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Embedding
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1=head1 NAME
2
cb1a09d0 3perlembed - how to embed perl in your C program
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4
5=head1 DESCRIPTION
6
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7=head2 PREAMBLE
8
9Do you want to:
10
11=over 5
12
96dbc785 13=item B<Use C from Perl?>
cb1a09d0 14
4929bf7b 15Read L<perlxstut>, L<perlxs>, L<h2xs>, L<perlguts>, and L<perlapi>.
cb1a09d0 16
54310121 17=item B<Use a Unix program from Perl?>
cb1a09d0 18
5f05dabc 19Read about back-quotes and about C<system> and C<exec> in L<perlfunc>.
cb1a09d0 20
96dbc785 21=item B<Use Perl from Perl?>
cb1a09d0 22
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23Read about L<perlfunc/do> and L<perlfunc/eval> and L<perlfunc/require>
24and L<perlfunc/use>.
cb1a09d0 25
96dbc785 26=item B<Use C from C?>
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27
28Rethink your design.
29
96dbc785 30=item B<Use Perl from C?>
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31
32Read on...
33
34=back
35
36=head2 ROADMAP
37
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38=over 5
39
551e1d92 40=item *
cb1a09d0 41
551e1d92 42Compiling your C program
cb1a09d0 43
551e1d92 44=item *
cb1a09d0 45
551e1d92 46Adding a Perl interpreter to your C program
cb1a09d0 47
551e1d92 48=item *
cb1a09d0 49
551e1d92 50Calling a Perl subroutine from your C program
cb1a09d0 51
551e1d92 52=item *
cb1a09d0 53
551e1d92 54Evaluating a Perl statement from your C program
a6006777 55
551e1d92 56=item *
8ebc5c01 57
551e1d92
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58Performing Perl pattern matches and substitutions from your C program
59
60=item *
61
62Fiddling with the Perl stack from your C program
63
64=item *
65
66Maintaining a persistent interpreter
67
68=item *
69
70Maintaining multiple interpreter instances
71
72=item *
73
74Using Perl modules, which themselves use C libraries, from your C program
75
76=item *
77
78Embedding Perl under Win32
96dbc785 79
e010571f 80=back
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81
82=head2 Compiling your C program
83
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84If you have trouble compiling the scripts in this documentation,
85you're not alone. The cardinal rule: COMPILE THE PROGRAMS IN EXACTLY
86THE SAME WAY THAT YOUR PERL WAS COMPILED. (Sorry for yelling.)
cb1a09d0 87
8a7dc658 88Also, every C program that uses Perl must link in the I<perl library>.
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89What's that, you ask? Perl is itself written in C; the perl library
90is the collection of compiled C programs that were used to create your
91perl executable (I</usr/bin/perl> or equivalent). (Corollary: you
92can't use Perl from your C program unless Perl has been compiled on
93your machine, or installed properly--that's why you shouldn't blithely
94copy Perl executables from machine to machine without also copying the
95I<lib> directory.)
96
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97When you use Perl from C, your C program will--usually--allocate,
98"run", and deallocate a I<PerlInterpreter> object, which is defined by
99the perl library.
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100
101If your copy of Perl is recent enough to contain this documentation
a6006777 102(version 5.002 or later), then the perl library (and I<EXTERN.h> and
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103I<perl.h>, which you'll also need) will reside in a directory
104that looks like this:
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105
106 /usr/local/lib/perl5/your_architecture_here/CORE
107
108or perhaps just
109
110 /usr/local/lib/perl5/CORE
111
112or maybe something like
113
114 /usr/opt/perl5/CORE
115
116Execute this statement for a hint about where to find CORE:
117
96dbc785 118 perl -MConfig -e 'print $Config{archlib}'
cb1a09d0 119
54310121 120Here's how you'd compile the example in the next section,
e010571f 121L<Adding a Perl interpreter to your C program>, on my Linux box:
cb1a09d0 122
54310121 123 % gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include
8a7dc658 124 -I/usr/local/lib/perl5/i586-linux/5.003/CORE
54310121 125 -L/usr/local/lib/perl5/i586-linux/5.003/CORE
8a7dc658 126 -o interp interp.c -lperl -lm
cb1a09d0 127
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128(That's all one line.) On my DEC Alpha running old 5.003_05, the
129incantation is a bit different:
8a7dc658 130
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131 % cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include
132 -I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE
133 -L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib
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134 -D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm
135
136How can you figure out what to add? Assuming your Perl is post-5.001,
137execute a C<perl -V> command and pay special attention to the "cc" and
54310121 138"ccflags" information.
8a7dc658 139
54310121 140You'll have to choose the appropriate compiler (I<cc>, I<gcc>, et al.) for
8a7dc658 141your machine: C<perl -MConfig -e 'print $Config{cc}'> will tell you what
54310121 142to use.
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143
144You'll also have to choose the appropriate library directory
145(I</usr/local/lib/...>) for your machine. If your compiler complains
146that certain functions are undefined, or that it can't locate
147I<-lperl>, then you need to change the path following the C<-L>. If it
148complains that it can't find I<EXTERN.h> and I<perl.h>, you need to
149change the path following the C<-I>.
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150
151You may have to add extra libraries as well. Which ones?
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152Perhaps those printed by
153
154 perl -MConfig -e 'print $Config{libs}'
155
54310121 156Provided your perl binary was properly configured and installed the
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157B<ExtUtils::Embed> module will determine all of this information for
158you:
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159
160 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
161
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162If the B<ExtUtils::Embed> module isn't part of your Perl distribution,
163you can retrieve it from
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164http://www.perl.com/perl/CPAN/modules/by-module/ExtUtils/
165(If this documentation came from your Perl distribution, then you're
8a7dc658 166running 5.004 or better and you already have it.)
96dbc785 167
8a7dc658 168The B<ExtUtils::Embed> kit on CPAN also contains all source code for
54310121 169the examples in this document, tests, additional examples and other
8a7dc658 170information you may find useful.
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171
172=head2 Adding a Perl interpreter to your C program
173
174In a sense, perl (the C program) is a good example of embedding Perl
175(the language), so I'll demonstrate embedding with I<miniperlmain.c>,
e010571f 176included in the source distribution. Here's a bastardized, nonportable
8a7dc658 177version of I<miniperlmain.c> containing the essentials of embedding:
cb1a09d0 178
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179 #include <EXTERN.h> /* from the Perl distribution */
180 #include <perl.h> /* from the Perl distribution */
96dbc785 181
cb1a09d0 182 static PerlInterpreter *my_perl; /*** The Perl interpreter ***/
96dbc785 183
c07a80fd 184 int main(int argc, char **argv, char **env)
cb1a09d0 185 {
1ccffcf5 186 PERL_SYS_INIT3(&argc,&argv,&env);
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187 my_perl = perl_alloc();
188 perl_construct(my_perl);
d95b23b2 189 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
96dbc785 190 perl_parse(my_perl, NULL, argc, argv, (char **)NULL);
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191 perl_run(my_perl);
192 perl_destruct(my_perl);
193 perl_free(my_perl);
1ccffcf5 194 PERL_SYS_TERM();
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195 }
196
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197Notice that we don't use the C<env> pointer. Normally handed to
198C<perl_parse> as its final argument, C<env> here is replaced by
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199C<NULL>, which means that the current environment will be used. The macros
200PERL_SYS_INIT3() and PERL_SYS_TERM() provide system-specific tune up
201of the C runtime environment necessary to run Perl interpreters; since
202PERL_SYS_INIT3() may change C<env>, it may be more appropriate to provide
203C<env> as an argument to perl_parse().
96dbc785 204
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205Now compile this program (I'll call it I<interp.c>) into an executable:
206
96dbc785 207 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
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208
209After a successful compilation, you'll be able to use I<interp> just
210like perl itself:
211
212 % interp
213 print "Pretty Good Perl \n";
214 print "10890 - 9801 is ", 10890 - 9801;
215 <CTRL-D>
216 Pretty Good Perl
217 10890 - 9801 is 1089
218
219or
220
221 % interp -e 'printf("%x", 3735928559)'
222 deadbeef
223
224You can also read and execute Perl statements from a file while in the
225midst of your C program, by placing the filename in I<argv[1]> before
e010571f 226calling I<perl_run>.
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227
228=head2 Calling a Perl subroutine from your C program
229
4929bf7b 230To call individual Perl subroutines, you can use any of the B<call_*>
7b8d334a 231functions documented in L<perlcall>.
4929bf7b 232In this example we'll use C<call_argv>.
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233
234That's shown below, in a program I'll call I<showtime.c>.
235
cb1a09d0 236 #include <EXTERN.h>
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237 #include <perl.h>
238
239 static PerlInterpreter *my_perl;
240
c07a80fd 241 int main(int argc, char **argv, char **env)
cb1a09d0 242 {
8ebc5c01 243 char *args[] = { NULL };
1ccffcf5 244 PERL_SYS_INIT3(&argc,&argv,&env);
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245 my_perl = perl_alloc();
246 perl_construct(my_perl);
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247
248 perl_parse(my_perl, NULL, argc, argv, NULL);
d95b23b2 249 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
96dbc785 250
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251 /*** skipping perl_run() ***/
252
4929bf7b 253 call_argv("showtime", G_DISCARD | G_NOARGS, args);
8ebc5c01 254
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255 perl_destruct(my_perl);
256 perl_free(my_perl);
1ccffcf5 257 PERL_SYS_TERM();
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258 }
259
260where I<showtime> is a Perl subroutine that takes no arguments (that's the
96dbc785 261I<G_NOARGS>) and for which I'll ignore the return value (that's the
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262I<G_DISCARD>). Those flags, and others, are discussed in L<perlcall>.
263
264I'll define the I<showtime> subroutine in a file called I<showtime.pl>:
265
266 print "I shan't be printed.";
96dbc785 267
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268 sub showtime {
269 print time;
270 }
271
272Simple enough. Now compile and run:
273
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274 % cc -o showtime showtime.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
275
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276 % showtime showtime.pl
277 818284590
278
279yielding the number of seconds that elapsed between January 1, 1970
8a7dc658 280(the beginning of the Unix epoch), and the moment I began writing this
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281sentence.
282
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283In this particular case we don't have to call I<perl_run>, as we set
284the PL_exit_flag PERL_EXIT_DESTRUCT_END which executes END blocks in
285perl_destruct.
8ebc5c01 286
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287If you want to pass arguments to the Perl subroutine, you can add
288strings to the C<NULL>-terminated C<args> list passed to
4929bf7b 289I<call_argv>. For other data types, or to examine return values,
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290you'll need to manipulate the Perl stack. That's demonstrated in
291L<Fiddling with the Perl stack from your C program>.
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292
293=head2 Evaluating a Perl statement from your C program
294
137443ea 295Perl provides two API functions to evaluate pieces of Perl code.
4929bf7b 296These are L<perlapi/eval_sv> and L<perlapi/eval_pv>.
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297
298Arguably, these are the only routines you'll ever need to execute
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299snippets of Perl code from within your C program. Your code can be as
300long as you wish; it can contain multiple statements; it can employ
301L<perlfunc/use>, L<perlfunc/require>, and L<perlfunc/do> to
302include external Perl files.
cb1a09d0 303
4929bf7b 304I<eval_pv> lets us evaluate individual Perl strings, and then
96dbc785 305extract variables for coercion into C types. The following program,
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306I<string.c>, executes three Perl strings, extracting an C<int> from
307the first, a C<float> from the second, and a C<char *> from the third.
308
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309 #include <EXTERN.h>
310 #include <perl.h>
c47ff5f1 311
cb1a09d0 312 static PerlInterpreter *my_perl;
c47ff5f1 313
c07a80fd 314 main (int argc, char **argv, char **env)
cb1a09d0 315 {
2d8e6c8d 316 STRLEN n_a;
137443ea 317 char *embedding[] = { "", "-e", "0" };
c47ff5f1 318
1ccffcf5 319 PERL_SYS_INIT3(&argc,&argv,&env);
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320 my_perl = perl_alloc();
321 perl_construct( my_perl );
c47ff5f1 322
137443ea 323 perl_parse(my_perl, NULL, 3, embedding, NULL);
d95b23b2 324 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
137443ea 325 perl_run(my_perl);
c47ff5f1 326
137443ea 327 /** Treat $a as an integer **/
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328 eval_pv("$a = 3; $a **= 2", TRUE);
329 printf("a = %d\n", SvIV(get_sv("a", FALSE)));
c47ff5f1 330
137443ea 331 /** Treat $a as a float **/
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332 eval_pv("$a = 3.14; $a **= 2", TRUE);
333 printf("a = %f\n", SvNV(get_sv("a", FALSE)));
c47ff5f1 334
137443ea 335 /** Treat $a as a string **/
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336 eval_pv("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
337 printf("a = %s\n", SvPV(get_sv("a", FALSE), n_a));
c47ff5f1 338
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339 perl_destruct(my_perl);
340 perl_free(my_perl);
1ccffcf5 341 PERL_SYS_TERM();
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342 }
343
4929bf7b 344All of those strange functions with I<sv> in their names help convert Perl scalars to C types. They're described in L<perlguts> and L<perlapi>.
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345
346If you compile and run I<string.c>, you'll see the results of using
347I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and
348I<SvPV()> to create a string:
349
350 a = 9
351 a = 9.859600
352 a = Just Another Perl Hacker
353
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354In the example above, we've created a global variable to temporarily
355store the computed value of our eval'd expression. It is also
356possible and in most cases a better strategy to fetch the return value
4929bf7b 357from I<eval_pv()> instead. Example:
8f183262 358
8f183262 359 ...
2d8e6c8d 360 STRLEN n_a;
4929bf7b 361 SV *val = eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
2d8e6c8d 362 printf("%s\n", SvPV(val,n_a));
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363 ...
364
365This way, we avoid namespace pollution by not creating global
366variables and we've simplified our code as well.
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367
368=head2 Performing Perl pattern matches and substitutions from your C program
369
4929bf7b 370The I<eval_sv()> function lets us evaluate strings of Perl code, so we can
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371define some functions that use it to "specialize" in matches and
372substitutions: I<match()>, I<substitute()>, and I<matches()>.
373
e010571f 374 I32 match(SV *string, char *pattern);
cb1a09d0 375
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376Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which
377in your C program might appear as "/\\b\\w*\\b/"), match()
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378returns 1 if the string matches the pattern and 0 otherwise.
379
1f05cdcd 380 int substitute(SV **string, char *pattern);
cb1a09d0 381
1f05cdcd 382Given a pointer to an C<SV> and an C<=~> operation (e.g.,
8a7dc658 383C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string
1f05cdcd 384within the C<AV> at according to the operation, returning the number of substitutions
8a7dc658 385made.
cb1a09d0 386
1f05cdcd 387 int matches(SV *string, char *pattern, AV **matches);
cb1a09d0 388
1f05cdcd 389Given an C<SV>, a pattern, and a pointer to an empty C<AV>,
90fdbbb7 390matches() evaluates C<$string =~ $pattern> in a list context, and
1f05cdcd 391fills in I<matches> with the array elements, returning the number of matches found.
cb1a09d0 392
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393Here's a sample program, I<match.c>, that uses all three (long lines have
394been wrapped here):
cb1a09d0 395
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396 #include <EXTERN.h>
397 #include <perl.h>
c47ff5f1 398
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399 static PerlInterpreter *my_perl;
400
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401 /** my_eval_sv(code, error_check)
402 ** kinda like eval_sv(),
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403 ** but we pop the return value off the stack
404 **/
4929bf7b 405 SV* my_eval_sv(SV *sv, I32 croak_on_error)
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406 {
407 dSP;
408 SV* retval;
2d8e6c8d 409 STRLEN n_a;
c47ff5f1 410
924508f0 411 PUSHMARK(SP);
4929bf7b 412 eval_sv(sv, G_SCALAR);
c47ff5f1 413
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414 SPAGAIN;
415 retval = POPs;
416 PUTBACK;
c47ff5f1 417
9cde0e7f 418 if (croak_on_error && SvTRUE(ERRSV))
2d8e6c8d 419 croak(SvPVx(ERRSV, n_a));
c47ff5f1 420
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421 return retval;
422 }
c47ff5f1 423
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424 /** match(string, pattern)
425 **
426 ** Used for matches in a scalar context.
427 **
428 ** Returns 1 if the match was successful; 0 otherwise.
429 **/
c47ff5f1 430
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431 I32 match(SV *string, char *pattern)
432 {
8c52afec 433 SV *command = NEWSV(1099, 0), *retval;
2d8e6c8d 434 STRLEN n_a;
c47ff5f1 435
1f05cdcd 436 sv_setpvf(command, "my $string = '%s'; $string =~ %s",
2d8e6c8d 437 SvPV(string,n_a), pattern);
c47ff5f1 438
4929bf7b 439 retval = my_eval_sv(command, TRUE);
1f05cdcd 440 SvREFCNT_dec(command);
c47ff5f1 441
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442 return SvIV(retval);
443 }
c47ff5f1 444
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445 /** substitute(string, pattern)
446 **
447 ** Used for =~ operations that modify their left-hand side (s/// and tr///)
448 **
449 ** Returns the number of successful matches, and
450 ** modifies the input string if there were any.
451 **/
c47ff5f1 452
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453 I32 substitute(SV **string, char *pattern)
454 {
8c52afec 455 SV *command = NEWSV(1099, 0), *retval;
2d8e6c8d 456 STRLEN n_a;
c47ff5f1 457
1f05cdcd 458 sv_setpvf(command, "$string = '%s'; ($string =~ %s)",
2d8e6c8d 459 SvPV(*string,n_a), pattern);
c47ff5f1 460
4929bf7b 461 retval = my_eval_sv(command, TRUE);
1f05cdcd 462 SvREFCNT_dec(command);
c47ff5f1 463
4929bf7b 464 *string = get_sv("string", FALSE);
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465 return SvIV(retval);
466 }
c47ff5f1 467
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468 /** matches(string, pattern, matches)
469 **
90fdbbb7 470 ** Used for matches in a list context.
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471 **
472 ** Returns the number of matches,
473 ** and fills in **matches with the matching substrings
474 **/
c47ff5f1 475
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476 I32 matches(SV *string, char *pattern, AV **match_list)
477 {
8c52afec 478 SV *command = NEWSV(1099, 0);
cb1a09d0 479 I32 num_matches;
2d8e6c8d 480 STRLEN n_a;
c47ff5f1 481
1f05cdcd 482 sv_setpvf(command, "my $string = '%s'; @array = ($string =~ %s)",
2d8e6c8d 483 SvPV(string,n_a), pattern);
c47ff5f1 484
4929bf7b 485 my_eval_sv(command, TRUE);
1f05cdcd 486 SvREFCNT_dec(command);
c47ff5f1 487
4929bf7b 488 *match_list = get_av("array", FALSE);
1f05cdcd 489 num_matches = av_len(*match_list) + 1; /** assume $[ is 0 **/
c47ff5f1 490
cb1a09d0 491 return num_matches;
1f05cdcd 492 }
c47ff5f1 493
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494 main (int argc, char **argv, char **env)
495 {
a6006777 496 char *embedding[] = { "", "-e", "0" };
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497 AV *match_list;
498 I32 num_matches, i;
7fef744d 499 SV *text;
2d8e6c8d 500 STRLEN n_a;
c47ff5f1 501
1ccffcf5 502 PERL_SYS_INIT3(&argc,&argv,&env);
7fef744d 503 my_perl = perl_alloc();
1f05cdcd 504 perl_construct(my_perl);
96dbc785 505 perl_parse(my_perl, NULL, 3, embedding, NULL);
d95b23b2 506 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
c47ff5f1 507
7fef744d 508 text = NEWSV(1099,0);
1f05cdcd 509 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");
c47ff5f1 510
96dbc785 511 if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
1f05cdcd 512 printf("match: Text contains the word 'quarter'.\n\n");
96dbc785 513 else
1f05cdcd 514 printf("match: Text doesn't contain the word 'quarter'.\n\n");
c47ff5f1 515
96dbc785 516 if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
1f05cdcd 517 printf("match: Text contains the word 'eighth'.\n\n");
96dbc785 518 else
1f05cdcd 519 printf("match: Text doesn't contain the word 'eighth'.\n\n");
c47ff5f1 520
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521 /** Match all occurrences of /wi../ **/
522 num_matches = matches(text, "m/(wi..)/g", &match_list);
523 printf("matches: m/(wi..)/g found %d matches...\n", num_matches);
c47ff5f1 524
96dbc785 525 for (i = 0; i < num_matches; i++)
2d8e6c8d 526 printf("match: %s\n", SvPV(*av_fetch(match_list, i, FALSE),n_a));
cb1a09d0 527 printf("\n");
c47ff5f1 528
96dbc785
PP
529 /** Remove all vowels from text **/
530 num_matches = substitute(&text, "s/[aeiou]//gi");
cb1a09d0 531 if (num_matches) {
1f05cdcd
DM
532 printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
533 num_matches);
2d8e6c8d 534 printf("Now text is: %s\n\n", SvPV(text,n_a));
cb1a09d0 535 }
c47ff5f1 536
96dbc785
PP
537 /** Attempt a substitution **/
538 if (!substitute(&text, "s/Perl/C/")) {
1f05cdcd 539 printf("substitute: s/Perl/C...No substitution made.\n\n");
cb1a09d0 540 }
c47ff5f1 541
1f05cdcd 542 SvREFCNT_dec(text);
9cde0e7f 543 PL_perl_destruct_level = 1;
cb1a09d0
AD
544 perl_destruct(my_perl);
545 perl_free(my_perl);
1ccffcf5 546 PERL_SYS_TERM();
1f05cdcd 547 }
cb1a09d0 548
96dbc785 549which produces the output (again, long lines have been wrapped here)
cb1a09d0 550
8a7dc658 551 match: Text contains the word 'quarter'.
96dbc785 552
8a7dc658 553 match: Text doesn't contain the word 'eighth'.
96dbc785 554
8a7dc658 555 matches: m/(wi..)/g found 2 matches...
cb1a09d0
AD
556 match: will
557 match: with
96dbc785 558
8a7dc658 559 substitute: s/[aeiou]//gi...139 substitutions made.
54310121 560 Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
96dbc785
PP
561 Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt bck
562 qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd gvs th by
563 thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct mnt. Th by gvs
564 hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s hs prz. -RCHH
565
8a7dc658 566 substitute: s/Perl/C...No substitution made.
96dbc785 567
cb1a09d0
AD
568=head2 Fiddling with the Perl stack from your C program
569
570When trying to explain stacks, most computer science textbooks mumble
571something about spring-loaded columns of cafeteria plates: the last
572thing you pushed on the stack is the first thing you pop off. That'll
573do for our purposes: your C program will push some arguments onto "the Perl
574stack", shut its eyes while some magic happens, and then pop the
575results--the return value of your Perl subroutine--off the stack.
96dbc785 576
cb1a09d0
AD
577First you'll need to know how to convert between C types and Perl
578types, with newSViv() and sv_setnv() and newAV() and all their
4929bf7b 579friends. They're described in L<perlguts> and L<perlapi>.
cb1a09d0
AD
580
581Then you'll need to know how to manipulate the Perl stack. That's
582described in L<perlcall>.
583
96dbc785 584Once you've understood those, embedding Perl in C is easy.
cb1a09d0 585
54310121 586Because C has no builtin function for integer exponentiation, let's
cb1a09d0 587make Perl's ** operator available to it (this is less useful than it
5f05dabc 588sounds, because Perl implements ** with C's I<pow()> function). First
cb1a09d0
AD
589I'll create a stub exponentiation function in I<power.pl>:
590
591 sub expo {
592 my ($a, $b) = @_;
593 return $a ** $b;
594 }
595
596Now I'll create a C program, I<power.c>, with a function
597I<PerlPower()> that contains all the perlguts necessary to push the
598two arguments into I<expo()> and to pop the return value out. Take a
599deep breath...
600
cb1a09d0
AD
601 #include <EXTERN.h>
602 #include <perl.h>
96dbc785 603
cb1a09d0 604 static PerlInterpreter *my_perl;
96dbc785 605
cb1a09d0
AD
606 static void
607 PerlPower(int a, int b)
608 {
609 dSP; /* initialize stack pointer */
610 ENTER; /* everything created after here */
611 SAVETMPS; /* ...is a temporary variable. */
924508f0 612 PUSHMARK(SP); /* remember the stack pointer */
cb1a09d0
AD
613 XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */
614 XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */
615 PUTBACK; /* make local stack pointer global */
4929bf7b 616 call_pv("expo", G_SCALAR); /* call the function */
cb1a09d0
AD
617 SPAGAIN; /* refresh stack pointer */
618 /* pop the return value from stack */
619 printf ("%d to the %dth power is %d.\n", a, b, POPi);
96dbc785 620 PUTBACK;
cb1a09d0
AD
621 FREETMPS; /* free that return value */
622 LEAVE; /* ...and the XPUSHed "mortal" args.*/
623 }
96dbc785
PP
624
625 int main (int argc, char **argv, char **env)
cb1a09d0 626 {
95b76e31 627 char *my_argv[] = { "", "power.pl" };
96dbc785 628
1ccffcf5 629 PERL_SYS_INIT3(&argc,&argv,&env);
cb1a09d0
AD
630 my_perl = perl_alloc();
631 perl_construct( my_perl );
96dbc785 632
95b76e31 633 perl_parse(my_perl, NULL, 2, my_argv, (char **)NULL);
d95b23b2 634 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
8ebc5c01 635 perl_run(my_perl);
96dbc785 636
cb1a09d0 637 PerlPower(3, 4); /*** Compute 3 ** 4 ***/
96dbc785 638
cb1a09d0
AD
639 perl_destruct(my_perl);
640 perl_free(my_perl);
1ccffcf5 641 PERL_SYS_TERM();
cb1a09d0 642 }
96dbc785 643
cb1a09d0
AD
644
645
646Compile and run:
647
96dbc785
PP
648 % cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
649
650 % power
cb1a09d0
AD
651 3 to the 4th power is 81.
652
a6006777
PP
653=head2 Maintaining a persistent interpreter
654
8a7dc658
JO
655When developing interactive and/or potentially long-running
656applications, it's a good idea to maintain a persistent interpreter
657rather than allocating and constructing a new interpreter multiple
658times. The major reason is speed: since Perl will only be loaded into
54310121 659memory once.
8a7dc658
JO
660
661However, you have to be more cautious with namespace and variable
662scoping when using a persistent interpreter. In previous examples
663we've been using global variables in the default package C<main>. We
664knew exactly what code would be run, and assumed we could avoid
665variable collisions and outrageous symbol table growth.
666
667Let's say your application is a server that will occasionally run Perl
668code from some arbitrary file. Your server has no way of knowing what
669code it's going to run. Very dangerous.
670
671If the file is pulled in by C<perl_parse()>, compiled into a newly
672constructed interpreter, and subsequently cleaned out with
673C<perl_destruct()> afterwards, you're shielded from most namespace
674troubles.
675
676One way to avoid namespace collisions in this scenario is to translate
677the filename into a guaranteed-unique package name, and then compile
e010571f 678the code into that package using L<perlfunc/eval>. In the example
8a7dc658
JO
679below, each file will only be compiled once. Or, the application
680might choose to clean out the symbol table associated with the file
4929bf7b 681after it's no longer needed. Using L<perlapi/call_argv>, We'll
8a7dc658
JO
682call the subroutine C<Embed::Persistent::eval_file> which lives in the
683file C<persistent.pl> and pass the filename and boolean cleanup/cache
a6006777
PP
684flag as arguments.
685
8a7dc658
JO
686Note that the process will continue to grow for each file that it
687uses. In addition, there might be C<AUTOLOAD>ed subroutines and other
688conditions that cause Perl's symbol table to grow. You might want to
689add some logic that keeps track of the process size, or restarts
690itself after a certain number of requests, to ensure that memory
691consumption is minimized. You'll also want to scope your variables
e010571f 692with L<perlfunc/my> whenever possible.
a6006777 693
54310121 694
a6006777
PP
695 package Embed::Persistent;
696 #persistent.pl
54310121 697
a6006777 698 use strict;
77ca0c92 699 our %Cache;
1ee082b7 700 use Symbol qw(delete_package);
54310121 701
a6006777
PP
702 sub valid_package_name {
703 my($string) = @_;
704 $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
705 # second pass only for words starting with a digit
706 $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;
54310121 707
a6006777
PP
708 # Dress it up as a real package name
709 $string =~ s|/|::|g;
710 return "Embed" . $string;
711 }
54310121 712
a6006777
PP
713 sub eval_file {
714 my($filename, $delete) = @_;
715 my $package = valid_package_name($filename);
716 my $mtime = -M $filename;
717 if(defined $Cache{$package}{mtime}
718 &&
54310121 719 $Cache{$package}{mtime} <= $mtime)
a6006777 720 {
54310121 721 # we have compiled this subroutine already,
8ebc5c01
PP
722 # it has not been updated on disk, nothing left to do
723 print STDERR "already compiled $package->handler\n";
a6006777
PP
724 }
725 else {
8ebc5c01
PP
726 local *FH;
727 open FH, $filename or die "open '$filename' $!";
728 local($/) = undef;
729 my $sub = <FH>;
730 close FH;
54310121 731
8ebc5c01
PP
732 #wrap the code into a subroutine inside our unique package
733 my $eval = qq{package $package; sub handler { $sub; }};
734 {
735 # hide our variables within this block
736 my($filename,$mtime,$package,$sub);
737 eval $eval;
738 }
739 die $@ if $@;
54310121 740
8ebc5c01
PP
741 #cache it unless we're cleaning out each time
742 $Cache{$package}{mtime} = $mtime unless $delete;
a6006777 743 }
54310121 744
a6006777
PP
745 eval {$package->handler;};
746 die $@ if $@;
54310121 747
a6006777 748 delete_package($package) if $delete;
54310121 749
a6006777
PP
750 #take a look if you want
751 #print Devel::Symdump->rnew($package)->as_string, $/;
752 }
54310121 753
a6006777 754 1;
54310121 755
a6006777
PP
756 __END__
757
758 /* persistent.c */
54310121
PP
759 #include <EXTERN.h>
760 #include <perl.h>
761
a6006777
PP
762 /* 1 = clean out filename's symbol table after each request, 0 = don't */
763 #ifndef DO_CLEAN
764 #define DO_CLEAN 0
765 #endif
54310121 766
2307c6d0
SB
767 #define BUFFER_SIZE 1024
768
7fef744d 769 static PerlInterpreter *my_perl = NULL;
54310121 770
a6006777
PP
771 int
772 main(int argc, char **argv, char **env)
773 {
774 char *embedding[] = { "", "persistent.pl" };
775 char *args[] = { "", DO_CLEAN, NULL };
2307c6d0 776 char filename[BUFFER_SIZE];
a6006777 777 int exitstatus = 0;
2d8e6c8d 778 STRLEN n_a;
54310121 779
1ccffcf5 780 PERL_SYS_INIT3(&argc,&argv,&env);
7fef744d 781 if((my_perl = perl_alloc()) == NULL) {
8ebc5c01
PP
782 fprintf(stderr, "no memory!");
783 exit(1);
a6006777 784 }
7fef744d 785 perl_construct(my_perl);
54310121 786
7fef744d 787 exitstatus = perl_parse(my_perl, NULL, 2, embedding, NULL);
d95b23b2 788 PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
54310121 789 if(!exitstatus) {
7fef744d 790 exitstatus = perl_run(my_perl);
54310121 791
2307c6d0
SB
792 while(printf("Enter file name: ") &&
793 fgets(filename, BUFFER_SIZE, stdin)) {
54310121 794
2307c6d0 795 filename[strlen(filename)-1] = '\0'; /* strip \n */
8ebc5c01
PP
796 /* call the subroutine, passing it the filename as an argument */
797 args[0] = filename;
4929bf7b 798 call_argv("Embed::Persistent::eval_file",
8ebc5c01 799 G_DISCARD | G_EVAL, args);
54310121 800
8ebc5c01 801 /* check $@ */
9cde0e7f 802 if(SvTRUE(ERRSV))
2d8e6c8d 803 fprintf(stderr, "eval error: %s\n", SvPV(ERRSV,n_a));
8ebc5c01 804 }
a6006777 805 }
54310121 806
9cde0e7f 807 PL_perl_destruct_level = 0;
7fef744d
BD
808 perl_destruct(my_perl);
809 perl_free(my_perl);
1ccffcf5 810 PERL_SYS_TERM();
a6006777
PP
811 exit(exitstatus);
812 }
813
a6006777
PP
814Now compile:
815
54310121 816 % cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
a6006777 817
d1be9408 818Here's an example script file:
a6006777
PP
819
820 #test.pl
821 my $string = "hello";
822 foo($string);
823
824 sub foo {
825 print "foo says: @_\n";
826 }
827
828Now run:
829
830 % persistent
831 Enter file name: test.pl
832 foo says: hello
833 Enter file name: test.pl
834 already compiled Embed::test_2epl->handler
835 foo says: hello
836 Enter file name: ^C
837
d95b23b2
AB
838=head2 Execution of END blocks
839
840Traditionally END blocks have been executed at the end of the perl_run.
841This causes problems for applications that never call perl_run. Since
842perl 5.7.2 you can specify C<PL_exit_flags |= PERL_EXIT_DESTRUCT_END>
843to get the new behaviour. This also enables the running of END blocks if
844the perl_prase fails and C<perl_destruct> will return the exit value.
845
8ebc5c01
PP
846=head2 Maintaining multiple interpreter instances
847
8a7dc658
JO
848Some rare applications will need to create more than one interpreter
849during a session. Such an application might sporadically decide to
54310121 850release any resources associated with the interpreter.
8a7dc658
JO
851
852The program must take care to ensure that this takes place I<before>
9bbedd82
JH
853the next interpreter is constructed. By default, when perl is not
854built with any special options, the global variable
9cde0e7f 855C<PL_perl_destruct_level> is set to C<0>, since extra cleaning isn't
9bbedd82
JH
856usually needed when a program only ever creates a single interpreter
857in its entire lifetime.
8a7dc658 858
9cde0e7f 859Setting C<PL_perl_destruct_level> to C<1> makes everything squeaky clean:
8a7dc658 860
9cde0e7f 861 PL_perl_destruct_level = 1;
8ebc5c01 862
8ebc5c01
PP
863 while(1) {
864 ...
9cde0e7f 865 /* reset global variables here with PL_perl_destruct_level = 1 */
54310121 866 perl_construct(my_perl);
8ebc5c01
PP
867 ...
868 /* clean and reset _everything_ during perl_destruct */
54310121
PP
869 perl_destruct(my_perl);
870 perl_free(my_perl);
8ebc5c01
PP
871 ...
872 /* let's go do it again! */
873 }
874
54310121
PP
875When I<perl_destruct()> is called, the interpreter's syntax parse tree
876and symbol tables are cleaned up, and global variables are reset.
8ebc5c01 877
8a7dc658 878Now suppose we have more than one interpreter instance running at the
9bbedd82
JH
879same time. This is feasible, but only if you used the Configure option
880C<-Dusemultiplicity> or the options C<-Dusethreads -Duseithreads> when
881building Perl. By default, enabling one of these Configure options
882sets the per-interpreter global variable C<PL_perl_destruct_level> to
883C<1>, so that thorough cleaning is automatic.
884
885Using C<-Dusethreads -Duseithreads> rather than C<-Dusemultiplicity>
886is more appropriate if you intend to run multiple interpreters
887concurrently in different threads, because it enables support for
888linking in the thread libraries of your system with the interpreter.
8ebc5c01
PP
889
890Let's give it a try:
891
892
893 #include <EXTERN.h>
8a7dc658 894 #include <perl.h>
8ebc5c01
PP
895
896 /* we're going to embed two interpreters */
897 /* we're going to embed two interpreters */
898
8ebc5c01
PP
899 #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"
900
8ebc5c01
PP
901 int main(int argc, char **argv, char **env)
902 {
1ccffcf5 903 PerlInterpreter *one_perl, *two_perl;
8ebc5c01
PP
904 char *one_args[] = { "one_perl", SAY_HELLO };
905 char *two_args[] = { "two_perl", SAY_HELLO };
906
1ccffcf5
IZ
907 PERL_SYS_INIT3(&argc,&argv,&env);
908 one_perl = perl_alloc();
909 two_perl = perl_alloc();
910
9bbedd82 911 PERL_SET_CONTEXT(one_perl);
8ebc5c01 912 perl_construct(one_perl);
9bbedd82 913 PERL_SET_CONTEXT(two_perl);
8ebc5c01
PP
914 perl_construct(two_perl);
915
9bbedd82 916 PERL_SET_CONTEXT(one_perl);
8ebc5c01 917 perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
9bbedd82 918 PERL_SET_CONTEXT(two_perl);
8ebc5c01
PP
919 perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
920
9bbedd82 921 PERL_SET_CONTEXT(one_perl);
8ebc5c01 922 perl_run(one_perl);
9bbedd82 923 PERL_SET_CONTEXT(two_perl);
8ebc5c01
PP
924 perl_run(two_perl);
925
9bbedd82 926 PERL_SET_CONTEXT(one_perl);
8ebc5c01 927 perl_destruct(one_perl);
9bbedd82 928 PERL_SET_CONTEXT(two_perl);
8ebc5c01
PP
929 perl_destruct(two_perl);
930
9bbedd82 931 PERL_SET_CONTEXT(one_perl);
8ebc5c01 932 perl_free(one_perl);
9bbedd82 933 PERL_SET_CONTEXT(two_perl);
8ebc5c01 934 perl_free(two_perl);
1ccffcf5 935 PERL_SYS_TERM();
8ebc5c01
PP
936 }
937
9bbedd82
JH
938Note the calls to PERL_SET_CONTEXT(). These are necessary to initialize
939the global state that tracks which interpreter is the "current" one on
940the particular process or thread that may be running it. It should
941always be used if you have more than one interpreter and are making
942perl API calls on both interpreters in an interleaved fashion.
943
944PERL_SET_CONTEXT(interp) should also be called whenever C<interp> is
945used by a thread that did not create it (using either perl_alloc(), or
946the more esoteric perl_clone()).
8ebc5c01
PP
947
948Compile as usual:
949
950 % cc -o multiplicity multiplicity.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
951
952Run it, Run it:
953
954 % multiplicity
955 Hi, I'm one_perl
956 Hi, I'm two_perl
957
96dbc785
PP
958=head2 Using Perl modules, which themselves use C libraries, from your C program
959
960If you've played with the examples above and tried to embed a script
961that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++ library,
962this probably happened:
963
964
965 Can't load module Socket, dynamic loading not available in this perl.
966 (You may need to build a new perl executable which either supports
967 dynamic loading or has the Socket module statically linked into it.)
968
969
970What's wrong?
971
972Your interpreter doesn't know how to communicate with these extensions
973on its own. A little glue will help. Up until now you've been
974calling I<perl_parse()>, handing it NULL for the second argument:
975
976 perl_parse(my_perl, NULL, argc, my_argv, NULL);
977
978That's where the glue code can be inserted to create the initial contact between
979Perl and linked C/C++ routines. Let's take a look some pieces of I<perlmain.c>
980to see how Perl does this:
981
cc7dda15 982 static void xs_init (pTHX);
96dbc785 983
cc7dda15
GS
984 EXTERN_C void boot_DynaLoader (pTHX_ CV* cv);
985 EXTERN_C void boot_Socket (pTHX_ CV* cv);
96dbc785
PP
986
987
988 EXTERN_C void
cc7dda15 989 xs_init(pTHX)
96dbc785
PP
990 {
991 char *file = __FILE__;
992 /* DynaLoader is a special case */
993 newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
994 newXS("Socket::bootstrap", boot_Socket, file);
995 }
996
997Simply put: for each extension linked with your Perl executable
998(determined during its initial configuration on your
999computer or when adding a new extension),
1000a Perl subroutine is created to incorporate the extension's
1001routines. Normally, that subroutine is named
1002I<Module::bootstrap()> and is invoked when you say I<use Module>. In
1003turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl
1004counterpart for each of the extension's XSUBs. Don't worry about this
1005part; leave that to the I<xsubpp> and extension authors. If your
1006extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()>
1007for you on the fly. In fact, if you have a working DynaLoader then there
5f05dabc 1008is rarely any need to link in any other extensions statically.
96dbc785
PP
1009
1010
1011Once you have this code, slap it into the second argument of I<perl_parse()>:
1012
1013
1014 perl_parse(my_perl, xs_init, argc, my_argv, NULL);
1015
1016
1017Then compile:
1018
8a7dc658 1019 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
96dbc785
PP
1020
1021 % interp
1022 use Socket;
1023 use SomeDynamicallyLoadedModule;
1024
1025 print "Now I can use extensions!\n"'
1026
1027B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code.
1028
8a7dc658 1029 % perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c
96dbc785
PP
1030 % cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts`
1031 % cc -c interp.c `perl -MExtUtils::Embed -e ccopts`
8a7dc658 1032 % cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts`
96dbc785 1033
4929bf7b 1034Consult L<perlxs>, L<perlguts>, and L<perlapi> for more details.
96dbc785 1035
13a2d996 1036=head1 Embedding Perl under Win32
53f52f58 1037
cc7dda15
GS
1038In general, all of the source code shown here should work unmodified under
1039Windows.
53f52f58 1040
cc7dda15
GS
1041However, there are some caveats about the command-line examples shown.
1042For starters, backticks won't work under the Win32 native command shell.
53f52f58
DM
1043The ExtUtils::Embed kit on CPAN ships with a script called
1044B<genmake>, which generates a simple makefile to build a program from
e010571f 1045a single C source file. It can be used like this:
53f52f58
DM
1046
1047 C:\ExtUtils-Embed\eg> perl genmake interp.c
1048 C:\ExtUtils-Embed\eg> nmake
1049 C:\ExtUtils-Embed\eg> interp -e "print qq{I'm embedded in Win32!\n}"
1050
e010571f
GS
1051You may wish to use a more robust environment such as the Microsoft
1052Developer Studio. In this case, run this to generate perlxsi.c:
53f52f58
DM
1053
1054 perl -MExtUtils::Embed -e xsinit
1055
e010571f
GS
1056Create a new project and Insert -> Files into Project: perlxsi.c,
1057perl.lib, and your own source files, e.g. interp.c. Typically you'll
1058find perl.lib in B<C:\perl\lib\CORE>, if not, you should see the
1059B<CORE> directory relative to C<perl -V:archlib>. The studio will
1060also need this path so it knows where to find Perl include files.
1061This path can be added via the Tools -> Options -> Directories menu.
1062Finally, select Build -> Build interp.exe and you're ready to go.
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1064=head1 Hiding Perl_
1065
1066If you completely hide the short forms forms of the Perl public API,
d51482e4 1067add -DPERL_NO_SHORT_NAMES to the compilation flags. This means that
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1068for example instead of writing
1069
1070 warn("%d bottles of beer on the wall", bottlecount);
1071
1072you will have to write the explicit full form
1073
1074 Perl_warn(aTHX_ "%d bottles of beer on the wall", bottlecount);
1075
1076(See L<perlguts/Background and PERL_IMPLICIT_CONTEXT for the explanation
1077of the C<aTHX_>.> ) Hiding the short forms is very useful for avoiding
1078all sorts of nasty (C preprocessor or otherwise) conflicts with other
1079software packages (Perl defines about 2400 APIs with these short names,
1080take or leave few hundred, so there certainly is room for conflict.)
1081
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1082=head1 MORAL
1083
1084You can sometimes I<write faster code> in C, but
5f05dabc 1085you can always I<write code faster> in Perl. Because you can use
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1086each from the other, combine them as you wish.
1087
1088
1089=head1 AUTHOR
1090
e010571f
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1091Jon Orwant <F<orwant@tpj.com>> and Doug MacEachern
1092<F<dougm@osf.org>>, with small contributions from Tim Bunce, Tom
1093Christiansen, Guy Decoux, Hallvard Furuseth, Dov Grobgeld, and Ilya
1094Zakharevich.
cb1a09d0 1095
e010571f 1096Doug MacEachern has an article on embedding in Volume 1, Issue 4 of
f224927c 1097The Perl Journal ( http://www.tpj.com/ ). Doug is also the developer of the
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1098most widely-used Perl embedding: the mod_perl system
1099(perl.apache.org), which embeds Perl in the Apache web server.
1100Oracle, Binary Evolution, ActiveState, and Ben Sugars's nsapi_perl
1101have used this model for Oracle, Netscape and Internet Information
1102Server Perl plugins.
cb1a09d0 1103
e010571f 1104July 22, 1998
8a7dc658
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1105
1106=head1 COPYRIGHT
1107
e010571f 1108Copyright (C) 1995, 1996, 1997, 1998 Doug MacEachern and Jon Orwant. All
8a7dc658
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1109Rights Reserved.
1110
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1111Permission is granted to make and distribute verbatim copies of this
1112documentation provided the copyright notice and this permission notice are
1113preserved on all copies.
1114
1115Permission is granted to copy and distribute modified versions of this
1116documentation under the conditions for verbatim copying, provided also
1117that they are marked clearly as modified versions, that the authors'
1118names and title are unchanged (though subtitles and additional
1119authors' names may be added), and that the entire resulting derived
1120work is distributed under the terms of a permission notice identical
1121to this one.
1122
1123Permission is granted to copy and distribute translations of this
1124documentation into another language, under the above conditions for
1125modified versions.