std::numeric_limits::digits

From Cppreference

C++ Standard Library
Language Utilities library Strings library Containers library Algorithms library Iterators library Numerics library Input/output library Localizations library Regular expressions library (C++11) Atomic operations library (C++11) Thread support library (C++11)
Type support
std::numeric_limits
Static constants numeric_limits::is_specialized numeric_limits::is_signed numeric_limits::is_integer numeric_limits::is_exact numeric_limits::has_infinity numeric_limits::has_quiet_NaN numeric_limits::has_signaling_NaN numeric_limits::has_denorm numeric_limits::has_denorm_loss numeric_limits::round_style numeric_limits::is_iec559 numeric_limits::is_bounded numeric_limits::is_modulo numeric_limits::digits numeric_limits::digits10 numeric_limits::max_digits10 (C++11) numeric_limits::radix numeric_limits::min_exponent numeric_limits::min_exponent10 numeric_limits::max_exponent numeric_limits::max_exponent10 numeric_limits::traps numeric_limits::tinyness_before Static member functions numeric_limits::min numeric_limits::lowest (C++11) numeric_limits::max numeric_limits::epsilon numeric_limits::round_error numeric_limits::infinity numeric_limits::quiet_NaN numeric_limits::signaling_NaN numeric_limits::denorm_min Helper types float_round_style float_denorm_style

static const int digits		(pre-C++11 version)
static constexpr int digits		(C++11 version)

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. For floating-point types, this is the number of digits in the mantissa.

[edit] Standard specializations

T	value of std::numeric_limits<T>::digits
/* 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)
float	FLT_MANT_DIG
double	DBL_MANT_DIG
long double	LDBL_MANT_DIG

[edit] See also

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