std::numeric_limits::signaling_NaN

From Cppreference

Returns the special value "signaling not-a-number", as represented by the floating-point type T. Only meaningful if std::numeric_limits<T>::has_quiet_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 singaling NaNs, and whether the sign bit is meaningful.

[edit] Return value

[edit] Exceptions

[edit] 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.

[edit] 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 queted 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 queted NaN was multiplied by 2 no exceptions are raised
The result is nan

[edit] See also