Read L<perlcall> and L<perlxs>.
-=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>.
L<Using Perl modules, which themselves use C libraries, from your C program>
This documentation is Unix specific; if you have information about how
-to embed Perl on other platforms, please send e-mail to
-orwant@tpj.com.
+to embed Perl on other platforms, please send e-mail to <F<orwant@tpj.com>>.
=head2 Compiling your C program
perl -MConfig -e 'print $Config{archlib}'
-Here's how you'd compile the example in the next section,
+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
+ % 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
+ -L/usr/local/lib/perl5/i586-linux/5.003/CORE
-o interp interp.c -lperl -lm
-(That's all one line.) On my DEC Alpha running 5.00305, the incantation
+(That's all one line.) On my DEC Alpha running 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
+ % cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include
+ -I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE
+ -L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib
-D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm
How can you figure out what to add? Assuming your Perl is post-5.001,
execute a C<perl -V> command and pay special attention to the "cc" and
-"ccflags" information.
+"ccflags" information.
-You'll have to choose the appropriate compiler (I<cc>, I<gcc>, et al.) for
+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.
+to use.
You'll also have to choose the appropriate library directory
(I</usr/local/lib/...>) for your machine. If your compiler complains
perl -MConfig -e 'print $Config{libs}'
-Provided your perl binary was properly configured and installed the
+Provided your perl binary was properly configured and installed the
B<ExtUtils::Embed> module will determine all of this information for
you:
running 5.004 or better and you already have it.)
The B<ExtUtils::Embed> kit on CPAN also contains all source code for
-the examples in this document, tests, additional examples and other
+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
+from the source distribution. Here's a bastardized, nonportable
version of I<miniperlmain.c> containing the essentials of embedding:
#include <EXTERN.h> /* from the Perl distribution */
=head2 Calling a Perl subroutine from your C program
To call individual Perl subroutines, you can use any of the B<perl_call_*>
-functions documented in the L<perlcall> man page.
+functions documented in the L<perlcall> manpage.
In this example we'll use I<perl_call_argv>.
That's shown below, in a program I'll call I<showtime.c>.
=head2 Evaluating a Perl statement from your C program
-One way to evaluate pieces of Perl code is to use
-L<perlguts/perl_eval_sv()>. We've wrapped this inside our own
-I<perl_eval()> function, which converts a command string to an SV,
-passing this and the L<perlcall/G_DISCARD> flag to
-L<perlguts/perl_eval_sv()>.
+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
+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 <EXTERN.h>
#include <perl.h>
-
+
static PerlInterpreter *my_perl;
-
- I32 perl_eval(char *string)
- {
- return perl_eval_sv(newSVpv(string,0), G_DISCARD);
- }
-
+
main (int argc, char **argv, char **env)
{
- char *embedding[] = { "", "-e", "0" };
- STRLEN length;
-
- my_perl = perl_alloc();
- perl_construct( my_perl );
-
- perl_parse(my_perl, NULL, 3, embedding, NULL);
- perl_run(my_perl);
- /** Treat $a as an integer **/
- perl_eval("$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);
+ char *embedding[] = { "", "-e", "0" };
+
+ my_perl = perl_alloc();
+ perl_construct( my_perl );
+
+ perl_parse(my_perl, NULL, 3, embedding, NULL);
+ perl_run(my_perl);
+
+ /** Treat $a as an integer **/
+ perl_eval_pv("$a = 3; $a **= 2", TRUE);
+ printf("a = %d\n", SvIV(perl_get_sv("a", FALSE)));
+
+ /** Treat $a as a float **/
+ perl_eval_pv("$a = 3.14; $a **= 2", TRUE);
+ printf("a = %f\n", SvNV(perl_get_sv("a", FALSE)));
+
+ /** Treat $a as a string **/
+ perl_eval_pv("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
+ printf("a = %s\n", SvPV(perl_get_sv("a", FALSE), na));
+
+ perl_destruct(my_perl);
+ perl_free(my_perl);
}
All of those strange functions with 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 L<perl_eval_pv> instead. Example:
+
+ ...
+ SV *val = perl_eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
+ printf("%s\n", SvPV(val,na));
+ ...
+
+This way, we avoid namespace pollution by not creating 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_pv()> 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()>.
#include <perl.h>
static PerlInterpreter *my_perl;
- I32 perl_eval(char *string)
- {
- return perl_eval_sv(newSVpv(string,0), G_DISCARD);
- }
+
/** match(string, pattern)
**
** Used for matches in a scalar context.
command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 37);
sprintf(command, "$string = '%s'; $return = $string =~ %s",
string, pattern);
- perl_eval(command);
+ perl_eval_pv(command, TRUE);
free(command);
return SvIV(perl_get_sv("return", FALSE));
}
command = malloc(sizeof(char) * strlen(*string) + strlen(pattern) + 35);
sprintf(command, "$string = '%s'; $ret = ($string =~ %s)",
*string, pattern);
- perl_eval(command);
+ perl_eval_pv(command, TRUE);
free(command);
*string = SvPV(perl_get_sv("string", FALSE), length);
return SvIV(perl_get_sv("ret", FALSE));
command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 38);
sprintf(command, "$string = '%s'; @array = ($string =~ %s)",
string, pattern);
- perl_eval(command);
+ perl_eval_pv(command, TRUE);
free(command);
array = perl_get_av("array", FALSE);
num_matches = av_len(array) + 1; /** assume $[ is 0 **/
match: with
substitute: s/[aeiou]//gi...139 substitutions made.
- Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
+ Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt bck
qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd gvs th by
thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct mnt. Th by gvs
Once you've understood those, embedding Perl in C is easy.
-Because C has no built-in function for integer exponentiation, let's
+Because C has no builtin function for integer exponentiation, let's
make Perl's ** operator available to it (this is less useful than it
sounds, because Perl implements ** with C's I<pow()> function). First
I'll create a stub exponentiation function in I<power.pl>:
applications, it's a good idea to maintain a persistent interpreter
rather than allocating and constructing a new interpreter multiple
times. The major reason is speed: since Perl will only be loaded into
-memory once.
+memory once.
However, you have to be more cautious with namespace and variable
scoping when using a persistent interpreter. In previous examples
consumption is minimized. You'll also want to scope your variables
with L<perlfunc/my> whenever possible.
-
+
package Embed::Persistent;
#persistent.pl
-
+
use strict;
use vars '%Cache';
-
+
sub valid_package_name {
my($string) = @_;
$string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
# second pass only for words starting with a digit
$string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;
-
+
# Dress it up as a real package name
$string =~ s|/|::|g;
return "Embed" . $string;
}
-
+
#borrowed from Safe.pm
sub delete_package {
my $pkg = shift;
my ($stem, $leaf);
-
+
no strict 'refs';
$pkg = "main::$pkg\::"; # expand to full symbol table name
($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
-
+
my $stem_symtab = *{$stem}{HASH};
-
+
delete $stem_symtab->{$leaf};
}
-
+
sub eval_file {
my($filename, $delete) = @_;
my $package = valid_package_name($filename);
my $mtime = -M $filename;
if(defined $Cache{$package}{mtime}
&&
- $Cache{$package}{mtime} <= $mtime)
+ $Cache{$package}{mtime} <= $mtime)
{
- # we have compiled this subroutine already,
+ # we have compiled this subroutine already,
# it has not been updated on disk, nothing left to do
print STDERR "already compiled $package->handler\n";
}
local($/) = undef;
my $sub = <FH>;
close FH;
-
+
#wrap the code into a subroutine inside our unique package
my $eval = qq{package $package; sub handler { $sub; }};
{
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>
-
+ #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 *args[] = { "", DO_CLEAN, NULL };
char filename [1024];
int exitstatus = 0;
-
+
if((perl = perl_alloc()) == NULL) {
fprintf(stderr, "no memory!");
exit(1);
}
- perl_construct(perl);
-
+ perl_construct(perl);
+
exitstatus = perl_parse(perl, NULL, 2, embedding, NULL);
-
- if(!exitstatus) {
+
+ 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",
+ perl_call_argv("Embed::Persistent::eval_file",
G_DISCARD | G_EVAL, args);
-
+
/* check $@ */
- if(SvTRUE(GvSV(errgv)))
+ if(SvTRUE(GvSV(errgv)))
fprintf(stderr, "eval error: %s\n", SvPV(GvSV(errgv),na));
}
}
-
+
perl_destruct_level = 0;
- perl_destruct(perl);
- perl_free(perl);
+ perl_destruct(perl);
+ perl_free(perl);
exit(exitstatus);
}
-
Now compile:
- % cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
+ % cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
Here's a example script file:
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.
+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
Setting C<perl_destruct_level> to C<1> makes everything squeaky clean:
- perl_destruct_level = 1;
+ perl_destruct_level = 1;
while(1) {
...
/* reset global variables here with perl_destruct_level = 1 */
- perl_construct(my_perl);
+ perl_construct(my_perl);
...
/* clean and reset _everything_ during perl_destruct */
- perl_destruct(my_perl);
- perl_free(my_perl);
+ 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.
+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
int main(int argc, char **argv, char **env)
{
- PerlInterpreter
+ PerlInterpreter
*one_perl = perl_alloc(),
- *two_perl = perl_alloc();
+ *two_perl = perl_alloc();
char *one_args[] = { "one_perl", SAY_HELLO };
char *two_args[] = { "two_perl", SAY_HELLO };
=head1 AUTHOR
-Jon Orwant and F<E<lt>orwant@media.mit.eduE<gt>> and Doug MacEachern
-F<E<lt>dougm@osf.orgE<gt>>, with small contributions from Tim Bunce,
-Tom Christiansen, Hallvard Furuseth, Dov Grobgeld, and Ilya Zakharevich.
+Jon Orwant and <F<orwant@tpj.com>> and Doug MacEachern <F<dougm@osf.org>>,
+with small contributions from Tim Bunce, Tom Christiansen, Hallvard Furuseth,
+Dov Grobgeld, and Ilya Zakharevich.
Check out Doug's article on embedding in Volume 1, Issue 4 of The Perl
Journal. Info about TPJ is available from http://tpj.com.
-February 1, 1997
+April 14, 1997
Some of this material is excerpted from Jon Orwant's book: I<Perl 5
Interactive>, Waite Group Press, 1996 (ISBN 1-57169-064-6) and appears
projects / p5sagit/p5-mst-13.2.git / blobdiff