shlib.pl -- Utility library for loading foreign objects (DLLs, shared objects)

This section discusses the functionality of the (autoload) library(shlib), providing an interface to manage shared libraries. We describe the procedure for using a foreign resource (DLL in Windows and shared object in Unix) called mylib.

First, one must assemble the resource and make it compatible to SWI-Prolog. The details for this vary between platforms. The swipl-ld(1) utility can be used to deal with this in a portable manner. The typical commandline is:

swipl-ld -o mylib file.{c,o,cc,C} ...

Make sure that one of the files provides a global function install_mylib() that initialises the module using calls to PL_register_foreign(). Here is a simple example file mylib.c, which creates a Windows MessageBox:

#include <windows.h>
#include <SWI-Prolog.h>

static foreign_t
pl_say_hello(term_t to)
{ char *a;

  if ( PL_get_atom_chars(to, &a) )
  { MessageBox(NULL, a, "DLL test", MB_OK|MB_TASKMODAL);

    PL_succeed;
  }

  PL_fail;
}

install_t
install_mylib()
{ PL_register_foreign("say_hello", 1, pl_say_hello, 0);
}

Now write a file mylib.pl:

:- module(mylib, [ say_hello/1 ]).
:- use_foreign_library(foreign(mylib)).

The file mylib.pl can be loaded as a normal Prolog file and provides the predicate defined in C.

Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

 unload_foreign_library(Arg1)

 load_foreign_library(Arg1)

 load_foreign_library(Arg1, Arg2)

 unload_foreign_library(Arg1, Arg2)

 current_foreign_library(Arg1, Arg2)

 reload_foreign_libraries

 use_foreign_library(Arg1)

 use_foreign_library(Arg1, Arg2)