std::numeric_limits::max_digits10

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std::numeric_limits
Static constants 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 Static member functions 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 types float_round_style float_denorm_style

static constexpr int max_digits10		(C++11 feature)

The value of std::numeric_limits<T>::max_digits10 is the number of base-10 digits that are necessary to uniquely represent all distinct values of the type T, such as necessary for serialization/deserialization to text. This constant is meaningful for all floating-point types.

[edit] Standard specializations

T	value of std::numeric_limits<T>::max_digits10
/* non-specialized */	​0​
bool	​0​
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	std::floor(std::numeric_limits<float>::digits * std::log10(2) + 2)
double	std::floor(std::numeric_limits<double>::digits * std::log10(2) + 2)
long double	std::floor(std::numeric_limits<long double>::digits * std::log10(2) + 2)

[edit] See also

radix	the radix or integer base used by the representation of the given type (public static member constant)
digits	number of radix digits that can be represented without change (public static member constant)
digits10	number of decimal digits that can be represented without change (public static member constant)
min_exponent	one more than the smallest negative power of the radix that is a valid normalized floating-point value (public static member constant)
max_exponent	one more than the largest integer power of the radix that is a valid finite floating-point value (public static member constant)