Did you know ... | Search Documentation: |
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.
now
. This is similar to using:
:- initialization(load_foreign_library(foreign(mylib))).
but using the initialization/1 wrapper causes the library to be loaded after loading of the file in which it appears is completed, while use_foreign_library/1 loads the library immediately. I.e. the difference is only relevant if the remainder of the file uses functionality of the C-library.
As of SWI-Prolog 8.1.22, use_foreign_library/1,2 is in provided as a built-in predicate that, if necessary, loads library(shlib). This implies that these directives can be used without explicitly loading library(shlib) or relying on demand loading.
install_mylib()
. If the platform
prefixes extern functions with =_=, this prefix is added before
calling. Options provided are below. Other options are passed to
open_shared_object/3.
default(install)
,
which derives the function from FileSpec.... load_foreign_library(foreign(mylib)), ...
The following predicates are exported from this file while their implementation is defined in imported modules or non-module files loaded by this module.
install_mylib()
. If the platform
prefixes extern functions with =_=, this prefix is added before
calling. Options provided are below. Other options are passed to
open_shared_object/3.
default(install)
,
which derives the function from FileSpec.... load_foreign_library(foreign(mylib)), ...
The following predicates are exported, but not or incorrectly documented.