation-defined
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[編集] 例外

noexcept specification:  
noexcept
  (C + + 11以来)

[編集] ノート

NaNはそれ自体に等しいことはありません。 NaNをコピーすると、そのビット表現を保存しないかもしれない.
Original:
A NaN never compares equal to itself. Copying a NaN may not preserve its bit representation.
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シグナリングNaNが算術式への引数として使用される場合は、適切な浮動小数点例外が発生することができるとNaNは "静かに"されている、つまり、式は静かなNaNを返します。.
Original:
When a signaling NaN is used as an argument to an arithmetic expression, the appropriate floating-point exception may be raised and the NaN is "quieted", that is, the expression returns a quiet NaN.
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[編集]

浮動小数点の例外を発生させるシグナルNaNを使用する方法を示します
Original:
Demonstrates the use of a signaling NaN to raise a floating-point exception
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#include <iostream>
#include <limits>
#include <cfenv>
#pragma STDC_FENV_ACCESS on
void show_fe_exceptions()
{
    int n = std::fetestexcept(FE_ALL_EXCEPT);
    if(n & FE_INVALID) std::cout << "FE_INVALID is raised\n";
    else if(n == 0)    std::cout << "no exceptions are raised\n";
    std::feclearexcept(FE_ALL_EXCEPT);
}
int main()
{
    double snan = std::numeric_limits<double>::signaling_NaN();
    std::cout << "After sNaN was obtained ";
    show_fe_exceptions();
    double qnan = snan * 2.0;
    std::cout << "After sNaN was multiplied by 2 ";
    show_fe_exceptions();
    double qnan2 = qnan * 2.0;
    std::cout << "After the quieted NaN was multiplied by 2 ";
    show_fe_exceptions();
    std::cout << "The result is " << qnan2 << '\n';
}

Output:

After sNaN was obtained no exceptions are raised
After sNaN was multiplied by 2 FE_INVALID is raised
After the quieted NaN was multiplied by 2 no exceptions are raised
The result is nan

[編集] も参照してください

(NaN)の "非数値を合図する"特別な値を表すことができる浮動小数点型を識別します
Original:
identifies floating-point types that can represent the special value "signaling not-a-number" (NaN)
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(公共の静的メンバ定数) [edit]
[静的]
与えられた浮動小数点型の静かなNaN値を返します
Original:
returns a quiet NaN value of the given floating-point type
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(公共の静的メンバ関数) [edit]