Fortran problem

[Willem Grooters]

See attachement (Fortan 8.2, Alpha)

The documentation is not clear about specifying STRUCTURE in an INTERFACE block.
What worries me most is that the strcucure isn't recognized at all. If I remove the Interface block or use INTEGER*4 and CHARACTER*(*), it's no problem at all.

What did I miss?

[John Reagan · Accepted solution]

The manual clearly says: "An interface block comprises its own scoping unit, and does not inherit anything from its host though host association." That means that the structure X declared earlier is not visible inside the interface block. Things like INTERGER*4 or CHAR*(*) are builtin types that are available at any time.

[Jess Goodman]

You do need to define an explicit interface for function Y because it has an optional argument. However there are other ways to do this besides using an interface block.

You could just make function Y an internal procedure by defining it after a CONTAINS statement and moving the END PROGRAM to after END FUNCTION Y. You would then not need the INCLUDE statement inside the Y function definition.

Or you could define function Y in a MODULE. You would then add a "USE module_name" statement right after the PROGRAM X line.

For either of these alternatives remove the interface block from the include file.

[Willem Grooters]

John:
I must have overlooked that sentence, so that explaines why the strcuture isn't recognized in the INTERFACE block. I _think_ I found a way to get around it.

Jess:
This is just the reproducer, and in that context you are right, and I would have followed your suggestion anyway. In real, the problem occurs where the called routine ("Y" in the reproducer) is one of many in a library, called by many others. So your solution doesn't work here.

[Willem Grooters]

Jess:
Overlooked the second alternative :) That might work, if that allows "PRESENT" as a check whether an argument has been passed or not (IARGCOUNT may be sufficient in some cases and ís used where possible. But in some cases, this is not enough)

[Willem Grooters]

Could get around the problem - those routines that have a STRUCTURE typed argument have no optional arguments so can be kept outsize INTERFACE - for the sources at hand.