4 Advanced Uses of the FLI

4.4 Using DLLs within the LispWorks FLI

In order to use functions defined in a dynamically linked library (DLL) within the LispWorks FLI, the functions need to be exported from the DLL. This can be done in three ways:

: 1. Use a__declspec(ddlexport) declaration in the C file.
: In this case you should also make the functions use thestdcall calling convention, which removes another level of name mangling.
: 2. Use an/export directive in the link command.
: 3. Use a.def file.

An example of method 3 follows. Let us assume you have the following C code in a file calledexample.c.

int _stdcall MultiplyMain(void *hinstDll,unsigned long 
                          dwReason,void *reserved)
 {
  return(1);
 }

int multiply (int i1, int i2)
 { int result;
  result = i1 * i2 * 500;
  return result;
 }

Then you can create a DLL by, for example, using a 32 bit C compiler such as lcc.

lcc -O -g2 example.c
lcclnk.exe -dll -entry MultiplyMain example.obj 
example.def -subsystem
windows

You now need to create amultiply.def file that contains the following line

exports multiply=multiply

to export the functionmultiply as the symbolmultiply. If you only include the line "exports multiply" then the name of the external symbol is likely to be "_multiply" or "_multiply@8" depending on whether the function is compiled as__cdecl or__stdcall. The addition of the "= multiply" overrides the internal function name with the new name.

If you run either Windows 95 or Windows NT4, then you can view the list of exported symbols from a given DLL by selecting the DLL from an explorer, then right clicking on it and selecting QuickView. This brings up some text about the DLL.

Finally, you should use the LispWorks FLI to define your C function in your Lisp code. This definition should look something like:

(fli:define-foreign-function (multiply "multiply")
     ((x :int)
      (y :int))
   :result-type int
   :module :my-dll
   :calling-convention :cdecl)

Note that thedefine-foreign-function also includes a:calling-convention keyword to specify that the function we are interfacing to is defined as using the__cdecl calling convention.