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 Perl provides two API functions to evaluate pieces of Perl code.
267 These are L<perlguts/perl_eval_sv()> and L<perlguts/perl_eval_pv()>.
269 Arguably, these are the only routines you'll ever need to execute
270 snippets of Perl code from within your C program. Your code can be
271 as long as you wish; it can contain multiple statements; it can employ
272 L<perlfunc/use>, L<perlfunc/require> and L<perlfunc/do> to include
275 I<perl_eval_pv()> lets us evaluate individual Perl strings, and then
276 extract variables for coercion into C types. The following program,
277 I<string.c>, executes three Perl strings, extracting an C<int> from
278 the first, a C<float> from the second, and a C<char *> from the third.
283 static PerlInterpreter *my_perl;
285 main (int argc, char **argv, char **env)
287 char *embedding[] = { "", "-e", "0" };
289 my_perl = perl_alloc();
290 perl_construct( my_perl );
292 perl_parse(my_perl, NULL, 3, embedding, NULL);
295 /** Treat $a as an integer **/
296 perl_eval_pv("$a = 3; $a **= 2", TRUE);
297 printf("a = %d\n", SvIV(perl_get_sv("a", FALSE)));
299 /** Treat $a as a float **/
300 perl_eval_pv("$a = 3.14; $a **= 2", TRUE);
301 printf("a = %f\n", SvNV(perl_get_sv("a", FALSE)));
303 /** Treat $a as a string **/
304 perl_eval_pv("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
305 printf("a = %s\n", SvPV(perl_get_sv("a", FALSE), na));
307 perl_destruct(my_perl);
311 All of those strange functions with I<sv> in their names help convert Perl scalars to C types. They're described in L<perlguts>.
313 If you compile and run I<string.c>, you'll see the results of using
314 I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and
315 I<SvPV()> to create a string:
319 a = Just Another Perl Hacker
321 In the example above, we've created a global variable to temporarily
322 store the computed value of our eval'd expression. It is also
323 possible and in most cases a better strategy to fetch the return value
324 from L<perl_eval_pv> instead. Example:
327 SV *val = perl_eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
328 printf("%s\n", SvPV(val,na));
331 This way, we avoid namespace pollution by not creating global
332 variables and we've simplified our code as well.
334 =head2 Performing Perl pattern matches and substitutions from your C program
336 The I<perl_eval_pv()> function lets us evaluate strings of Perl code, so we can
337 define some functions that use it to "specialize" in matches and
338 substitutions: I<match()>, I<substitute()>, and I<matches()>.
340 char match(char *string, char *pattern);
342 Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which
343 in your C program might appear as "/\\b\\w*\\b/"), match()
344 returns 1 if the string matches the pattern and 0 otherwise.
346 int substitute(char *string[], char *pattern);
348 Given a pointer to a string and an C<=~> operation (e.g.,
349 C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string
350 according to the operation, returning the number of substitutions
353 int matches(char *string, char *pattern, char **matches[]);
355 Given a string, a pattern, and a pointer to an empty array of strings,
356 matches() evaluates C<$string =~ $pattern> in an array context, and
357 fills in I<matches> with the array elements (allocating memory as it
358 does so), returning the number of matches found.
360 Here's a sample program, I<match.c>, that uses all three (long lines have
366 static PerlInterpreter *my_perl;
368 /** match(string, pattern)
370 ** Used for matches in a scalar context.
372 ** Returns 1 if the match was successful; 0 otherwise.
374 char match(char *string, char *pattern)
377 command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 37);
378 sprintf(command, "$string = '%s'; $return = $string =~ %s",
380 perl_eval_pv(command, TRUE);
382 return SvIV(perl_get_sv("return", FALSE));
384 /** substitute(string, pattern)
386 ** Used for =~ operations that modify their left-hand side (s/// and tr///)
388 ** Returns the number of successful matches, and
389 ** modifies the input string if there were any.
391 int substitute(char *string[], char *pattern)
395 command = malloc(sizeof(char) * strlen(*string) + strlen(pattern) + 35);
396 sprintf(command, "$string = '%s'; $ret = ($string =~ %s)",
398 perl_eval_pv(command, TRUE);
400 *string = SvPV(perl_get_sv("string", FALSE), length);
401 return SvIV(perl_get_sv("ret", FALSE));
403 /** matches(string, pattern, matches)
405 ** Used for matches in an array context.
407 ** Returns the number of matches,
408 ** and fills in **matches with the matching substrings (allocates memory!)
410 int matches(char *string, char *pattern, char **match_list[])
418 command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 38);
419 sprintf(command, "$string = '%s'; @array = ($string =~ %s)",
421 perl_eval_pv(command, TRUE);
423 array = perl_get_av("array", FALSE);
424 num_matches = av_len(array) + 1; /** assume $[ is 0 **/
425 *match_list = (char **) malloc(sizeof(char *) * num_matches);
426 for (i = 0; i <= num_matches; i++) {
427 current_match = av_shift(array);
428 (*match_list)[i] = SvPV(current_match, length);
432 main (int argc, char **argv, char **env)
434 char *embedding[] = { "", "-e", "0" };
435 char *text, **match_list;
438 my_perl = perl_alloc();
439 perl_construct( my_perl );
440 perl_parse(my_perl, NULL, 3, embedding, NULL);
443 text = (char *) malloc(sizeof(char) * 486); /** A long string follows! **/
444 sprintf(text, "%s", "When he is at a convenience store and the bill \
445 comes to some amount like 76 cents, Maynard is aware that there is \
446 something he *should* do, something that will enable him to get back \
447 a quarter, but he has no idea *what*. He fumbles through his red \
448 squeezey changepurse and gives the boy three extra pennies with his \
449 dollar, hoping that he might luck into the correct amount. The boy \
450 gives him back two of his own pennies and then the big shiny quarter \
451 that is his prize. -RICHH");
452 if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
453 printf("match: Text contains the word 'quarter'.\n\n");
455 printf("match: Text doesn't contain the word 'quarter'.\n\n");
456 if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
457 printf("match: Text contains the word 'eighth'.\n\n");
459 printf("match: Text doesn't contain the word 'eighth'.\n\n");
460 /** Match all occurrences of /wi../ **/
461 num_matches = matches(text, "m/(wi..)/g", &match_list);
462 printf("matches: m/(wi..)/g found %d matches...\n", num_matches);
463 for (i = 0; i < num_matches; i++)
464 printf("match: %s\n", match_list[i]);
466 for (i = 0; i < num_matches; i++) {
470 /** Remove all vowels from text **/
471 num_matches = substitute(&text, "s/[aeiou]//gi");
473 printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
475 printf("Now text is: %s\n\n", text);
477 /** Attempt a substitution **/
478 if (!substitute(&text, "s/Perl/C/")) {
479 printf("substitute: s/Perl/C...No substitution made.\n\n");
482 perl_destruct(my_perl);
486 which produces the output (again, long lines have been wrapped here)
488 match: Text contains the word 'quarter'.
490 match: Text doesn't contain the word 'eighth'.
492 matches: m/(wi..)/g found 2 matches...
496 substitute: s/[aeiou]//gi...139 substitutions made.
497 Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
498 Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt bck
499 qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd gvs th by
500 thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct mnt. Th by gvs
501 hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s hs prz. -RCHH
503 substitute: s/Perl/C...No substitution made.
505 =head2 Fiddling with the Perl stack from your C program
507 When trying to explain stacks, most computer science textbooks mumble
508 something about spring-loaded columns of cafeteria plates: the last
509 thing you pushed on the stack is the first thing you pop off. That'll
510 do for our purposes: your C program will push some arguments onto "the Perl
511 stack", shut its eyes while some magic happens, and then pop the
512 results--the return value of your Perl subroutine--off the stack.
514 First you'll need to know how to convert between C types and Perl
515 types, with newSViv() and sv_setnv() and newAV() and all their
516 friends. They're described in L<perlguts>.
518 Then you'll need to know how to manipulate the Perl stack. That's
519 described in L<perlcall>.
521 Once you've understood those, embedding Perl in C is easy.
523 Because C has no builtin function for integer exponentiation, let's
524 make Perl's ** operator available to it (this is less useful than it
525 sounds, because Perl implements ** with C's I<pow()> function). First
526 I'll create a stub exponentiation function in I<power.pl>:
533 Now I'll create a C program, I<power.c>, with a function
534 I<PerlPower()> that contains all the perlguts necessary to push the
535 two arguments into I<expo()> and to pop the return value out. Take a
541 static PerlInterpreter *my_perl;
544 PerlPower(int a, int b)
546 dSP; /* initialize stack pointer */
547 ENTER; /* everything created after here */
548 SAVETMPS; /* ...is a temporary variable. */
549 PUSHMARK(sp); /* remember the stack pointer */
550 XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */
551 XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */
552 PUTBACK; /* make local stack pointer global */
553 perl_call_pv("expo", G_SCALAR); /* call the function */
554 SPAGAIN; /* refresh stack pointer */
555 /* pop the return value from stack */
556 printf ("%d to the %dth power is %d.\n", a, b, POPi);
558 FREETMPS; /* free that return value */
559 LEAVE; /* ...and the XPUSHed "mortal" args.*/
562 int main (int argc, char **argv, char **env)
566 my_perl = perl_alloc();
567 perl_construct( my_perl );
569 my_argv[1] = (char *) malloc(10);
570 sprintf(my_argv[1], "power.pl");
572 perl_parse(my_perl, NULL, argc, my_argv, NULL);
575 PerlPower(3, 4); /*** Compute 3 ** 4 ***/
577 perl_destruct(my_perl);
585 % cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
588 3 to the 4th power is 81.
590 =head2 Maintaining a persistent interpreter
592 When developing interactive and/or potentially long-running
593 applications, it's a good idea to maintain a persistent interpreter
594 rather than allocating and constructing a new interpreter multiple
595 times. The major reason is speed: since Perl will only be loaded into
598 However, you have to be more cautious with namespace and variable
599 scoping when using a persistent interpreter. In previous examples
600 we've been using global variables in the default package C<main>. We
601 knew exactly what code would be run, and assumed we could avoid
602 variable collisions and outrageous symbol table growth.
604 Let's say your application is a server that will occasionally run Perl
605 code from some arbitrary file. Your server has no way of knowing what
606 code it's going to run. Very dangerous.
608 If the file is pulled in by C<perl_parse()>, compiled into a newly
609 constructed interpreter, and subsequently cleaned out with
610 C<perl_destruct()> afterwards, you're shielded from most namespace
613 One way to avoid namespace collisions in this scenario is to translate
614 the filename into a guaranteed-unique package name, and then compile
615 the code into that package using L<perlfunc/eval>. In the example
616 below, each file will only be compiled once. Or, the application
617 might choose to clean out the symbol table associated with the file
618 after it's no longer needed. Using L<perlcall/perl_call_argv>, We'll
619 call the subroutine C<Embed::Persistent::eval_file> which lives in the
620 file C<persistent.pl> and pass the filename and boolean cleanup/cache
623 Note that the process will continue to grow for each file that it
624 uses. In addition, there might be C<AUTOLOAD>ed subroutines and other
625 conditions that cause Perl's symbol table to grow. You might want to
626 add some logic that keeps track of the process size, or restarts
627 itself after a certain number of requests, to ensure that memory
628 consumption is minimized. You'll also want to scope your variables
629 with L<perlfunc/my> whenever possible.
632 package Embed::Persistent;
638 sub valid_package_name {
640 $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
641 # second pass only for words starting with a digit
642 $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;
644 # Dress it up as a real package name
646 return "Embed" . $string;
649 #borrowed from Safe.pm
655 $pkg = "main::$pkg\::"; # expand to full symbol table name
656 ($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
658 my $stem_symtab = *{$stem}{HASH};
660 delete $stem_symtab->{$leaf};
664 my($filename, $delete) = @_;
665 my $package = valid_package_name($filename);
666 my $mtime = -M $filename;
667 if(defined $Cache{$package}{mtime}
669 $Cache{$package}{mtime} <= $mtime)
671 # we have compiled this subroutine already,
672 # it has not been updated on disk, nothing left to do
673 print STDERR "already compiled $package->handler\n";
677 open FH, $filename or die "open '$filename' $!";
682 #wrap the code into a subroutine inside our unique package
683 my $eval = qq{package $package; sub handler { $sub; }};
685 # hide our variables within this block
686 my($filename,$mtime,$package,$sub);
691 #cache it unless we're cleaning out each time
692 $Cache{$package}{mtime} = $mtime unless $delete;
695 eval {$package->handler;};
698 delete_package($package) if $delete;
700 #take a look if you want
701 #print Devel::Symdump->rnew($package)->as_string, $/;
712 /* 1 = clean out filename's symbol table after each request, 0 = don't */
717 static PerlInterpreter *perl = NULL;
720 main(int argc, char **argv, char **env)
722 char *embedding[] = { "", "persistent.pl" };
723 char *args[] = { "", DO_CLEAN, NULL };
724 char filename [1024];
727 if((perl = perl_alloc()) == NULL) {
728 fprintf(stderr, "no memory!");
731 perl_construct(perl);
733 exitstatus = perl_parse(perl, NULL, 2, embedding, NULL);
736 exitstatus = perl_run(perl);
738 while(printf("Enter file name: ") && gets(filename)) {
740 /* call the subroutine, passing it the filename as an argument */
742 perl_call_argv("Embed::Persistent::eval_file",
743 G_DISCARD | G_EVAL, args);
746 if(SvTRUE(GvSV(errgv)))
747 fprintf(stderr, "eval error: %s\n", SvPV(GvSV(errgv),na));
751 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.