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 nine 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 L<Embedding Perl under Win32>
60 =head2 Compiling your C program
62 If you have trouble compiling the scripts in this documentation,
63 you're not alone. The cardinal rule: COMPILE THE PROGRAMS IN EXACTLY
64 THE SAME WAY THAT YOUR PERL WAS COMPILED. (Sorry for yelling.)
66 Also, every C program that uses Perl must link in the I<perl library>.
67 What's that, you ask? Perl is itself written in C; the perl library
68 is the collection of compiled C programs that were used to create your
69 perl executable (I</usr/bin/perl> or equivalent). (Corollary: you
70 can't use Perl from your C program unless Perl has been compiled on
71 your machine, or installed properly--that's why you shouldn't blithely
72 copy Perl executables from machine to machine without also copying the
75 When you use Perl from C, your C program will--usually--allocate,
76 "run", and deallocate a I<PerlInterpreter> object, which is defined by
79 If your copy of Perl is recent enough to contain this documentation
80 (version 5.002 or later), then the perl library (and I<EXTERN.h> and
81 I<perl.h>, which you'll also need) will reside in a directory
84 /usr/local/lib/perl5/your_architecture_here/CORE
88 /usr/local/lib/perl5/CORE
90 or maybe something like
94 Execute this statement for a hint about where to find CORE:
96 perl -MConfig -e 'print $Config{archlib}'
98 Here's how you'd compile the example in the next section,
99 L<Adding a Perl interpreter to your C program>, on my Linux box:
101 % gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include
102 -I/usr/local/lib/perl5/i586-linux/5.003/CORE
103 -L/usr/local/lib/perl5/i586-linux/5.003/CORE
104 -o interp interp.c -lperl -lm
106 (That's all one line.) On my DEC Alpha running 5.003_05, the incantation
109 % cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include
110 -I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE
111 -L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib
112 -D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm
114 How can you figure out what to add? Assuming your Perl is post-5.001,
115 execute a C<perl -V> command and pay special attention to the "cc" and
116 "ccflags" information.
118 You'll have to choose the appropriate compiler (I<cc>, I<gcc>, et al.) for
119 your machine: C<perl -MConfig -e 'print $Config{cc}'> will tell you what
122 You'll also have to choose the appropriate library directory
123 (I</usr/local/lib/...>) for your machine. If your compiler complains
124 that certain functions are undefined, or that it can't locate
125 I<-lperl>, then you need to change the path following the C<-L>. If it
126 complains that it can't find I<EXTERN.h> and I<perl.h>, you need to
127 change the path following the C<-I>.
129 You may have to add extra libraries as well. Which ones?
130 Perhaps those printed by
132 perl -MConfig -e 'print $Config{libs}'
134 Provided your perl binary was properly configured and installed the
135 B<ExtUtils::Embed> module will determine all of this information for
138 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
140 If the B<ExtUtils::Embed> module isn't part of your Perl distribution,
141 you can retrieve it from
142 http://www.perl.com/perl/CPAN/modules/by-module/ExtUtils::Embed. (If
143 this documentation came from your Perl distribution, then you're
144 running 5.004 or better and you already have it.)
146 The B<ExtUtils::Embed> kit on CPAN also contains all source code for
147 the examples in this document, tests, additional examples and other
148 information you may find useful.
150 =head2 Adding a Perl interpreter to your C program
152 In a sense, perl (the C program) is a good example of embedding Perl
153 (the language), so I'll demonstrate embedding with I<miniperlmain.c>,
154 from the source distribution. Here's a bastardized, nonportable
155 version of I<miniperlmain.c> containing the essentials of embedding:
157 #include <EXTERN.h> /* from the Perl distribution */
158 #include <perl.h> /* from the Perl distribution */
160 static PerlInterpreter *my_perl; /*** The Perl interpreter ***/
162 int main(int argc, char **argv, char **env)
164 my_perl = perl_alloc();
165 perl_construct(my_perl);
166 perl_parse(my_perl, NULL, argc, argv, (char **)NULL);
168 perl_destruct(my_perl);
172 Notice that we don't use the C<env> pointer. Normally handed to
173 C<perl_parse> as its final argument, C<env> here is replaced by
174 C<NULL>, which means that the current environment will be used.
176 Now compile this program (I'll call it I<interp.c>) into an executable:
178 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
180 After a successful compilation, you'll be able to use I<interp> just
184 print "Pretty Good Perl \n";
185 print "10890 - 9801 is ", 10890 - 9801;
192 % interp -e 'printf("%x", 3735928559)'
195 You can also read and execute Perl statements from a file while in the
196 midst of your C program, by placing the filename in I<argv[1]> before
197 calling I<perl_run()>.
199 =head2 Calling a Perl subroutine from your C program
201 To call individual Perl subroutines, you can use any of the B<perl_call_*>
202 functions documented in the L<perlcall> manpage.
203 In this example we'll use I<perl_call_argv>.
205 That's shown below, in a program I'll call I<showtime.c>.
210 static PerlInterpreter *my_perl;
212 int main(int argc, char **argv, char **env)
214 char *args[] = { NULL };
215 my_perl = perl_alloc();
216 perl_construct(my_perl);
218 perl_parse(my_perl, NULL, argc, argv, NULL);
220 /*** skipping perl_run() ***/
222 perl_call_argv("showtime", G_DISCARD | G_NOARGS, args);
224 perl_destruct(my_perl);
228 where I<showtime> is a Perl subroutine that takes no arguments (that's the
229 I<G_NOARGS>) and for which I'll ignore the return value (that's the
230 I<G_DISCARD>). Those flags, and others, are discussed in L<perlcall>.
232 I'll define the I<showtime> subroutine in a file called I<showtime.pl>:
234 print "I shan't be printed.";
240 Simple enough. Now compile and run:
242 % cc -o showtime showtime.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
244 % showtime showtime.pl
247 yielding the number of seconds that elapsed between January 1, 1970
248 (the beginning of the Unix epoch), and the moment I began writing this
251 In this particular case we don't have to call I<perl_run>, but in
252 general it's considered good practice to ensure proper initialization
253 of library code, including execution of all object C<DESTROY> methods
254 and package C<END {}> blocks.
256 If you want to pass arguments to the Perl subroutine, you can add
257 strings to the C<NULL>-terminated C<args> list passed to
258 I<perl_call_argv>. For other data types, or to examine return values,
259 you'll need to manipulate the Perl stack. That's demonstrated in the
260 last section of this document: L<Fiddling with the Perl stack from
263 =head2 Evaluating a Perl statement from your C program
265 Perl provides two API functions to evaluate pieces of Perl code.
266 These are L<perlguts/perl_eval_sv()> and L<perlguts/perl_eval_pv()>.
268 Arguably, these are the only routines you'll ever need to execute
269 snippets of Perl code from within your C program. Your code can be
270 as long as you wish; it can contain multiple statements; it can employ
271 L<perlfunc/use>, L<perlfunc/require> and L<perlfunc/do> to include
274 I<perl_eval_pv()> lets us evaluate individual Perl strings, and then
275 extract variables for coercion into C types. The following program,
276 I<string.c>, executes three Perl strings, extracting an C<int> from
277 the first, a C<float> from the second, and a C<char *> from the third.
282 static PerlInterpreter *my_perl;
284 main (int argc, char **argv, char **env)
286 char *embedding[] = { "", "-e", "0" };
288 my_perl = perl_alloc();
289 perl_construct( my_perl );
291 perl_parse(my_perl, NULL, 3, embedding, NULL);
294 /** Treat $a as an integer **/
295 perl_eval_pv("$a = 3; $a **= 2", TRUE);
296 printf("a = %d\n", SvIV(perl_get_sv("a", FALSE)));
298 /** Treat $a as a float **/
299 perl_eval_pv("$a = 3.14; $a **= 2", TRUE);
300 printf("a = %f\n", SvNV(perl_get_sv("a", FALSE)));
302 /** Treat $a as a string **/
303 perl_eval_pv("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
304 printf("a = %s\n", SvPV(perl_get_sv("a", FALSE), na));
306 perl_destruct(my_perl);
310 All of those strange functions with I<sv> in their names help convert Perl scalars to C types. They're described in L<perlguts>.
312 If you compile and run I<string.c>, you'll see the results of using
313 I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and
314 I<SvPV()> to create a string:
318 a = Just Another Perl Hacker
320 In the example above, we've created a global variable to temporarily
321 store the computed value of our eval'd expression. It is also
322 possible and in most cases a better strategy to fetch the return value
323 from L<perl_eval_pv> instead. Example:
326 SV *val = perl_eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
327 printf("%s\n", SvPV(val,na));
330 This way, we avoid namespace pollution by not creating global
331 variables and we've simplified our code as well.
333 =head2 Performing Perl pattern matches and substitutions from your C program
335 The I<perl_eval_pv()> function lets us evaluate strings of Perl code, so we can
336 define some functions that use it to "specialize" in matches and
337 substitutions: I<match()>, I<substitute()>, and I<matches()>.
339 char match(char *string, char *pattern);
341 Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which
342 in your C program might appear as "/\\b\\w*\\b/"), match()
343 returns 1 if the string matches the pattern and 0 otherwise.
345 int substitute(char *string[], char *pattern);
347 Given a pointer to a string and an C<=~> operation (e.g.,
348 C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string
349 according to the operation, returning the number of substitutions
352 int matches(char *string, char *pattern, char **matches[]);
354 Given a string, a pattern, and a pointer to an empty array of strings,
355 matches() evaluates C<$string =~ $pattern> in an array context, and
356 fills in I<matches> with the array elements (allocating memory as it
357 does so), returning the number of matches found.
359 Here's a sample program, I<match.c>, that uses all three (long lines have
365 static PerlInterpreter *my_perl;
367 /** match(string, pattern)
369 ** Used for matches in a scalar context.
371 ** Returns 1 if the match was successful; 0 otherwise.
373 char match(char *string, char *pattern)
376 command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 37);
377 sprintf(command, "$string = '%s'; $return = $string =~ %s",
379 perl_eval_pv(command, TRUE);
381 return SvIV(perl_get_sv("return", FALSE));
383 /** substitute(string, pattern)
385 ** Used for =~ operations that modify their left-hand side (s/// and tr///)
387 ** Returns the number of successful matches, and
388 ** modifies the input string if there were any.
390 int substitute(char *string[], char *pattern)
394 command = malloc(sizeof(char) * strlen(*string) + strlen(pattern) + 35);
395 sprintf(command, "$string = '%s'; $ret = ($string =~ %s)",
397 perl_eval_pv(command, TRUE);
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)",
420 perl_eval_pv(command, TRUE);
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 builtin 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;
758 % cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
760 Here's a example script file:
763 my $string = "hello";
767 print "foo says: @_\n";
773 Enter file name: test.pl
775 Enter file name: test.pl
776 already compiled Embed::test_2epl->handler
780 =head2 Maintaining multiple interpreter instances
782 Some rare applications will need to create more than one interpreter
783 during a session. Such an application might sporadically decide to
784 release any resources associated with the interpreter.
786 The program must take care to ensure that this takes place I<before>
787 the next interpreter is constructed. By default, the global variable
788 C<perl_destruct_level> is set to C<0>, since extra cleaning isn't
789 needed when a program has only one interpreter.
791 Setting C<perl_destruct_level> to C<1> makes everything squeaky clean:
793 perl_destruct_level = 1;
797 /* reset global variables here with perl_destruct_level = 1 */
798 perl_construct(my_perl);
800 /* clean and reset _everything_ during perl_destruct */
801 perl_destruct(my_perl);
804 /* let's go do it again! */
807 When I<perl_destruct()> is called, the interpreter's syntax parse tree
808 and symbol tables are cleaned up, and global variables are reset.
810 Now suppose we have more than one interpreter instance running at the
811 same time. This is feasible, but only if you used the
812 C<-DMULTIPLICITY> flag when building Perl. By default, that sets
813 C<perl_destruct_level> to C<1>.
821 /* we're going to embed two interpreters */
822 /* we're going to embed two interpreters */
824 #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"
826 int main(int argc, char **argv, char **env)
829 *one_perl = perl_alloc(),
830 *two_perl = perl_alloc();
831 char *one_args[] = { "one_perl", SAY_HELLO };
832 char *two_args[] = { "two_perl", SAY_HELLO };
834 perl_construct(one_perl);
835 perl_construct(two_perl);
837 perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
838 perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
843 perl_destruct(one_perl);
844 perl_destruct(two_perl);
853 % cc -o multiplicity multiplicity.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
861 =head2 Using Perl modules, which themselves use C libraries, from your C program
863 If you've played with the examples above and tried to embed a script
864 that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++ library,
865 this probably happened:
868 Can't load module Socket, dynamic loading not available in this perl.
869 (You may need to build a new perl executable which either supports
870 dynamic loading or has the Socket module statically linked into it.)
875 Your interpreter doesn't know how to communicate with these extensions
876 on its own. A little glue will help. Up until now you've been
877 calling I<perl_parse()>, handing it NULL for the second argument:
879 perl_parse(my_perl, NULL, argc, my_argv, NULL);
881 That's where the glue code can be inserted to create the initial contact between
882 Perl and linked C/C++ routines. Let's take a look some pieces of I<perlmain.c>
883 to see how Perl does this:
887 # define EXTERN_C extern "C"
889 # define EXTERN_C extern
892 static void xs_init _((void));
894 EXTERN_C void boot_DynaLoader _((CV* cv));
895 EXTERN_C void boot_Socket _((CV* cv));
901 char *file = __FILE__;
902 /* DynaLoader is a special case */
903 newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
904 newXS("Socket::bootstrap", boot_Socket, file);
907 Simply put: for each extension linked with your Perl executable
908 (determined during its initial configuration on your
909 computer or when adding a new extension),
910 a Perl subroutine is created to incorporate the extension's
911 routines. Normally, that subroutine is named
912 I<Module::bootstrap()> and is invoked when you say I<use Module>. In
913 turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl
914 counterpart for each of the extension's XSUBs. Don't worry about this
915 part; leave that to the I<xsubpp> and extension authors. If your
916 extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()>
917 for you on the fly. In fact, if you have a working DynaLoader then there
918 is rarely any need to link in any other extensions statically.
921 Once you have this code, slap it into the second argument of I<perl_parse()>:
924 perl_parse(my_perl, xs_init, argc, my_argv, NULL);
929 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
933 use SomeDynamicallyLoadedModule;
935 print "Now I can use extensions!\n"'
937 B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code.
939 % perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c
940 % cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts`
941 % cc -c interp.c `perl -MExtUtils::Embed -e ccopts`
942 % cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts`
944 Consult L<perlxs> and L<perlguts> for more details.
946 =head1 Embedding Perl under Win32
948 At the time of this writing, there are two versions of Perl which run
949 under Win32. Interfacing to Activeware's Perl library is quite
950 different from the examples in this documentation, as significant
951 changes were made to the internal Perl API. However, it is possible
952 to embed Activeware's Perl runtime, see the Perl for Win32 FAQ:
953 http://www.perl.com/perl/faq/win32/Perl_for_Win32_FAQ.html
955 With the "official" Perl version 5.004 or higher, all the examples
956 within this documentation will compile and run untouched, although,
957 the build process is slightly different between Unix and Win32.
959 For starters, backticks don't work under the Win32 native command shell!
960 The ExtUtils::Embed kit on CPAN ships with a script called
961 B<genmake>, which generates a simple makefile to build a program from
962 a single C source file. It can be used like so:
964 C:\ExtUtils-Embed\eg> perl genmake interp.c
965 C:\ExtUtils-Embed\eg> nmake
966 C:\ExtUtils-Embed\eg> interp -e "print qq{I'm embedded in Win32!\n}"
968 You may wish to use a more robust environment such as the MS Developer
969 stdio. In this case, to generate perlxsi.c run:
971 perl -MExtUtils::Embed -e xsinit
973 Create a new project, Insert -> Files into Project: perlxsi.c, perl.lib,
974 and your own source files, e.g. interp.c. Typically you'll find
975 perl.lib in B<C:\perl\lib\CORE>, if not, you should see the B<CORE>
976 directory relative to C<perl -V:archlib>.
977 The studio will also need this path so it knows where to find Perl
978 include files. This path can be added via the Tools -> Options ->
979 Directories menu. Finnally, select Build -> Build interp.exe and
984 You can sometimes I<write faster code> in C, but
985 you can always I<write code faster> in Perl. Because you can use
986 each from the other, combine them as you wish.
991 Jon Orwant and <F<orwant@tpj.com>> and Doug MacEachern <F<dougm@osf.org>>,
992 with small contributions from Tim Bunce, Tom Christiansen, Hallvard Furuseth,
993 Dov Grobgeld, and Ilya Zakharevich.
995 Check out Doug's article on embedding in Volume 1, Issue 4 of The Perl
996 Journal. Info about TPJ is available from http://tpj.com.
1000 Some of this material is excerpted from Jon Orwant's book: I<Perl 5
1001 Interactive>, Waite Group Press, 1996 (ISBN 1-57169-064-6) and appears
1002 courtesy of Waite Group Press.
1006 Copyright (C) 1995, 1996, 1997 Doug MacEachern and Jon Orwant. All
1009 Although destined for release with the standard Perl distribution,
1010 this document is not public domain, nor is any of Perl and its
1011 documentation. Permission is granted to freely distribute verbatim
1012 copies of this document provided that no modifications outside of
1013 formatting be made, and that this notice remain intact. You are
1014 permitted and encouraged to use its code and derivatives thereof in
1015 your own source code for fun or for profit as you see fit.