std::numeric_limits<T>::denorm_min

 

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numeric_limits::denorm_min

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static T denorm_min() throw();		(until C++11)
static constexpr T denorm_min() noexcept;		(since C++11)

Returns the minimum positive subnormal value of the type T, if std::numeric_limits<T>::has_denorm != std::denorm_absent, otherwise returns std::numeric_limits<T>::min() for floating point types and T() for all other types. Only meaningful for floating-point types.

Return value

T	std::numeric_limits<T>::denorm_min()
/* non-specialized */	T()
bool	false
char	​0​
signed char	​0​
unsigned char	​0​
wchar_t	​0​
char8_t (C++20)	​0​
char16_t (C++11)	​0​
char32_t (C++11)	​0​
short	​0​
unsigned short	​0​
int	​0​
unsigned int	​0​
long	​0​
unsigned long	​0​
long long (C++11)	​0​
unsigned long long (C++11)	​0​
float	FLT_TRUE_MIN (\(\scriptsize 2^{-149}\)2-149 if std::numeric_limits<float>::is_iec559 is true)
double	DBL_TRUE_MIN (\(\scriptsize 2^{-1074}\)2-1074 if std::numeric_limits<double>::is_iec559 is true)
long double	LDBL_TRUE_MIN

Example

Demonstates the underlying bit structure of the denorm_min() and prints the values

Run this code

#include <cassert>
#include <cstdint>
#include <cstring>
#include <iostream>
#include <limits>
 
int main()
{
    // the smallest subnormal value has sign bit = 0, exponent = 0
    // and only the least significant bit of the fraction is 1
    std::uint32_t denorm_bits = 0x0001;
    float denorm_float;
    std::memcpy(&denorm_float, &denorm_bits, sizeof(float));
 
    assert(denorm_float == std::numeric_limits<float>::denorm_min());
 
    std::cout << "float\tmin()\t\tdenorm_min()\n";
    std::cout << "\t" << std::numeric_limits<float>::min() << '\t';
    std::cout <<         std::numeric_limits<float>::denorm_min() << '\n';
 
    std::cout << "double\tmin()\t\tdenorm_min()\n";
    std::cout << "\t" << std::numeric_limits<double>::min() << '\t';
    std::cout <<         std::numeric_limits<double>::denorm_min() << '\n';
}

Possible output:

float	min()		denorm_min()
	1.17549e-38	1.4013e-45
double	min()		denorm_min()
	2.22507e-308	4.94066e-324

See also

min [static]	returns the smallest finite value of the given type (public static member function)
has_denorm [static]	identifies the denormalization style used by the floating-point type (public static member constant)
lowest [static] (C++11)	returns the lowest finite value of the given type (public static member function)