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isnan, _isnan, _isnanf


The latest version of this topic can be found at 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 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.

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.

RoutineRequired 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.

Floating-Point Support
_finite, _finitef
_fpclass, _fpclassf