PublicShow -- 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_register_foreign("say_hello", 1, pl_say_hello, 0);

Now write a file

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

The file 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.

Source unload_foreign_library(Arg1)
Source load_foreign_library(Arg1)
Source load_foreign_library(Arg1, Arg2)
Source unload_foreign_library(Arg1, Arg2)
Source current_foreign_library(Arg1, Arg2)
Source reload_foreign_libraries
Source use_foreign_library(Arg1)
Source use_foreign_library(Arg1, Arg2)