=item B<Use C from Perl?>
-Read L<perlcall> and L<perlxs>.
+Read L<perlxstut>, L<perlxs>, L<h2xs>, and L<perlguts>.
-=item B<Use a UNIX program from Perl?>
+=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>.
+Read about L<perlfunc/do> and L<perlfunc/eval> and L<perlfunc/require>
+and L<perlfunc/use>.
=item B<Use C from C?>
=head2 ROADMAP
-L<Compiling your C program>
+=over 5
-There's one example in each of the six sections:
+L<Compiling your C program>
L<Adding a Perl interpreter to your C program>
L<Fiddling with the Perl stack from your C program>
+L<Maintaining a persistent interpreter>
+
+L<Maintaining multiple interpreter instances>
+
L<Using Perl modules, which themselves use C libraries, from your C program>
-This documentation is UNIX specific.
+L<Embedding Perl under Win32>
+
+=back
=head2 Compiling your C program
-Every C program that uses Perl must link in the I<perl library>.
+If you have trouble compiling the scripts in this documentation,
+you're not alone. The cardinal rule: COMPILE THE PROGRAMS IN EXACTLY
+THE SAME WAY THAT YOUR PERL WAS COMPILED. (Sorry for yelling.)
+Also, 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
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.
+When you use Perl from C, your C program will--usually--allocate,
+"run", and deallocate a I<PerlInterpreter> object, which is defined by
+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:
+(version 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
+that looks like this:
/usr/local/lib/perl5/your_architecture_here/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:
+Here's how you'd compile the example in the next section,
+L<Adding a Perl interpreter to your C program>, on my Linux box:
+
+ % gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include
+ -I/usr/local/lib/perl5/i586-linux/5.003/CORE
+ -L/usr/local/lib/perl5/i586-linux/5.003/CORE
+ -o interp interp.c -lperl -lm
+
+(That's all one line.) On my DEC Alpha running old 5.003_05, the
+incantation is a bit different:
+
+ % cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include
+ -I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE
+ -L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib
+ -D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm
- % 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
+How can you figure out what to add? Assuming your Perl is post-5.001,
+execute a C<perl -V> command and pay special attention to the "cc" and
+"ccflags" information.
-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'll have to choose the appropriate compiler (I<cc>, I<gcc>, et al.) for
+your machine: C<perl -MConfig -e 'print $Config{cc}'> will tell you what
+to use.
+
+You'll also have to choose the appropriate 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 C<-L>. If it
+complains that it can't find I<EXTERN.h> and I<perl.h>, you need to
+change the path following the C<-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:
+Provided your perl binary was properly configured and installed the
+B<ExtUtils::Embed> module will 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 isn't part of your Perl distribution,
+you can retrieve it from
+http://www.perl.com/perl/CPAN/modules/by-module/ExtUtils/. (If
+this documentation came from your Perl distribution, then you're
+running 5.004 or better and you already have it.)
-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.
-
+The B<ExtUtils::Embed> kit on CPAN also contains all source code for
+the examples in this document, tests, additional examples and other
+information you may find useful.
=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:
+included in the source distribution. Here's a bastardized, nonportable
+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 */
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.
+Notice that we don't use the C<env> pointer. Normally handed to
+C<perl_parse> as its final argument, C<env> here is replaced by
+C<NULL>, which means that the current environment will be used.
Now compile this program (I'll call it I<interp.c>) into an executable:
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
-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()>.
+To call individual Perl subroutines, you can use any of the B<perl_call_*>
+functions documented in L<perlcall>.
+In this example we'll use C<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>
int main(int argc, char **argv, char **env)
{
+ char *args[] = { NULL };
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, argc, argv, NULL);
- /*** This replaces perl_run() ***/
- perl_call_argv("showtime", G_DISCARD | G_NOARGS, argv);
+ /*** skipping perl_run() ***/
+
+ perl_call_argv("showtime", G_DISCARD | G_NOARGS, args);
+
perl_destruct(my_perl);
perl_free(my_perl);
}
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
+(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>
+In this particular case we don't have to call I<perl_run>, but in
+general it's considered good practice to ensure proper initialization
+of library code, including execution of all object C<DESTROY> methods
+and package C<END {}> blocks.
-=head2 Evaluating a Perl statement from your C program
+If you want to pass arguments to the Perl subroutine, you can add
+strings to the C<NULL>-terminated C<args> list passed to
+I<perl_call_argv>. For other data types, or to examine return values,
+you'll need to manipulate the Perl stack. That's demonstrated in the
+last section of this document: L<Fiddling with the Perl stack 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.
+=head2 Evaluating a Perl statement from your C program
-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>.
+Perl provides two API functions to evaluate pieces of Perl code.
+These are L<perlguts/perl_eval_sv> and L<perlguts/perl_eval_pv>.
-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.
+Arguably, these are the only routines you'll ever need to execute
+snippets of Perl code from within your C program. Your code can be as
+long as you wish; it can contain multiple statements; it can employ
+L<perlfunc/use>, L<perlfunc/require>, and L<perlfunc/do> to
+include external Perl files.
-Our I<perl_eval()> lets us evaluate individual Perl strings, and then
+I<perl_eval_pv> 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);
+ STRLEN n_a;
+ char *embedding[] = { "", "-e", "0" };
+
+ my_perl = perl_alloc();
+ perl_construct( my_perl );
+
+ perl_parse(my_perl, NULL, 3, embedding, NULL);
+ perl_run(my_perl);
+
+ /** Treat $a as an integer **/
+ perl_eval_pv("$a = 3; $a **= 2", TRUE);
+ printf("a = %d\n", SvIV(perl_get_sv("a", FALSE)));
+
+ /** Treat $a as a float **/
+ perl_eval_pv("$a = 3.14; $a **= 2", TRUE);
+ printf("a = %f\n", SvNV(perl_get_sv("a", FALSE)));
+
+ /** Treat $a as a string **/
+ perl_eval_pv("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
+ printf("a = %s\n", SvPV(perl_get_sv("a", FALSE), n_a));
+
+ 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>.
a = 9.859600
a = Just Another Perl Hacker
+In the example above, we've created a global variable to temporarily
+store the computed value of our eval'd expression. It is also
+possible and in most cases a better strategy to fetch the return value
+from I<perl_eval_pv()> instead. Example:
+
+ ...
+ STRLEN n_a;
+ SV *val = perl_eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
+ printf("%s\n", SvPV(val,n_a));
+ ...
+
+This way, we avoid namespace pollution by not creating global
+variables and we've simplified our code as well.
=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
+The I<perl_eval_sv()> function 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);
+ I32 match(SV *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/">),
+Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which
+in your C program might appear as "/\\b\\w*\\b/"), match()
returns 1 if the string matches the pattern and 0 otherwise.
+ int substitute(SV **string, char *pattern);
- int substitute(char *string[], char *pattern);
+Given a pointer to an C<SV> and an C<=~> operation (e.g.,
+C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string
+within the C<AV> at according to the operation, returning the number of substitutions
+made.
-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(SV *string, char *pattern, AV **matches);
- 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 =~ $pattern> in an array context, and fills in
-I<matches> with the array elements (allocating memory as it does so),
-returning the number of matches found.
+Given an C<SV>, a pattern, and a pointer to an empty C<AV>,
+matches() evaluates C<$string =~ $pattern> in an array context, and
+fills in I<matches> with the array elements, returning the number of matches found.
Here's a sample program, I<match.c>, that uses all three (long lines have
been wrapped here):
- #include <stdio.h>
- #include <EXTERN.h>
- #include <perl.h>
- static PerlInterpreter *my_perl;
- int perl_eval(char *string)
- {
- char *argv[2];
- argv[0] = string;
- argv[1] = NULL;
- perl_call_argv("_eval_", 0, argv);
- }
- /** match(string, pattern)
- **
- ** Used for matches in a scalar context.
- **
- ** Returns 1 if the match was successful; 0 otherwise.
- **/
- char match(char *string, char *pattern)
- {
- char *command;
- command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 37);
- sprintf(command, "$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;
+ #include <EXTERN.h>
+ #include <perl.h>
+
+ /** my_perl_eval_sv(code, error_check)
+ ** kinda like perl_eval_sv(),
+ ** but we pop the return value off the stack
+ **/
+ SV* my_perl_eval_sv(SV *sv, I32 croak_on_error)
+ {
+ dSP;
+ SV* retval;
+ STRLEN n_a;
+
+ PUSHMARK(SP);
+ perl_eval_sv(sv, G_SCALAR);
+
+ SPAGAIN;
+ retval = POPs;
+ PUTBACK;
+
+ if (croak_on_error && SvTRUE(ERRSV))
+ croak(SvPVx(ERRSV, n_a));
+
+ return retval;
+ }
+
+ /** match(string, pattern)
+ **
+ ** Used for matches in a scalar context.
+ **
+ ** Returns 1 if the match was successful; 0 otherwise.
+ **/
+
+ I32 match(SV *string, char *pattern)
+ {
+ SV *command = NEWSV(1099, 0), *retval;
+ STRLEN n_a;
+
+ sv_setpvf(command, "my $string = '%s'; $string =~ %s",
+ SvPV(string,n_a), pattern);
+
+ retval = my_perl_eval_sv(command, TRUE);
+ SvREFCNT_dec(command);
+
+ return SvIV(retval);
+ }
+
+ /** substitute(string, pattern)
+ **
+ ** Used for =~ operations that modify their left-hand side (s/// and tr///)
+ **
+ ** Returns the number of successful matches, and
+ ** modifies the input string if there were any.
+ **/
+
+ I32 substitute(SV **string, char *pattern)
+ {
+ SV *command = NEWSV(1099, 0), *retval;
+ STRLEN n_a;
+
+ sv_setpvf(command, "$string = '%s'; ($string =~ %s)",
+ SvPV(*string,n_a), pattern);
+
+ retval = my_perl_eval_sv(command, TRUE);
+ SvREFCNT_dec(command);
+
+ *string = perl_get_sv("string", FALSE);
+ return SvIV(retval);
+ }
+
+ /** matches(string, pattern, matches)
+ **
+ ** Used for matches in an array context.
+ **
+ ** Returns the number of matches,
+ ** and fills in **matches with the matching substrings
+ **/
+
+ I32 matches(SV *string, char *pattern, AV **match_list)
+ {
+ SV *command = NEWSV(1099, 0);
I32 num_matches;
- STRLEN length;
- int i;
- command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 38);
- sprintf(command, "$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);
- }
+ STRLEN n_a;
+
+ sv_setpvf(command, "my $string = '%s'; @array = ($string =~ %s)",
+ SvPV(string,n_a), pattern);
+
+ my_perl_eval_sv(command, TRUE);
+ SvREFCNT_dec(command);
+
+ *match_list = perl_get_av("array", FALSE);
+ num_matches = av_len(*match_list) + 1; /** assume $[ is 0 **/
+
return num_matches;
- }
- main (int argc, char **argv, char **env)
- {
- 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 );
+ }
+
+ main (int argc, char **argv, char **env)
+ {
+ PerlInterpreter *my_perl = perl_alloc();
+ char *embedding[] = { "", "-e", "0" };
+ AV *match_list;
+ I32 num_matches, i;
+ SV *text = NEWSV(1099,0);
+ STRLEN n_a;
+
+ 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");
+
+ sv_setpv(text, "When he is at a convenience store and the bill comes to some amount like 76 cents, Maynard is aware that there is something he *should* do, something that will enable him to get back a quarter, but he has no idea *what*. He fumbles through his red squeezey changepurse and gives the boy three extra pennies with his dollar, hoping that he might luck into the correct amount. The boy gives him back two of his own pennies and then the big shiny quarter that is his prize. -RICHH");
+
if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
- printf("match: Text contains the word 'quarter'.\n\n");
+ printf("match: Text contains the word 'quarter'.\n\n");
else
- printf("match: Text doesn't contain the word 'quarter'.\n\n");
+ 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");
+ printf("match: Text contains the word 'eighth'.\n\n");
else
- printf("match: Text doesn't contain the word 'eighth'.\n\n");
+ 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("match: %s\n", SvPV(*av_fetch(match_list, i, FALSE),n_a));
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);
+ printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
+ num_matches);
+ printf("Now text is: %s\n\n", SvPV(text,n_a));
}
+
/** Attempt a substitution **/
if (!substitute(&text, "s/Perl/C/")) {
- printf("substitute: s/Perl/C...No substitution made.\n\n");
+ printf("substitute: s/Perl/C...No substitution made.\n\n");
}
- free(text);
+
+ SvREFCNT_dec(text);
+ PL_perl_destruct_level = 1;
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'.
+ match: Text contains the word 'quarter'.
- perl_match: Text doesn't contain the word 'eighth'.
+ match: Text doesn't contain the word 'eighth'.
- perl_matches: m/(wi..)/g found 2 matches...
+ 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,
+ 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.
+ substitute: s/Perl/C...No substitution made.
=head2 Fiddling with the Perl stack from your C program
Once you've understood those, embedding Perl in C is easy.
-Because C has no built-in function for integer exponentiation, let's
+Because C has no builtin 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>:
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>
dSP; /* initialize stack pointer */
ENTER; /* everything created after here */
SAVETMPS; /* ...is a temporary variable. */
- PUSHMARK(sp); /* remember the stack pointer */
+ 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 */
int main (int argc, char **argv, char **env)
{
- char *my_argv[2];
+ char *my_argv[] = { "", "power.pl" };
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);
+ perl_parse(my_perl, NULL, 2, my_argv, (char **)NULL);
+ perl_run(my_perl);
PerlPower(3, 4); /*** Compute 3 ** 4 ***/
% power
3 to the 4th power is 81.
+=head2 Maintaining a persistent interpreter
+
+When developing interactive and/or potentially long-running
+applications, it's a good idea to maintain a persistent interpreter
+rather than allocating and constructing a new interpreter multiple
+times. The major reason is speed: since Perl will only be loaded into
+memory once.
+
+However, you have to be more cautious with namespace and variable
+scoping when using a persistent interpreter. In previous examples
+we've been using global variables in the default package C<main>. We
+knew exactly what code would be run, and assumed we could avoid
+variable collisions and outrageous symbol table growth.
+
+Let's say your application is a server that will occasionally run Perl
+code from some arbitrary file. Your server has no way of knowing what
+code it's going to run. Very dangerous.
+
+If the file is pulled in by C<perl_parse()>, compiled into a newly
+constructed interpreter, and subsequently cleaned out with
+C<perl_destruct()> afterwards, you're shielded from most namespace
+troubles.
+
+One way to avoid namespace collisions in this scenario is to translate
+the filename into a guaranteed-unique package name, and then compile
+the code into that package using L<perlfunc/eval>. In the example
+below, each file will only be compiled once. Or, the application
+might choose to clean out the symbol table associated with the file
+after it's no longer needed. Using L<perlcall/perl_call_argv>, We'll
+call the subroutine C<Embed::Persistent::eval_file> which lives in the
+file C<persistent.pl> and pass the filename and boolean cleanup/cache
+flag as arguments.
+
+Note that the process will continue to grow for each file that it
+uses. In addition, there might be C<AUTOLOAD>ed subroutines and other
+conditions that cause Perl's symbol table to grow. You might want to
+add some logic that keeps track of the process size, or restarts
+itself after a certain number of requests, to ensure that memory
+consumption is minimized. You'll also want to scope your variables
+with L<perlfunc/my> whenever possible.
+
+
+ package Embed::Persistent;
+ #persistent.pl
+
+ use strict;
+ our %Cache;
+ use Symbol qw(delete_package);
+
+ sub valid_package_name {
+ my($string) = @_;
+ $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
+ # second pass only for words starting with a digit
+ $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;
+
+ # Dress it up as a real package name
+ $string =~ s|/|::|g;
+ return "Embed" . $string;
+ }
+
+ sub eval_file {
+ my($filename, $delete) = @_;
+ my $package = valid_package_name($filename);
+ my $mtime = -M $filename;
+ if(defined $Cache{$package}{mtime}
+ &&
+ $Cache{$package}{mtime} <= $mtime)
+ {
+ # we have compiled this subroutine already,
+ # it has not been updated on disk, nothing left to do
+ print STDERR "already compiled $package->handler\n";
+ }
+ else {
+ local *FH;
+ open FH, $filename or die "open '$filename' $!";
+ local($/) = undef;
+ my $sub = <FH>;
+ close FH;
+
+ #wrap the code into a subroutine inside our unique package
+ my $eval = qq{package $package; sub handler { $sub; }};
+ {
+ # hide our variables within this block
+ my($filename,$mtime,$package,$sub);
+ eval $eval;
+ }
+ die $@ if $@;
+
+ #cache it unless we're cleaning out each time
+ $Cache{$package}{mtime} = $mtime unless $delete;
+ }
+
+ eval {$package->handler;};
+ die $@ if $@;
+
+ delete_package($package) if $delete;
+
+ #take a look if you want
+ #print Devel::Symdump->rnew($package)->as_string, $/;
+ }
+
+ 1;
+
+ __END__
+
+ /* persistent.c */
+ #include <EXTERN.h>
+ #include <perl.h>
+
+ /* 1 = clean out filename's symbol table after each request, 0 = don't */
+ #ifndef DO_CLEAN
+ #define DO_CLEAN 0
+ #endif
+
+ static PerlInterpreter *perl = NULL;
+
+ int
+ main(int argc, char **argv, char **env)
+ {
+ char *embedding[] = { "", "persistent.pl" };
+ char *args[] = { "", DO_CLEAN, NULL };
+ char filename [1024];
+ int exitstatus = 0;
+ STRLEN n_a;
+
+ if((perl = perl_alloc()) == NULL) {
+ fprintf(stderr, "no memory!");
+ exit(1);
+ }
+ perl_construct(perl);
+
+ exitstatus = perl_parse(perl, NULL, 2, embedding, NULL);
+
+ if(!exitstatus) {
+ exitstatus = perl_run(perl);
+
+ while(printf("Enter file name: ") && gets(filename)) {
+
+ /* call the subroutine, passing it the filename as an argument */
+ args[0] = filename;
+ perl_call_argv("Embed::Persistent::eval_file",
+ G_DISCARD | G_EVAL, args);
+
+ /* check $@ */
+ if(SvTRUE(ERRSV))
+ fprintf(stderr, "eval error: %s\n", SvPV(ERRSV,n_a));
+ }
+ }
+
+ PL_perl_destruct_level = 0;
+ perl_destruct(perl);
+ perl_free(perl);
+ exit(exitstatus);
+ }
+
+Now compile:
+
+ % cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
+
+Here's a example script file:
+
+ #test.pl
+ my $string = "hello";
+ foo($string);
+
+ sub foo {
+ print "foo says: @_\n";
+ }
+
+Now run:
+
+ % persistent
+ Enter file name: test.pl
+ foo says: hello
+ Enter file name: test.pl
+ already compiled Embed::test_2epl->handler
+ foo says: hello
+ Enter file name: ^C
+
+=head2 Maintaining multiple interpreter instances
+
+Some rare applications will need to create more than one interpreter
+during a session. Such an application might sporadically decide to
+release any resources associated with the interpreter.
+
+The program must take care to ensure that this takes place I<before>
+the next interpreter is constructed. By default, the global variable
+C<PL_perl_destruct_level> is set to C<0>, since extra cleaning isn't
+needed when a program has only one interpreter.
+
+Setting C<PL_perl_destruct_level> to C<1> makes everything squeaky clean:
+
+ PL_perl_destruct_level = 1;
+
+ while(1) {
+ ...
+ /* reset global variables here with PL_perl_destruct_level = 1 */
+ perl_construct(my_perl);
+ ...
+ /* clean and reset _everything_ during perl_destruct */
+ perl_destruct(my_perl);
+ perl_free(my_perl);
+ ...
+ /* let's go do it again! */
+ }
+
+When I<perl_destruct()> is called, the interpreter's syntax parse tree
+and symbol tables are cleaned up, and global variables are reset.
+
+Now suppose we have more than one interpreter instance running at the
+same time. This is feasible, but only if you used the
+C<-DMULTIPLICITY> flag when building Perl. By default, that sets
+C<PL_perl_destruct_level> to C<1>.
+
+Let's give it a try:
+
+
+ #include <EXTERN.h>
+ #include <perl.h>
+
+ /* we're going to embed two interpreters */
+ /* we're going to embed two interpreters */
+
+ #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"
+
+ int main(int argc, char **argv, char **env)
+ {
+ PerlInterpreter
+ *one_perl = perl_alloc(),
+ *two_perl = perl_alloc();
+ char *one_args[] = { "one_perl", SAY_HELLO };
+ char *two_args[] = { "two_perl", SAY_HELLO };
+
+ perl_construct(one_perl);
+ perl_construct(two_perl);
+
+ perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
+ perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
+
+ perl_run(one_perl);
+ perl_run(two_perl);
+
+ perl_destruct(one_perl);
+ perl_destruct(two_perl);
+
+ perl_free(one_perl);
+ perl_free(two_perl);
+ }
+
+
+Compile as usual:
+
+ % cc -o multiplicity multiplicity.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
+
+Run it, Run it:
+
+ % multiplicity
+ Hi, I'm one_perl
+ Hi, I'm two_perl
+
=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
# define EXTERN_C extern
#endif
- static void xs_init _((void));
+ static void xs_init (void);
- EXTERN_C void boot_DynaLoader _((CV* cv));
- EXTERN_C void boot_Socket _((CV* cv));
+ EXTERN_C void boot_DynaLoader (CV* cv);
+ EXTERN_C void boot_Socket (CV* cv);
EXTERN_C void
Then compile:
- % cc -o interp interp.c `perl -MExtUtils::Embed -e ldopts`
+ % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
% interp
use Socket;
B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code.
- % perl -MExtUtils::Embed -e xsinit -o perlxsi.c
+ % 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 Embedding Perl under Win32
+
+At the time of this writing (5.004), there are two versions of Perl
+which run under Win32. (The two versions are merging in 5.005.)
+Interfacing to ActiveState's Perl library is quite different from the
+examples in this documentation, as significant changes were made to
+the internal Perl API. However, it is possible to embed ActiveState's
+Perl runtime. For details, see the Perl for Win32 FAQ at
+http://www.perl.com/CPAN/doc/FAQs/win32/perlwin32faq.html.
+
+With the "official" Perl version 5.004 or higher, all the examples
+within this documentation will compile and run untouched, although
+the build process is slightly different between Unix and Win32.
+
+For starters, backticks don't work under the Win32 native command shell.
+The ExtUtils::Embed kit on CPAN ships with a script called
+B<genmake>, which generates a simple makefile to build a program from
+a single C source file. It can be used like this:
+
+ C:\ExtUtils-Embed\eg> perl genmake interp.c
+ C:\ExtUtils-Embed\eg> nmake
+ C:\ExtUtils-Embed\eg> interp -e "print qq{I'm embedded in Win32!\n}"
+
+You may wish to use a more robust environment such as the Microsoft
+Developer Studio. In this case, run this to generate perlxsi.c:
+
+ perl -MExtUtils::Embed -e xsinit
+
+Create a new project and Insert -> Files into Project: perlxsi.c,
+perl.lib, and your own source files, e.g. interp.c. Typically you'll
+find perl.lib in B<C:\perl\lib\CORE>, if not, you should see the
+B<CORE> directory relative to C<perl -V:archlib>. The studio will
+also need this path so it knows where to find Perl include files.
+This path can be added via the Tools -> Options -> Directories menu.
+Finally, select Build -> Build interp.exe and you're ready to go.
=head1 MORAL
=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
+Jon Orwant <F<orwant@tpj.com>> and Doug MacEachern
+<F<dougm@osf.org>>, with small contributions from Tim Bunce, Tom
+Christiansen, Guy Decoux, Hallvard Furuseth, Dov Grobgeld, and Ilya
Zakharevich.
-June 17, 1996
+Doug MacEachern has an article on embedding in Volume 1, Issue 4 of
+The Perl Journal (http://tpj.com). Doug is also the developer of the
+most widely-used Perl embedding: the mod_perl system
+(perl.apache.org), which embeds Perl in the Apache web server.
+Oracle, Binary Evolution, ActiveState, and Ben Sugars's nsapi_perl
+have used this model for Oracle, Netscape and Internet Information
+Server Perl plugins.
+
+July 22, 1998
+
+=head1 COPYRIGHT
+
+Copyright (C) 1995, 1996, 1997, 1998 Doug MacEachern and Jon Orwant. All
+Rights Reserved.
+
+Permission is granted to make and distribute verbatim copies of this
+documentation provided the copyright notice and this permission notice are
+preserved on all copies.
+
+Permission is granted to copy and distribute modified versions of this
+documentation under the conditions for verbatim copying, provided also
+that they are marked clearly as modified versions, that the authors'
+names and title are unchanged (though subtitles and additional
+authors' names may be added), and that the entire resulting derived
+work is distributed under the terms of a permission notice identical
+to this one.
-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.
+Permission is granted to copy and distribute translations of this
+documentation into another language, under the above conditions for
+modified versions.
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