isnan-isnan-isnanf.md

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isnan, _isnan, _isnanf | Microsoft Docs		11/04/2016			cpp-standard-libraries		article	_isnan _isnanf isnan	msvcrt.dll msvcr80.dll msvcr90.dll msvcr100.dll msvcr100_clr0400.dll msvcr110.dll msvcr110_clr0400.dll msvcr120.dll msvcr120_clr0400.dll ucrtbase.dll api-ms-win-crt-math-l1-1-0.dll	DLLExport	_isnan isnan math/isnan math/_isnan math/_isnanf _isnanf	C++	NAN (not a number) _isnan function IEEE floating-point representation Not a Number (NANs) isnan function	391fbc5b-89a4-4fba-997e-68f1131caf82	11	corob-msft	corob	ghogen

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.

See Also

Floating-Point Support
_finite, _finitef
_fpclass, _fpclassf