[thirdparty/gcc.git] / gcc / fortran / doc / gfortran / intrinsic-procedures / isnan.rst

..
  Copyright 1988-2022 Free Software Foundation, Inc.
  This is part of the GCC manual.
  For copying conditions, see the copyright.rst file.

.. _isnan:

ISNAN --- Test for a NaN
************************

.. index:: ISNAN, IEEE, ISNAN

.. function:: ISNAN(X)

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

  :param X:
    Variable of the type ``REAL``.

  :return:
    Returns a default-kind ``LOGICAL``. The returned value is ``TRUE``
    if :samp:`{X}` is a NaN and ``FALSE`` otherwise.

  Standard:
    GNU extension

  Class:
    Elemental function

  Syntax:
    .. code-block:: fortran

      ISNAN(X)

  Example:
    .. code-block:: fortran

      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
Commit	Line	Data
c63539ff ML	1	..
	2	Copyright 1988-2022 Free Software Foundation, Inc.
	3	This is part of the GCC manual.
	4	For copying conditions, see the copyright.rst file.
	5
	6	.. _isnan:
	7
	8	ISNAN --- Test for a NaN
	9	************************
	10
	11	.. index:: ISNAN, IEEE, ISNAN
	12
	13	.. function:: ISNAN(X)
	14
	15	``ISNAN`` tests whether a floating-point value is an IEEE
	16	Not-a-Number (NaN).
	17
	18	:param X:
	19	Variable of the type ``REAL``.
	20
	21	:return:
	22	Returns a default-kind ``LOGICAL``. The returned value is ``TRUE``
	23	if :samp:`{X}` is a NaN and ``FALSE`` otherwise.
	24
	25	Standard:
	26	GNU extension
	27
	28	Class:
	29	Elemental function
	30
	31	Syntax:
	32	.. code-block:: fortran
	33
	34	ISNAN(X)
	35
	36	Example:
	37	.. code-block:: fortran
	38
	39	program test_nan
	40	implicit none
	41	real :: x
	42	x = -1.0
	43	x = sqrt(x)
	44	if (isnan(x)) stop '"x" is a NaN'
3ed1b4ce	45	end program test_nan