ISNAN — Test for a NaN#

ISNAN(X)#

ISNAN tests whether a floating-point value is an IEEE Not-a-Number (NaN).

Parameters: X – Variable of the type REAL.
Returns: Returns a default-kind LOGICAL. The returned value is TRUE if X is a NaN and FALSE otherwise.

Standard:

GNU extension

Class:

Elemental function

Syntax:

ISNAN(X)

Example:

program test_nan
  implicit none
  real :: x
  x = -1.0
  x = sqrt(x)
  if (isnan(x)) stop '"x" is a NaN'
end program test_nan