Returns the special value "signalingnot-a-number", as represented by the floating-point typeT. Only meaningful ifstd::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.

[edit]Return value

[edit]Notes

A NaN never compares equal to itself. Copying a NaN is not required, by IEEE-754, to preserve its bit representation (sign andpayload), though most implementation do.

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

#include <cfenv>#include <iostream>#include <limits> #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";elseif(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';}

After sNaN was obtained, no exceptions are raisedAfter sNaN was multiplied by 2, FE_INVALID is raisedAfter the quieted NaN was multiplied by 2, no exceptions are raisedThe result is nan

[edit]See also

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