3 perlembed - how to embed perl in your C program
13 =item B<Use C from Perl?>
15 Read L<perlxstut>, L<perlxs>, L<h2xs>, L<perlguts>, and L<perlapi>.
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?>
42 Compiling your C program
46 Adding a Perl interpreter to your C program
50 Calling a Perl subroutine from your C program
54 Evaluating a Perl statement from your C program
58 Performing Perl pattern matches and substitutions from your C program
62 Fiddling with the Perl stack from your C program
66 Maintaining a persistent interpreter
70 Maintaining multiple interpreter instances
74 Using Perl modules, which themselves use C libraries, from your C program
78 Embedding Perl under Win32
82 =head2 Compiling your C program
84 If you have trouble compiling the scripts in this documentation,
85 you're not alone. The cardinal rule: COMPILE THE PROGRAMS IN EXACTLY
86 THE SAME WAY THAT YOUR PERL WAS COMPILED. (Sorry for yelling.)
88 Also, every C program that uses Perl must link in the I<perl library>.
89 What's that, you ask? Perl is itself written in C; the perl library
90 is the collection of compiled C programs that were used to create your
91 perl executable (I</usr/bin/perl> or equivalent). (Corollary: you
92 can't use Perl from your C program unless Perl has been compiled on
93 your machine, or installed properly--that's why you shouldn't blithely
94 copy Perl executables from machine to machine without also copying the
97 When you use Perl from C, your C program will--usually--allocate,
98 "run", and deallocate a I<PerlInterpreter> object, which is defined by
101 If your copy of Perl is recent enough to contain this documentation
102 (version 5.002 or later), then the perl library (and I<EXTERN.h> and
103 I<perl.h>, which you'll also need) will reside in a directory
104 that looks like this:
106 /usr/local/lib/perl5/your_architecture_here/CORE
110 /usr/local/lib/perl5/CORE
112 or maybe something like
116 Execute this statement for a hint about where to find CORE:
118 perl -MConfig -e 'print $Config{archlib}'
120 Here's how you'd compile the example in the next section,
121 L<Adding a Perl interpreter to your C program>, on my Linux box:
123 % gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include
124 -I/usr/local/lib/perl5/i586-linux/5.003/CORE
125 -L/usr/local/lib/perl5/i586-linux/5.003/CORE
126 -o interp interp.c -lperl -lm
128 (That's all one line.) On my DEC Alpha running old 5.003_05, the
129 incantation is a bit different:
131 % cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include
132 -I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE
133 -L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib
134 -D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm
136 How can you figure out what to add? Assuming your Perl is post-5.001,
137 execute a C<perl -V> command and pay special attention to the "cc" and
138 "ccflags" information.
140 You'll have to choose the appropriate compiler (I<cc>, I<gcc>, et al.) for
141 your machine: C<perl -MConfig -e 'print $Config{cc}'> will tell you what
144 You'll also have to choose the appropriate library directory
145 (I</usr/local/lib/...>) for your machine. If your compiler complains
146 that certain functions are undefined, or that it can't locate
147 I<-lperl>, then you need to change the path following the C<-L>. If it
148 complains that it can't find I<EXTERN.h> and I<perl.h>, you need to
149 change the path following the C<-I>.
151 You may have to add extra libraries as well. Which ones?
152 Perhaps those printed by
154 perl -MConfig -e 'print $Config{libs}'
156 Provided your perl binary was properly configured and installed the
157 B<ExtUtils::Embed> module will determine all of this information for
160 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
162 If the B<ExtUtils::Embed> module isn't part of your Perl distribution,
163 you can retrieve it from
164 http://www.perl.com/perl/CPAN/modules/by-module/ExtUtils/
165 (If this documentation came from your Perl distribution, then you're
166 running 5.004 or better and you already have it.)
168 The B<ExtUtils::Embed> kit on CPAN also contains all source code for
169 the examples in this document, tests, additional examples and other
170 information you may find useful.
172 =head2 Adding a Perl interpreter to your C program
174 In a sense, perl (the C program) is a good example of embedding Perl
175 (the language), so I'll demonstrate embedding with I<miniperlmain.c>,
176 included in the source distribution. Here's a bastardized, nonportable
177 version of I<miniperlmain.c> containing the essentials of embedding:
179 #include <EXTERN.h> /* from the Perl distribution */
180 #include <perl.h> /* from the Perl distribution */
182 static PerlInterpreter *my_perl; /*** The Perl interpreter ***/
184 int main(int argc, char **argv, char **env)
186 my_perl = perl_alloc();
187 perl_construct(my_perl);
188 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
189 perl_parse(my_perl, NULL, argc, argv, (char **)NULL);
191 perl_destruct(my_perl);
195 Notice that we don't use the C<env> pointer. Normally handed to
196 C<perl_parse> as its final argument, C<env> here is replaced by
197 C<NULL>, which means that the current environment will be used.
199 Now compile this program (I'll call it I<interp.c>) into an executable:
201 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
203 After a successful compilation, you'll be able to use I<interp> just
207 print "Pretty Good Perl \n";
208 print "10890 - 9801 is ", 10890 - 9801;
215 % interp -e 'printf("%x", 3735928559)'
218 You can also read and execute Perl statements from a file while in the
219 midst of your C program, by placing the filename in I<argv[1]> before
222 =head2 Calling a Perl subroutine from your C program
224 To call individual Perl subroutines, you can use any of the B<call_*>
225 functions documented in L<perlcall>.
226 In this example we'll use C<call_argv>.
228 That's shown below, in a program I'll call I<showtime.c>.
233 static PerlInterpreter *my_perl;
235 int main(int argc, char **argv, char **env)
237 char *args[] = { NULL };
238 my_perl = perl_alloc();
239 perl_construct(my_perl);
241 perl_parse(my_perl, NULL, argc, argv, NULL);
242 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
244 /*** skipping perl_run() ***/
246 call_argv("showtime", G_DISCARD | G_NOARGS, args);
248 perl_destruct(my_perl);
252 where I<showtime> is a Perl subroutine that takes no arguments (that's the
253 I<G_NOARGS>) and for which I'll ignore the return value (that's the
254 I<G_DISCARD>). Those flags, and others, are discussed in L<perlcall>.
256 I'll define the I<showtime> subroutine in a file called I<showtime.pl>:
258 print "I shan't be printed.";
264 Simple enough. Now compile and run:
266 % cc -o showtime showtime.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
268 % showtime showtime.pl
271 yielding the number of seconds that elapsed between January 1, 1970
272 (the beginning of the Unix epoch), and the moment I began writing this
275 In this particular case we don't have to call I<perl_run>, as we set
276 the PL_exit_flag PERL_EXIT_DESTRUCT_END which executes END blocks in
279 If you want to pass arguments to the Perl subroutine, you can add
280 strings to the C<NULL>-terminated C<args> list passed to
281 I<call_argv>. For other data types, or to examine return values,
282 you'll need to manipulate the Perl stack. That's demonstrated in
283 L<Fiddling with the Perl stack from your C program>.
285 =head2 Evaluating a Perl statement from your C program
287 Perl provides two API functions to evaluate pieces of Perl code.
288 These are L<perlapi/eval_sv> and L<perlapi/eval_pv>.
290 Arguably, these are the only routines you'll ever need to execute
291 snippets of Perl code from within your C program. Your code can be as
292 long as you wish; it can contain multiple statements; it can employ
293 L<perlfunc/use>, L<perlfunc/require>, and L<perlfunc/do> to
294 include external Perl files.
296 I<eval_pv> lets us evaluate individual Perl strings, and then
297 extract variables for coercion into C types. The following program,
298 I<string.c>, executes three Perl strings, extracting an C<int> from
299 the first, a C<float> from the second, and a C<char *> from the third.
304 static PerlInterpreter *my_perl;
306 main (int argc, char **argv, char **env)
309 char *embedding[] = { "", "-e", "0" };
311 my_perl = perl_alloc();
312 perl_construct( my_perl );
314 perl_parse(my_perl, NULL, 3, embedding, NULL);
315 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
318 /** Treat $a as an integer **/
319 eval_pv("$a = 3; $a **= 2", TRUE);
320 printf("a = %d\n", SvIV(get_sv("a", FALSE)));
322 /** Treat $a as a float **/
323 eval_pv("$a = 3.14; $a **= 2", TRUE);
324 printf("a = %f\n", SvNV(get_sv("a", FALSE)));
326 /** Treat $a as a string **/
327 eval_pv("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
328 printf("a = %s\n", SvPV(get_sv("a", FALSE), n_a));
330 perl_destruct(my_perl);
334 All of those strange functions with I<sv> in their names help convert Perl scalars to C types. They're described in L<perlguts> and L<perlapi>.
336 If you compile and run I<string.c>, you'll see the results of using
337 I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and
338 I<SvPV()> to create a string:
342 a = Just Another Perl Hacker
344 In the example above, we've created a global variable to temporarily
345 store the computed value of our eval'd expression. It is also
346 possible and in most cases a better strategy to fetch the return value
347 from I<eval_pv()> instead. Example:
351 SV *val = eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
352 printf("%s\n", SvPV(val,n_a));
355 This way, we avoid namespace pollution by not creating global
356 variables and we've simplified our code as well.
358 =head2 Performing Perl pattern matches and substitutions from your C program
360 The I<eval_sv()> function lets us evaluate strings of Perl code, so we can
361 define some functions that use it to "specialize" in matches and
362 substitutions: I<match()>, I<substitute()>, and I<matches()>.
364 I32 match(SV *string, char *pattern);
366 Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which
367 in your C program might appear as "/\\b\\w*\\b/"), match()
368 returns 1 if the string matches the pattern and 0 otherwise.
370 int substitute(SV **string, char *pattern);
372 Given a pointer to an C<SV> and an C<=~> operation (e.g.,
373 C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string
374 within the C<AV> at according to the operation, returning the number of substitutions
377 int matches(SV *string, char *pattern, AV **matches);
379 Given an C<SV>, a pattern, and a pointer to an empty C<AV>,
380 matches() evaluates C<$string =~ $pattern> in a list context, and
381 fills in I<matches> with the array elements, returning the number of matches found.
383 Here's a sample program, I<match.c>, that uses all three (long lines have
389 static PerlInterpreter *my_perl;
391 /** my_eval_sv(code, error_check)
392 ** kinda like eval_sv(),
393 ** but we pop the return value off the stack
395 SV* my_eval_sv(SV *sv, I32 croak_on_error)
402 eval_sv(sv, G_SCALAR);
408 if (croak_on_error && SvTRUE(ERRSV))
409 croak(SvPVx(ERRSV, n_a));
414 /** match(string, pattern)
416 ** Used for matches in a scalar context.
418 ** Returns 1 if the match was successful; 0 otherwise.
421 I32 match(SV *string, char *pattern)
423 SV *command = NEWSV(1099, 0), *retval;
426 sv_setpvf(command, "my $string = '%s'; $string =~ %s",
427 SvPV(string,n_a), pattern);
429 retval = my_eval_sv(command, TRUE);
430 SvREFCNT_dec(command);
435 /** substitute(string, pattern)
437 ** Used for =~ operations that modify their left-hand side (s/// and tr///)
439 ** Returns the number of successful matches, and
440 ** modifies the input string if there were any.
443 I32 substitute(SV **string, char *pattern)
445 SV *command = NEWSV(1099, 0), *retval;
448 sv_setpvf(command, "$string = '%s'; ($string =~ %s)",
449 SvPV(*string,n_a), pattern);
451 retval = my_eval_sv(command, TRUE);
452 SvREFCNT_dec(command);
454 *string = get_sv("string", FALSE);
458 /** matches(string, pattern, matches)
460 ** Used for matches in a list context.
462 ** Returns the number of matches,
463 ** and fills in **matches with the matching substrings
466 I32 matches(SV *string, char *pattern, AV **match_list)
468 SV *command = NEWSV(1099, 0);
472 sv_setpvf(command, "my $string = '%s'; @array = ($string =~ %s)",
473 SvPV(string,n_a), pattern);
475 my_eval_sv(command, TRUE);
476 SvREFCNT_dec(command);
478 *match_list = get_av("array", FALSE);
479 num_matches = av_len(*match_list) + 1; /** assume $[ is 0 **/
484 main (int argc, char **argv, char **env)
486 char *embedding[] = { "", "-e", "0" };
492 my_perl = perl_alloc();
493 perl_construct(my_perl);
494 perl_parse(my_perl, NULL, 3, embedding, NULL);
495 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
497 text = NEWSV(1099,0);
498 sv_setpv(text, "When he is at a convenience store and the bill comes to some amount like 76 cents, Maynard is aware that there is something he *should* do, something that will enable him to get back a quarter, but he has no idea *what*. He fumbles through his red squeezey changepurse and gives the boy three extra pennies with his dollar, hoping that he might luck into the correct amount. The boy gives him back two of his own pennies and then the big shiny quarter that is his prize. -RICHH");
500 if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
501 printf("match: Text contains the word 'quarter'.\n\n");
503 printf("match: Text doesn't contain the word 'quarter'.\n\n");
505 if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
506 printf("match: Text contains the word 'eighth'.\n\n");
508 printf("match: Text doesn't contain the word 'eighth'.\n\n");
510 /** Match all occurrences of /wi../ **/
511 num_matches = matches(text, "m/(wi..)/g", &match_list);
512 printf("matches: m/(wi..)/g found %d matches...\n", num_matches);
514 for (i = 0; i < num_matches; i++)
515 printf("match: %s\n", SvPV(*av_fetch(match_list, i, FALSE),n_a));
518 /** Remove all vowels from text **/
519 num_matches = substitute(&text, "s/[aeiou]//gi");
521 printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
523 printf("Now text is: %s\n\n", SvPV(text,n_a));
526 /** Attempt a substitution **/
527 if (!substitute(&text, "s/Perl/C/")) {
528 printf("substitute: s/Perl/C...No substitution made.\n\n");
532 PL_perl_destruct_level = 1;
533 perl_destruct(my_perl);
537 which produces the output (again, long lines have been wrapped here)
539 match: Text contains the word 'quarter'.
541 match: Text doesn't contain the word 'eighth'.
543 matches: m/(wi..)/g found 2 matches...
547 substitute: s/[aeiou]//gi...139 substitutions made.
548 Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
549 Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt bck
550 qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd gvs th by
551 thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct mnt. Th by gvs
552 hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s hs prz. -RCHH
554 substitute: s/Perl/C...No substitution made.
556 =head2 Fiddling with the Perl stack from your C program
558 When trying to explain stacks, most computer science textbooks mumble
559 something about spring-loaded columns of cafeteria plates: the last
560 thing you pushed on the stack is the first thing you pop off. That'll
561 do for our purposes: your C program will push some arguments onto "the Perl
562 stack", shut its eyes while some magic happens, and then pop the
563 results--the return value of your Perl subroutine--off the stack.
565 First you'll need to know how to convert between C types and Perl
566 types, with newSViv() and sv_setnv() and newAV() and all their
567 friends. They're described in L<perlguts> and L<perlapi>.
569 Then you'll need to know how to manipulate the Perl stack. That's
570 described in L<perlcall>.
572 Once you've understood those, embedding Perl in C is easy.
574 Because C has no builtin function for integer exponentiation, let's
575 make Perl's ** operator available to it (this is less useful than it
576 sounds, because Perl implements ** with C's I<pow()> function). First
577 I'll create a stub exponentiation function in I<power.pl>:
584 Now I'll create a C program, I<power.c>, with a function
585 I<PerlPower()> that contains all the perlguts necessary to push the
586 two arguments into I<expo()> and to pop the return value out. Take a
592 static PerlInterpreter *my_perl;
595 PerlPower(int a, int b)
597 dSP; /* initialize stack pointer */
598 ENTER; /* everything created after here */
599 SAVETMPS; /* ...is a temporary variable. */
600 PUSHMARK(SP); /* remember the stack pointer */
601 XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */
602 XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */
603 PUTBACK; /* make local stack pointer global */
604 call_pv("expo", G_SCALAR); /* call the function */
605 SPAGAIN; /* refresh stack pointer */
606 /* pop the return value from stack */
607 printf ("%d to the %dth power is %d.\n", a, b, POPi);
609 FREETMPS; /* free that return value */
610 LEAVE; /* ...and the XPUSHed "mortal" args.*/
613 int main (int argc, char **argv, char **env)
615 char *my_argv[] = { "", "power.pl" };
617 my_perl = perl_alloc();
618 perl_construct( my_perl );
620 perl_parse(my_perl, NULL, 2, my_argv, (char **)NULL);
621 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
624 PerlPower(3, 4); /*** Compute 3 ** 4 ***/
626 perl_destruct(my_perl);
634 % cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
637 3 to the 4th power is 81.
639 =head2 Maintaining a persistent interpreter
641 When developing interactive and/or potentially long-running
642 applications, it's a good idea to maintain a persistent interpreter
643 rather than allocating and constructing a new interpreter multiple
644 times. The major reason is speed: since Perl will only be loaded into
647 However, you have to be more cautious with namespace and variable
648 scoping when using a persistent interpreter. In previous examples
649 we've been using global variables in the default package C<main>. We
650 knew exactly what code would be run, and assumed we could avoid
651 variable collisions and outrageous symbol table growth.
653 Let's say your application is a server that will occasionally run Perl
654 code from some arbitrary file. Your server has no way of knowing what
655 code it's going to run. Very dangerous.
657 If the file is pulled in by C<perl_parse()>, compiled into a newly
658 constructed interpreter, and subsequently cleaned out with
659 C<perl_destruct()> afterwards, you're shielded from most namespace
662 One way to avoid namespace collisions in this scenario is to translate
663 the filename into a guaranteed-unique package name, and then compile
664 the code into that package using L<perlfunc/eval>. In the example
665 below, each file will only be compiled once. Or, the application
666 might choose to clean out the symbol table associated with the file
667 after it's no longer needed. Using L<perlapi/call_argv>, We'll
668 call the subroutine C<Embed::Persistent::eval_file> which lives in the
669 file C<persistent.pl> and pass the filename and boolean cleanup/cache
672 Note that the process will continue to grow for each file that it
673 uses. In addition, there might be C<AUTOLOAD>ed subroutines and other
674 conditions that cause Perl's symbol table to grow. You might want to
675 add some logic that keeps track of the process size, or restarts
676 itself after a certain number of requests, to ensure that memory
677 consumption is minimized. You'll also want to scope your variables
678 with L<perlfunc/my> whenever possible.
681 package Embed::Persistent;
686 use Symbol qw(delete_package);
688 sub valid_package_name {
690 $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
691 # second pass only for words starting with a digit
692 $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;
694 # Dress it up as a real package name
696 return "Embed" . $string;
700 my($filename, $delete) = @_;
701 my $package = valid_package_name($filename);
702 my $mtime = -M $filename;
703 if(defined $Cache{$package}{mtime}
705 $Cache{$package}{mtime} <= $mtime)
707 # we have compiled this subroutine already,
708 # it has not been updated on disk, nothing left to do
709 print STDERR "already compiled $package->handler\n";
713 open FH, $filename or die "open '$filename' $!";
718 #wrap the code into a subroutine inside our unique package
719 my $eval = qq{package $package; sub handler { $sub; }};
721 # hide our variables within this block
722 my($filename,$mtime,$package,$sub);
727 #cache it unless we're cleaning out each time
728 $Cache{$package}{mtime} = $mtime unless $delete;
731 eval {$package->handler;};
734 delete_package($package) if $delete;
736 #take a look if you want
737 #print Devel::Symdump->rnew($package)->as_string, $/;
748 /* 1 = clean out filename's symbol table after each request, 0 = don't */
753 #define BUFFER_SIZE 1024
755 static PerlInterpreter *my_perl = NULL;
758 main(int argc, char **argv, char **env)
760 char *embedding[] = { "", "persistent.pl" };
761 char *args[] = { "", DO_CLEAN, NULL };
762 char filename[BUFFER_SIZE];
766 if((my_perl = perl_alloc()) == NULL) {
767 fprintf(stderr, "no memory!");
770 perl_construct(my_perl);
772 exitstatus = perl_parse(my_perl, NULL, 2, embedding, NULL);
773 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
775 exitstatus = perl_run(my_perl);
777 while(printf("Enter file name: ") &&
778 fgets(filename, BUFFER_SIZE, stdin)) {
780 filename[strlen(filename)-1] = '\0'; /* strip \n */
781 /* call the subroutine, passing it the filename as an argument */
783 call_argv("Embed::Persistent::eval_file",
784 G_DISCARD | G_EVAL, args);
788 fprintf(stderr, "eval error: %s\n", SvPV(ERRSV,n_a));
792 PL_perl_destruct_level = 0;
793 perl_destruct(my_perl);
800 % cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
802 Here's an example script file:
805 my $string = "hello";
809 print "foo says: @_\n";
815 Enter file name: test.pl
817 Enter file name: test.pl
818 already compiled Embed::test_2epl->handler
822 =head2 Execution of END blocks
824 Traditionally END blocks have been executed at the end of the perl_run.
825 This causes problems for applications that never call perl_run. Since
826 perl 5.7.2 you can specify C<PL_exit_flags |= PERL_EXIT_DESTRUCT_END>
827 to get the new behaviour. This also enables the running of END blocks if
828 the perl_prase fails and C<perl_destruct> will return the exit value.
830 =head2 Maintaining multiple interpreter instances
832 Some rare applications will need to create more than one interpreter
833 during a session. Such an application might sporadically decide to
834 release any resources associated with the interpreter.
836 The program must take care to ensure that this takes place I<before>
837 the next interpreter is constructed. By default, when perl is not
838 built with any special options, the global variable
839 C<PL_perl_destruct_level> is set to C<0>, since extra cleaning isn't
840 usually needed when a program only ever creates a single interpreter
841 in its entire lifetime.
843 Setting C<PL_perl_destruct_level> to C<1> makes everything squeaky clean:
845 PL_perl_destruct_level = 1;
849 /* reset global variables here with PL_perl_destruct_level = 1 */
850 perl_construct(my_perl);
852 /* clean and reset _everything_ during perl_destruct */
853 perl_destruct(my_perl);
856 /* let's go do it again! */
859 When I<perl_destruct()> is called, the interpreter's syntax parse tree
860 and symbol tables are cleaned up, and global variables are reset.
862 Now suppose we have more than one interpreter instance running at the
863 same time. This is feasible, but only if you used the Configure option
864 C<-Dusemultiplicity> or the options C<-Dusethreads -Duseithreads> when
865 building Perl. By default, enabling one of these Configure options
866 sets the per-interpreter global variable C<PL_perl_destruct_level> to
867 C<1>, so that thorough cleaning is automatic.
869 Using C<-Dusethreads -Duseithreads> rather than C<-Dusemultiplicity>
870 is more appropriate if you intend to run multiple interpreters
871 concurrently in different threads, because it enables support for
872 linking in the thread libraries of your system with the interpreter.
880 /* we're going to embed two interpreters */
881 /* we're going to embed two interpreters */
883 #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"
885 int main(int argc, char **argv, char **env)
888 *one_perl = perl_alloc(),
889 *two_perl = perl_alloc();
890 char *one_args[] = { "one_perl", SAY_HELLO };
891 char *two_args[] = { "two_perl", SAY_HELLO };
893 PERL_SET_CONTEXT(one_perl);
894 perl_construct(one_perl);
895 PERL_SET_CONTEXT(two_perl);
896 perl_construct(two_perl);
898 PERL_SET_CONTEXT(one_perl);
899 perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
900 PERL_SET_CONTEXT(two_perl);
901 perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
903 PERL_SET_CONTEXT(one_perl);
905 PERL_SET_CONTEXT(two_perl);
908 PERL_SET_CONTEXT(one_perl);
909 perl_destruct(one_perl);
910 PERL_SET_CONTEXT(two_perl);
911 perl_destruct(two_perl);
913 PERL_SET_CONTEXT(one_perl);
915 PERL_SET_CONTEXT(two_perl);
919 Note the calls to PERL_SET_CONTEXT(). These are necessary to initialize
920 the global state that tracks which interpreter is the "current" one on
921 the particular process or thread that may be running it. It should
922 always be used if you have more than one interpreter and are making
923 perl API calls on both interpreters in an interleaved fashion.
925 PERL_SET_CONTEXT(interp) should also be called whenever C<interp> is
926 used by a thread that did not create it (using either perl_alloc(), or
927 the more esoteric perl_clone()).
931 % cc -o multiplicity multiplicity.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
939 =head2 Using Perl modules, which themselves use C libraries, from your C program
941 If you've played with the examples above and tried to embed a script
942 that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++ library,
943 this probably happened:
946 Can't load module Socket, dynamic loading not available in this perl.
947 (You may need to build a new perl executable which either supports
948 dynamic loading or has the Socket module statically linked into it.)
953 Your interpreter doesn't know how to communicate with these extensions
954 on its own. A little glue will help. Up until now you've been
955 calling I<perl_parse()>, handing it NULL for the second argument:
957 perl_parse(my_perl, NULL, argc, my_argv, NULL);
959 That's where the glue code can be inserted to create the initial contact between
960 Perl and linked C/C++ routines. Let's take a look some pieces of I<perlmain.c>
961 to see how Perl does this:
963 static void xs_init (pTHX);
965 EXTERN_C void boot_DynaLoader (pTHX_ CV* cv);
966 EXTERN_C void boot_Socket (pTHX_ CV* cv);
972 char *file = __FILE__;
973 /* DynaLoader is a special case */
974 newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
975 newXS("Socket::bootstrap", boot_Socket, file);
978 Simply put: for each extension linked with your Perl executable
979 (determined during its initial configuration on your
980 computer or when adding a new extension),
981 a Perl subroutine is created to incorporate the extension's
982 routines. Normally, that subroutine is named
983 I<Module::bootstrap()> and is invoked when you say I<use Module>. In
984 turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl
985 counterpart for each of the extension's XSUBs. Don't worry about this
986 part; leave that to the I<xsubpp> and extension authors. If your
987 extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()>
988 for you on the fly. In fact, if you have a working DynaLoader then there
989 is rarely any need to link in any other extensions statically.
992 Once you have this code, slap it into the second argument of I<perl_parse()>:
995 perl_parse(my_perl, xs_init, argc, my_argv, NULL);
1000 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
1004 use SomeDynamicallyLoadedModule;
1006 print "Now I can use extensions!\n"'
1008 B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code.
1010 % perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c
1011 % cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts`
1012 % cc -c interp.c `perl -MExtUtils::Embed -e ccopts`
1013 % cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts`
1015 Consult L<perlxs>, L<perlguts>, and L<perlapi> for more details.
1017 =head1 Embedding Perl under Win32
1019 In general, all of the source code shown here should work unmodified under
1022 However, there are some caveats about the command-line examples shown.
1023 For starters, backticks won't work under the Win32 native command shell.
1024 The ExtUtils::Embed kit on CPAN ships with a script called
1025 B<genmake>, which generates a simple makefile to build a program from
1026 a single C source file. It can be used like this:
1028 C:\ExtUtils-Embed\eg> perl genmake interp.c
1029 C:\ExtUtils-Embed\eg> nmake
1030 C:\ExtUtils-Embed\eg> interp -e "print qq{I'm embedded in Win32!\n}"
1032 You may wish to use a more robust environment such as the Microsoft
1033 Developer Studio. In this case, run this to generate perlxsi.c:
1035 perl -MExtUtils::Embed -e xsinit
1037 Create a new project and Insert -> Files into Project: perlxsi.c,
1038 perl.lib, and your own source files, e.g. interp.c. Typically you'll
1039 find perl.lib in B<C:\perl\lib\CORE>, if not, you should see the
1040 B<CORE> directory relative to C<perl -V:archlib>. The studio will
1041 also need this path so it knows where to find Perl include files.
1042 This path can be added via the Tools -> Options -> Directories menu.
1043 Finally, select Build -> Build interp.exe and you're ready to go.
1047 If you completely hide the short forms forms of the Perl public API,
1048 add -DPERL_NO_SHORT_NAMES to the compilation flags. This means that
1049 for example instead of writing
1051 warn("%d bottles of beer on the wall", bottlecount);
1053 you will have to write the explicit full form
1055 Perl_warn(aTHX_ "%d bottles of beer on the wall", bottlecount);
1057 (See L<perlguts/Background and PERL_IMPLICIT_CONTEXT for the explanation
1058 of the C<aTHX_>.> ) Hiding the short forms is very useful for avoiding
1059 all sorts of nasty (C preprocessor or otherwise) conflicts with other
1060 software packages (Perl defines about 2400 APIs with these short names,
1061 take or leave few hundred, so there certainly is room for conflict.)
1065 You can sometimes I<write faster code> in C, but
1066 you can always I<write code faster> in Perl. Because you can use
1067 each from the other, combine them as you wish.
1072 Jon Orwant <F<orwant@tpj.com>> and Doug MacEachern
1073 <F<dougm@osf.org>>, with small contributions from Tim Bunce, Tom
1074 Christiansen, Guy Decoux, Hallvard Furuseth, Dov Grobgeld, and Ilya
1077 Doug MacEachern has an article on embedding in Volume 1, Issue 4 of
1078 The Perl Journal ( http://www.tpj.com/ ). Doug is also the developer of the
1079 most widely-used Perl embedding: the mod_perl system
1080 (perl.apache.org), which embeds Perl in the Apache web server.
1081 Oracle, Binary Evolution, ActiveState, and Ben Sugars's nsapi_perl
1082 have used this model for Oracle, Netscape and Internet Information
1083 Server Perl plugins.
1089 Copyright (C) 1995, 1996, 1997, 1998 Doug MacEachern and Jon Orwant. All
1092 Permission is granted to make and distribute verbatim copies of this
1093 documentation provided the copyright notice and this permission notice are
1094 preserved on all copies.
1096 Permission is granted to copy and distribute modified versions of this
1097 documentation under the conditions for verbatim copying, provided also
1098 that they are marked clearly as modified versions, that the authors'
1099 names and title are unchanged (though subtitles and additional
1100 authors' names may be added), and that the entire resulting derived
1101 work is distributed under the terms of a permission notice identical
1104 Permission is granted to copy and distribute translations of this
1105 documentation into another language, under the above conditions for