isnan, _isnan, _isnanf

Article
12/18/2017

The latest version of this topic can be found at isnan, _isnan, _isnanf.

Tests if a floating-point value is not a number (NAN).

Syntax

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 */

Parameters

x
The floating-point value to test.

Return Value

In C, the isnan macro and the _isnan and _isnanf functions return a nonzero value if the argument x is a NAN; otherwise they return 0.

In C++, the isnan template functions return true if the argument x is a NAN; otherwise they return false.

Remarks

The C isnan macro and the _isnan and _isnanf functions test floating-point value x, returning a nonzero value if x is a Not a Number (NAN) value. 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 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.

Requirements

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.