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 5.003_05, 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, nonportable
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> manpage.
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
329 In the example above, we've created a global variable to temporarily
330 store the computed value of our eval'd expression. It is also
331 possible and in most cases a better strategy to fetch the return value
332 from L<perl_eval_sv> instead. Example:
334 SV *perl_eval(char *string, int croak_on_error)
337 SV *sv = newSVpv(string,0);
340 perl_eval_sv(sv, G_SCALAR);
347 if (croak_on_error && SvTRUE(GvSV(errgv)))
348 croak(SvPV(GvSV(errgv),na));
353 SV *val = perl_eval("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
354 printf("%s\n", SvPV(val,na));
357 This way, we avoid namespace pollution by not creating global
358 variables and we've simplified our code as well.
360 =head2 Performing Perl pattern matches and substitutions from your C program
362 Our I<perl_eval()> lets us evaluate strings of Perl code, so we can
363 define some functions that use it to "specialize" in matches and
364 substitutions: I<match()>, I<substitute()>, and I<matches()>.
366 char match(char *string, char *pattern);
368 Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which
369 in your C program might appear as "/\\b\\w*\\b/"), match()
370 returns 1 if the string matches the pattern and 0 otherwise.
372 int substitute(char *string[], char *pattern);
374 Given a pointer to a string and an C<=~> operation (e.g.,
375 C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string
376 according to the operation, returning the number of substitutions
379 int matches(char *string, char *pattern, char **matches[]);
381 Given a string, a pattern, and a pointer to an empty array of strings,
382 matches() evaluates C<$string =~ $pattern> in an array context, and
383 fills in I<matches> with the array elements (allocating memory as it
384 does so), returning the number of matches found.
386 Here's a sample program, I<match.c>, that uses all three (long lines have
392 static PerlInterpreter *my_perl;
393 I32 perl_eval(char *string)
395 return perl_eval_sv(newSVpv(string,0), G_DISCARD);
397 /** match(string, pattern)
399 ** Used for matches in a scalar context.
401 ** Returns 1 if the match was successful; 0 otherwise.
403 char match(char *string, char *pattern)
406 command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 37);
407 sprintf(command, "$string = '%s'; $return = $string =~ %s",
411 return SvIV(perl_get_sv("return", FALSE));
413 /** substitute(string, pattern)
415 ** Used for =~ operations that modify their left-hand side (s/// and tr///)
417 ** Returns the number of successful matches, and
418 ** modifies the input string if there were any.
420 int substitute(char *string[], char *pattern)
424 command = malloc(sizeof(char) * strlen(*string) + strlen(pattern) + 35);
425 sprintf(command, "$string = '%s'; $ret = ($string =~ %s)",
429 *string = SvPV(perl_get_sv("string", FALSE), length);
430 return SvIV(perl_get_sv("ret", FALSE));
432 /** matches(string, pattern, matches)
434 ** Used for matches in an array context.
436 ** Returns the number of matches,
437 ** and fills in **matches with the matching substrings (allocates memory!)
439 int matches(char *string, char *pattern, char **match_list[])
447 command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 38);
448 sprintf(command, "$string = '%s'; @array = ($string =~ %s)",
452 array = perl_get_av("array", FALSE);
453 num_matches = av_len(array) + 1; /** assume $[ is 0 **/
454 *match_list = (char **) malloc(sizeof(char *) * num_matches);
455 for (i = 0; i <= num_matches; i++) {
456 current_match = av_shift(array);
457 (*match_list)[i] = SvPV(current_match, length);
461 main (int argc, char **argv, char **env)
463 char *embedding[] = { "", "-e", "0" };
464 char *text, **match_list;
467 my_perl = perl_alloc();
468 perl_construct( my_perl );
469 perl_parse(my_perl, NULL, 3, embedding, NULL);
472 text = (char *) malloc(sizeof(char) * 486); /** A long string follows! **/
473 sprintf(text, "%s", "When he is at a convenience store and the bill \
474 comes to some amount like 76 cents, Maynard is aware that there is \
475 something he *should* do, something that will enable him to get back \
476 a quarter, but he has no idea *what*. He fumbles through his red \
477 squeezey changepurse and gives the boy three extra pennies with his \
478 dollar, hoping that he might luck into the correct amount. The boy \
479 gives him back two of his own pennies and then the big shiny quarter \
480 that is his prize. -RICHH");
481 if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
482 printf("match: Text contains the word 'quarter'.\n\n");
484 printf("match: Text doesn't contain the word 'quarter'.\n\n");
485 if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
486 printf("match: Text contains the word 'eighth'.\n\n");
488 printf("match: Text doesn't contain the word 'eighth'.\n\n");
489 /** Match all occurrences of /wi../ **/
490 num_matches = matches(text, "m/(wi..)/g", &match_list);
491 printf("matches: m/(wi..)/g found %d matches...\n", num_matches);
492 for (i = 0; i < num_matches; i++)
493 printf("match: %s\n", match_list[i]);
495 for (i = 0; i < num_matches; i++) {
499 /** Remove all vowels from text **/
500 num_matches = substitute(&text, "s/[aeiou]//gi");
502 printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
504 printf("Now text is: %s\n\n", text);
506 /** Attempt a substitution **/
507 if (!substitute(&text, "s/Perl/C/")) {
508 printf("substitute: s/Perl/C...No substitution made.\n\n");
511 perl_destruct(my_perl);
515 which produces the output (again, long lines have been wrapped here)
517 match: Text contains the word 'quarter'.
519 match: Text doesn't contain the word 'eighth'.
521 matches: m/(wi..)/g found 2 matches...
525 substitute: s/[aeiou]//gi...139 substitutions made.
526 Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
527 Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt bck
528 qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd gvs th by
529 thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct mnt. Th by gvs
530 hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s hs prz. -RCHH
532 substitute: s/Perl/C...No substitution made.
534 =head2 Fiddling with the Perl stack from your C program
536 When trying to explain stacks, most computer science textbooks mumble
537 something about spring-loaded columns of cafeteria plates: the last
538 thing you pushed on the stack is the first thing you pop off. That'll
539 do for our purposes: your C program will push some arguments onto "the Perl
540 stack", shut its eyes while some magic happens, and then pop the
541 results--the return value of your Perl subroutine--off the stack.
543 First you'll need to know how to convert between C types and Perl
544 types, with newSViv() and sv_setnv() and newAV() and all their
545 friends. They're described in L<perlguts>.
547 Then you'll need to know how to manipulate the Perl stack. That's
548 described in L<perlcall>.
550 Once you've understood those, embedding Perl in C is easy.
552 Because C has no builtin function for integer exponentiation, let's
553 make Perl's ** operator available to it (this is less useful than it
554 sounds, because Perl implements ** with C's I<pow()> function). First
555 I'll create a stub exponentiation function in I<power.pl>:
562 Now I'll create a C program, I<power.c>, with a function
563 I<PerlPower()> that contains all the perlguts necessary to push the
564 two arguments into I<expo()> and to pop the return value out. Take a
570 static PerlInterpreter *my_perl;
573 PerlPower(int a, int b)
575 dSP; /* initialize stack pointer */
576 ENTER; /* everything created after here */
577 SAVETMPS; /* ...is a temporary variable. */
578 PUSHMARK(sp); /* remember the stack pointer */
579 XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */
580 XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */
581 PUTBACK; /* make local stack pointer global */
582 perl_call_pv("expo", G_SCALAR); /* call the function */
583 SPAGAIN; /* refresh stack pointer */
584 /* pop the return value from stack */
585 printf ("%d to the %dth power is %d.\n", a, b, POPi);
587 FREETMPS; /* free that return value */
588 LEAVE; /* ...and the XPUSHed "mortal" args.*/
591 int main (int argc, char **argv, char **env)
595 my_perl = perl_alloc();
596 perl_construct( my_perl );
598 my_argv[1] = (char *) malloc(10);
599 sprintf(my_argv[1], "power.pl");
601 perl_parse(my_perl, NULL, argc, my_argv, NULL);
604 PerlPower(3, 4); /*** Compute 3 ** 4 ***/
606 perl_destruct(my_perl);
614 % cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
617 3 to the 4th power is 81.
619 =head2 Maintaining a persistent interpreter
621 When developing interactive and/or potentially long-running
622 applications, it's a good idea to maintain a persistent interpreter
623 rather than allocating and constructing a new interpreter multiple
624 times. The major reason is speed: since Perl will only be loaded into
627 However, you have to be more cautious with namespace and variable
628 scoping when using a persistent interpreter. In previous examples
629 we've been using global variables in the default package C<main>. We
630 knew exactly what code would be run, and assumed we could avoid
631 variable collisions and outrageous symbol table growth.
633 Let's say your application is a server that will occasionally run Perl
634 code from some arbitrary file. Your server has no way of knowing what
635 code it's going to run. Very dangerous.
637 If the file is pulled in by C<perl_parse()>, compiled into a newly
638 constructed interpreter, and subsequently cleaned out with
639 C<perl_destruct()> afterwards, you're shielded from most namespace
642 One way to avoid namespace collisions in this scenario is to translate
643 the filename into a guaranteed-unique package name, and then compile
644 the code into that package using L<perlfunc/eval>. In the example
645 below, each file will only be compiled once. Or, the application
646 might choose to clean out the symbol table associated with the file
647 after it's no longer needed. Using L<perlcall/perl_call_argv>, We'll
648 call the subroutine C<Embed::Persistent::eval_file> which lives in the
649 file C<persistent.pl> and pass the filename and boolean cleanup/cache
652 Note that the process will continue to grow for each file that it
653 uses. In addition, there might be C<AUTOLOAD>ed subroutines and other
654 conditions that cause Perl's symbol table to grow. You might want to
655 add some logic that keeps track of the process size, or restarts
656 itself after a certain number of requests, to ensure that memory
657 consumption is minimized. You'll also want to scope your variables
658 with L<perlfunc/my> whenever possible.
661 package Embed::Persistent;
667 sub valid_package_name {
669 $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
670 # second pass only for words starting with a digit
671 $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;
673 # Dress it up as a real package name
675 return "Embed" . $string;
678 #borrowed from Safe.pm
684 $pkg = "main::$pkg\::"; # expand to full symbol table name
685 ($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
687 my $stem_symtab = *{$stem}{HASH};
689 delete $stem_symtab->{$leaf};
693 my($filename, $delete) = @_;
694 my $package = valid_package_name($filename);
695 my $mtime = -M $filename;
696 if(defined $Cache{$package}{mtime}
698 $Cache{$package}{mtime} <= $mtime)
700 # we have compiled this subroutine already,
701 # it has not been updated on disk, nothing left to do
702 print STDERR "already compiled $package->handler\n";
706 open FH, $filename or die "open '$filename' $!";
711 #wrap the code into a subroutine inside our unique package
712 my $eval = qq{package $package; sub handler { $sub; }};
714 # hide our variables within this block
715 my($filename,$mtime,$package,$sub);
720 #cache it unless we're cleaning out each time
721 $Cache{$package}{mtime} = $mtime unless $delete;
724 eval {$package->handler;};
727 delete_package($package) if $delete;
729 #take a look if you want
730 #print Devel::Symdump->rnew($package)->as_string, $/;
741 /* 1 = clean out filename's symbol table after each request, 0 = don't */
746 static PerlInterpreter *perl = NULL;
749 main(int argc, char **argv, char **env)
751 char *embedding[] = { "", "persistent.pl" };
752 char *args[] = { "", DO_CLEAN, NULL };
753 char filename [1024];
756 if((perl = perl_alloc()) == NULL) {
757 fprintf(stderr, "no memory!");
760 perl_construct(perl);
762 exitstatus = perl_parse(perl, NULL, 2, embedding, NULL);
765 exitstatus = perl_run(perl);
767 while(printf("Enter file name: ") && gets(filename)) {
769 /* call the subroutine, passing it the filename as an argument */
771 perl_call_argv("Embed::Persistent::eval_file",
772 G_DISCARD | G_EVAL, args);
775 if(SvTRUE(GvSV(errgv)))
776 fprintf(stderr, "eval error: %s\n", SvPV(GvSV(errgv),na));
780 perl_destruct_level = 0;
788 % cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
790 Here's a example script file:
793 my $string = "hello";
797 print "foo says: @_\n";
803 Enter file name: test.pl
805 Enter file name: test.pl
806 already compiled Embed::test_2epl->handler
810 =head2 Maintaining multiple interpreter instances
812 Some rare applications will need to create more than one interpreter
813 during a session. Such an application might sporadically decide to
814 release any resources associated with the interpreter.
816 The program must take care to ensure that this takes place I<before>
817 the next interpreter is constructed. By default, the global variable
818 C<perl_destruct_level> is set to C<0>, since extra cleaning isn't
819 needed when a program has only one interpreter.
821 Setting C<perl_destruct_level> to C<1> makes everything squeaky clean:
823 perl_destruct_level = 1;
827 /* reset global variables here with perl_destruct_level = 1 */
828 perl_construct(my_perl);
830 /* clean and reset _everything_ during perl_destruct */
831 perl_destruct(my_perl);
834 /* let's go do it again! */
837 When I<perl_destruct()> is called, the interpreter's syntax parse tree
838 and symbol tables are cleaned up, and global variables are reset.
840 Now suppose we have more than one interpreter instance running at the
841 same time. This is feasible, but only if you used the
842 C<-DMULTIPLICITY> flag when building Perl. By default, that sets
843 C<perl_destruct_level> to C<1>.
851 /* we're going to embed two interpreters */
852 /* we're going to embed two interpreters */
854 #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"
856 int main(int argc, char **argv, char **env)
859 *one_perl = perl_alloc(),
860 *two_perl = perl_alloc();
861 char *one_args[] = { "one_perl", SAY_HELLO };
862 char *two_args[] = { "two_perl", SAY_HELLO };
864 perl_construct(one_perl);
865 perl_construct(two_perl);
867 perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
868 perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
873 perl_destruct(one_perl);
874 perl_destruct(two_perl);
883 % cc -o multiplicity multiplicity.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
891 =head2 Using Perl modules, which themselves use C libraries, from your C program
893 If you've played with the examples above and tried to embed a script
894 that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++ library,
895 this probably happened:
898 Can't load module Socket, dynamic loading not available in this perl.
899 (You may need to build a new perl executable which either supports
900 dynamic loading or has the Socket module statically linked into it.)
905 Your interpreter doesn't know how to communicate with these extensions
906 on its own. A little glue will help. Up until now you've been
907 calling I<perl_parse()>, handing it NULL for the second argument:
909 perl_parse(my_perl, NULL, argc, my_argv, NULL);
911 That's where the glue code can be inserted to create the initial contact between
912 Perl and linked C/C++ routines. Let's take a look some pieces of I<perlmain.c>
913 to see how Perl does this:
917 # define EXTERN_C extern "C"
919 # define EXTERN_C extern
922 static void xs_init _((void));
924 EXTERN_C void boot_DynaLoader _((CV* cv));
925 EXTERN_C void boot_Socket _((CV* cv));
931 char *file = __FILE__;
932 /* DynaLoader is a special case */
933 newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
934 newXS("Socket::bootstrap", boot_Socket, file);
937 Simply put: for each extension linked with your Perl executable
938 (determined during its initial configuration on your
939 computer or when adding a new extension),
940 a Perl subroutine is created to incorporate the extension's
941 routines. Normally, that subroutine is named
942 I<Module::bootstrap()> and is invoked when you say I<use Module>. In
943 turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl
944 counterpart for each of the extension's XSUBs. Don't worry about this
945 part; leave that to the I<xsubpp> and extension authors. If your
946 extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()>
947 for you on the fly. In fact, if you have a working DynaLoader then there
948 is rarely any need to link in any other extensions statically.
951 Once you have this code, slap it into the second argument of I<perl_parse()>:
954 perl_parse(my_perl, xs_init, argc, my_argv, NULL);
959 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
963 use SomeDynamicallyLoadedModule;
965 print "Now I can use extensions!\n"'
967 B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code.
969 % perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c
970 % cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts`
971 % cc -c interp.c `perl -MExtUtils::Embed -e ccopts`
972 % cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts`
974 Consult L<perlxs> and L<perlguts> for more details.
979 You can sometimes I<write faster code> in C, but
980 you can always I<write code faster> in Perl. Because you can use
981 each from the other, combine them as you wish.
986 Jon Orwant and <F<orwant@tpj.com>> and Doug MacEachern <F<dougm@osf.org>>,
987 with small contributions from Tim Bunce, Tom Christiansen, Hallvard Furuseth,
988 Dov Grobgeld, and Ilya Zakharevich.
990 Check out Doug's article on embedding in Volume 1, Issue 4 of The Perl
991 Journal. Info about TPJ is available from http://tpj.com.
995 Some of this material is excerpted from Jon Orwant's book: I<Perl 5
996 Interactive>, Waite Group Press, 1996 (ISBN 1-57169-064-6) and appears
997 courtesy of Waite Group Press.
1001 Copyright (C) 1995, 1996, 1997 Doug MacEachern and Jon Orwant. All
1004 Although destined for release with the standard Perl distribution,
1005 this document is not public domain, nor is any of Perl and its
1006 documentation. Permission is granted to freely distribute verbatim
1007 copies of this document provided that no modifications outside of
1008 formatting be made, and that this notice remain intact. You are
1009 permitted and encouraged to use its code and derivatives thereof in
1010 your own source code for fun or for profit as you see fit.