The utility program swipl-ld (Win32: swipl-ld.exe) may be used to link a combination of C files and Prolog files into a stand-alone executable. swipl-ld automates most of what is described in the previous sections.
In normal usage, a copy is made of the default embedding template
.../swipl/include/stub.c. The main() routine is modified to
suit your application. PL_initialise() must
be passed the program name (argv[0]) (Win32: the executing
program can be obtained using GetModuleFileName()). The other elements
of the command line may be modified. Next, swipl-ld is typically
invoked as:
swipl-ld -o output stubfile.c [other-c-or-o-files] [plfiles]
swipl-ld will first split the options into various groups for both the C compiler and the Prolog compiler. Next, it will add various default options to the C compiler and call it to create an executable holding the user's C code and the Prolog kernel. Then, it will call the SWI-Prolog compiler to create a saved state from the provided Prolog files and finally, it will attach this saved state to the created emulator to create the requested executable.
Below, it is described how the options are split and which additional options are passed.
.c files found on the command line. Default is
the compiler used to build SWI-Prolog accessible through the Prolog flag
c_cc (Win32: cl.exe).
.cpp, .cxx,
.cc or .C) found on the command line. Default
is
c++ or g++ if the C compiler is gcc (Win32:
cl.exe).cat <kernel> <state>
> <out> (Win32: copy /b <kernel>+<state> <out>).pl-options is used as
separator and translated to spaces when the argument is built. Example: -pl-options,-F,xpce
passes -F xpce as additional flags to Prolog.
-lswipl
(Win32: libpl.lib) and the libraries needed by the Prolog kernel are
given.
SWI-Prolog.h is passed. swipl-ld
adds two additional * -Ddef flags:
__SWI_PROLOG____SWI_EMBEDDED__*The following is a very simple example going through all the steps
outlined above. It provides an arithmetic expression evaluator. We will
call the application calc and define it in the files calc.c
and calc.pl. The Prolog file is simple:
calc(Atom) :-
term_to_atom(Expr, Atom),
A is Expr,
write(A),
nl.
The C part of the application parses the command line options,
initialises the Prolog engine, locates the calc/1 predicate
and calls it. The coder is in figure
8.
#include <stdio.h>
#include <string.h>
#include <SWI-Prolog.h>
#define MAXLINE 1024
int
main(int argc, char **argv)
{ char expression[MAXLINE];
char *e = expression;
char *program = argv[0];
char *plav[2];
int n;
/* combine all the arguments in a single string */
for(n=1; n<argc; n++)
{ if ( n != 1 )
*e++ = ' ';
strcpy(e, argv[n]);
e += strlen(e);
}
/* make the argument vector for Prolog */
plav[0] = program;
plav[1] = NULL;
/* initialise Prolog */
if ( !PL_initialise(1, plav) )
PL_halt(1);
/* Lookup calc/1 and make the arguments and call */
{ predicate_t pred = PL_predicate("calc", 1, "user");
term_t h0 = PL_new_term_refs(1);
int rval;
PL_put_atom_chars(h0, expression);
rval = PL_call_predicate(NULL, PL_Q_NORMAL, pred, h0);
PL_halt(rval ? 0 : 1);
}
return 0;
}
The application is now created using the command line below. The
option
-goal true sets the Prolog initialization goal to suppress
the banner. Note that the -o calc does not specify an
extension. If the platform uses a file extension for executables, swipl-ld
will add this (e.g., .exe on Windows).
% swipl-ld -goal true -o calc calc.c calc.pl
The created program calc is a native executable with the
Prolog code attached to it. Note that the program typically depends on
the shared object libswipl and, depending on the platform
and configuration, on several external shared objects.
% ./calc pi/2 1.5708