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[simon]

I believe that it is part of the Fortran standard that optional arguments can be passed as optional arguments to other routines without having to check whether they are present - their present status is passed automatically.

But consider the following code, which does not work in either FTN95 or NAGWare. My understanding is that the call to s2 should definitely work, but what about the call to s3 at line 11? This generates an error message indicating that the optional arguments are undefined. Indeed the optional arguments are not passed to s1, but given that they are optional in s3 surely that should not matter.

[mecej4]

This is an example that justifies one's sitting on the fence with a copy of the Fortran standard, but here is my take: Line 11 of your code tries to split a hair that is not present, so the code is not valid. Whether a compiler should detect the violation at compile time or at run time is a separate question.

Let us look at the question from an implementation perspective, as well. When j is used as an argument, whether present or not, its address is passed; a NULL gets passed if it is not present. However, you want to pass j(1) and j(2) as arguments, and that cannot be done unless you start treating NULLs in the same way as infinity, i.e., half a NULL equals a NULL, etc.

I am open to arguments supporting the claim that the opposite should be true.

P.S.: After writing my reply above, I tested your code with the Sun Fortran compiler 12.4 on Linux. The run-time error was:

[davidb]

I thought the problem here was that the actual arguments are arrays but the dummy arguments are scalars?

Generally speaking, if a subprogram "A" has optional dummy arguments there is no need to test using present() if they are simply passed and associated to optional dummy arguments in another subprogram "B".

So, if A and B have explicit interfaces, there is no need to write

[mecej4]

DavidB, only the optional second argument of Subroutine S1 is an array. In the only call of S1 in the example, this argument is absent.

The main issue is: if an optional argument is an array (or structure), in an instance where it is not present, how should array elements (or structure components) be treated? I think that consistency requires that if J is an optional array arguments, both J(1), J(2), etc., should all be seen as absent.

Here is a second example to make this clear.