5.5 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.

5.5.1 Using C DLLs

You can export C functions in three ways:

1. Use a __declspec(dllexport) declaration in the C file.

   In this case you should also make the functions use the cdecl 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 2 follows. Let us assume you have the following C code in a file called example.c.

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 cl.exe.

cl /LD example.c /link /export:multiply

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 the define-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 (the default for cl.exe).

5.5.1.1 Testing whether a function is defined

Having loaded your DLLs (with register-module) you may wish to test whether certain functions are now available.

To detect when a C function name is defined, call:

(not (fli:null-pointer-p
      (fli:make-pointer :symbol-name name
                        :errorp nil)))

You can also return a list of unresolved foreign symbol names by calling module-unresolved-symbols.

5.5.2 Using C++ DLLs

You must make the exported names match the FLI definitions. To do this:

• If you can alter the C++ code, wrap extern "C" {} around the C++ function definitions, or:
• Create a second DLL with C functions that wrap around each C++ function, and make those C functions accessible as described in 5.5.1 Using C DLLs.

Note: watch out for the calling convention of the exported function, which must match the :calling-convention in the FLI definitions.