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std::numeric_limits::digits10

Da cppreference.com.

 
 
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static const int digits10
(C fino + 11)
static constexpr int digits10
(dal C++11)
Il valore std::numeric_limits<T>::digits10 è il numero di base 10 cifre che può essere rappresentato dal tipo T senza cambiamento, cioè, qualsiasi con questo numero di molte cifre decimali può essere convertito in un valore di tipo T e ritorno alla forma decimale, senza modifiche a causa degli arrotondamenti o troppo pieno. Per base-radix tipi, è il valore di digits (digits-1 per tipi a virgola mobile) moltiplicato da log
10
(radix)
e arrotondato verso il basso.
Original:
The value of std::numeric_limits<T>::digits10 is the number of base-10 digits that can be represented by the type T without change, that is, any number with this many decimal digits can be converted to a value of type T and back to decimal form, without change due to rounding or overflow. For base-radix types, it is the value of digits (digits-1 for floating-point types) multiplied by log
10
(radix)
and rounded down.
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[modifica] Specializzazioni standard

T
valore di std::numeric_limits<T>::digits10
Original:
value of std::numeric_limits<T>::digits10
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/* non-specialized */ 0
bool 0
char std::numeric_limits<char>::digits * std::log10(2)
signed char std::numeric_limits<signed char>::digits * std::log10(2)
unsigned char std::numeric_limits<unsigned char>::digits * std::log10(2)
wchar_t std::numeric_limits<wchar_t>::digits * std::log10(2)
char16_t std::numeric_limits<char16_t>::digits * std::log10(2)
char32_t std::numeric_limits<char32_t>::digits * std::log10(2)
short std::numeric_limits<short>::digits * std::log10(2)
unsigned short std::numeric_limits<signed short>::digits * std::log10(2)
int std::numeric_limits<int>::digits * std::log10(2)
unsigned int std::numeric_limits<signed int>::digits * std::log10(2)
long std::numeric_limits<long>::digits * std::log10(2)
unsigned long std::numeric_limits<unsigned long>::digits * std::log10(2)
long long std::numeric_limits<long long>::digits * std::log10(2)
unsigned long long std::numeric_limits<unsigned long long>::digits * std::log10(2)
float FLT_DIG
double DBL_DIG
long double LDBL_DIG

[modifica] Esempio

a 8 bit tipo binario può rappresentare qualsiasi numero di due cifre decimali esattamente, ma i numeri a 3 cifre decimali 256.. 999 non può essere rappresentato. Il valore di digits10 per un 8 bit tipo è 2 (8 * std::log10(2) è 2.41)
Original:
An 8-bit binary type can represent any two-digit decimal number exactly, but 3-digit decimal numbers 256..999 cannot be represented. The value of digits10 for an 8-bit type is 2 (8 * std::log10(2) is 2.41)
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Lo standard a 32 bit IEEE 754 in virgola mobile di tipo ha una parte frazionaria a 24 bit (23 bit scritto, una implicita), che può suggerire che può rappresentare sette cifre decimali (24 * std::log10(2) è 7.22) , ma gli errori di arrotondamento relativi non sono uniformi e alcuni valori a virgola mobile con 7 cifre decimali non sopravvivono conversione a 32-bit a virgola mobile e viceversa: il più piccolo esempio positivo è 8.589973e9, che diventa 8.589974e9 dopo l'andata e ritorno Questi errori di arrotondamento non può superare. un bit nella rappresentazione, e digits10 è calcolato come (24-1)*std::log10(2), che è 6.92. arrotondamento verso il basso risulta il valore 6.
Original:
The standard 32-bit IEEE 754 floating-point type has a 24 bit fractional part (23 bits written, one implied), which may suggest that it can represent 7 digit decimals (24 * std::log10(2) is 7.22), but relative rounding errors are non-uniform and some floating-point values with 7 decimal digits do not survive conversion to 32-bit float and back: the smallest positive example is 8.589973e9, which becomes 8.589974e9 after the roundtrip. These rounding errors cannot exceed one bit in the representation, and digits10 is calculated as (24-1)*std::log10(2), which is 6.92. Rounding down results in the value 6.
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[modifica] Vedi anche

[statico]
la radice o base intero utilizzato dalla rappresentazione del tipo specificato
Original:
the radix or integer base used by the representation of the given type
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(pubblico membro statico costante) [edit]
[statico]
numero di cifre radix che possono essere rappresentati senza cambiamenti
Original:
number of radix digits that can be represented without change
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(pubblico membro statico costante) [edit]
[statico]
oltre la più piccola potenza negativa della radice che è una valida virgola mobile normalizzato valore uno
Original:
one more than the smallest negative power of the radix that is a valid normalized floating-point value
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(pubblico membro statico costante) [edit]
[statico]
maggiore della massima potenza intera della radice che è una valida finita valore a virgola mobile uno
Original:
one more than the largest integer power of the radix that is a valid finite floating-point value
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(pubblico membro statico costante) [edit]