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std::numeric_limits::quiet_NaN

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std::numeric_limits
 
static T quiet_NaN()
(avant C++11)
static constexpr T quiet_NaN()
(depuis C++11)
Retourne la valeur spéciale "pas-un-nombre tranquille», représentée par le T type virgule flottante. N'a de sens que si std::numeric_limits<T>::has_quiet_NaN == true. Dans IEEE 754, la représentation binaire la plus courante de nombres à virgule flottante, avec une valeur de tous les bits de l'ensemble d'exposants et au moins un bit de l'ensemble de la fraction représente un NaN. Il est défini par l'implémentation dont les valeurs de la fraction de représenter NaN silencieux ou singaling, et si le bit de signe est significatif .
Original:
Returns the special value "quiet pas-un-nombre", 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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Sommaire

[modifier] Retourne la valeur

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 ou d'une autre définition de l'implémentation NaN
Original:
NAN or another implementation-defined NaN
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double
défini par l'implémentation
Original:
implementation-defined
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long double
défini par l'implémentation
Original:
implementation-defined
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[modifier] Exceptions

noexcept specification:  
noexcept
   (depuis C++11)

[modifier] Notes

Un NaN jamais compare égal à lui-même. Copie d'un NaN ne peut préserver sa représentation binaire .
Original:
A NaN never compares equal to itself. Copying a NaN may not preserve its bit representation.
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[modifier] Exemple

Plusieurs façons de générer un NaN (la chaîne de sortie du compilateur spécifique)
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';
}

Résultat :

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

[modifier] Voir aussi

[
statique
Original:
static
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]
identifie types à virgule flottante qui peuvent représenter la valeur spéciale "calme pas-a-number» (NaN)
Original:
identifies floating-point types that can represent the special value "quiet not-a-number" (NaN)
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(constante membre statique publique) [edit]
[
statique
Original:
static
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]
renvoie une valeur NaN de signalisation de la donnée à virgule flottante de type
Original:
returns a signaling NaN value of the given floating-point type
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(fonction membre publique statique) [edit]