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# 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 | FLT_DECIMAL_DIG or std::ceil(std::numeric_limits<float>::digits * std::log10(2) + 1)
double | DBL_DECIMAL_DIG orstd::ceil(std::numeric_limits<double>::digits * std::log10(2) + 1)
long double | DECIMAL_DIG or LDBL_DECIMAL_DIG orstd::ceil(std::numeric_limits<long double>::digits * std::log10(2) + 1)

### [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

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

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