PRESENT - The GNU Fortran Compiler
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### 8.195 `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