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Checks given double-precision floating-point value for not a number (NAN).

int _isnan(
   double x 


Double-precision floating-point value.

Return Value

_isnan returns a nonzero value if the argument x is a NAN; otherwise it returns 0.


The _isnan function tests a given double-precision floating-point value x, returning a nonzero value if x is a not a number (NAN). A NAN is generated when the result of a floating-point operation cannot be represented in Institute of Electrical and Electronics Engineers (IEEE) format. For information about how a NAN is represented for output, see printf.


Routine Required header Compatibility
_isnan <float.h> Win 98, Win Me, Win NT, Win 2000, Win XP

For additional compatibility information, see Compatibility in the Introduction.


All versions of the C run-time libraries.

See Also

Floating-Point Support Routines | _finite | _fpclass | Run-Time Routines and .NET Framework Equivalents