# Overloading an external procedure **URL:** \ **Category:** Help\ **Created:** [July 7, 2022, 10:45am UTC](https://fortran-lang.discourse.group/t/overloading-an-external-procedure/3943 "2022-07-07T10:45:45Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Blaise](https://avatars.discourse-cdn.com/v4/letter/b/ecae2f/32.png) [@Blaise](https://fortran-lang.discourse.group/u/Blaise)\ **Post date:** [July 7, 2022, 10:45am UTC](https://fortran-lang.discourse.group/t/overloading-an-external-procedure/3943/1 "2022-07-07T10:45:45Z")
Hi, I am trying to write modern fortran wrappers for the exodusII library [GitHub - sandialabs/seacas: The Sandia Engineering Analysis Code Access System (SEACAS) is a suite of preprocessing, postprocessing, translation, and utility applications supporting finite element analysis software using the Exodus database file format.](https://github.com/sandialabs/seacas) Their fortran wrapper system is convoluted and predates iso\_c\_bindings by a very long time. Re-writing them completely with iso\_c\_binding is not practical at this point. For historical reason, C functions were given short 6-8 characters long names in Fortran. I’d like to allow the use of the full C name, as well as the short name, and was thinking of doing so by writing an abstract interface. but can’t figure how to do so. For instance, the following does not compile under gfortran (GNU Fortran (Homebrew GCC 11.3.0\_2) 11.3.0 macOS), when exppv is an external function implemented in C. ```auto interface subroutine exppv(idexo, time_step, var_type, var_index, & obj_id, start_index, num_entities, & var_vals, ierr) INTEGER idexo ! ® INTEGER time_step ! ® INTEGER var_type ! ® INTEGER var_index ! ® INTEGER obj_id ! ® INTEGER start_index ! ® INTEGER num_entities ! ® REAL var_vals(*) ! (W) INTEGER ierr ! (W) end subroutine exppv end interface interface ex_put_partial_var subroutine exppv end interface ex_put_partial_var ``` Any suggestion? There quite a few functions to wrap, so tensity is a plus… ---
**Author:** ![Arjen](https://avatars.discourse-cdn.com/v4/letter/a/b9bd4f/32.png) [@Arjen](https://fortran-lang.discourse.group/u/Arjen)\ **Post date:** [July 7, 2022, 11:04am UTC](https://fortran-lang.discourse.group/t/overloading-an-external-procedure/3943/2 "2022-07-07T11:04:50Z")
How about: ```auto module beliavsky abstract interface subroutine exppv_(idexo, time_step, var_type, var_index, & obj_id, start_index, num_entities, & var_vals, ierr) bind(c) INTEGER idexo ! INTEGER time_step ! INTEGER var_type ! INTEGER var_index ! INTEGER obj_id ! INTEGER start_index ! INTEGER num_entities ! REAL var_vals(*) ! (W) INTEGER ierr ! (W) end subroutine exppv_ end interface procedure(exppv_), pointer :: exppv, ex_put_partial_var end module beliavsky ``` This compiles with both gfortran and Intel Fortran oneAPI. I left in the “bind(c)” bit, that may or may not be useful when it comes to name mangling/decoration. The essence is that you define an abstract interface and then use it with two different entities. Fortunately the call to a procedure pointer is syntactically the same as to a regular routine. ---
**Author:** ![Arjen](https://avatars.discourse-cdn.com/v4/letter/a/b9bd4f/32.png) [@Arjen](https://fortran-lang.discourse.group/u/Arjen)\ **Post date:** [July 7, 2022, 11:08am UTC](https://fortran-lang.discourse.group/t/overloading-an-external-procedure/3943/3 "2022-07-07T11:08:29Z")
There may be other, more concise solutions, but this works 🙂 ---
**Author:** ![Blaise](https://avatars.discourse-cdn.com/v4/letter/b/ecae2f/32.png) [@Blaise](https://fortran-lang.discourse.group/u/Blaise)\ **Post date:** [July 7, 2022, 3:17pm UTC](https://fortran-lang.discourse.group/t/overloading-an-external-procedure/3943/4 "2022-07-07T15:17:03Z")
That works, thanks. ---
**Author:** ![rwmsu](https://avatars.discourse-cdn.com/v4/letter/r/48db29/32.png) [@rwmsu](https://fortran-lang.discourse.group/u/rwmsu)\ **Post date:** [July 7, 2022, 3:44pm UTC](https://fortran-lang.discourse.group/t/overloading-an-external-procedure/3943/5 "2022-07-07T15:44:09Z")
Just curious, I can’t find the EXPPV function in any current Exodus distribution at least on the Fortran side. Are you trying to implement all of the C functions including the ones not supported by the existing Fortran wrappers. I’ve already done my own C-Interop wrappers to Exodus but just implemented the ones described in the Fortran manual. My approach to the naming was to give everything the C names and then use module procedure interfaces to give access to the old Fortran 6 character names. Unfortunately, I can’t release my code without consent from my DoD sponsor. ---
**Author:** ![Blaise](https://avatars.discourse-cdn.com/v4/letter/b/ecae2f/32.png) [@Blaise](https://fortran-lang.discourse.group/u/Blaise)\ **Post date:** [July 7, 2022, 3:55pm UTC](https://fortran-lang.discourse.group/t/overloading-an-external-procedure/3943/6 "2022-07-07T15:55:33Z")
I am writing a few of the missing wrappers, mainly the one dealing with partial input output. Considering that exodus is developed at Sandia national lab (on the military side, if I remember correctly), I would assume that getting clearance to release this type of contribution would be feasible. Out of curiosity, if you were to write a C-interop wrapper to a function EXPPV (not in exodus), whose prototype is int EXPPV(int exoid, int time\_step, int var\_type, int var\_index, Int obj\_id, int64\_t start\_index, int64\_t num\_entities, const void \*var\_vals), How would you proceed? ---
**Author:** ![rwmsu](https://avatars.discourse-cdn.com/v4/letter/r/48db29/32.png) [@rwmsu](https://fortran-lang.discourse.group/u/rwmsu)\ **Post date:** [July 7, 2022, 5:03pm UTC](https://fortran-lang.discourse.group/t/overloading-an-external-procedure/3943/7 "2022-07-07T17:03:07Z")
@Blaise Here is how I would implement ex\_put\_partial\_var Sorry for the length ```auto Subroutine ex_put_partial_var(exoid, time_step, var_type, var_index, & obj_id, start_index, num_entities, & var_vals, ierr) USE ISO_FORTRAN_ENV USE ISO_C_BINDING USE exodus_data, ONLY : EX_IK, EX_ENTITY_ID Integer(EX_IK), Intent(IN) :: exoid Integer(EX_IK), Intent(IN) :: time_step Integer(EX_IK), Intent(IN) :: var_type Integer(EX_IK), Intent(IN) :: var_index Integer(EX_IK), Intent(IN) :: obj_id Integer(INT64), Intent(IN) :: start_index Integer(INT64), Intent(IN) :: num_entities Type(*), Intent(IN) :: var_vals(*) Integer(EX_IK), Intent(OUT) :: ierr Integer(C_INT) :: exoid_c, ierr_c, var_index_c, time_step_c Integer(C_INT64_T) :: start_index_c, num_entities_c Integer(EX_ENTITY_ID) :: var_type_c, obj_id_c Interface Function ex_put_partial_var_c(exoid, time_step, var_type, var_index, & obj_id, start_index, num_entities, & var_vals) & BIND(C, NAME="ex_put_partial_var") IMPORT :: C_INT, C_INT64_T, EX_ENTITY_ID Integer(C_INT), VALUE :: exoid Integer(C_INT), VALUE :: time_step Integer(EX_ENTITY_ID), VALUE :: var_type Integer(C_INT), VALUE :: var_index Integer(EX_ENTITY_ID), VALUE :: obj_id Integer(C_INT64_T), VALUE :: start_index Integer(C_INT64_T), VALUE :: num_entities Type(*), Intent(IN) :: var_vals(*) Integer(C_INT) :: ex_put_partial_var_c End Function ex_put_partial_var_c End Interface exoid_c = INT(exoid, C_INT) time_step_c = INT(time_step, C_INT) var_index_c = INT(var_index, C_INT) start_index_c = start_index num_entities_c = num_entities var_type_c = INT(var_type, EX_ENTITY_ID) obj_id_c = INT(obj_id, EX_ENTITY_ID) ierr_c = ex_put_partial_var_c(exoid_c, timestep_c, var_type_c, & var_index_c, obj_id_c, start_index_c, & num_entities_c, var_vals) ierr = INT(ierr_c, EX_IK) End Subroutine ex_put_partial_var ``` A few comments. 1. I define my own parameter for EX\_ENTITY\_ID (its C\_INT64\_T in exodusii.h) just to make the interfaces visually consistent with the C interfaces 2. I create extra C specific variables for the arguments passed to C and convert the Fortran arguments defined with the EX\_IK type to the required C data types. I do this so I can create a Fortran version that uses 64 bit integers on the Fortran side and converts to the required C types prior to calling the underlying C function 3. I would try passing var\_vals as an assumed TYPE value since it can be any of several different types in the C code. Depending on how mature your compiler support is for assumed TYPE you might have to resort to passing it as a TYPE(C\_PTR) instead Also I put all these routines in a module and use a module procedure interface to give it a pre-historic Fortran 6 character name. ie Interface EXPPV module procedure ex\_put\_partial\_var End Interface Hope this helps. I’ll check into releasing my code but I might be up against ITAR restrictions ---
**Author:** ![FortranFan](https://avatars.discourse-cdn.com/v4/letter/f/96bed5/32.png) [@FortranFan](https://fortran-lang.discourse.group/u/FortranFan)\ **Post date:** [July 8, 2022, 11:43pm UTC](https://fortran-lang.discourse.group/t/overloading-an-external-procedure/3943/8 "2022-07-08T23:43:56Z")
> [@Blaise](#): > > Any suggestion? There quite a few functions to wrap, so tensity is a plus… @Blaise, it appears what is of interest to you is a renaming facility and not “overloading”, you may want to give this further thought. If you do decide what you’re after is simple renaming, look into whether basic `USE` functionality along with `ONLY` which has been available since Fortran 90 might suit your purpose - see below. ```auto #include void Cfunction1() { printf("Hello World!\n"); } void Cfunction2() { printf("Who wants to KISS anymore!\n"); } ``` ```fortran module m interface subroutine Cfunction1() bind(C, name="Cfunction1") end subroutine subroutine Cfunction2() bind(C, name="Cfunction2") end subroutine end interface end module use m, only : Cfunction1, Cfunction2 use m, Cfunc1 => Cfunction1 call Cfunc1() call Cfunction1() call Cfunction2() end ``` ```auto C:\Temp>gfortran -c c.c C:\Temp>gfortran -c p.f90 C:\Temp>gfortran p.o c.o -o p.exe C:\Temp>p.exe Hello World! Hello World! Who wants to KISS anymore! ```