isnan, _isnan, _isnanf
Tests if a floating-point value is not a number (NAN).
int isnan( /* floating-point */ x ); /* C-only macro */ int _isnan( double x ); int _isnanf( float x ); /* x64 only */ template <class T> bool isnan( T x ) throw(); /* C++ only */
The floating-point value to test.
In C, the isnan macro and the _isnan and _isnanf functions return a non-zero value if the argument x is a NAN; otherwise they return 0.
In C++, the isnan template function returns true if the argument x is a NaN; otherwise it returns false.
Because a NaN value does not compare as equal to any other NaN value, you must use one of these functions or macros to detect one. A NaN is generated when the result of a floating-point operation can't be represented in IEEE-754 floating-point format for the specified type. For information about how a NaN is represented for output, see printf.
When compiled as C++, the isnan macro is not defined, and an isnan template function is defined instead. It behaves the same way as the macro, but returns a value of type bool instead of an integer.
The _isnan and _isnanf functions are Microsoft-specific. The _isnanf function is only available when compiled for x64.
|Routine||Required header (C)||Required header (C++)|
|isnan, _isnanf||<math.h>||<math.h> or <cmath>|
|_isnan||<float.h>||<float.h> or <cfloat>|
For more compatibility information, see Compatibility.