std::numeric_limits::max_digits10
From cppreference.com
< cpp | types | numeric limits
| static constexpr int max_digits10 |
(since C++11) | |
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] Notes
Unlike most mathematical operations, the conversion of a floating-point value to text and back is exact as long as at least max_digits10 were used (9 for float, 17 for double): it is guaranteed to produce the same floating-point value, even though the intermediate text representation is not exact. It may take over a hundred decimal digits to represent the precise value of a float in decimal notation.
[edit] See also
| [static] |
the radix or integer base used by the representation of the given type (public static member constant) |
| [static] |
number of radix digits that can be represented without change (public static member constant) |
| [static] |
number of decimal digits that can be represented without change (public static member constant) |
| [static] |
one more than the smallest negative power of the radix that is a valid normalized floating-point value (public static member constant) |
| [static] |
one more than the largest integer power of the radix that is a valid finite floating-point value (public static member constant) |