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jlb
Joined: 21 Oct 2020
Posts: 67
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 Posted: Fri Mar 08, 2024 12:22 pm Post subject: Workaround for C_F_POINTER |
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Is there any workaround code for the F2003 intrinsic procedure C_F_POINTER?
I am trying to adapt a DLL interface to FTN95 using the following function calling C_F_POINTER:
| Code: | function C_to_F_string(c_string_pointer) result(f_string)
use, intrinsic :: iso_c_binding, only: c_ptr,c_f_pointer,c_char,c_null_char
type(c_ptr), intent(in) :: c_string_pointer
character(len=:), allocatable :: f_string
character(kind=c_char), dimension(:), pointer :: char_array_pointer => null()
character(len=255) :: aux_string
integer :: i,length
call c_f_pointer(c_string_pointer,char_array_pointer,[255])
if (.not.associated(char_array_pointer)) then
allocate(character(len=4)::f_string); f_string="NULL"; return
end if
aux_string=" "
do i=1,255
if (char_array_pointer(i)==c_null_char) then
length=i-1; exit
end if
aux_string(i:i)=char_array_pointer(i)
end do
allocate(character(len=length)::f_string)
f_string=aux_string(1:length)
end function C_to_F_string |
Courtesy of: https://stackoverflow.com/questions/9972743/creating-a-fortran-interface-to-a-c-function-that-returns-a-char |
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wahorger
Joined: 13 Oct 2014
Posts: 1226
Location: Morrison, CO, USA
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| Posted: Fri Mar 08, 2024 11:35 pm Post subject: |
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Interesting problem.
So this function takes a pointer to a string (null terminated) and transfers this to a FORTRAN compatible CHARACTER*(*).
Do you need it to be fully portable, or can it be compatible with FTN95 alone? |
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PaulLaidler
Site Admin
Joined: 21 Feb 2005
Posts: 8018
Location: Salford, UK
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| Posted: Sat Mar 09, 2024 8:57 am Post subject: |
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| I am not able to provide an immediate answer to this question but I will add it to my list of issues to investigate. |
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jlb
Joined: 21 Oct 2020
Posts: 67
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| Posted: Sat Mar 09, 2024 9:47 am Post subject: |
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Bill
I "only" need a FTN95 compatible workaround. I encountered two difficulties: the F2003 intrinsic procedure C_F_POINTER and the dynamic allocation of a string length allocate(character(len=length)::f_string).
Paul
Thanks for your help. |
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wahorger
Joined: 13 Oct 2014
Posts: 1226
Location: Morrison, CO, USA
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| Posted: Sat Mar 09, 2024 4:29 pm Post subject: |
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jlb,
Can you give me an example of how this function would be used?
I'll admit to not being 2003 aware of all the changes in syntax, etc. That said, I may have an answer to your query, albeit perhaps not as powerful as the intrinsic might have been.
Bill |
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wahorger
Joined: 13 Oct 2014
Posts: 1226
Location: Morrison, CO, USA
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| Posted: Sat Mar 09, 2024 6:12 pm Post subject: |
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Here's the code that take a pointer to a "C" style string and returns the characters in a FORTRAN CHARACTER data type.
Note: You have to declare the function in the calling program with a specific length. That said, you could use a similar function to return the length of the string BEFORE calling the routine that declares the function and use that, if it something that really, truly needs to be variable.
| Code: | !FTN95 application...
PROGRAM main
INTEGER k
character*(255),external:: C_TO_F_STRING ! has to be assigned a specific length here
character*255:: my_string='This is me'//char(0) ! simulated "C" string, length s/b 10
character*32:: result
! loc(mystring might be the return value of a "C" funtion of the form
! char* c_function(variables)
result = c_to_f_string(loc(my_string))
print *,'Actual non blank data returned=',len_trim(result),'=',trim(result),' full result=[',result,']'
k= len(c_to_f_string(loc(my_string)))
print *,'Function length returned=',k
pause
END PROGRAM main
character*(*) function C_TO_F_STRING(c_string_pointer)
! no error checking has been performed here (like for a NULL result from the allocate()
integer(7):: c_string_pointer ! this is a pointer to somewhere in memory
character(:) , allocatable:: f_string
integer:: array_index ! this will be used to determine how long the string is before allocation
array_index = 0
do while(ichar(ccore1(c_string_pointer+array_index)) .ne.0)
array_index = array_index+1
end do
if(array_index.le.0)array_index = 1 ! always return something
allocate(character*(array_index):: f_string)
f_string = " " ! make the entire string blank, regardless
print *,'Length of result string to be allocated=',len(f_string) ! comment out for production
do i=1,array_index
f_string(i:i) = ccore1(c_string_pointer+i-1)
end do
c_to_f_string = f_string
deallocate(f_string)
return
end
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Here's the run-time. Note: The "full result" here is shown truncated because multiple spaces are removed when posting.
| Quote: | Length of result string to be allocated= 10
Actual non blank data returned= 10=This is me full result=[This is me ]
Length of result string to be allocated= 10
Function length returned= 255 |
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jlb
Joined: 21 Oct 2020
Posts: 67
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| Posted: Sat Mar 09, 2024 6:53 pm Post subject: |
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Bill
Thanks a lot for your help. I didn't know about the FTN95-function CCORE1. I will test your code as soon as possible.
For your complete information, here is the interface module to the 3rd part DLL in its Intel Fortran version:
| Code: | MODULE Test
USE, INTRINSIC::ISO_C_BINDING
INTERFACE
TYPE(C_PTR) FUNCTION FuncPtr(handle) BIND(C, NAME='FuncPtrA')
USE, INTRINSIC :: ISO_C_BINDING
TYPE(C_PTR), VALUE :: handle
END FUNCTION
END INTERFACE
CONTAINS
FUNCTION C_to_F_string(c_string_pointer) RESULT(f_string)
USE, INTRINSIC :: ISO_C_BINDING, ONLY: C_PTR, C_F_POINTER, C_CHAR, C_NULL_CHAR
type(C_PTR), INTENT(IN) :: c_string_pointer
CHARACTER(LEN=:), ALLOCATABLE :: f_string
CHARACTER(KIND=C_CHAR), DIMENSION(:), POINTER :: char_array_pointer => NULL()
CHARACTER(LEN=255) :: aux_string
INTEGER :: i, length
CALL C_F_POINTER(c_string_pointer, char_array_pointer, [255])
IF (.NOT.ASSOCIATED(char_array_pointer)) THEN
ALLOCATE(CHARACTER(LEN=4)::f_string); f_string="NULL"; RETURN
END IF
aux_string=" "
DO i=1,255
IF (char_array_pointer(i)==c_null_char) THEN
length=i-1; EXIT
END IF
aux_string(i:i)=char_array_pointer(i)
END DO
ALLOCATE(CHARACTER(LEN=length)::f_string)
f_string=aux_string(1:length)
END FUNCTION C_to_F_string
FUNCTION Func(handle) RESULT(f_string)
USE ISO_C_BINDING
TYPE(C_PTR), VALUE :: handle
CHARACTER(:), ALLOCATABLE :: f_string
f_string = C_to_F_string(FuncPtr(handle))
END FUNCTION
END MODULE |
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wahorger
Joined: 13 Oct 2014
Posts: 1226
Location: Morrison, CO, USA
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| Posted: Sun Mar 10, 2024 12:06 am Post subject: |
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Just an FYI. Here's the FTN95 statement for the interface to one of my DLL's. It returns the pointer to a file handle from "C". So, it's size will be either 32-bit or 64-bit depending on the memory model.
| Code: | C_EXTERNAL OPEN_LOG_FILE 'open_log_file'(string,string):INTEGER(7)! returns the file pointer
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And. here's the function definition for that call:
| Code: | compile_header
FILE *open_log_file(char *name,char *option) // returns the file pointer
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where "compile_header" is:
| Code: | #define compile_header extern "C"
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I'm finding that for 64-bit, no header is needed, depending on the "C" compiler. |
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jlb
Joined: 21 Oct 2020
Posts: 67
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| Posted: Mon Mar 11, 2024 1:12 pm Post subject: |
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Bill
Thanks a lot for this workaround, which does the trick. |
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wahorger
Joined: 13 Oct 2014
Posts: 1226
Location: Morrison, CO, USA
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| Posted: Tue Mar 12, 2024 2:51 pm Post subject: |
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jlb,
Happy to help!
Bill |
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PaulLaidler
Site Admin
Joined: 21 Feb 2005
Posts: 8018
Location: Salford, UK
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| Posted: Tue Mar 19, 2024 2:22 pm Post subject: |
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jib
The ClearWin+ interfaces in \Silverfrost\FTN95\source64\clrwin.f95 illustrate one way to pass C strings to and from Fortran code.
See, for example, send_accelerator$ which sends a null terminated string.
For strings passed from C to Fortran, see the subroutine called PAD and note how it is used. |
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PaulLaidler
Site Admin
Joined: 21 Feb 2005
Posts: 8018
Location: Salford, UK
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| Posted: Thu Mar 21, 2024 5:07 pm Post subject: |
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C_F_POINTER in the ISO_C_BINDING module (2003 Fortran Standard) has now been implemented for the next full release of FTN95.
It will appear in the next interim release but will also require an extended definition for the ISO_C_BINDING module (in \Silverfrost\FTN95\include). |
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jlb
Joined: 21 Oct 2020
Posts: 67
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| Posted: Fri Mar 22, 2024 10:42 am Post subject: |
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Paul
Thanks for pointing out the send_accelerator$ and PAD subroutines, i wasn't aware of them, as well as for the C_F_POINTER implementation. |
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