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std::numeric_limits::signaling_NaN

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Template:ddcl list begin <tr class="t-dcl-sep"><td></td><td></td><td></td></tr>

<tr class="t-dcl ">

<td >
static T signaling_NaN()
</td>

<td class="t-dcl-nopad"> </td> <td > (until C++11) </td> </tr> <tr class="t-dcl-sep"><td></td><td></td><td></td></tr>

<tr class="t-dcl ">

<td >
static constexpr T signaling_NaN()
</td>

<td class="t-dcl-nopad"> </td> <td > (since C++11) </td> </tr> Template:ddcl list end

Returns the special value "signaling not-a-number", as represented by the floating-point type T. Only meaningful if std::numeric_limits<T>::has_signaling_NaN == true. In IEEE 754, the most common binary representation of floating-point numbers, any value with all bits of the exponent set and at least one bit of the fraction set represents a NaN. It is implementation-defined which values of the fraction represent quiet or signaling NaNs, and whether the sign bit is meaningful.

Contents

Return value

T std::numeric_limits<T>::quiet_NaN()
/* non-specialized */ T();
bool false
char 0
signed char 0
unsigned char 0
wchar_t 0
char16_t 0
char32_t 0
short 0
unsigned short 0
int 0
unsigned int 0
long 0
unsigned long 0
long long 0
unsigned long long 0
float implementation-defined
double implementation-defined
long double implementation-defined

Exceptions

noexcept specification:  
noexcept
  

Notes

A NaN never compares equal to itself. Copying a NaN may not preserve its bit representation.

When a signaling NaN is used as an argument to an arithmetic expression, the appropriate floating-point exception may be raised and the NaN is "quieted", that is, the expression returns a quiet NaN.

Example

Demonstrates the use of a signaling NaN to raise a floating-point exception

#include <iostream>
#include <limits>
#include <cfenv>
#pragma STDC_FENV_ACCESS on
void show_fe_exceptions()
{
    int n = std::fetestexcept(FE_ALL_EXCEPT);
    if(n & FE_INVALID) std::cout << "FE_INVALID is raised\n";
    else if(n == 0)    std::cout << "no exceptions are raised\n";
    std::feclearexcept(FE_ALL_EXCEPT);
}
int main()
{
    double snan = std::numeric_limits<double>::signaling_NaN();
    std::cout << "After sNaN was obtained ";
    show_fe_exceptions();
    double qnan = snan * 2.0;
    std::cout << "After sNaN was multiplied by 2 ";
    show_fe_exceptions();
    double qnan2 = qnan * 2.0;
    std::cout << "After the quieted NaN was multiplied by 2 ";
    show_fe_exceptions();
    std::cout << "The result is " << qnan2 << '\n';
}

Output:

After sNaN was obtained no exceptions are raised
After sNaN was multiplied by 2 FE_INVALID is raised
After the quieted NaN was multiplied by 2 no exceptions are raised
The result is nan

See also

identifies floating-point types that can represent the special value "signaling not-a-number" (NaN)
(public static member constant) [edit]
[static]
returns a quiet NaN value of the given floating-point type
(public static member function) [edit]