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std::numeric_limits::signaling_NaN

Da cppreference.com.

 
 
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static T signaling_NaN()
(C fino + 11)
static constexpr T signaling_NaN()
(dal C++11)
Restituisce la speciale "segnalazione not-a-numero" valore, come rappresentato dalla virgola mobile T tipo. Ha senso solo se std::numeric_limits<T>::has_signaling_NaN == true. In IEEE 754, la rappresentazione binaria più comune di numeri in virgola mobile, qualsiasi valore con tutti i bit del set esponente e almeno un bit del set frazione rappresenta un NaN. Esso è definito dall'implementazione quali valori della frazione rappresentano NaN tranquillo o segnalazione, e se il bit di segno è significativo.
Original:
Returns the special value "signaling not-a-numero", 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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Indice

[modifica] Valore di ritorno

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
implementazione definita
Original:
implementation-defined
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double
implementazione definita
Original:
implementation-defined
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long double
implementazione definita
Original:
implementation-defined
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[modifica] Eccezioni

noexcept specification:  
noexcept
  (dal C++11)

[modifica] Note

Un NaN mai uguale a se stesso confronto. Copia di un NaN non può conservare la sua rappresentazione po.
Original:
A NaN never compares equal to itself. Copying a NaN may not preserve its bit representation.
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Quando un NaN di segnalazione viene utilizzato come argomento per un'espressione aritmetica, l'appropriato virgola mobile eccezione può essere sollevata e il NaN è "calmato", cioè, l'espressione restituisce un tranquillo NaN.
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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[modifica] Esempio

Dimostra l'uso di una segnalazione NaN sollevare una virgola mobile eccezione
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

[modifica] Vedi anche

identifica i tipi a virgola mobile che possono rappresentare il valore speciale "segnalazione non-a-number" (NaN)
Original:
identifies floating-point types that can represent the special value "signaling not-a-number" (NaN)
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(pubblico membro statico costante) [edit]
[statico]
restituisce un valore NaN tranquilla di un dato tipo a virgola mobile
Original:
returns a quiet NaN value of the given floating-point type
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(public static membro funzione) [edit]