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std::numeric_limits::digits10

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std::numeric_limits
 
static const int digits10
(até C + 11)
static constexpr int digits10
(a partir do C++ 11)
O valor de std::numeric_limits<T>::digits10 é o número de base-10 dígitos, que pode ser representado pela T tipo sem alteração, isto é, qualquer número com este número de dígitos decimais pode ser convertido para um valor de T tipo e de volta para a forma decimal, sem alteração devido ao arredondamento ou extravasamento. Para radix tipos-base, que é o valor de digits (digits-1 para tipos de ponto flutuante) multiplicado por log
10
(radix)
e arredondado para baixo.
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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[editar] Especializações padrão

T
valor de 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

[editar] Exemplo

Um tipo binário de 8 bits pode representar qualquer número decimal de dois dígitos exatamente, mas três dígitos decimais 256.. 999 não pode ser representado. digits10 O valor para um tipo de 8 bits é 2 (8 * std::log10(2) é 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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O padrão de 32 bits IEEE 754 tipo de ponto flutuante tem uma parte fracionária de 24 bits (23 bits por escrito, um implícito), o que pode sugerir que ele pode representar sete casas decimais dígitos (24 * std::log10(2) é 7.22) , mas os erros de arredondamento relativos são não-uniforme e alguns valores de ponto flutuante, com 7 dígitos decimais não sobrevivem a conversão para 32-bit float e volta: o menor exemplo positivo é 8.589973e9, que se torna 8.589974e9 após a ida Esses erros de arredondamento não pode exceder. um pouco na representação, e digits10 é calculado como (24-1)*std::log10(2), que é 6,92. arredondamento para baixo resulta no valor 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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[editar] Veja também

[estática]
a raiz ou base inteiro usado pela representação do tipo de dado
Original:
the radix or integer base used by the representation of the given type
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(membro estático público constante) [edit]
[estática]
número de dígitos radix que podem ser representadas sem alterações
Original:
number of radix digits that can be represented without change
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(membro estático público constante) [edit]
[estática]
mais um do que o menor poder negativo do radix que é um valor válido de ponto flutuante normalizado
Original:
one more than the smallest negative power of the radix that is a valid normalized floating-point value
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(membro estático público constante) [edit]
[estática]
um a mais que o maior poder inteiro da raiz que é um valor válido de ponto flutuante finita
Original:
one more than the largest integer power of the radix that is a valid finite floating-point value
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(membro estático público constante) [edit]