std::numeric_limits<T>::signaling_NaN (3) - Linux Man Pages
static T signaling_NaN() throw(); (until C++11)
static constexpr T signaling_NaN() noexcept; (since C++11)
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.
/* non-specialized */ T()
signed char 0
unsigned char 0
unsigned short 0
unsigned int 0
unsigned long 0
long long 0
unsigned long long 0
long double implementation-defined
A NaN never compares equal to itself. Copying a NaN is not required, by IEEE-754, to preserve its bit representation (sign and payload), 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.
Demonstrates the use of a signaling NaN to raise a floating-point exception
// Run this code
has_signaling_NaN identifies floating-point types that can represent the special value "signaling not-a-number" (NaN)
quiet_NaN returns a quiet NaN value of the given floating-point type
isnan checks if the given number is NaN