PRESENT
— Determine whether an optional dummy argument is specifiedRESULT = PRESENT(A)
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. |
TRUE
if the optional argument A is present, or FALSE
otherwise. 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
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https://gcc.gnu.org/onlinedocs/gcc-5.4.0/gfortran/PRESENT.html