X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlembed.pod;h=ea0e8331f2f2127f6e177ce12e3279fad95c4e16;hb=982b4e8fc47473059e209787b589853f4c8f8f9e;hp=5ac5a9e0c6eea978e905c2f2a2c02577651c6a93;hpb=a0d0e21ea6ea90a22318550944fe6cb09ae10cda;p=p5sagit%2Fp5-mst-13.2.git

diff --git a/pod/perlembed.pod b/pod/perlembed.pod
index 5ac5a9e..ea0e833 100644
--- a/pod/perlembed.pod
+++ b/pod/perlembed.pod
@@ -1,7 +1,663 @@
 =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.