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MAN page from Old RedHat 5.X perl-5.004-4.i386.rpm

PERLEMBED

Section: Perl Programmers Reference Guide (1)
Updated: perl 5.004, patch 04
Index 

NAME

perlembed - how to embed perl in your C program 

DESCRIPTION

 

PREAMBLE

Do you want to:
Use C from Perl?
Read the perlcall manpage and the perlxs manpage.
Use a Unix program from Perl?
Read about back-quotes and about system and exec in the perlfunc manpage.
Use Perl from Perl?
Read about the do entry in the perlfunc manpage and the eval entry in the perlfunc manpage and the require entry in the perlfunc manpageand the use entry in the perlfunc manpage.
Use C from C?
Rethink your design.
Use Perl from C?
Read on...
 

ROADMAP

the section on Compiling your C program

There's one example in each of the nine sections:

the section on Adding a Perl interpreter to your C program

the section on Calling a Perl subroutine from your C program

the section on Evaluating a Perl statement from your C program

the section on Performing Perl pattern matches and substitutions from your C program

the section on Fiddling with the Perl stack from your C program

the section on Maintaining a persistent interpreter

the section on Maintaining multiple interpreter instances

the section on Using Perl modules, which themselves use C libraries, from your C program

the section on Embedding Perl under Win32 

Compiling your C program

If you have trouble compiling the scripts in this documentation,you're not alone. The cardinal rule: COMPILE THE PROGRAMS IN EXACTLYTHE SAME WAY THAT YOUR PERL WAS COMPILED. (Sorry for yelling.)

Also, every C program that uses Perl must link in the perl library.What's that, you ask? Perl is itself written in C; the perl libraryis the collection of compiled C programs that were used to create yourperl executable (/usr/bin/perl or equivalent). (Corollary: youcan't use Perl from your C program unless Perl has been compiled onyour machine, or installed properly---that's why you shouldn't blithelycopy Perl executables from machine to machine without also copying thelib directory.)

When you use Perl from C, your C program will---usually---allocate,``run'', and deallocate a PerlInterpreter object, which is defined bythe perl library.

If your copy of Perl is recent enough to contain this documentation(version 5.002 or later), then the perl library (and EXTERN.h andperl.h, which you'll also need) will reside in a directorythat looks like 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'd compile the example in the next section,the section on Adding a Perl interpreter to your C program, on my Linux box:

    % gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include    -I/usr/local/lib/perl5/i586-linux/5.003/CORE    -L/usr/local/lib/perl5/i586-linux/5.003/CORE    -o interp interp.c -lperl -lm
(That's all one line.) On my DEC Alpha running 5.003_05, the incantationis a bit different:

    % cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include    -I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE    -L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib    -D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm
How can you figure out what to add? Assuming your Perl is post-5.001,execute a perl -V command and pay special attention to the ``cc'' and``ccflags'' information.

You'll have to choose the appropriate compiler (cc, gcc, et al.) foryour machine: perl -MConfig -e 'print $Config{cc}' will tell you whatto use.

You'll also have to choose the appropriate library directory(/usr/local/lib/...) for your machine. If your compiler complainsthat certain functions are undefined, or that it can't locate-lperl, then you need to change the path following the -L. If itcomplains that it can't find EXTERN.h and perl.h, you need tochange 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}'
Provided your perl binary was properly configured and installed theExtUtils::Embed module will determine all of this information foryou:

   % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
If the ExtUtils::Embed module isn't part of your Perl distribution,you can retrieve it fromhttp://www.perl.com/perl/CPAN/modules/by-module/ExtUtils::Embed. (Ifthis documentation came from your Perl distribution, then you'rerunning 5.004 or better and you already have it.)

The ExtUtils::Embed kit on CPAN also contains all source code forthe examples in this document, tests, additional examples and otherinformation you may find useful. 

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 miniperlmain.c,from the source distribution. Here's a bastardized, nonportableversion of miniperlmain.c containing the essentials of embedding:

    #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);    }
Notice that we don't use the env pointer. Normally handed toperl_parse as its final argument, env here is replaced byNULL, which means that the current environment will be used.

Now compile this program (I'll call it 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 interp justlike 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 themidst of your C program, by placing the filename in argv[1] beforecalling perl_run(). 

Calling a Perl subroutine from your C program

To call individual Perl subroutines, you can use any of the perl_call_*functions documented in the the perlcall manpage manpage.In this example we'll use perl_call_argv.

That's shown below, in a program I'll call showtime.c.

    #include <EXTERN.h>    #include <perl.h>
    static PerlInterpreter *my_perl;
    int main(int argc, char **argv, char **env)    {        char *args[] = { NULL };        my_perl = perl_alloc();        perl_construct(my_perl);
        perl_parse(my_perl, NULL, argc, argv, NULL);
        /*** skipping perl_run() ***/
        perl_call_argv("showtime", G_DISCARD | G_NOARGS, args);
        perl_destruct(my_perl);        perl_free(my_perl);    }
where showtime is a Perl subroutine that takes no arguments (that's theG_NOARGS) and for which I'll ignore the return value (that's theG_DISCARD). Those flags, and others, are discussed in the perlcall manpage.

I'll define the showtime subroutine in a file called 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 thissentence.

In this particular case we don't have to call perl_run, but ingeneral it's considered good practice to ensure proper initializationof library code, including execution of all object DESTROY methodsand package END {} blocks.

If you want to pass arguments to the Perl subroutine, you can addstrings to the NULL-terminated args list passed toperl_call_argv. For other data types, or to examine return values,you'll need to manipulate the Perl stack. That's demonstrated in thelast section of this document: the section on Fiddling with the Perl stack fromyour C program. 

Evaluating a Perl statement from your C program

Perl provides two API functions to evaluate pieces of Perl code.These are the perl_eval_sv() entry in the perlguts manpage and the perl_eval_pv() entry in the perlguts manpage.

Arguably, these are the only routines you'll ever need to executesnippets of Perl code from within your C program. Your code can beas long as you wish; it can contain multiple statements; it can employthe use entry in the perlfunc manpage, the require entry in the perlfunc manpage and the do entry in the perlfunc manpage to includeexternal Perl files.

perl_eval_pv() lets us evaluate individual Perl strings, and thenextract variables for coercion into C types. The following program,string.c, executes three Perl strings, extracting an int fromthe first, a float from the second, and a char * from the third.

   #include <EXTERN.h>   #include <perl.h>      static PerlInterpreter *my_perl;      main (int argc, char **argv, char **env)   {       char *embedding[] = { "", "-e", "0" };          my_perl = perl_alloc();       perl_construct( my_perl );          perl_parse(my_perl, NULL, 3, embedding, NULL);       perl_run(my_perl);          /** Treat $a as an integer **/       perl_eval_pv("$a = 3; $a **= 2", TRUE);       printf("a = %d\n", SvIV(perl_get_sv("a", FALSE)));          /** Treat $a as a float **/       perl_eval_pv("$a = 3.14; $a **= 2", TRUE);       printf("a = %f\n", SvNV(perl_get_sv("a", FALSE)));          /** Treat $a as a string **/       perl_eval_pv("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);       printf("a = %s\n", SvPV(perl_get_sv("a", FALSE), na));          perl_destruct(my_perl);       perl_free(my_perl);   }
All of those strange functions with sv in their names help convert Perl scalars to C types. They're described in the perlguts manpage.

If you compile and run string.c, you'll see the results of usingSvIV() to create an int, SvNV() to create a float, andSvPV() to create a string:

   a = 9   a = 9.859600   a = Just Another Perl Hacker
In the example above, we've created a global variable to temporarilystore the computed value of our eval'd expression. It is alsopossible and in most cases a better strategy to fetch the return valuefrom the perl_eval_pv manpage instead. Example:

   ...   SV *val = perl_eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);   printf("%s\n", SvPV(val,na));   ...
This way, we avoid namespace pollution by not creating globalvariables and we've simplified our code as well. 

Performing Perl pattern matches and substitutions from your C program

The perl_eval_sv() function lets us evaluate chunks of Perl code, so we candefine some functions that use it to ``specialize'' in matches andsubstitutions: match(), substitute(), and matches().

   char match(SV *string, char *pattern);
Given a string and a pattern (e.g., m/clasp/ or /\b\w*\b/, whichin your C program might appear as ``/\\b\\w*\\b/"), match()returns 1 if the string matches the pattern and 0 otherwise.

   int substitute(SV **string, char *pattern);
Given a pointer to an SV and an =~ operation (e.g.,s/bob/robert/g or tr[A-Z][a-z]), substitute() modifies the stringwithin the AV at according to the operation, returning the number of substitutionsmade.

   int matches(SV *string, char *pattern, AV **matches);
Given an SV, a pattern, and a pointer to an empty AV,matches() evaluates $string =~ $pattern in an array context, andfills in matches with the array elements, returning the number of matches found.

Here's a sample program, match.c, that uses all three (long lines havebeen wrapped here):

 #include <EXTERN.h> #include <perl.h>  /** my_perl_eval_sv(code, error_check) ** kinda like perl_eval_sv(),  ** but we pop the return value off the stack  **/ SV* my_perl_eval_sv(SV *sv, I32 croak_on_error) {     dSP;     SV* retval;      PUSHMARK(sp);     perl_eval_sv(sv, G_SCALAR);      SPAGAIN;     retval = POPs;     PUTBACK;      if (croak_on_error && SvTRUE(GvSV(errgv)))        croak(SvPVx(GvSV(errgv), na));      return retval; }  /** match(string, pattern) ** ** Used for matches in a scalar context. ** ** Returns 1 if the match was successful; 0 otherwise. **/  I32 match(SV *string, char *pattern) {     SV *command = newSV(0), *retval;      sv_setpvf(command, "my $string = '%s'; $string =~ %s",              SvPV(string,na), pattern);      retval = my_perl_eval_sv(command, TRUE);     SvREFCNT_dec(command);      return SvIV(retval); }  /** substitute(string, pattern) ** ** Used for =~ operations that modify their left-hand side (s/// and tr///) ** ** Returns the number of successful matches, and ** modifies the input string if there were any. **/  I32 substitute(SV **string, char *pattern) {     SV *command = newSV(0), *retval;      sv_setpvf(command, "$string = '%s'; ($string =~ %s)",              SvPV(*string,na), pattern);      retval = my_perl_eval_sv(command, TRUE);     SvREFCNT_dec(command);      *string = perl_get_sv("string", FALSE);     return SvIV(retval); }  /** matches(string, pattern, matches) ** ** Used for matches in an array context. ** ** Returns the number of matches, ** and fills in **matches with the matching substrings **/  I32 matches(SV *string, char *pattern, AV **match_list) {     SV *command = newSV(0);     I32 num_matches;      sv_setpvf(command, "my $string = '%s'; @array = ($string =~ %s)",              SvPV(string,na), pattern);      my_perl_eval_sv(command, TRUE);     SvREFCNT_dec(command);      *match_list = perl_get_av("array", FALSE);     num_matches = av_len(*match_list) + 1; /** assume $[ is 0 **/      return num_matches; }  main (int argc, char **argv, char **env) {     PerlInterpreter *my_perl = perl_alloc();     char *embedding[] = { "", "-e", "0" };     AV *match_list;     I32 num_matches, i;     SV *text = newSV(0);      perl_construct(my_perl);     perl_parse(my_perl, NULL, 3, embedding, NULL);      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");      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", SvPV(*av_fetch(match_list, i, FALSE),na));     printf("\n");      /** 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", SvPV(text,na));     }      /** Attempt a substitution **/     if (!substitute(&text, "s/Perl/C/")) {        printf("substitute: s/Perl/C...No substitution made.\n\n");     }      SvREFCNT_dec(text);     perl_destruct_level = 1;     perl_destruct(my_perl);     perl_free(my_perl); }
which produces the output (again, long lines have been wrapped here)

   match: Text contains the word 'quarter'.
   match: Text doesn't contain the word 'eighth'.
   matches: m/(wi..)/g found 2 matches...   match: will   match: with
   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
   substitute: s/Perl/C...No substitution made.
 

Fiddling with the Perl stack from your C program

When trying to explain stacks, most computer science textbooks mumblesomething about spring-loaded columns of cafeteria plates: the lastthing you pushed on the stack is the first thing you pop off. That'lldo for our purposes: your C program will push some arguments onto ``the Perlstack'', shut its eyes while some magic happens, and then pop theresults---the return value of your Perl subroutine---off the stack.

First you'll need to know how to convert between C types and Perltypes, with newSViv() and sv_setnv() and newAV() and all theirfriends. They're described in the perlguts manpage.

Then you'll need to know how to manipulate the Perl stack. That'sdescribed in the perlcall manpage.

Once you've understood those, embedding Perl in C is easy.

Because C has no builtin function for integer exponentiation, let'smake Perl's ** operator available to it (this is less useful than itsounds, because Perl implements ** with C's pow() function). FirstI'll create a stub exponentiation function in power.pl:

    sub expo {        my ($a, $b) = @_;        return $a ** $b;    }
Now I'll create a C program, power.c, with a functionPerlPower() that contains all the perlguts necessary to push thetwo arguments into expo() and to pop the return value out. Take adeep breath...

    #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[] = { "", "power.pl" };
      my_perl = perl_alloc();      perl_construct( my_perl );
      perl_parse(my_perl, NULL, 2, my_argv, (char **)NULL);      perl_run(my_perl);
      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.
 

Maintaining a persistent interpreter

When developing interactive and/or potentially long-runningapplications, it's a good idea to maintain a persistent interpreterrather than allocating and constructing a new interpreter multipletimes. The major reason is speed: since Perl will only be loaded intomemory once.

However, you have to be more cautious with namespace and variablescoping when using a persistent interpreter. In previous exampleswe've been using global variables in the default package main. Weknew exactly what code would be run, and assumed we could avoidvariable collisions and outrageous symbol table growth.

Let's say your application is a server that will occasionally run Perlcode from some arbitrary file. Your server has no way of knowing whatcode it's going to run. Very dangerous.

If the file is pulled in by perl_parse(), compiled into a newlyconstructed interpreter, and subsequently cleaned out withperl_destruct() afterwards, you're shielded from most namespacetroubles.

One way to avoid namespace collisions in this scenario is to translatethe filename into a guaranteed-unique package name, and then compilethe code into that package using the eval entry in the perlfunc manpage. In the examplebelow, each file will only be compiled once. Or, the applicationmight choose to clean out the symbol table associated with the fileafter it's no longer needed. Using the perl_call_argv entry in the perlcall manpage, We'llcall the subroutine Embed::Persistent::eval_file which lives in thefile persistent.pl and pass the filename and boolean cleanup/cacheflag as arguments.

Note that the process will continue to grow for each file that ituses. In addition, there might be AUTOLOADed subroutines and otherconditions that cause Perl's symbol table to grow. You might want toadd some logic that keeps track of the process size, or restartsitself after a certain number of requests, to ensure that memoryconsumption is minimized. You'll also want to scope your variableswith the my entry in the perlfunc manpage whenever possible.

 package Embed::Persistent; #persistent.pl
 use strict; use vars '%Cache';
 sub valid_package_name {     my($string) = @_;     $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;     # second pass only for words starting with a digit     $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;
     # Dress it up as a real package name     $string =~ s|/|::|g;     return "Embed" . $string; }
 #borrowed from Safe.pm sub delete_package {     my $pkg = shift;     my ($stem, $leaf);
     no strict 'refs';     $pkg = "main::$pkg\::";    # expand to full symbol table name     ($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
     my $stem_symtab = *{$stem}{HASH};
     delete $stem_symtab->{$leaf}; }
 sub eval_file {     my($filename, $delete) = @_;     my $package = valid_package_name($filename);     my $mtime = -M $filename;     if(defined $Cache{$package}{mtime}        &&        $Cache{$package}{mtime} <= $mtime)     {        # we have compiled this subroutine already,        # it has not been updated on disk, nothing left to do        print STDERR "already compiled $package->handler\n";     }     else {        local *FH;        open FH, $filename or die "open '$filename' $!";        local($/) = undef;        my $sub = <FH>;        close FH;
        #wrap the code into a subroutine inside our unique package        my $eval = qq{package $package; sub handler { $sub; }};        {            # hide our variables within this block            my($filename,$mtime,$package,$sub);            eval $eval;        }        die $@ if $@;
        #cache it unless we're cleaning out each time        $Cache{$package}{mtime} = $mtime unless $delete;     }
     eval {$package->handler;};     die $@ if $@;
     delete_package($package) if $delete;
     #take a look if you want     #print Devel::Symdump->rnew($package)->as_string, $/; }
 1;
 __END__
 /* persistent.c */ #include <EXTERN.h> #include <perl.h>
 /* 1 = clean out filename's symbol table after each request, 0 = don't */ #ifndef DO_CLEAN #define DO_CLEAN 0 #endif
 static PerlInterpreter *perl = NULL;
 int main(int argc, char **argv, char **env) {     char *embedding[] = { "", "persistent.pl" };     char *args[] = { "", DO_CLEAN, NULL };     char filename [1024];     int exitstatus = 0;
     if((perl = perl_alloc()) == NULL) {        fprintf(stderr, "no memory!");        exit(1);     }     perl_construct(perl);
     exitstatus = perl_parse(perl, NULL, 2, embedding, NULL);
     if(!exitstatus) {        exitstatus = perl_run(perl);
        while(printf("Enter file name: ") && gets(filename)) {
            /* call the subroutine, passing it the filename as an argument */            args[0] = filename;            perl_call_argv("Embed::Persistent::eval_file",                           G_DISCARD | G_EVAL, args);
            /* check $@ */            if(SvTRUE(GvSV(errgv)))                fprintf(stderr, "eval error: %s\n", SvPV(GvSV(errgv),na));        }     }
     perl_destruct_level = 0;     perl_destruct(perl);     perl_free(perl);     exit(exitstatus); }
Now compile:

 % cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
Here's a example script file:

 #test.pl my $string = "hello"; foo($string);
 sub foo {     print "foo says: @_\n"; }
Now run:

 % persistent Enter file name: test.pl foo says: hello Enter file name: test.pl already compiled Embed::test_2epl->handler foo says: hello Enter file name: ^C
 

Maintaining multiple interpreter instances

Some rare applications will need to create more than one interpreterduring a session. Such an application might sporadically decide torelease any resources associated with the interpreter.

The program must take care to ensure that this takes place beforethe next interpreter is constructed. By default, the global variableperl_destruct_level is set to 0, since extra cleaning isn'tneeded when a program has only one interpreter.

Setting perl_destruct_level to 1 makes everything squeaky clean:

 perl_destruct_level = 1;
 while(1) {     ...     /* reset global variables here with perl_destruct_level = 1 */     perl_construct(my_perl);     ...     /* clean and reset _everything_ during perl_destruct */     perl_destruct(my_perl);     perl_free(my_perl);     ...     /* let's go do it again! */ }
When perl_destruct() is called, the interpreter's syntax parse treeand symbol tables are cleaned up, and global variables are reset.

Now suppose we have more than one interpreter instance running at thesame time. This is feasible, but only if you used the-DMULTIPLICITY flag when building Perl. By default, that setsperl_destruct_level to 1.

Let's give it a try:

 #include <EXTERN.h> #include <perl.h>
 /* we're going to embed two interpreters */ /* we're going to embed two interpreters */
 #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"
 int main(int argc, char **argv, char **env) {     PerlInterpreter         *one_perl = perl_alloc(),         *two_perl = perl_alloc();     char *one_args[] = { "one_perl", SAY_HELLO };     char *two_args[] = { "two_perl", SAY_HELLO };
     perl_construct(one_perl);     perl_construct(two_perl);
     perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);     perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
     perl_run(one_perl);     perl_run(two_perl);
     perl_destruct(one_perl);     perl_destruct(two_perl);
     perl_free(one_perl);     perl_free(two_perl); }
Compile as usual:

 % cc -o multiplicity multiplicity.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
Run it, Run it:

 % multiplicity Hi, I'm one_perl Hi, I'm two_perl
 

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 scriptthat use()s a Perl module (such as 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 extensionson its own. A little glue will help. Up until now you've beencalling 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 betweenPerl and linked C/C++ routines. Let's take a look some pieces of perlmain.cto 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 yourcomputer or when adding a new extension),a Perl subroutine is created to incorporate the extension'sroutines. Normally, that subroutine is namedModule::bootstrap() and is invoked when you say use Module. Inturn, this hooks into an XSUB, boot_Module, which creates a Perlcounterpart for each of the extension's XSUBs. Don't worry about thispart; leave that to the xsubpp and extension authors. If yourextension is dynamically loaded, DynaLoader creates Module::bootstrap()for you on the fly. In fact, if you have a working DynaLoader then thereis rarely any need to link in any other extensions statically.

Once you have this code, slap it into the second argument of perl_parse():

 perl_parse(my_perl, xs_init, argc, my_argv, NULL);
Then compile:

 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
 % interp   use Socket;   use SomeDynamicallyLoadedModule;
   print "Now I can use extensions!\n"'
ExtUtils::Embed can also automate writing the 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 the perlxs manpage and the perlguts manpage for more details. 

Embedding Perl under Win32

At the time of this writing, there are two versions of Perl which rununder Win32. Interfacing to Activeware's Perl library is quitedifferent from the examples in this documentation, as significantchanges were made to the internal Perl API. However, it is possibleto embed Activeware's Perl runtime, see the Perl for Win32 FAQ:http://www.perl.com/perl/faq/win32/Perl_for_Win32_FAQ.html

With the ``official'' Perl version 5.004 or higher, all the exampleswithin this documentation will compile and run untouched, although,the build process is slightly different between Unix and Win32.

For starters, backticks don't work under the Win32 native command shell!The ExtUtils::Embed kit on CPAN ships with a script calledgenmake, which generates a simple makefile to build a program froma single C source file. It can be used like so:

 C:\ExtUtils-Embed\eg> perl genmake interp.c C:\ExtUtils-Embed\eg> nmake C:\ExtUtils-Embed\eg> interp -e "print qq{I'm embedded in Win32!\n}"
You may wish to use a more robust environment such as the MS Developerstdio. In this case, to generate perlxsi.c run:

 perl -MExtUtils::Embed -e xsinit
Create a new project, Insert -> Files into Project: perlxsi.c, perl.lib,and your own source files, e.g. interp.c. Typically you'll findperl.lib in C:\perl\lib\CORE, if not, you should see the COREdirectory relative to perl -V:archlib.The studio will also need this path so it knows where to find Perlinclude files. This path can be added via the Tools -> Options ->Directories menu. Finnally, select Build -> Build interp.exe andyou're ready to go! 

MORAL

You can sometimes write faster code in C, butyou can always write code faster in Perl. Because you can useeach from the other, combine them as you wish. 

AUTHOR

Jon Orwant and <orwant@tpj.com> and Doug MacEachern <dougmAATTosf.org>,with small contributions from Tim Bunce, Tom Christiansen, Hallvard Furuseth,Dov Grobgeld, and Ilya Zakharevich.

Check out Doug's article on embedding in Volume 1, Issue 4 of The PerlJournal. Info about TPJ is available from http://tpj.com.

July 17, 1997

Some of this material is excerpted from Jon Orwant's book: Perl 5Interactive, Waite Group Press, 1996 (ISBN 1-57169-064-6) and appearscourtesy of Waite Group Press. 

COPYRIGHT

Copyright (C) 1995, 1996, 1997 Doug MacEachern and Jon Orwant. AllRights Reserved.

Although destined for release with the standard Perl distribution,this document is not public domain, nor is any of Perl and itsdocumentation. Permission is granted to freely distribute verbatimcopies of this document provided that no modifications outside offormatting be made, and that this notice remain intact. You arepermitted and encouraged to use its code and derivatives thereof inyour own source code for fun or for profit as you see fit.

 

Index

NAME
DESCRIPTION
PREAMBLE
ROADMAP
Compiling your C program
Adding a Perl interpreter to your C program
Calling a Perl subroutine from your C program
Evaluating a Perl statement from your C program
Performing Perl pattern matches and substitutions from your C program
Fiddling with the Perl stack from your C program
Maintaining a persistent interpreter
Maintaining multiple interpreter instances
Using Perl modules, which themselves use C libraries, from your C program
Embedding Perl under Win32
MORAL
AUTHOR
COPYRIGHT
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