.DLL
and .so
filesThis section discusses the functionality of the (autoload) library
shlib.pl
, providing an interface to shared libraries. This
library can only be used if the prolog-flag open_shared_object
is enabled.
foreign
, which refers to
the directories <plhome>/lib/<arch>
and
<plhome>/lib
, in this order.
If the library can be loaded, the function called Entry will be called without arguments. The return value of the function is ignored.
The Entry function will normally call PL_register_foreign() to declare functions in the library as foreign predicates.
install-
<base>. On failure it will try to
function install(). Otherwise no install function will be called.
Figure 7 connects a Windows message-box using a foreign function. This example was tested using Windows NT and Microsoft Visual C++ 2.0.
#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() { PL_register_foreign("say_hello", 1, pl_say_hello, 0); }
Figure 7 : MessageBox() example in Windows NT |
Below is an outline of the files structure required for statically
linking SWI-Prolog with foreign extensions. \ldots/pl
refers to the SWI-Prolog home directory (see current_prolog_flag/2). <arch>
refers to the architecture identifier that may be obtained using
current_prolog_flag/2.
.../pl/runtime/<arch>/libpl.a | SWI-Library |
.../pl/include/SWI-Prolog.h | Include file |
.../pl/include/SWI-Stream.h | Stream I/O include file |
.../pl/include/SWI-Exports | Export declarations (AIX only) |
.../pl/include/stub.c | Extension stub |
The definition of the foreign predicates is the same as for dynamic
linking. Unlike with dynamic linking however, there is no initialisation
function. Instead, the file \ldots/pl/include/stub.c
may be
copied to your project and modified to define the foreign extensions.
Below is stub.c, modified to link the lowercase example described later
in this chapter:
#include <stdio.h> #include <SWI-Prolog.h> extern foreign_t pl_lowercase(term, term); PL_extension predicates[] = { /*{ "name", arity, function, PL_FA_<flags> },*/ { "lowercase", 2 pl_lowercase, 0 }, { NULL, 0, NULL, 0 } /* terminating line */ }; int main(int argc, char **argv) { PL_register_extensions(predicates); if ( !PL_initialise(argc, argv) ) PL_halt(1); PL_install_readline(); /* delete if not required */ PL_halt(PL_toplevel() ? 0 : 1); }
Now, a new executable may be created by compiling this file and
linking it to libpl.a
from the runtime directory and the
libraries required by both the extensions and the SWI-Prolog kernel.
This may be done by hand, or using the plld utility described in
secrefplld. If the linking is performed `by hand', the command-line
option -dump-runtime-variables
(see section
2.4) can be used to obtain the required paths, libraries and linking
options to link the new executable.