isnan()

Test for not-a-number (NAN)

Synopsis:

#include <math.h>

#define isnan ( x ) ...

Arguments:

x

The number you want to test.

Library:

libm

Use the -l m option to qcc to link against this library.

Description:

The isnan() macro determines if x is Not-A-Number (NAN).

Returns:

1

The value of x is NAN.

≠ 1

The value of x is a number.

Examples:

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <inttypes.h>
#include <math.h>
#include <fpstatus.h>

int main(int argc, char** argv) 
{
  double a, b, c, d;

  a = 2;
  b = -0.5;
  c = NAN;
  fp_exception_mask(_FP_EXC_DIVZERO, 1);
  d = 1.0/0.0;
  printf("%f is %s \n", a, 
         (isnan(a)) ? "not a number" : "a number");
  printf("%f is %s \n", b,
         (isnan(b)) ? "not a number" : "a number");
  printf("%f is %s \n", c,
         (isnan(c)) ? "not a number" : "a number");
  printf("%f is %s \n", d,
         (isnan(d)) ? "not a number" : "a number");
  return EXIT_SUCCESS;
}

produces the output:

2.000000 is a number
-0.500000 is a number
NAN is not a number
Inf is a number

Classification:

POSIX 1003.1

See also:

isfinite(), isinf()