gcc/fortran/doc/gfortran/intrinsic-procedures/present.rst

   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 .. index:: PRESENT
   7
   8 .. _present:
   9
  10 PRESENT --- Determine whether an optional dummy argument is specified
  11 *********************************************************************
  12
  13 .. function:: PRESENT(A)
  14
  15   Determines whether an optional dummy argument is present.
  16
  17   :param A:
  18     May be of any type and may be a pointer, scalar or array
  19     value, or a dummy procedure. It shall be the name of an optional dummy argument
  20     accessible within the current subroutine or function.
  21
  22   :return:
  23     Returns either ``TRUE`` if the optional argument :samp:`{A}` is present, or
  24     ``FALSE`` otherwise.
  25
  26   Standard:
  27     Fortran 90 and later
  28
  29   Class:
  30     Inquiry function
  31
  32   Syntax:
  33     .. code-block:: fortran
  34
  35       RESULT = PRESENT(A)
  36
  37   Example:
  38     .. code-block:: fortran
  39
  40       PROGRAM test_present
  41         WRITE(*,*) f(), f(42)      ! "F T"
  42       CONTAINS
  43         LOGICAL FUNCTION f(x)
  44           INTEGER, INTENT(IN), OPTIONAL :: x
  45           f = PRESENT(x)
  46         END FUNCTION
  47       END PROGRAM