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std::numeric_limits::epsilon

Da cppreference.com.

 
 
Utilità libreria
Tipo di supporto (basic types, RTTI, type traits)
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Funzione oggetti
initializer_list(C++11)
bitset
hash(C++11)
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rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
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Pairs and tuples
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pair
tuple(C++11)
piecewise_construct_t(C++11)
piecewise_construct(C++11)
Swap, in avanti e spostare
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Swap, forward and move
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swap
forward(C++11)
move(C++11)
move_if_noexcept(C++11)
declval(C++11)
 
Tipo di supporto
Tipi base
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Basic types
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Tipi fondamentali
Larghezza fissa interi tipi (C++11)
Limiti numerici
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Numeric limits
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numeric_limits
C numerico limita interfaccia
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is_class(C++11)
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is_scalar(C++11)
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is_integral(C++11)
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is_fundamental(C++11)
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Operazioni supportate
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(C++11)
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(C++11)
(C++11)
is_move_constructible
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(C++11)
(C++11)
is_assignable
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(C++11)
(C++11)
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(C++11)
(C++11)
(C++11)
is_move_assignable
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is_destructible
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(C++11)
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I rapporti e le query di proprietà
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aligned_union(C++11)
decay(C++11)
enable_if(C++11)
conditional(C++11)
common_type(C++11)
underlying_type(C++11)
result_of(C++11)
Digitare costanti tratto
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Type trait constants
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integral_constant(C++11)
 
 
static T epsilon()
(C fino + 11)
static constexpr T epsilon()
(dal C++11)
Restituisce l'epsilon macchina, cioè la differenza tra 1.0 e il successivo valore rappresentabile dalla virgola mobile T tipo. E ha senso solo se std::numeric_limits<T>::is_integer == false.
Original:
Returns the machine epsilon, that is, the difference between 1.0 and the next value representable by the floating-point type T. It is only meaningful if std::numeric_limits<T>::is_integer == false.
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Indice

[modifica] Valore di ritorno

T std::numeric_limits<T>::epsilon()
/* 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 FLT_EPSILON
double DBL_EPSILON
long double LDBL_EPSILON

[modifica] Eccezioni

noexcept specification:  
noexcept
  (dal C++11)

[modifica] Esempio

Viene illustrato l'utilizzo semplicistica di epsilon macchina di confrontare i valori in virgola mobile .
Original:
Demonstrates the simplistic use of machine epsilon to compare floating-point values.
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#include <cmath>
#include <limits>
#include <iomanip>
#include <iostream>
#include <type_traits>
 
template<class T>
typename std::enable_if<!std::numeric_limits<T>::is_integer, bool>::type
    almost_equal(T x, T y, int ulp)
{
    // the machine epsilon has to be scaled to the magnitude of the larger value
    // and multiplied by the desired precision in ULPs (units in the last place)
    return std::abs(x-y) <=   std::numeric_limits<T>::epsilon()
                            * std::max(std::abs(x), std::abs(y))
                            * ulp;
}
int main()
{
    double d1 = 0.2;
    double d2 = 1 / std::sqrt(5) / std::sqrt(5);
 
    if(d1 == d2)
            std::cout << "d1 == d2\n";
    else
            std::cout << "d1 != d2\n";
 
    if(almost_equal(d1, d2, 2))
            std::cout << "d1 almost equals d2\n";
    else
            std::cout << "d1 does not almost equal d2\n";
}

Output:

d1 != d2
d1 almost equals d2

[modifica] Vedi anche

(C++11)
(C++11)
prossimo valore rappresentabile in virgola mobile verso il valore dato
Original:
next representable floating point value towards the given value
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(funzione) [edit]