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std::numeric_limits::quiet_NaN

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static T quiet_NaN()
 (fino al c++11)
static constexpr T quiet_NaN()
 (dal C++11)
Restituisce la speciale "not-a-numero tranquilla" valore, come rappresentato dalla virgola mobile T tipo. Ha senso solo se std::numeric_limits<T>::has_quiet_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 singaling, e se il bit di segno è significativo.
Original:
Returns the special value "quiet not-a-numero", as represented by the floating-point type T. Only meaningful if std::numeric_limits<T>::has_quiet_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 singaling 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
NAN o un'altra implementazione definita NaN
Original:
NAN or another implementation-defined NaN
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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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[modifica] Esempio

Diversi modi per generare un NaN (la stringa di uscita è specifica del compilatore)
Original:
Several ways to generate a NaN (the output string is compiler-specific)
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#include <iostream>
#include <limits>
#include <cmath>
int main()
{
    std::cout << std::numeric_limits<double>::quiet_NaN() << ' '
              << std::numeric_limits<double>::signaling_NaN() << ' '
              << std::acos(2) << ' '
              << std::tgamma(-1) << ' '
              << std::log(-1) << ' '
              << std::sqrt(-1) << ' '
              << 0 / 0.0 << '\n';
 
    std::cout << "NaN == NaN? " << std::boolalpha
              << ( std::numeric_limits<double>::quiet_NaN()
                   == std::numeric_limits<double>::quiet_NaN() ) << '\n';
}

Output: 

nan nan nan nan nan -nan -nan
NaN == NaN? false

[modifica] Vedi anche

[statico]
identifica i tipi a virgola mobile che possono rappresentare il valore speciale "tranquilla, non-a-number" (NaN)
Original:
identifies floating-point types that can represent the special value "quiet not-a-number" (NaN)
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(pubblico membro statico costante) [modifica]
[statico]
restituisce un valore NaN segnalazione di un dato tipo a virgola mobile
Original:
returns a signaling NaN value of the given floating-point type
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(metodo pubblico statico) [modifica]
Estratto da "https://it.cppreference.com/mwiki/index.php?title=cpp/types/numeric_limits/quiet_NaN&oldid=27089"