— Macro: float NAN An expression representing a value which is “not a number”. This macro is a GNU extension, available only on machines that support the “not a number” value—that is to say, on all machines that support IEEE floating point.

How do you know if a float is a NaN?

To check whether a floating point or double number is NaN (Not a Number) in C++, we can use the isnan() function. The isnan() function is present into the cmath library. This function is introduced in C++ version 11.

How do you know if a value is NaN?

The Number. isNaN() method determines whether a value is NaN (Not-A-Number). This method returns true if the value is of the type Number, and equates to NaN. Otherwise it returns false.