Defining a FORTRAN routine callable from C++

[anthonyrichards]

I use a third-party application which permits access to a user-writtenroutine via a DDE interface. The DDE interface is managed by a client program written in C++. I have access to the code. This client program assumes that the userroutine is written in C++, but since FORTRAN is my language, I want the client program to access a FORTRAN function. WIthin the client program code, the reference to the user function is thus:

void UserFunction(char *szCommandLine);

The argument is defined as a 260-character string variable. What I would be glad to know is what whould this definition statement be changed to in the C-codeand what matching compiler directive I should use in my FORTRAN version of USERFUNCTION? For the latter, I have in mind

SUBROUTINE USERFUNCTION( STRING)
!DEC$ ATTRIBUTES REFERENCE, C :: USERFUNCTION

CHARACTER*(*)STRING

I have a C++ compiler, so I envisage compiling the C-code (which contains the WINMAIN)seperately into an .OBJ file and includingthe .OBJ fileinto a FORTRAN project consisting of my USERFUNCTION and creating an executable from it. ANy other tips would be appreciated. Thanks in advance.

[Steven_L_Intel1]

You're on the right track. You will also need a:

!DEC$ ATTRIBUTES REFERENCE :: STRING

to tell the compiler not to look for a separate length argument. You;'ll then need to use INDEX to find the trailing NUL to find the string length or be sure to write a NUL (or CHAR(0) or ""C) to define the length.

Remember also that C is case sensitive, and that because you used attribute C, the external name will be _userfunction.

[anthonyrichards]

Thanks, Steve, for that tip. I was getting access errors and crashing the program trying to play with the STRING. even though a MESSAGEBOX call in the FORTRAN routine displayed it OK. The following works for me

In the C++ code:(I made the function name UPPERCASE)

Code:

extern "C" { void __cdecl USERFUNCTION(char *szCommandLine); }
...
...
char szCommandLine[260];
...
...
 USERFUNCTION(szCommandLine);

(This produces an .OBJ with the symbol _USERFUNCTION in it)

In the FORTRAN:

Code:

SUBROUTINE USERFUNCTION(STRING)
!
!DEC$ ATTRIBUTES  C, REFERENCE, ALIAS : '_USERFUNCTION' :: USERFUNCTION
!DEC$ ATTRIBUTES REFERENCE :: STRING
CHARACTER(260) STRING

I found if I used '__stdcall' on the C++ side, the symbol _USERFUNCTION@4 was produced in the .OBJ, so I have to change the ALIAS on the FORTRAN side to match it. Thanks again.