perl 5.003_01: pod/perlembed.pod

Whitespace trimmed
Include references to ExtUtils::Embed
Wrap long lines in examples
Expanded discussion of dynamic loading from embedded Perl

1 files changed, 256 insertions, 158 deletions

diff --git a/pod/perlembed.pod b/pod/perlembed.pod
index 2f0e9c30fb..646cd670a1 100644
--- a/pod/perlembed.pod
+++ b/pod/perlembed.pod
@@ -10,24 +10,24 @@ Do you want to:
 
 =over 5
 
-=item B<Use C from Perl?>  
+=item B<Use C from Perl?>
 
 Read L<perlcall> and L<perlxs>.
 
-=item B<Use a UNIX program from Perl?>  
+=item B<Use a UNIX program from Perl?>
 
 Read about backquotes and L<perlfunc/system> and L<perlfunc/exec>.
 
-=item B<Use Perl from Perl?>  
+=item B<Use Perl from Perl?>
 
-Read about L<perlfunc/do> and L<perlfunc/eval> and L<perlmod/use> 
+Read about L<perlfunc/do> and L<perlfunc/eval> and L<perlmod/use>
 and L<perlmod/require>.
 
-=item B<Use C from C?>  
+=item B<Use C from C?>
 
 Rethink your design.
 
-=item B<Use Perl from C?>  
+=item B<Use Perl from C?>
 
 Read on...
 
@@ -37,7 +37,7 @@ Read on...
 
 L<Compiling your C program>
 
-There's one example in each of the five sections:
+There's one example in each of the six sections:
 
 L<Adding a Perl interpreter to your C program>
 
@@ -49,11 +49,13 @@ 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>.  
+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
@@ -64,7 +66,7 @@ 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.  
+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
@@ -83,13 +85,13 @@ or maybe something like
 
 Execute this statement for a hint about where to find CORE:
 
-    perl -e 'use Config; print $Config{archlib}'
+    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 
+    % 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
@@ -97,12 +99,23 @@ 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.  
+to change the path following the -I.
 
 You may have to add extra libraries as well.  Which ones?
-Perhaps those printed by 
+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.
 
-   perl -e 'use Config; print $Config{libs}'
 
 =head2 Adding a Perl interpreter to your C program
 
@@ -114,23 +127,28 @@ 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, env);
+        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 it's 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 -L/usr/local/lib/perl5/alpha-dec_osf/CORE 
-    -I/usr/local/lib/perl5/alpha-dec_osf/CORE -lperl -lm
+    % 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:
@@ -149,7 +167,7 @@ or
 
 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()>.  
+calling I<perl_run()>.
 
 =head2 Calling a Perl subroutine from your C program
 
@@ -160,17 +178,17 @@ 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;  
-    
+    #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, env);
-    
+
+        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);
@@ -178,22 +196,21 @@ That's shown below, in a program I'll call I<showtime.c>.
     }
 
 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_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 -L/usr/local/lib/perl5/alpha-dec_osf/CORE 
-    -I/usr/local/lib/perl5/alpha-dec_osf/CORE -lperl -lm
-    
+    % cc -o showtime showtime.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
+
     % showtime showtime.pl
     818284590
 
@@ -203,7 +220,7 @@ 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: 
+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
@@ -213,26 +230,26 @@ for evaluting 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 
+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<perlmod/require> or L<perlfunc/do> to include external Perl
-files.  
+files.
 
-Our I<perl_eval()> lets us evaluate individual Perl strings, and then 
-extract variables for coercion into C types.  The following program, 
+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];
@@ -240,29 +257,29 @@ the first, a C<float> from the second, and a C<char *> from the third.
      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, env);
-   
+
+     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);
    }
@@ -284,7 +301,7 @@ 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); 
+   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/">),
@@ -293,7 +310,7 @@ 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 
+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.
 
@@ -301,70 +318,66 @@ returning the number of substitutions made.
 
 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), 
+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:
+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 eval(char *string)
+   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) 
+   **
+   ** 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 = $string =~ %s", 
-	string, pattern); 
+     sprintf(command, "$string = '%s'; $return = $string =~ %s",
+   	  string, pattern);
      perl_eval(command);
      free(command);
      return SvIV(perl_get_sv("return", FALSE));
    }
-   
    /** substitute(string, pattern)
-    **
-    ** Used for =~ operations that modify their left-hand side (s/// and tr///)
-    **
-    ** Returns the number of successful matches, and
-    ** modifies the input string if there were any.
-    **/
-   int substitute(char *string[], char *pattern) 
+   **
+   ** Used for =~ operations that modify their left-hand side (s/// and tr///)
+   **
+   ** Returns the number of successful matches, and
+   ** modifies the input string if there were any.
+   **/
+   int substitute(char *string[], char *pattern)
    {
      char *command;
      STRLEN length;
      command = malloc(sizeof(char) * strlen(*string) + strlen(pattern) + 35);
-     sprintf(command, "$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));
+     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 **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;
@@ -372,93 +385,91 @@ Here's a sample program, I<match.c>, that uses all three:
      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); 
+     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 **/
-     *matches = (char **) malloc(sizeof(char *) * num_matches);
-     for (i = 0; i <= num_matches; i++) {  
+     *match_list = (char **) malloc(sizeof(char *) * num_matches);
+     for (i = 0; i <= num_matches; i++) {
        current_match = av_shift(array);
-       (*matches)[i] = SvPV(current_match, length);
+       (*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, **matches;
+     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, env);
-   
+     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 (perl_match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
-       printf("perl_match: Text contains the word 'quarter'.\n\n");
-     else 
-       printf("perl_match: Text doesn't contain the word 'quarter'.\n\n");
-   
-     if (perl_match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
-       printf("perl_match: Text contains the word 'eighth'.\n\n");
-     else 
-       printf("perl_match: Text doesn't contain the word 'eighth'.\n\n");
-   
-	                               /** Match all occurrences of /wi../ **/
-     num_matches = perl_matches(text, "m/(wi..)/g", &matches);
-     
-     printf("perl_matches: m/(wi..)/g found %d matches...\n", num_matches);
-     for (i = 0; i < num_matches; i++) 
-       printf("match: %s\n", matches[i]);
+     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(matches[i]);
+       free(match_list[i]);
      }
-     free(matches);
-   
-                                       /** Remove all vowels from text **/
-     num_matches = perl_substitute(&text, "s/[aeiou]//gi");
+     free(match_list);
+     /** Remove all vowels from text **/
+     num_matches = substitute(&text, "s/[aeiou]//gi");
      if (num_matches) {
-       printf("perl_substitute: s/[aeiou]//gi...%d substitutions made.\n", 
-	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 (!perl_substitute(&text, "s/Perl/C/")) {
-       printf("perl_substitute: s/Perl/C...No substitution made.\n\n");
+     /** 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
+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
-   
+   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
@@ -467,7 +478,7 @@ 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>.
@@ -475,7 +486,7 @@ 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.  
+Once you've understood those, embedding Perl in C is easy.
 
 Since C has no built-in function for integer exponentiation, let's
 make Perl's ** operator available to it (this is less useful than it
@@ -495,9 +506,9 @@ deep breath...
     #include <stdio.h>
     #include <EXTERN.h>
     #include <perl.h>
-    
+
     static PerlInterpreter *my_perl;
-    
+
     static void
     PerlPower(int a, int b)
     {
@@ -512,39 +523,124 @@ deep breath...
       SPAGAIN;                        /* refresh stack pointer         */
                                     /* pop the return value from stack */
       printf ("%d to the %dth power is %d.\n", a, b, POPi);
-      PUTBACK;                               
+      PUTBACK;
       FREETMPS;                       /* free that return value        */
       LEAVE;                       /* ...and the XPUSHed "mortal" args.*/
     }
-    
-    int main (int argc, char **argv, char **env) 
+
+    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, env);
-      
+
+      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 -L/usr/local/lib/perl5/alpha-dec_osf/CORE 
-    -I/usr/local/lib/perl5/alpha-dec_osf/CORE -lperl -lm
-    
-    % power 
+    % 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 statically link in any other extensions.
+
+
+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
@@ -554,12 +650,14 @@ each from the other, combine them as you wish.
 
 =head1 AUTHOR
 
-Jon Orwant F<E<lt>orwant@media.mit.eduE<gt>>, with contributions from
-Tim Bunce, Tom Christiansen, Dov Grobgeld, and Ilya Zakharevich.
+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.
 
-December 18, 1995
+June 17, 1996
 
-Some of this material is excerpted from my book: I<Perl 5 Interactive>, 
+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.
-