std::numeric_limits::epsilon

 

C++

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Libreria di Utilità

Stringhe

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Localizzazione

Espressioni regolari(C++11)

Operazioni atomicche(C++11)

Multithreading(C++11)

 

Utilità libreria

Tipo di supporto (basic types, RTTI, type traits)

Gestione della memoria dinamica

La gestione degli errori

Programma di utilità

Funzioni variadic

Data e ora

Funzione oggetti

initializer_list (C++11)

bitset

hash (C++11)

Gli operatori relazionali Original: Relational operators The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

rel_ops::operator!= rel_ops::operator> rel_ops::operator<= rel_ops::operator>=

Coppie e tuple Original: Pairs and tuples The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

pair

tuple (C++11)

piecewise_construct_t (C++11)

piecewise_construct (C++11)

Swap, in avanti e spostare Original: Swap, forward and move The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

swap

forward (C++11)

move (C++11)

move_if_noexcept (C++11)

declval (C++11)

 

Tipo di supporto

Tipi base Original: Basic types The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
Tipi fondamentali
Larghezza fissa interi tipi(C++11)
ptrdiff_t size_t max_align_t (C++11)	nullptr_t (C++11) offsetof NULL
Limiti numerici Original: Numeric limits The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
numeric_limits
C numerico limita interfaccia
Informazioni sul tipo di runtime Original: Runtime type information The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
type_info type_index (C++11)	bad_typeid bad_cast
Tipo tratti Original: Type traits The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
Categorie di tipo primario Original: Primary type categories The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
is_void (C++11) is_array (C++11) is_pointer (C++11) is_enum (C++11) is_union (C++11) is_class (C++11) is_function (C++11)	is_object (C++11) is_scalar (C++11) is_compound (C++11) is_integral (C++11) is_floating_point (C++11) is_fundamental (C++11) is_arithmetic (C++11)
is_reference (C++11)
is_lvalue_reference (C++11)
is_rvalue_reference (C++11)
is_member_pointer (C++11)
is_member_object_pointer (C++11)
is_member_function_pointer (C++11)

Proprietà del tipo Original: Type properties The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
is_const (C++11) is_volatile (C++11) is_pod (C++11) is_empty (C++11) is_polymorphic (C++11) is_abstract (C++11)	is_trivial (C++11) is_trivially_copyable (C++11) is_standard_layout (C++11) is_literal_type (C++11) is_signed (C++11) is_unsigned (C++11)

Operazioni supportate Original: Supported operations The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
is_constructible is_trivially_constructible is_nothrow_constructible (C++11) (C++11) (C++11)
is_default_constructible is_trivially_default_constructible is_nothrow_default_constructible (C++11) (C++11) (C++11)
is_copy_constructible is_trivially_copy_constructible is_nothrow_copy_constructible (C++11) (C++11) (C++11)
is_move_constructible is_trivially_move_constructible is_nothrow_move_constructible (C++11) (C++11) (C++11)
is_assignable is_trivially_assignable is_nothrow_assignable (C++11) (C++11) (C++11)
is_copy_assignable is_trivially_copy_assignable is_nothrow_copy_assignable (C++11) (C++11) (C++11)
is_move_assignable is_trivially_move_assignable is_nothrow_move_assignable (C++11) (C++11) (C++11)
is_destructible is_trivially_destructible is_nothrow_destructible (C++11) (C++11) (C++11)
has_virtual_destructor (C++11)
I rapporti e le query di proprietà Original: Relationships and property queries The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
is_same (C++11) is_base_of (C++11) is_convertible (C++11)	alignment_of (C++11) rank (C++11) extent (C++11)
Tipo modifiche Original: Type modifications The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
remove_cv remove_const remove_volatile (C++11) (C++11) (C++11) add_cv add_const add_volatile (C++11) (C++11) (C++11) make_signed (C++11) make_unsigned (C++11)	remove_reference (C++11) add_lvalue_reference add_rvalue_reference (C++11) (C++11) remove_pointer (C++11) add_pointer (C++11) remove_extent (C++11) remove_all_extents (C++11)
Tipo di trasformazioni Original: Type transformations The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
aligned_storage (C++11) 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 Original: Type trait constants The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
integral_constant (C++11)

 

std::numeric_limits

Costanti statiche Original: Static constants The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

numeric_limits::is_specialized

numeric_limits::is_signed

numeric_limits::is_integer

numeric_limits::is_exact

numeric_limits::has_infinity

numeric_limits::has_quiet_NaN

numeric_limits::has_signaling_NaN

numeric_limits::has_denorm

numeric_limits::has_denorm_loss

numeric_limits::round_style

numeric_limits::is_iec559

numeric_limits::is_bounded

numeric_limits::is_modulo

numeric_limits::digits

numeric_limits::digits10

numeric_limits::max_digits10 (C++11)

numeric_limits::radix

numeric_limits::min_exponent

numeric_limits::min_exponent10

numeric_limits::max_exponent

numeric_limits::max_exponent10

numeric_limits::traps

numeric_limits::tinyness_before

Funzioni membro statiche Original: Static member functions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

numeric_limits::min

numeric_limits::lowest (C++11)

numeric_limits::max

numeric_limits::epsilon

numeric_limits::round_error

numeric_limits::infinity

numeric_limits::quiet_NaN

numeric_limits::signaling_NaN

numeric_limits::denorm_min

Helper tipi Original: Helper types The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

float_round_style

float_denorm_style

 

static T epsilon()		(fino al c++11)
staticconstexpr 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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Valore di ritorno

T	std::numeric_limits<T>::epsilon()
/* non-specialized */	T();
bool	false
char	​0​
signedchar	​0​
unsignedchar	​0​
wchar_t	​0​
char16_t	​0​
char32_t	​0​
short	​0​
unsignedshort	​0​
int	​0​
unsignedint	​0​
long	​0​
unsignedlong	​0​
longlong	​0​
unsignedlonglong	​0​
float	FLT_EPSILON
double	DBL_EPSILON
longdouble	LDBL_EPSILON

Eccezioni

noexcept specification:  

noexcept

  (dal C++11)

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>typenamestd::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";elsestd::cout<<"d1 != d2\n";   if(almost_equal(d1, d2, 2))std::cout<<"d1 almost equals d2\n";elsestd::cout<<"d1 does not almost equal d2\n";}

Output:

d1 != d2 d1 almost equals d2

Vedi anche

nextafter nexttoward (C++11) (C++11)	prossimo valore rappresentabile in virgola mobile verso il valore dato Original: next representable floating point value towards the given value The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (funzione)