std::numeric_limits<T>::digits

static const int digits;		(until C++11)
static constexpr int digits;			(since C++11)

The value of std::numeric_limits<T>::digits is the number of digits in base-radix that can be represented by the type T without change. For integer types, this is the number of bits not counting the sign bit and the padding bits (if any). For floating-point types, this is the digits of the mantissa (for IEC 559/IEEE 754 implementations, this is the number of digits stored for the mantissa plus one, because the mantissa has an implicit leading 1 and binary point).

Standard specializations

`T`	value of `std::numeric_limits<T>::digits` (assuming no padding bits)
/* non-specialized */	`0`
bool	`1`
char	`CHAR_BIT - std::numeric_limits<char>::is_signed`
signedchar	`CHAR_BIT - 1`
unsignedchar	`CHAR_BIT`
wchar_t	CHAR_BIT * sizeof(wchar_t) - std::numeric_limits<wchar_t>::is_signed
char8_t (since C++20)	`CHAR_BIT`
char16_t (since C++11)	`CHAR_BIT * sizeof(char16_t)`
char32_t (since C++11)	`CHAR_BIT * sizeof(char32_t)`
short	`CHAR_BIT * sizeof(short) - 1`
unsignedshort	`CHAR_BIT * sizeof(short)`
int	`CHAR_BIT * sizeof(int) - 1`
unsignedint	`CHAR_BIT * sizeof(int)`
long	`CHAR_BIT * sizeof(long) - 1`
unsignedlong	`CHAR_BIT * sizeof(long)`
longlong (since C++11)	`CHAR_BIT * sizeof(long long) - 1`
unsignedlonglong (since C++11)	`CHAR_BIT * sizeof(long long)`
float	`FLT_MANT_DIG`
double	`DBL_MANT_DIG`
longdouble	`LDBL_MANT_DIG`

Example

#include <concepts>
#include <iomanip>
#include <iostream>
#include <limits>
#include <meta>
#include <string_view>
#include <type_traits>
using namespace std::literals;

template<typename T>
    requires std::integral<T> or std::floating_point<T>
constexpr void digit()
{
    constexpr int w{(int)"unsigned long long"sv.size()};
    std::cout << std::right << std::setw(w)
              << std::meta::display_string_of(^^T) << " : "
              << std::numeric_limits<T>::digits << '\n';
}

template<typename... T>
constexpr void digits()
{
    (digit<T>(), ...);
}

int main()
{
    digits<
        bool, char, signed char, unsigned char, wchar_t, char8_t, char16_t,
        char32_t, short, unsigned short, int, unsigned int, long, unsigned long,
        long long, unsigned long long, float, double, long double
    >();
}

Possible output:

              bool : 1
              char : 7
       signed char : 7
     unsigned char : 8
           wchar_t : 31
           char8_t : 8
          char16_t : 16
          char32_t : 32
             short : 15
    unsigned short : 16
               int : 31
      unsigned int : 32
              long : 63
     unsigned long : 64
         long long : 63
unsigned long long : 64
             float : 24
            double : 53
       long double : 64

radix [static]	the radix or integer base used by the representation of the given type (public static member constant)
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)
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)

std::numeric_limits<T>::digits

Standard specializations

Example

See also