=head1 NAME
-perlembed - how to embed perl in your C or C++ app
+perlembed - how to embed perl in your C program
=head1 DESCRIPTION
-Look at perlmain.c, and do something like that.
+=head2 PREAMBLE
+
+Do you want to:
+
+=over 5
+
+=item B<Use C from Perl?>
+
+Read L<perlcall> and L<perlxs>.
+
+=item B<Use a UNIX program from Perl?>
+
+Read about back-quotes and about C<system> and C<exec> in L<perlfunc>.
+
+=item B<Use Perl from Perl?>
+
+Read about C<do> and C<eval> in L<perlfunc/do> and L<perlfunc/eval> and C<use>
+and C<require> in L<perlmod> and L<perlfunc/require>, L<perlfunc/use>.
+
+=item B<Use C from C?>
+
+Rethink your design.
+
+=item B<Use Perl from C?>
+
+Read on...
+
+=back
+
+=head2 ROADMAP
+
+L<Compiling your C program>
+
+There's one example in each of the six sections:
+
+L<Adding a Perl interpreter to your C program>
+
+L<Calling a Perl subroutine from your C program>
+
+L<Evaluating a Perl statement from your C program>
+
+L<Performing Perl pattern matches and substitutions from your C program>
+
+L<Fiddling with the Perl stack from your C program>
+
+L<Using Perl modules, which themselves use C libraries, from your C program>
+
+This documentation is UNIX specific.
+
+=head2 Compiling your C program
+
+Every C program that uses Perl must link in the I<perl library>.
+
+What's that, you ask? Perl is itself written in C; the perl library
+is the collection of compiled C programs that were used to create your
+perl executable (I</usr/bin/perl> or equivalent). (Corollary: you
+can't use Perl from your C program unless Perl has been compiled on
+your machine, or installed properly--that's why you shouldn't blithely
+copy Perl executables from machine to machine without also copying the
+I<lib> directory.)
+
+Your C program will--usually--allocate, "run", and deallocate a
+I<PerlInterpreter> object, which is defined in the perl library.
+
+If your copy of Perl is recent enough to contain this documentation
+(5.002 or later), then the perl library (and I<EXTERN.h> and
+I<perl.h>, which you'll also need) will
+reside in a directory resembling this:
+
+ /usr/local/lib/perl5/your_architecture_here/CORE
+
+or perhaps just
+
+ /usr/local/lib/perl5/CORE
+
+or maybe something like
+
+ /usr/opt/perl5/CORE
+
+Execute this statement for a hint about where to find CORE:
+
+ perl -MConfig -e 'print $Config{archlib}'
+
+Here's how you might compile the example in the next section,
+L<Adding a Perl interpreter to your C program>,
+on a DEC Alpha running the OSF operating system:
+
+ % cc -o interp interp.c -L/usr/local/lib/perl5/alpha-dec_osf/CORE
+ -I/usr/local/lib/perl5/alpha-dec_osf/CORE -lperl -lm
+
+You'll have to choose the appropriate compiler (I<cc>, I<gcc>, et al.) and
+library directory (I</usr/local/lib/...>) for your machine. If your
+compiler complains that certain functions are undefined, or that it
+can't locate I<-lperl>, then you need to change the path following the
+-L. If it complains that it can't find I<EXTERN.h> or I<perl.h>, you need
+to change the path following the -I.
+
+You may have to add extra libraries as well. Which ones?
+Perhaps those printed by
+
+ perl -MConfig -e 'print $Config{libs}'
+
+We strongly recommend you use the B<ExtUtils::Embed> module to determine
+all of this information for you:
+
+ % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
+
+
+If the B<ExtUtils::Embed> module is not part of your perl kit's
+distribution you can retrieve it from:
+http://www.perl.com/cgi-bin/cpan_mod?module=ExtUtils::Embed.
+
+
+=head2 Adding a Perl interpreter to your C program
+
+In a sense, perl (the C program) is a good example of embedding Perl
+(the language), so I'll demonstrate embedding with I<miniperlmain.c>,
+from the source distribution. Here's a bastardized, non-portable version of
+I<miniperlmain.c> containing the essentials of embedding:
+
+ #include <stdio.h>
+ #include <EXTERN.h> /* from the Perl distribution */
+ #include <perl.h> /* from the Perl distribution */
+
+ static PerlInterpreter *my_perl; /*** The Perl interpreter ***/
+
+ int main(int argc, char **argv, char **env)
+ {
+ my_perl = perl_alloc();
+ perl_construct(my_perl);
+ perl_parse(my_perl, NULL, argc, argv, (char **)NULL);
+ perl_run(my_perl);
+ perl_destruct(my_perl);
+ perl_free(my_perl);
+ }
+
+Note that we do not use the C<env> pointer here or in any of the
+following examples.
+Normally handed to C<perl_parse> as its final argument,
+we hand it a B<NULL> instead, in which case the current environment
+is used.
+
+Now compile this program (I'll call it I<interp.c>) into an executable:
+
+ % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
+
+After a successful compilation, you'll be able to use I<interp> just
+like perl itself:
+
+ % interp
+ print "Pretty Good Perl \n";
+ print "10890 - 9801 is ", 10890 - 9801;
+ <CTRL-D>
+ Pretty Good Perl
+ 10890 - 9801 is 1089
+
+or
+
+ % interp -e 'printf("%x", 3735928559)'
+ deadbeef
+
+You can also read and execute Perl statements from a file while in the
+midst of your C program, by placing the filename in I<argv[1]> before
+calling I<perl_run()>.
+
+=head2 Calling a Perl subroutine from your C program
+
+To call individual Perl subroutines, you'll need to remove the call to
+I<perl_run()> and replace it with a call to I<perl_call_argv()>.
+
+That's shown below, in a program I'll call I<showtime.c>.
+
+ #include <stdio.h>
+ #include <EXTERN.h>
+ #include <perl.h>
+
+ static PerlInterpreter *my_perl;
+
+ int main(int argc, char **argv, char **env)
+ {
+ my_perl = perl_alloc();
+ perl_construct(my_perl);
+
+ perl_parse(my_perl, NULL, argc, argv, NULL);
+
+ /*** This replaces perl_run() ***/
+ perl_call_argv("showtime", G_DISCARD | G_NOARGS, argv);
+ perl_destruct(my_perl);
+ perl_free(my_perl);
+ }
+
+where I<showtime> is a Perl subroutine that takes no arguments (that's the
+I<G_NOARGS>) and for which I'll ignore the return value (that's the
+I<G_DISCARD>). Those flags, and others, are discussed in L<perlcall>.
+
+I'll define the I<showtime> subroutine in a file called I<showtime.pl>:
+
+ print "I shan't be printed.";
+
+ sub showtime {
+ print time;
+ }
+
+Simple enough. Now compile and run:
+
+ % cc -o showtime showtime.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
+
+ % showtime showtime.pl
+ 818284590
+
+yielding the number of seconds that elapsed between January 1, 1970
+(the beginning of the UNIX epoch), and the moment I began writing this
+sentence.
+
+If you want to pass some arguments to the Perl subroutine, or
+you want to access the return value, you'll need to manipulate the
+Perl stack, demonstrated in the last section of this document:
+L<Fiddling with the Perl stack from your C program>
+
+=head2 Evaluating a Perl statement from your C program
+
+NOTE: This section, and the next, employ some very brittle techniques
+for evaluating strings of Perl code. Perl 5.002 contains some nifty
+features that enable A Better Way (such as with L<perlguts/perl_eval_sv>).
+Look for updates to this document soon.
+
+One way to evaluate a Perl string is to define a function (we'll call
+ours I<perl_eval()>) that wraps around Perl's L<perlfunc/eval>.
+
+Arguably, this is the only routine you'll ever need to execute
+snippets of Perl code from within your C program. Your string can be
+as long as you wish; it can contain multiple statements; it can
+use L<perlfunc/require> or L<perlfunc/do> to include external Perl
+files.
+
+Our I<perl_eval()> lets us evaluate individual Perl strings, and then
+extract variables for coercion into C types. The following program,
+I<string.c>, executes three Perl strings, extracting an C<int> from
+the first, a C<float> from the second, and a C<char *> from the third.
+
+ #include <stdio.h>
+ #include <EXTERN.h>
+ #include <perl.h>
+
+ static PerlInterpreter *my_perl;
+
+ int perl_eval(char *string)
+ {
+ char *argv[2];
+ argv[0] = string;
+ argv[1] = NULL;
+ perl_call_argv("_eval_", 0, argv);
+ }
+
+ main (int argc, char **argv, char **env)
+ {
+ char *embedding[] = { "", "-e", "sub _eval_ { eval $_[0] }" };
+ STRLEN length;
+
+ my_perl = perl_alloc();
+ perl_construct( my_perl );
+
+ perl_parse(my_perl, NULL, 3, embedding, NULL);
+
+ /** Treat $a as an integer **/
+ perl_eval("$a = 3; $a **= 2");
+ printf("a = %d\n", SvIV(perl_get_sv("a", FALSE)));
+
+ /** Treat $a as a float **/
+ perl_eval("$a = 3.14; $a **= 2");
+ printf("a = %f\n", SvNV(perl_get_sv("a", FALSE)));
+
+ /** Treat $a as a string **/
+ perl_eval("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a); ");
+ printf("a = %s\n", SvPV(perl_get_sv("a", FALSE), length));
+
+ perl_destruct(my_perl);
+ perl_free(my_perl);
+ }
+
+All of those strange functions with I<sv> in their names help convert Perl scalars to C types. They're described in L<perlguts>.
+
+If you compile and run I<string.c>, you'll see the results of using
+I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and
+I<SvPV()> to create a string:
+
+ a = 9
+ a = 9.859600
+ a = Just Another Perl Hacker
+
+
+=head2 Performing Perl pattern matches and substitutions from your C program
+
+Our I<perl_eval()> lets us evaluate strings of Perl code, so we can
+define some functions that use it to "specialize" in matches and
+substitutions: I<match()>, I<substitute()>, and I<matches()>.
+
+ char match(char *string, char *pattern);
+
+Given a string and a pattern (e.g., "m/clasp/" or "/\b\w*\b/", which in
+your program might be represented as C<"/\\b\\w*\\b/">),
+returns 1 if the string matches the pattern and 0 otherwise.
+
+
+ int substitute(char *string[], char *pattern);
+
+Given a pointer to a string and an "=~" operation (e.g., "s/bob/robert/g" or
+"tr[A-Z][a-z]"), modifies the string according to the operation,
+returning the number of substitutions made.
+
+ int matches(char *string, char *pattern, char **matches[]);
+
+Given a string, a pattern, and a pointer to an empty array of strings,
+evaluates C<$string =~ $pattern> in an array context, and fills in
+I<matches> with the array elements (allocating memory as it does so),
+returning the number of matches found.
+
+Here's a sample program, I<match.c>, that uses all three (long lines have
+been wrapped here):
+
+ #include <stdio.h>
+ #include <EXTERN.h>
+ #include <perl.h>
+ static PerlInterpreter *my_perl;
+ int perl_eval(char *string)
+ {
+ char *argv[2];
+ argv[0] = string;
+ argv[1] = NULL;
+ perl_call_argv("_eval_", 0, argv);
+ }
+ /** match(string, pattern)
+ **
+ ** Used for matches in a scalar context.
+ **
+ ** Returns 1 if the match was successful; 0 otherwise.
+ **/
+ char match(char *string, char *pattern)
+ {
+ char *command;
+ command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 37);
+ sprintf(command, "$string = '%s'; $return = $string =~ %s",
+ string, pattern);
+ perl_eval(command);
+ free(command);
+ return SvIV(perl_get_sv("return", FALSE));
+ }
+ /** substitute(string, pattern)
+ **
+ ** Used for =~ operations that modify their left-hand side (s/// and tr///)
+ **
+ ** Returns the number of successful matches, and
+ ** modifies the input string if there were any.
+ **/
+ int substitute(char *string[], char *pattern)
+ {
+ char *command;
+ STRLEN length;
+ command = malloc(sizeof(char) * strlen(*string) + strlen(pattern) + 35);
+ sprintf(command, "$string = '%s'; $ret = ($string =~ %s)",
+ *string, pattern);
+ perl_eval(command);
+ free(command);
+ *string = SvPV(perl_get_sv("string", FALSE), length);
+ return SvIV(perl_get_sv("ret", FALSE));
+ }
+ /** matches(string, pattern, matches)
+ **
+ ** Used for matches in an array context.
+ **
+ ** Returns the number of matches,
+ ** and fills in **matches with the matching substrings (allocates memory!)
+ **/
+ int matches(char *string, char *pattern, char **match_list[])
+ {
+ char *command;
+ SV *current_match;
+ AV *array;
+ I32 num_matches;
+ STRLEN length;
+ int i;
+ command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 38);
+ sprintf(command, "$string = '%s'; @array = ($string =~ %s)",
+ string, pattern);
+ perl_eval(command);
+ free(command);
+ array = perl_get_av("array", FALSE);
+ num_matches = av_len(array) + 1; /** assume $[ is 0 **/
+ *match_list = (char **) malloc(sizeof(char *) * num_matches);
+ for (i = 0; i <= num_matches; i++) {
+ current_match = av_shift(array);
+ (*match_list)[i] = SvPV(current_match, length);
+ }
+ return num_matches;
+ }
+ main (int argc, char **argv, char **env)
+ {
+ char *embedding[] = { "", "-e", "sub _eval_ { eval $_[0] }" };
+ char *text, **match_list;
+ int num_matches, i;
+ int j;
+ my_perl = perl_alloc();
+ perl_construct( my_perl );
+ perl_parse(my_perl, NULL, 3, embedding, NULL);
+ text = (char *) malloc(sizeof(char) * 486); /** A long string follows! **/
+ sprintf(text, "%s", "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");
+ if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
+ printf("match: Text contains the word 'quarter'.\n\n");
+ else
+ printf("match: Text doesn't contain the word 'quarter'.\n\n");
+ if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
+ printf("match: Text contains the word 'eighth'.\n\n");
+ else
+ printf("match: Text doesn't contain the word 'eighth'.\n\n");
+ /** Match all occurrences of /wi../ **/
+ num_matches = matches(text, "m/(wi..)/g", &match_list);
+ printf("matches: m/(wi..)/g found %d matches...\n", num_matches);
+ for (i = 0; i < num_matches; i++)
+ printf("match: %s\n", match_list[i]);
+ printf("\n");
+ for (i = 0; i < num_matches; i++) {
+ free(match_list[i]);
+ }
+ free(match_list);
+ /** Remove all vowels from text **/
+ num_matches = substitute(&text, "s/[aeiou]//gi");
+ if (num_matches) {
+ printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
+ num_matches);
+ printf("Now text is: %s\n\n", text);
+ }
+ /** Attempt a substitution **/
+ if (!substitute(&text, "s/Perl/C/")) {
+ printf("substitute: s/Perl/C...No substitution made.\n\n");
+ }
+ free(text);
+ perl_destruct(my_perl);
+ perl_free(my_perl);
+ }
+
+which produces the output (again, long lines have been wrapped here)
+
+ perl_match: Text contains the word 'quarter'.
+
+ perl_match: Text doesn't contain the word 'eighth'.
+
+ perl_matches: m/(wi..)/g found 2 matches...
+ match: will
+ match: with
+
+ perl_substitute: s/[aeiou]//gi...139 substitutions made.
+ Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
+ Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt bck
+ qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd gvs th by
+ thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct mnt. Th by gvs
+ hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s hs prz. -RCHH
+
+ perl_substitute: s/Perl/C...No substitution made.
+
+=head2 Fiddling with the Perl stack from your C program
+
+When trying to explain stacks, most computer science textbooks mumble
+something about spring-loaded columns of cafeteria plates: the last
+thing you pushed on the stack is the first thing you pop off. That'll
+do for our purposes: your C program will push some arguments onto "the Perl
+stack", shut its eyes while some magic happens, and then pop the
+results--the return value of your Perl subroutine--off the stack.
+
+First you'll need to know how to convert between C types and Perl
+types, with newSViv() and sv_setnv() and newAV() and all their
+friends. They're described in L<perlguts>.
+
+Then you'll need to know how to manipulate the Perl stack. That's
+described in L<perlcall>.
+
+Once you've understood those, embedding Perl in C is easy.
+
+Because C has no built-in function for integer exponentiation, let's
+make Perl's ** operator available to it (this is less useful than it
+sounds, because Perl implements ** with C's I<pow()> function). First
+I'll create a stub exponentiation function in I<power.pl>:
+
+ sub expo {
+ my ($a, $b) = @_;
+ return $a ** $b;
+ }
+
+Now I'll create a C program, I<power.c>, with a function
+I<PerlPower()> that contains all the perlguts necessary to push the
+two arguments into I<expo()> and to pop the return value out. Take a
+deep breath...
+
+ #include <stdio.h>
+ #include <EXTERN.h>
+ #include <perl.h>
+
+ static PerlInterpreter *my_perl;
+
+ static void
+ PerlPower(int a, int b)
+ {
+ dSP; /* initialize stack pointer */
+ ENTER; /* everything created after here */
+ SAVETMPS; /* ...is a temporary variable. */
+ PUSHMARK(sp); /* remember the stack pointer */
+ XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */
+ XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */
+ PUTBACK; /* make local stack pointer global */
+ perl_call_pv("expo", G_SCALAR); /* call the function */
+ SPAGAIN; /* refresh stack pointer */
+ /* pop the return value from stack */
+ printf ("%d to the %dth power is %d.\n", a, b, POPi);
+ PUTBACK;
+ FREETMPS; /* free that return value */
+ LEAVE; /* ...and the XPUSHed "mortal" args.*/
+ }
+
+ int main (int argc, char **argv, char **env)
+ {
+ char *my_argv[2];
+
+ my_perl = perl_alloc();
+ perl_construct( my_perl );
+
+ my_argv[1] = (char *) malloc(10);
+ sprintf(my_argv[1], "power.pl");
+
+ perl_parse(my_perl, NULL, argc, my_argv, NULL);
+
+ PerlPower(3, 4); /*** Compute 3 ** 4 ***/
+
+ perl_destruct(my_perl);
+ perl_free(my_perl);
+ }
+
+
+
+Compile and run:
+
+ % cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
+
+ % power
+ 3 to the 4th power is 81.
+
+=head2 Using Perl modules, which themselves use C libraries, from your C program
+
+If you've played with the examples above and tried to embed a script
+that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++ library,
+this probably happened:
+
+
+ Can't load module Socket, dynamic loading not available in this perl.
+ (You may need to build a new perl executable which either supports
+ dynamic loading or has the Socket module statically linked into it.)
+
+
+What's wrong?
+
+Your interpreter doesn't know how to communicate with these extensions
+on its own. A little glue will help. Up until now you've been
+calling I<perl_parse()>, handing it NULL for the second argument:
+
+ perl_parse(my_perl, NULL, argc, my_argv, NULL);
+
+That's where the glue code can be inserted to create the initial contact between
+Perl and linked C/C++ routines. Let's take a look some pieces of I<perlmain.c>
+to see how Perl does this:
+
+
+ #ifdef __cplusplus
+ # define EXTERN_C extern "C"
+ #else
+ # define EXTERN_C extern
+ #endif
+
+ static void xs_init _((void));
+
+ EXTERN_C void boot_DynaLoader _((CV* cv));
+ EXTERN_C void boot_Socket _((CV* cv));
+
+
+ EXTERN_C void
+ xs_init()
+ {
+ char *file = __FILE__;
+ /* DynaLoader is a special case */
+ newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
+ newXS("Socket::bootstrap", boot_Socket, file);
+ }
+
+Simply put: for each extension linked with your Perl executable
+(determined during its initial configuration on your
+computer or when adding a new extension),
+a Perl subroutine is created to incorporate the extension's
+routines. Normally, that subroutine is named
+I<Module::bootstrap()> and is invoked when you say I<use Module>. In
+turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl
+counterpart for each of the extension's XSUBs. Don't worry about this
+part; leave that to the I<xsubpp> and extension authors. If your
+extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()>
+for you on the fly. In fact, if you have a working DynaLoader then there
+is rarely any need to link in any other extensions statically.
+
+
+Once you have this code, slap it into the second argument of I<perl_parse()>:
+
+
+ perl_parse(my_perl, xs_init, argc, my_argv, NULL);
+
+
+Then compile:
+
+ % cc -o interp interp.c `perl -MExtUtils::Embed -e ldopts`
+
+ % interp
+ use Socket;
+ use SomeDynamicallyLoadedModule;
+
+ print "Now I can use extensions!\n"'
+
+B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code.
+
+ % perl -MExtUtils::Embed -e xsinit -o perlxsi.c
+ % cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts`
+ % cc -c interp.c `perl -MExtUtils::Embed -e ccopts`
+ % cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts`
+
+Consult L<perlxs> and L<perlguts> for more details.
+
+
+=head1 MORAL
+
+You can sometimes I<write faster code> in C, but
+you can always I<write code faster> in Perl. Because you can use
+each from the other, combine them as you wish.
+
+
+=head1 AUTHOR
+
+Jon Orwant F<E<lt>orwant@media.mit.eduE<gt>>,
+co-authored by Doug MacEachern F<E<lt>dougm@osf.orgE<gt>>,
+with contributions from
+Tim Bunce, Tom Christiansen, Dov Grobgeld, and Ilya
+Zakharevich.
+
+June 17, 1996
+
+Some of this material is excerpted from my book: I<Perl 5 Interactive>,
+Waite Group Press, 1996 (ISBN 1-57169-064-6) and appears
+courtesy of Waite Group Press.
projects / p5sagit/p5-mst-13.2.git / blobdiff