std::numeric_limits::digits

 

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numeric_limits::min_exponent10

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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 number of digits in the mantissa.

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
wchar_t	CHAR_BIT*sizeof(wchar_t) - std::numeric_limits<wchar_t>::is_signed
char16_t	CHAR_BIT*sizeof(char16_t)
char32_t	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	CHAR_BIT*sizeof(long long)-1
unsigned long long	CHAR_BIT*sizeof(long long)
float	FLT_MANT_DIG
double	DBL_MANT_DIG
long double	LDBL_MANT_DIG

See also

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)