Lahey/GNU Fortran

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8.194 PRESENT — Determine whether an optional dummy argument is specified

Description:
Determines whether an optional dummy argument is present.
Standard:
Fortran 95 and later
Class:
Inquiry function
Syntax:
RESULT = PRESENT(A)
Arguments:

A May be of any type and may be a pointer, scalar or array value, or a dummy procedure. It shall be the name of an optional dummy argument accessible within the current subroutine or function.

Return value:
Returns either TRUE if the optional argument A is present, or FALSE otherwise.
Example:
          PROGRAM test_present
            WRITE(*,*) f(), f(42)      ! "F T"
          CONTAINS
            LOGICAL FUNCTION f(x)
              INTEGER, INTENT(IN), OPTIONAL :: x
              f = PRESENT(x)
            END FUNCTION
          END PROGRAM