isnan(3)                                                       isnan(3)

  isnan()

  NAME

    isnan(), isnanf() - test argument for Not A Number

  SYNOPSIS

    #include 

    int isnan (double x)
    int isnanf (float x)

  DESCRIPTION

    The isnan(3) and isnanf(3) functions test the argument x to see if it is
    not a number.

  RETURN VALUES

    The isnan(3) and isnanf(3) functions return 1 if the argument x is NaN,
    and return 0 otherwise.

  SEE ALSO

    isinf(3)

    math(3)

  USAGE NOTES

    All of these functions are thread safe.

    None of these functions are async-signal safe.