Test for a NaN. Returns 1 if the argument is NaN; 0 if not.

    This function is supported on OpenVMS Integrity servers and
    Alpha only.

    Format

      #include  <math.h>

      int isnan  (double x);

      int isnanf  (float x);

      int isnanl  (long double x);

1  –  Argument

 x

    A real value.

2  –  Description

    The isnan functions return the integer value 1 (TRUE) if x is NaN
    (the IEEE floating point reserved not-a-number value); otherwise,
    they return the value 0 (FALSE).