Mixed languages

[Giel_H_]

Steve Lionel has modified the C_CALL_Fortran mixed language samplefrom CVF into an IVF sample.

The sample uses a FDLL project which builds the Fortran source of subroutine FSUBas a DLL. FSUB has an integer and a character string input argument and an character string output argument. FSUB concatenates the input arguments tooneoutput string.

A c/c++ main programUSEDLL calls the dll version of FSUB.

As an extension to this sample I am interested in ac/c++DLL project (say CDLL) in whichthe cdllsource codecontains (an entry of)a character function that calls the FSUB dll and returns thec string constructed by FSUB.

Is that possible?

Giel

[Steven_L_Intel1]

Most anything is possible, but I don't fully understand your specification. How would you declare this C function in C? (Pretend Fortran isn't part of this.) What does it mean to be a "character function" in C?

[Giel_H_]

I admit that the use of "function" and "subroutine" is indeed confusing.

Iwould suggest anything like:

LPTSTR CFUN

LPSTR CFUN

char *CFUN

And for the definition of the function CFUN:

LPTSTR CFUN(int *int_arg,LPTSTR *str_in)

LPSTR CFUN(int *int_arg,LPSTR *str_in)

char *CFUN(int *int_arg, char *str_in)

The body of the latter CFUN wouldbe something like

{

char *str_out;

int STR_OUT_LEN;

STR_OUT_LEN= 512;

FSUB(&int_arg,str_in, str_out, strlen(str_in),STR_OUT_LEN);

return str_out;

}

Giel

[Jugoslav_Dujic]

Uh-oh. You see, the problem with Fortran strings is that they-re two-fold: the passed information must always contain both the address and the length. Now, since both cannot be returned through registers, Fortran compiler "internally" turns the character-valued function into:

FUNCTION StrRet()
CHARACTER(10):: StrRet
StrRet="1234567890"
END FUNCTION StrRet

extern "C" char* strret(char*, int)

Well, maybe, I didn't care to do complete reverse-engineering. There are similar issues with functions returning TYPEs, arrays etc. So, it's better to avoid functions returning anything other than plain vanilla ints or floats in mixed-language programming.

[Giel_H_]

OK. Exactly, therefore I would like to usethe CFUN.

Giel

[Steven_L_Intel1]

In C, your CFUN returns a pointer to a string, one that is presumably allocated within the function. You can do the same in Fortran. The equivalent Fortran function would be something like this:

function CFUN()
integer(int_ptr_kind()) :: CFUN
character(10) :: retstr = 'abcdefghij'
integer(1), dimension(*) :: temp
pointer (p, temp)

p = malloc (len(retstr)+1)
do i = 1,len(retstr)
  temp(i) = ichar(retstr(i:i)
  end do
temp(ubound(temp)) = 0
CFUN = P
return
end

It's then the caller's responsibility to deallocate the result.