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API with and without null-terminated strings #26

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7a1c5a5
WIP: Add a wrapper precicef_create and a precicec_create expecting n…
MakisH Mar 19, 2024
c43b133
Apply suggestions from code review
MakisH Mar 19, 2024
f35d846
Remove length arguments from precicef_create
MakisH Mar 19, 2024
b6d317a
Remove the sizes from solverdummy.f90
MakisH Mar 19, 2024
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2 changes: 1 addition & 1 deletion examples/solverdummy/solverdummy.f90
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Expand Up @@ -35,7 +35,7 @@ PROGRAM main
commsize = 1
dt = 1
numberOfVertices = 3
CALL precicef_create(participantName, config, rank, commsize, 50, 50)
CALL precicef_create(participantName, config, rank, commsize)

! Allocate dummy mesh with only one vertex
CALL precicef_get_mesh_dimensions(meshName, dimensions, 50)
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33 changes: 26 additions & 7 deletions precice.f90
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Expand Up @@ -3,20 +3,22 @@ module precice
implicit none

interface

! This interface contains subroutines of two kinds:
! - precicec_<name> expect C-style, null-terminated strings and their sizes
! - precicef_<name> automatically convert strings to null-terminated and call
! the corresponding `precicec_<name>`.

subroutine precicef_create(participantName, configFileName, &
& solverProcessIndex, solverProcessSize, &
& participantNameLength, configFileNameLength) &
& bind(c, name='precicef_create_')
subroutine precicec_create(participantName, configFileName, &
& solverProcessIndex, solverProcessSize) &
& bind(c, name='precicec_createParticipant')

use, intrinsic :: iso_c_binding
character(kind=c_char), dimension(*) :: participantName
character(kind=c_char), dimension(*) :: configFileName
integer(kind=c_int) :: solverProcessIndex
integer(kind=c_int) :: solverProcessSize
integer(kind=c_int), value :: participantNameLength
integer(kind=c_int), value :: configFileNameLength
end subroutine precicef_create
end subroutine precicec_create

subroutine precicef_initialize() &
& bind(c, name='precicef_initialize_')
Expand Down Expand Up @@ -312,4 +314,21 @@ end subroutine precicef_get_version_information

end interface

contains
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I still want that users call precicef_create, so they should be outside the contains block. However, it looks like I cannot call subroutines from inside an interface. What would be the right way here?

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But you have it now as a module procedure (a thin wrapper of the preCICE C API). Isn't that what you want?

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@MakisH MakisH Mar 19, 2024 •
edited
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I want that users call the precicef_create variant without having to provide neither null-terminated strings, nor placeholder lengths. For this, I would need the precicef_create to not be internal (inside the contains), no?

If I ask the users to call the precicec_create, then they need to provide null-terminated strings.

Should I maybe split it into two different modules? Not sure if I can modify the arguments in an interface.

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In Fortran parlance, interface blocks are like function declarations in C. They are specification statements (i.e. non-executable).

When you want to define a procedure, it must be in the "contains" part:

module precice
 ! ... specification ...
contains
 ! ... procedure definitions (including executable statements) ...
end module

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Ah, that helps! But then, I understand that both what I have in the interface and in the contains need to have the same name.


subroutine precicef_create(participantName, configFileName, &
& solverProcessIndex, solverProcessSize)

use, intrinsic :: iso_c_binding, only: c_char, c_int
character(len=*), intent(in) :: participantName
character(len=*), intent(in) :: configFileName
integer(c_int), intent(in) :: solverProcessIndex
integer(c_int), intent(in) :: solverProcessSize

call precicec_create( &
trim(participantName)//c_null_char, &
trim(configFileName)//c_null_char, &
solverProcessIndex, solverProcessSize)
end subroutine precicef_create

end module precice