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


Routine Required Header Compatibility
_isnan <float.h> Win 95, Win NT

For additional compatibility information, see Compatibility in the Introduction.


LIBC.LIB Single thread static library, retail version
LIBCMT.LIB Multithread static library, retail version
MSVCRT.LIB Import library for MSVCRT.DLL, retail version

Return Value

_isnan returns a nonzero value (TRUE) if the argument x is a NaN; otherwise it returns 0 (FALSE).



Double-precision floating-point value


The _isnan function tests a given double-precision floating-point value x, returning a nonzero value if x is a 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.

Floating-Point Support Routines

See Also   _finite, _fpclass