std::numeric_limits::digits(3)

NAME
std::numeric_limits::digits - std::numeric_limits::digits

Synopsis
   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
   signed char CHAR_BIT - 1
   unsigned char CHAR_BIT
                        CHAR_BIT * sizeof(wchar_t)
   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
   unsigned short CHAR_BIT * sizeof(short)
   int CHAR_BIT * sizeof(int) - 1
   unsigned int CHAR_BIT * sizeof(int)
   long CHAR_BIT * sizeof(long) - 1
   unsigned long CHAR_BIT * sizeof(long)
   long long (since C++11) CHAR_BIT * sizeof(long long) - 1
   unsigned long long (since C++11) CHAR_BIT * sizeof(long long)
   float FLT_MANT_DIG
   double DBL_MANT_DIG
   long double LDBL_MANT_DIG

See also
   radix the radix or integer base used by the representation of the given type
   [static] (public static member constant)
   min_exponent one more than the smallest negative power of the radix that is a valid
   [static] normalized floating-point value
                (public static member constant)
   max_exponent one more than the largest integer power of the radix that is a valid
   [static] finite floating-point value
                (public static member constant)