3 perlembed - how to embed perl in your C program
13 =item B<Use C from Perl?>
15 Read L<perlcall> and L<perlxs>.
17 =item B<Use a UNIX program from Perl?>
19 Read about back-quotes and about C<system> and C<exec> in L<perlfunc>.
21 =item B<Use Perl from Perl?>
23 Read about L<perlfunc/do> and L<perlfunc/eval> and L<perlfunc/require>
26 =item B<Use C from C?>
30 =item B<Use Perl from C?>
38 L<Compiling your C program>
40 There's one example in each of the eight sections:
42 L<Adding a Perl interpreter to your C program>
44 L<Calling a Perl subroutine from your C program>
46 L<Evaluating a Perl statement from your C program>
48 L<Performing Perl pattern matches and substitutions from your C program>
50 L<Fiddling with the Perl stack from your C program>
52 L<Maintaining a persistent interpreter>
54 L<Maintaining multiple interpreter instances>
56 L<Using Perl modules, which themselves use C libraries, from your C program>
58 This documentation is Unix specific; if you have information about how
59 to embed Perl on other platforms, please send e-mail to <F<orwant@tpj.com>>.
61 =head2 Compiling your C program
63 If you have trouble compiling the scripts in this documentation,
64 you're not alone. The cardinal rule: COMPILE THE PROGRAMS IN EXACTLY
65 THE SAME WAY THAT YOUR PERL WAS COMPILED. (Sorry for yelling.)
67 Also, every C program that uses Perl must link in the I<perl library>.
68 What's that, you ask? Perl is itself written in C; the perl library
69 is the collection of compiled C programs that were used to create your
70 perl executable (I</usr/bin/perl> or equivalent). (Corollary: you
71 can't use Perl from your C program unless Perl has been compiled on
72 your machine, or installed properly--that's why you shouldn't blithely
73 copy Perl executables from machine to machine without also copying the
76 When you use Perl from C, your C program will--usually--allocate,
77 "run", and deallocate a I<PerlInterpreter> object, which is defined by
80 If your copy of Perl is recent enough to contain this documentation
81 (version 5.002 or later), then the perl library (and I<EXTERN.h> and
82 I<perl.h>, which you'll also need) will reside in a directory
85 /usr/local/lib/perl5/your_architecture_here/CORE
89 /usr/local/lib/perl5/CORE
91 or maybe something like
95 Execute this statement for a hint about where to find CORE:
97 perl -MConfig -e 'print $Config{archlib}'
99 Here's how you'd compile the example in the next section,
100 L<Adding a Perl interpreter to your C program>, on my Linux box:
102 % gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include
103 -I/usr/local/lib/perl5/i586-linux/5.003/CORE
104 -L/usr/local/lib/perl5/i586-linux/5.003/CORE
105 -o interp interp.c -lperl -lm
107 (That's all one line.) On my DEC Alpha running 5.00305, the incantation
110 % cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include
111 -I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE
112 -L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib
113 -D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm
115 How can you figure out what to add? Assuming your Perl is post-5.001,
116 execute a C<perl -V> command and pay special attention to the "cc" and
117 "ccflags" information.
119 You'll have to choose the appropriate compiler (I<cc>, I<gcc>, et al.) for
120 your machine: C<perl -MConfig -e 'print $Config{cc}'> will tell you what
123 You'll also have to choose the appropriate library directory
124 (I</usr/local/lib/...>) for your machine. If your compiler complains
125 that certain functions are undefined, or that it can't locate
126 I<-lperl>, then you need to change the path following the C<-L>. If it
127 complains that it can't find I<EXTERN.h> and I<perl.h>, you need to
128 change the path following the C<-I>.
130 You may have to add extra libraries as well. Which ones?
131 Perhaps those printed by
133 perl -MConfig -e 'print $Config{libs}'
135 Provided your perl binary was properly configured and installed the
136 B<ExtUtils::Embed> module will determine all of this information for
139 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
141 If the B<ExtUtils::Embed> module isn't part of your Perl distribution,
142 you can retrieve it from
143 http://www.perl.com/perl/CPAN/modules/by-module/ExtUtils::Embed. (If
144 this documentation came from your Perl distribution, then you're
145 running 5.004 or better and you already have it.)
147 The B<ExtUtils::Embed> kit on CPAN also contains all source code for
148 the examples in this document, tests, additional examples and other
149 information you may find useful.
151 =head2 Adding a Perl interpreter to your C program
153 In a sense, perl (the C program) is a good example of embedding Perl
154 (the language), so I'll demonstrate embedding with I<miniperlmain.c>,
155 from the source distribution. Here's a bastardized, non-portable
156 version of I<miniperlmain.c> containing the essentials of embedding:
158 #include <EXTERN.h> /* from the Perl distribution */
159 #include <perl.h> /* from the Perl distribution */
161 static PerlInterpreter *my_perl; /*** The Perl interpreter ***/
163 int main(int argc, char **argv, char **env)
165 my_perl = perl_alloc();
166 perl_construct(my_perl);
167 perl_parse(my_perl, NULL, argc, argv, (char **)NULL);
169 perl_destruct(my_perl);
173 Notice that we don't use the C<env> pointer. Normally handed to
174 C<perl_parse> as its final argument, C<env> here is replaced by
175 C<NULL>, which means that the current environment will be used.
177 Now compile this program (I'll call it I<interp.c>) into an executable:
179 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
181 After a successful compilation, you'll be able to use I<interp> just
185 print "Pretty Good Perl \n";
186 print "10890 - 9801 is ", 10890 - 9801;
193 % interp -e 'printf("%x", 3735928559)'
196 You can also read and execute Perl statements from a file while in the
197 midst of your C program, by placing the filename in I<argv[1]> before
198 calling I<perl_run()>.
200 =head2 Calling a Perl subroutine from your C program
202 To call individual Perl subroutines, you can use any of the B<perl_call_*>
203 functions documented in the L<perlcall> man page.
204 In this example we'll use I<perl_call_argv>.
206 That's shown below, in a program I'll call I<showtime.c>.
211 static PerlInterpreter *my_perl;
213 int main(int argc, char **argv, char **env)
215 char *args[] = { NULL };
216 my_perl = perl_alloc();
217 perl_construct(my_perl);
219 perl_parse(my_perl, NULL, argc, argv, NULL);
221 /*** skipping perl_run() ***/
223 perl_call_argv("showtime", G_DISCARD | G_NOARGS, args);
225 perl_destruct(my_perl);
229 where I<showtime> is a Perl subroutine that takes no arguments (that's the
230 I<G_NOARGS>) and for which I'll ignore the return value (that's the
231 I<G_DISCARD>). Those flags, and others, are discussed in L<perlcall>.
233 I'll define the I<showtime> subroutine in a file called I<showtime.pl>:
235 print "I shan't be printed.";
241 Simple enough. Now compile and run:
243 % cc -o showtime showtime.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
245 % showtime showtime.pl
248 yielding the number of seconds that elapsed between January 1, 1970
249 (the beginning of the Unix epoch), and the moment I began writing this
252 In this particular case we don't have to call I<perl_run>, but in
253 general it's considered good practice to ensure proper initialization
254 of library code, including execution of all object C<DESTROY> methods
255 and package C<END {}> blocks.
257 If you want to pass arguments to the Perl subroutine, you can add
258 strings to the C<NULL>-terminated C<args> list passed to
259 I<perl_call_argv>. For other data types, or to examine return values,
260 you'll need to manipulate the Perl stack. That's demonstrated in the
261 last section of this document: L<Fiddling with the Perl stack from
264 =head2 Evaluating a Perl statement from your C program
266 One way to evaluate pieces of Perl code is to use
267 L<perlguts/perl_eval_sv()>. We've wrapped this inside our own
268 I<perl_eval()> function, which converts a command string to an SV,
269 passing this and the L<perlcall/G_DISCARD> flag to
270 L<perlguts/perl_eval_sv()>.
272 Arguably, this is the only routine you'll ever need to execute
273 snippets of Perl code from within your C program. Your string can be
274 as long as you wish; it can contain multiple statements; it can employ
275 L<perlfunc/use>, L<perlfunc/require> and L<perlfunc/do> to include
278 Our I<perl_eval()> lets us evaluate individual Perl strings, and then
279 extract variables for coercion into C types. The following program,
280 I<string.c>, executes three Perl strings, extracting an C<int> from
281 the first, a C<float> from the second, and a C<char *> from the third.
286 static PerlInterpreter *my_perl;
288 I32 perl_eval(char *string)
290 return perl_eval_sv(newSVpv(string,0), G_DISCARD);
293 main (int argc, char **argv, char **env)
295 char *embedding[] = { "", "-e", "0" };
298 my_perl = perl_alloc();
299 perl_construct( my_perl );
301 perl_parse(my_perl, NULL, 3, embedding, NULL);
303 /** Treat $a as an integer **/
304 perl_eval("$a = 3; $a **= 2");
305 printf("a = %d\n", SvIV(perl_get_sv("a", FALSE)));
307 /** Treat $a as a float **/
308 perl_eval("$a = 3.14; $a **= 2");
309 printf("a = %f\n", SvNV(perl_get_sv("a", FALSE)));
311 /** Treat $a as a string **/
312 perl_eval("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a); ");
313 printf("a = %s\n", SvPV(perl_get_sv("a", FALSE), length));
315 perl_destruct(my_perl);
319 All of those strange functions with I<sv> in their names help convert Perl scalars to C types. They're described in L<perlguts>.
321 If you compile and run I<string.c>, you'll see the results of using
322 I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and
323 I<SvPV()> to create a string:
327 a = Just Another Perl Hacker
330 =head2 Performing Perl pattern matches and substitutions from your C program
332 Our I<perl_eval()> lets us evaluate strings of Perl code, so we can
333 define some functions that use it to "specialize" in matches and
334 substitutions: I<match()>, I<substitute()>, and I<matches()>.
336 char match(char *string, char *pattern);
338 Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which
339 in your C program might appear as "/\\b\\w*\\b/"), match()
340 returns 1 if the string matches the pattern and 0 otherwise.
342 int substitute(char *string[], char *pattern);
344 Given a pointer to a string and an C<=~> operation (e.g.,
345 C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string
346 according to the operation, returning the number of substitutions
349 int matches(char *string, char *pattern, char **matches[]);
351 Given a string, a pattern, and a pointer to an empty array of strings,
352 matches() evaluates C<$string =~ $pattern> in an array context, and
353 fills in I<matches> with the array elements (allocating memory as it
354 does so), returning the number of matches found.
356 Here's a sample program, I<match.c>, that uses all three (long lines have
362 static PerlInterpreter *my_perl;
363 I32 perl_eval(char *string)
365 return perl_eval_sv(newSVpv(string,0), G_DISCARD);
367 /** match(string, pattern)
369 ** Used for matches in a scalar context.
371 ** Returns 1 if the match was successful; 0 otherwise.
373 char match(char *string, char *pattern)
376 command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 37);
377 sprintf(command, "$string = '%s'; $return = $string =~ %s",
381 return SvIV(perl_get_sv("return", FALSE));
383 /** substitute(string, pattern)
385 ** Used for =~ operations that modify their left-hand side (s/// and tr///)
387 ** Returns the number of successful matches, and
388 ** modifies the input string if there were any.
390 int substitute(char *string[], char *pattern)
394 command = malloc(sizeof(char) * strlen(*string) + strlen(pattern) + 35);
395 sprintf(command, "$string = '%s'; $ret = ($string =~ %s)",
399 *string = SvPV(perl_get_sv("string", FALSE), length);
400 return SvIV(perl_get_sv("ret", FALSE));
402 /** matches(string, pattern, matches)
404 ** Used for matches in an array context.
406 ** Returns the number of matches,
407 ** and fills in **matches with the matching substrings (allocates memory!)
409 int matches(char *string, char *pattern, char **match_list[])
417 command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 38);
418 sprintf(command, "$string = '%s'; @array = ($string =~ %s)",
422 array = perl_get_av("array", FALSE);
423 num_matches = av_len(array) + 1; /** assume $[ is 0 **/
424 *match_list = (char **) malloc(sizeof(char *) * num_matches);
425 for (i = 0; i <= num_matches; i++) {
426 current_match = av_shift(array);
427 (*match_list)[i] = SvPV(current_match, length);
431 main (int argc, char **argv, char **env)
433 char *embedding[] = { "", "-e", "0" };
434 char *text, **match_list;
437 my_perl = perl_alloc();
438 perl_construct( my_perl );
439 perl_parse(my_perl, NULL, 3, embedding, NULL);
442 text = (char *) malloc(sizeof(char) * 486); /** A long string follows! **/
443 sprintf(text, "%s", "When he is at a convenience store and the bill \
444 comes to some amount like 76 cents, Maynard is aware that there is \
445 something he *should* do, something that will enable him to get back \
446 a quarter, but he has no idea *what*. He fumbles through his red \
447 squeezey changepurse and gives the boy three extra pennies with his \
448 dollar, hoping that he might luck into the correct amount. The boy \
449 gives him back two of his own pennies and then the big shiny quarter \
450 that is his prize. -RICHH");
451 if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
452 printf("match: Text contains the word 'quarter'.\n\n");
454 printf("match: Text doesn't contain the word 'quarter'.\n\n");
455 if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
456 printf("match: Text contains the word 'eighth'.\n\n");
458 printf("match: Text doesn't contain the word 'eighth'.\n\n");
459 /** Match all occurrences of /wi../ **/
460 num_matches = matches(text, "m/(wi..)/g", &match_list);
461 printf("matches: m/(wi..)/g found %d matches...\n", num_matches);
462 for (i = 0; i < num_matches; i++)
463 printf("match: %s\n", match_list[i]);
465 for (i = 0; i < num_matches; i++) {
469 /** Remove all vowels from text **/
470 num_matches = substitute(&text, "s/[aeiou]//gi");
472 printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
474 printf("Now text is: %s\n\n", text);
476 /** Attempt a substitution **/
477 if (!substitute(&text, "s/Perl/C/")) {
478 printf("substitute: s/Perl/C...No substitution made.\n\n");
481 perl_destruct(my_perl);
485 which produces the output (again, long lines have been wrapped here)
487 match: Text contains the word 'quarter'.
489 match: Text doesn't contain the word 'eighth'.
491 matches: m/(wi..)/g found 2 matches...
495 substitute: s/[aeiou]//gi...139 substitutions made.
496 Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
497 Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt bck
498 qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd gvs th by
499 thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct mnt. Th by gvs
500 hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s hs prz. -RCHH
502 substitute: s/Perl/C...No substitution made.
504 =head2 Fiddling with the Perl stack from your C program
506 When trying to explain stacks, most computer science textbooks mumble
507 something about spring-loaded columns of cafeteria plates: the last
508 thing you pushed on the stack is the first thing you pop off. That'll
509 do for our purposes: your C program will push some arguments onto "the Perl
510 stack", shut its eyes while some magic happens, and then pop the
511 results--the return value of your Perl subroutine--off the stack.
513 First you'll need to know how to convert between C types and Perl
514 types, with newSViv() and sv_setnv() and newAV() and all their
515 friends. They're described in L<perlguts>.
517 Then you'll need to know how to manipulate the Perl stack. That's
518 described in L<perlcall>.
520 Once you've understood those, embedding Perl in C is easy.
522 Because C has no built-in function for integer exponentiation, let's
523 make Perl's ** operator available to it (this is less useful than it
524 sounds, because Perl implements ** with C's I<pow()> function). First
525 I'll create a stub exponentiation function in I<power.pl>:
532 Now I'll create a C program, I<power.c>, with a function
533 I<PerlPower()> that contains all the perlguts necessary to push the
534 two arguments into I<expo()> and to pop the return value out. Take a
540 static PerlInterpreter *my_perl;
543 PerlPower(int a, int b)
545 dSP; /* initialize stack pointer */
546 ENTER; /* everything created after here */
547 SAVETMPS; /* ...is a temporary variable. */
548 PUSHMARK(sp); /* remember the stack pointer */
549 XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */
550 XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */
551 PUTBACK; /* make local stack pointer global */
552 perl_call_pv("expo", G_SCALAR); /* call the function */
553 SPAGAIN; /* refresh stack pointer */
554 /* pop the return value from stack */
555 printf ("%d to the %dth power is %d.\n", a, b, POPi);
557 FREETMPS; /* free that return value */
558 LEAVE; /* ...and the XPUSHed "mortal" args.*/
561 int main (int argc, char **argv, char **env)
565 my_perl = perl_alloc();
566 perl_construct( my_perl );
568 my_argv[1] = (char *) malloc(10);
569 sprintf(my_argv[1], "power.pl");
571 perl_parse(my_perl, NULL, argc, my_argv, NULL);
574 PerlPower(3, 4); /*** Compute 3 ** 4 ***/
576 perl_destruct(my_perl);
584 % cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
587 3 to the 4th power is 81.
589 =head2 Maintaining a persistent interpreter
591 When developing interactive and/or potentially long-running
592 applications, it's a good idea to maintain a persistent interpreter
593 rather than allocating and constructing a new interpreter multiple
594 times. The major reason is speed: since Perl will only be loaded into
597 However, you have to be more cautious with namespace and variable
598 scoping when using a persistent interpreter. In previous examples
599 we've been using global variables in the default package C<main>. We
600 knew exactly what code would be run, and assumed we could avoid
601 variable collisions and outrageous symbol table growth.
603 Let's say your application is a server that will occasionally run Perl
604 code from some arbitrary file. Your server has no way of knowing what
605 code it's going to run. Very dangerous.
607 If the file is pulled in by C<perl_parse()>, compiled into a newly
608 constructed interpreter, and subsequently cleaned out with
609 C<perl_destruct()> afterwards, you're shielded from most namespace
612 One way to avoid namespace collisions in this scenario is to translate
613 the filename into a guaranteed-unique package name, and then compile
614 the code into that package using L<perlfunc/eval>. In the example
615 below, each file will only be compiled once. Or, the application
616 might choose to clean out the symbol table associated with the file
617 after it's no longer needed. Using L<perlcall/perl_call_argv>, We'll
618 call the subroutine C<Embed::Persistent::eval_file> which lives in the
619 file C<persistent.pl> and pass the filename and boolean cleanup/cache
622 Note that the process will continue to grow for each file that it
623 uses. In addition, there might be C<AUTOLOAD>ed subroutines and other
624 conditions that cause Perl's symbol table to grow. You might want to
625 add some logic that keeps track of the process size, or restarts
626 itself after a certain number of requests, to ensure that memory
627 consumption is minimized. You'll also want to scope your variables
628 with L<perlfunc/my> whenever possible.
631 package Embed::Persistent;
637 sub valid_package_name {
639 $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
640 # second pass only for words starting with a digit
641 $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;
643 # Dress it up as a real package name
645 return "Embed" . $string;
648 #borrowed from Safe.pm
654 $pkg = "main::$pkg\::"; # expand to full symbol table name
655 ($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
657 my $stem_symtab = *{$stem}{HASH};
659 delete $stem_symtab->{$leaf};
663 my($filename, $delete) = @_;
664 my $package = valid_package_name($filename);
665 my $mtime = -M $filename;
666 if(defined $Cache{$package}{mtime}
668 $Cache{$package}{mtime} <= $mtime)
670 # we have compiled this subroutine already,
671 # it has not been updated on disk, nothing left to do
672 print STDERR "already compiled $package->handler\n";
676 open FH, $filename or die "open '$filename' $!";
681 #wrap the code into a subroutine inside our unique package
682 my $eval = qq{package $package; sub handler { $sub; }};
684 # hide our variables within this block
685 my($filename,$mtime,$package,$sub);
690 #cache it unless we're cleaning out each time
691 $Cache{$package}{mtime} = $mtime unless $delete;
694 eval {$package->handler;};
697 delete_package($package) if $delete;
699 #take a look if you want
700 #print Devel::Symdump->rnew($package)->as_string, $/;
711 /* 1 = clean out filename's symbol table after each request, 0 = don't */
716 static PerlInterpreter *perl = NULL;
719 main(int argc, char **argv, char **env)
721 char *embedding[] = { "", "persistent.pl" };
722 char *args[] = { "", DO_CLEAN, NULL };
723 char filename [1024];
726 if((perl = perl_alloc()) == NULL) {
727 fprintf(stderr, "no memory!");
730 perl_construct(perl);
732 exitstatus = perl_parse(perl, NULL, 2, embedding, NULL);
735 exitstatus = perl_run(perl);
737 while(printf("Enter file name: ") && gets(filename)) {
739 /* call the subroutine, passing it the filename as an argument */
741 perl_call_argv("Embed::Persistent::eval_file",
742 G_DISCARD | G_EVAL, args);
745 if(SvTRUE(GvSV(errgv)))
746 fprintf(stderr, "eval error: %s\n", SvPV(GvSV(errgv),na));
750 perl_destruct_level = 0;
759 % cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
761 Here's a example script file:
764 my $string = "hello";
768 print "foo says: @_\n";
774 Enter file name: test.pl
776 Enter file name: test.pl
777 already compiled Embed::test_2epl->handler
781 =head2 Maintaining multiple interpreter instances
783 Some rare applications will need to create more than one interpreter
784 during a session. Such an application might sporadically decide to
785 release any resources associated with the interpreter.
787 The program must take care to ensure that this takes place I<before>
788 the next interpreter is constructed. By default, the global variable
789 C<perl_destruct_level> is set to C<0>, since extra cleaning isn't
790 needed when a program has only one interpreter.
792 Setting C<perl_destruct_level> to C<1> makes everything squeaky clean:
794 perl_destruct_level = 1;
798 /* reset global variables here with perl_destruct_level = 1 */
799 perl_construct(my_perl);
801 /* clean and reset _everything_ during perl_destruct */
802 perl_destruct(my_perl);
805 /* let's go do it again! */
808 When I<perl_destruct()> is called, the interpreter's syntax parse tree
809 and symbol tables are cleaned up, and global variables are reset.
811 Now suppose we have more than one interpreter instance running at the
812 same time. This is feasible, but only if you used the
813 C<-DMULTIPLICITY> flag when building Perl. By default, that sets
814 C<perl_destruct_level> to C<1>.
822 /* we're going to embed two interpreters */
823 /* we're going to embed two interpreters */
825 #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"
827 int main(int argc, char **argv, char **env)
830 *one_perl = perl_alloc(),
831 *two_perl = perl_alloc();
832 char *one_args[] = { "one_perl", SAY_HELLO };
833 char *two_args[] = { "two_perl", SAY_HELLO };
835 perl_construct(one_perl);
836 perl_construct(two_perl);
838 perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
839 perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
844 perl_destruct(one_perl);
845 perl_destruct(two_perl);
854 % cc -o multiplicity multiplicity.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
862 =head2 Using Perl modules, which themselves use C libraries, from your C program
864 If you've played with the examples above and tried to embed a script
865 that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++ library,
866 this probably happened:
869 Can't load module Socket, dynamic loading not available in this perl.
870 (You may need to build a new perl executable which either supports
871 dynamic loading or has the Socket module statically linked into it.)
876 Your interpreter doesn't know how to communicate with these extensions
877 on its own. A little glue will help. Up until now you've been
878 calling I<perl_parse()>, handing it NULL for the second argument:
880 perl_parse(my_perl, NULL, argc, my_argv, NULL);
882 That's where the glue code can be inserted to create the initial contact between
883 Perl and linked C/C++ routines. Let's take a look some pieces of I<perlmain.c>
884 to see how Perl does this:
888 # define EXTERN_C extern "C"
890 # define EXTERN_C extern
893 static void xs_init _((void));
895 EXTERN_C void boot_DynaLoader _((CV* cv));
896 EXTERN_C void boot_Socket _((CV* cv));
902 char *file = __FILE__;
903 /* DynaLoader is a special case */
904 newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
905 newXS("Socket::bootstrap", boot_Socket, file);
908 Simply put: for each extension linked with your Perl executable
909 (determined during its initial configuration on your
910 computer or when adding a new extension),
911 a Perl subroutine is created to incorporate the extension's
912 routines. Normally, that subroutine is named
913 I<Module::bootstrap()> and is invoked when you say I<use Module>. In
914 turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl
915 counterpart for each of the extension's XSUBs. Don't worry about this
916 part; leave that to the I<xsubpp> and extension authors. If your
917 extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()>
918 for you on the fly. In fact, if you have a working DynaLoader then there
919 is rarely any need to link in any other extensions statically.
922 Once you have this code, slap it into the second argument of I<perl_parse()>:
925 perl_parse(my_perl, xs_init, argc, my_argv, NULL);
930 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
934 use SomeDynamicallyLoadedModule;
936 print "Now I can use extensions!\n"'
938 B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code.
940 % perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c
941 % cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts`
942 % cc -c interp.c `perl -MExtUtils::Embed -e ccopts`
943 % cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts`
945 Consult L<perlxs> and L<perlguts> for more details.
950 You can sometimes I<write faster code> in C, but
951 you can always I<write code faster> in Perl. Because you can use
952 each from the other, combine them as you wish.
957 Jon Orwant and <F<orwant@tpj.com>> and Doug MacEachern <F<dougm@osf.org>>,
958 with small contributions from Tim Bunce, Tom Christiansen, Hallvard Furuseth,
959 Dov Grobgeld, and Ilya Zakharevich.
961 Check out Doug's article on embedding in Volume 1, Issue 4 of The Perl
962 Journal. Info about TPJ is available from http://tpj.com.
966 Some of this material is excerpted from Jon Orwant's book: I<Perl 5
967 Interactive>, Waite Group Press, 1996 (ISBN 1-57169-064-6) and appears
968 courtesy of Waite Group Press.
972 Copyright (C) 1995, 1996, 1997 Doug MacEachern and Jon Orwant. All
975 Although destined for release with the standard Perl distribution,
976 this document is not public domain, nor is any of Perl and its
977 documentation. Permission is granted to freely distribute verbatim
978 copies of this document provided that no modifications outside of
979 formatting be made, and that this notice remain intact. You are
980 permitted and encouraged to use its code and derivatives thereof in
981 your own source code for fun or for profit as you see fit.