STRUCTURE or COMMON in parameter

[sphost]

Another problem I meet, trying to call a Fortran function from a C++ program :

How can I pass a structure from C++ in the parameter of the Fortran Function ?

Example :

typedef struct _testst (int test1; int test2) testst, *lptestst;

extern "C" void f1(lptest rec);

What does my Fortran function f1 look like ? In fortran side, do I have to declare rec as a COMMON and how ? Is it also possible to declare it as a STRUCTURE (VMS keyword) ?

If you have any example, it would be great !

Thanks in advance for your answer !

[Steven_L_Intel1]

You can use the DEC STRUCTURE/RECORD extension, but I don't recommend it. You should use an "interoperable derived type" (and routine). For example:

subroutine f1 (rec) bind(C,name="f1")
use,intrinsic :: iso_c_binding
type, bind(C) :: testst
integer(C_INT) :: test1
integer(C_INT) :: test2
end type testst
type(testst), intent(inout) :: rec
! code goes here
! components are rec%test1 and rec%test2
end subroutine f1

[sphost]

Ok, thanks for the information, I will try this.

Nevertheless, if I want to use the DEC STRUCTURE/RECORD extension, what would be the syntax to use it in C++ ?

[Steven_L_Intel1]

In C++? That's a Fortran extension. You would use it in place of the TYPE declarations in Fortran code.

[sphost]

No, I want to know the syntax to declare a STRUCTURE in the Fortran Code as an intent(inout)

[Steven_L_Intel1]

structure /testst/
integer test1
integer test2
end structure
record /testst/ rec
intent(inout) :: rec

I don't know why you would want to do that rather than the standard-conforming method.

[sphost]

Well, this is very simple :

My C++ Project has to call Mathematical Fortran Model made by our technical department. This department used to do their model in VAX VMS.

Now they have to migrate it to a Linux server sothey would like to do the less modification as possible.
That's why I want to keep the syntax of VMS Fortran.

Thanks a lot for your answer !

[Steven_L_Intel1]

If you really mean VAX, then remove the INTENT line. DEC/Compaq/HP Fortran for OpenVMS Alpha will support INTENT. It also supports TYPE, though not BIND or ISO_C_BINDING.

[sphost]

Well, I don't want to keep my model in OpenVMS environnement, I have to migrate it to a Linux Server. So I have to add the intent and BIND and ISO_C_BINDING if I want my model to be called from C++. No ?

[Steven_L_Intel1]

"Have to"? No. People have been mixing C/C++ and Fortran for many years without these things, but always using extensions and assumed behavior. Now there is a standard-conforming way to do it.

The INTENT is optional and is primarily there to aid in error checking.

[sphost]

I understand, but the code of this model containt some call to SYS$ of OpenVMS system that cannot be use in linux.

So the code has to be change in this way. Nevertheless, you mean that the actual syntax used for OpenVMS will be applied to the linux system ? Won't I have any problem if I keep for examplea REAL*4 which has to be modified by C++ ?

[Steven_L_Intel1]

I don't see a problem with what you propose.

[sphost]

I mean, the size of a REAL in Fortran is not the same than in C++, that's why we have to put REAL(C_DOUBLE), so I have to modify my Fortran Code in this way to be able to access this fortran variable throw C++, that's right ?

[Steven_L_Intel1]

Well, USUALLY the size of default REAL in Fortran is the same as that of float in C, and the size of DOUBLE PRECISION is the same as C's double. Nothing requires that, of course. You can use REAL*4 and REAL*8 (extensions) to be explicit about the size, but you're still making an assumption about what C does. The use of the kind constants in ISO_C_BINDING is intended to eliminate the need for assumptions, but that doesn't mean the code won't work if you "guess right".