1162 lines
37 KiB
Plaintext
1162 lines
37 KiB
Plaintext
=head1 NAME
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perlembed - how to embed perl in your C program
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=head1 DESCRIPTION
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=head2 PREAMBLE
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Do you want to:
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=over 5
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=item B<Use C from Perl?>
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Read L<perlxstut>, L<perlxs>, L<h2xs>, L<perlguts>, and L<perlapi>.
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=item B<Use a Unix program from Perl?>
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Read about back-quotes and about C<system> and C<exec> in L<perlfunc>.
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=item B<Use Perl from Perl?>
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Read about L<perlfunc/do> and L<perlfunc/eval> and L<perlfunc/require>
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and L<perlfunc/use>.
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=item B<Use C from C?>
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Rethink your design.
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=item B<Use Perl from C?>
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Read on...
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=back
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=head2 ROADMAP
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=over 5
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=item *
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Compiling your C program
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=item *
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Adding a Perl interpreter to your C program
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=item *
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Calling a Perl subroutine from your C program
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=item *
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Evaluating a Perl statement from your C program
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=item *
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Performing Perl pattern matches and substitutions from your C program
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=item *
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Fiddling with the Perl stack from your C program
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=item *
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Maintaining a persistent interpreter
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=item *
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Maintaining multiple interpreter instances
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=item *
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Using Perl modules, which themselves use C libraries, from your C program
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=item *
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Embedding Perl under Win32
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=back
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=head2 Compiling your C program
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If you have trouble compiling the scripts in this documentation,
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you're not alone. The cardinal rule: COMPILE THE PROGRAMS IN EXACTLY
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THE SAME WAY THAT YOUR PERL WAS COMPILED. (Sorry for yelling.)
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Also, every C program that uses Perl must link in the I<perl library>.
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What's that, you ask? Perl is itself written in C; the perl library
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is the collection of compiled C programs that were used to create your
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perl executable (I</usr/bin/perl> or equivalent). (Corollary: you
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can't use Perl from your C program unless Perl has been compiled on
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your machine, or installed properly--that's why you shouldn't blithely
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copy Perl executables from machine to machine without also copying the
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I<lib> directory.)
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When you use Perl from C, your C program will--usually--allocate,
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"run", and deallocate a I<PerlInterpreter> object, which is defined by
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the perl library.
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If your copy of Perl is recent enough to contain this documentation
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(version 5.002 or later), then the perl library (and I<EXTERN.h> and
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I<perl.h>, which you'll also need) will reside in a directory
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that looks like this:
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/usr/local/lib/perl5/your_architecture_here/CORE
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or perhaps just
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/usr/local/lib/perl5/CORE
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or maybe something like
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/usr/opt/perl5/CORE
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Execute this statement for a hint about where to find CORE:
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perl -MConfig -e 'print $Config{archlib}'
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Here's how you'd compile the example in the next section,
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L</Adding a Perl interpreter to your C program>, on my Linux box:
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% gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include
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-I/usr/local/lib/perl5/i586-linux/5.003/CORE
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-L/usr/local/lib/perl5/i586-linux/5.003/CORE
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-o interp interp.c -lperl -lm
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(That's all one line.) On my DEC Alpha running old 5.003_05, the
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incantation is a bit different:
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% cc -O2 -Olimit 2900 -I/usr/local/include
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-I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE
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-L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib
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-D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm
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How can you figure out what to add? Assuming your Perl is post-5.001,
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execute a C<perl -V> command and pay special attention to the "cc" and
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"ccflags" information.
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You'll have to choose the appropriate compiler (I<cc>, I<gcc>, et al.) for
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your machine: C<perl -MConfig -e 'print $Config{cc}'> will tell you what
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to use.
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You'll also have to choose the appropriate library directory
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(I</usr/local/lib/...>) for your machine. If your compiler complains
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that certain functions are undefined, or that it can't locate
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I<-lperl>, then you need to change the path following the C<-L>. If it
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complains that it can't find I<EXTERN.h> and I<perl.h>, you need to
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change the path following the C<-I>.
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You may have to add extra libraries as well. Which ones?
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Perhaps those printed by
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perl -MConfig -e 'print $Config{libs}'
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Provided your perl binary was properly configured and installed the
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B<ExtUtils::Embed> module will determine all of this information for
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you:
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% cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
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If the B<ExtUtils::Embed> module isn't part of your Perl distribution,
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you can retrieve it from
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L<http://www.perl.com/perl/CPAN/modules/by-module/ExtUtils/>
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(If this documentation came from your Perl distribution, then you're
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running 5.004 or better and you already have it.)
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The B<ExtUtils::Embed> kit on CPAN also contains all source code for
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the examples in this document, tests, additional examples and other
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information you may find useful.
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=head2 Adding a Perl interpreter to your C program
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In a sense, perl (the C program) is a good example of embedding Perl
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(the language), so I'll demonstrate embedding with I<miniperlmain.c>,
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included in the source distribution. Here's a bastardized, non-portable
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version of I<miniperlmain.c> containing the essentials of embedding:
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#include <EXTERN.h> /* from the Perl distribution */
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#include <perl.h> /* from the Perl distribution */
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static PerlInterpreter *my_perl; /*** The Perl interpreter ***/
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int main(int argc, char **argv, char **env)
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{
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PERL_SYS_INIT3(&argc,&argv,&env);
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my_perl = perl_alloc();
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perl_construct(my_perl);
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PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
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perl_parse(my_perl, NULL, argc, argv, (char **)NULL);
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perl_run(my_perl);
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perl_destruct(my_perl);
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perl_free(my_perl);
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PERL_SYS_TERM();
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exit(EXIT_SUCCESS);
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}
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Notice that we don't use the C<env> pointer. Normally handed to
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C<perl_parse> as its final argument, C<env> here is replaced by
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C<NULL>, which means that the current environment will be used.
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The macros PERL_SYS_INIT3() and PERL_SYS_TERM() provide system-specific
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tune up of the C runtime environment necessary to run Perl interpreters;
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they should only be called once regardless of how many interpreters you
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create or destroy. Call PERL_SYS_INIT3() before you create your first
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interpreter, and PERL_SYS_TERM() after you free your last interpreter.
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Since PERL_SYS_INIT3() may change C<env>, it may be more appropriate to
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provide C<env> as an argument to perl_parse().
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Also notice that no matter what arguments you pass to perl_parse(),
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PERL_SYS_INIT3() must be invoked on the C main() argc, argv and env and
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only once.
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Mind that argv[argc] must be NULL, same as those passed to a main
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function in C.
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Now compile this program (I'll call it I<interp.c>) into an executable:
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% cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
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After a successful compilation, you'll be able to use I<interp> just
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like perl itself:
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% interp
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print "Pretty Good Perl \n";
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print "10890 - 9801 is ", 10890 - 9801;
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<CTRL-D>
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Pretty Good Perl
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10890 - 9801 is 1089
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or
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% interp -e 'printf("%x", 3735928559)'
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deadbeef
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You can also read and execute Perl statements from a file while in the
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midst of your C program, by placing the filename in I<argv[1]> before
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calling I<perl_run>.
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=head2 Calling a Perl subroutine from your C program
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To call individual Perl subroutines, you can use any of the B<call_*>
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functions documented in L<perlcall>.
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In this example we'll use C<call_argv>.
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That's shown below, in a program I'll call I<showtime.c>.
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#include <EXTERN.h>
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#include <perl.h>
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static PerlInterpreter *my_perl;
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int main(int argc, char **argv, char **env)
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{
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char *args[] = { NULL };
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PERL_SYS_INIT3(&argc,&argv,&env);
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my_perl = perl_alloc();
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perl_construct(my_perl);
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perl_parse(my_perl, NULL, argc, argv, NULL);
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PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
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/*** skipping perl_run() ***/
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call_argv("showtime", G_DISCARD | G_NOARGS, args);
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perl_destruct(my_perl);
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perl_free(my_perl);
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PERL_SYS_TERM();
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exit(EXIT_SUCCESS);
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}
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where I<showtime> is a Perl subroutine that takes no arguments (that's the
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I<G_NOARGS>) and for which I'll ignore the return value (that's the
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I<G_DISCARD>). Those flags, and others, are discussed in L<perlcall>.
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I'll define the I<showtime> subroutine in a file called I<showtime.pl>:
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print "I shan't be printed.";
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sub showtime {
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print time;
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}
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Simple enough. Now compile and run:
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% cc -o showtime showtime.c \
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`perl -MExtUtils::Embed -e ccopts -e ldopts`
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% showtime showtime.pl
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818284590
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yielding the number of seconds that elapsed between January 1, 1970
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(the beginning of the Unix epoch), and the moment I began writing this
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sentence.
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In this particular case we don't have to call I<perl_run>, as we set
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the PL_exit_flag PERL_EXIT_DESTRUCT_END which executes END blocks in
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perl_destruct.
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If you want to pass arguments to the Perl subroutine, you can add
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strings to the C<NULL>-terminated C<args> list passed to
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I<call_argv>. For other data types, or to examine return values,
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you'll need to manipulate the Perl stack. That's demonstrated in
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L</Fiddling with the Perl stack from your C program>.
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=head2 Evaluating a Perl statement from your C program
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Perl provides two API functions to evaluate pieces of Perl code.
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These are L<perlapi/eval_sv> and L<perlapi/eval_pv>.
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Arguably, these are the only routines you'll ever need to execute
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snippets of Perl code from within your C program. Your code can be as
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long as you wish; it can contain multiple statements; it can employ
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L<perlfunc/use>, L<perlfunc/require>, and L<perlfunc/do> to
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include external Perl files.
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I<eval_pv> lets us evaluate individual Perl strings, and then
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extract variables for coercion into C types. The following program,
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I<string.c>, executes three Perl strings, extracting an C<int> from
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the first, a C<float> from the second, and a C<char *> from the third.
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#include <EXTERN.h>
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#include <perl.h>
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static PerlInterpreter *my_perl;
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main (int argc, char **argv, char **env)
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{
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char *embedding[] = { "", "-e", "0", NULL };
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PERL_SYS_INIT3(&argc,&argv,&env);
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my_perl = perl_alloc();
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perl_construct( my_perl );
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perl_parse(my_perl, NULL, 3, embedding, NULL);
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PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
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perl_run(my_perl);
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/** Treat $a as an integer **/
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eval_pv("$a = 3; $a **= 2", TRUE);
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printf("a = %d\n", SvIV(get_sv("a", 0)));
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/** Treat $a as a float **/
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eval_pv("$a = 3.14; $a **= 2", TRUE);
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printf("a = %f\n", SvNV(get_sv("a", 0)));
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/** Treat $a as a string **/
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eval_pv(
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"$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
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printf("a = %s\n", SvPV_nolen(get_sv("a", 0)));
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perl_destruct(my_perl);
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perl_free(my_perl);
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PERL_SYS_TERM();
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}
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All of those strange functions with I<sv> in their names help convert Perl
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scalars to C types. They're described in L<perlguts> and L<perlapi>.
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If you compile and run I<string.c>, you'll see the results of using
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I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and
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I<SvPV()> to create a string:
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a = 9
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a = 9.859600
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a = Just Another Perl Hacker
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In the example above, we've created a global variable to temporarily
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store the computed value of our eval'ed expression. It is also
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possible and in most cases a better strategy to fetch the return value
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from I<eval_pv()> instead. Example:
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...
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SV *val = eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
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printf("%s\n", SvPV_nolen(val));
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...
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This way, we avoid namespace pollution by not creating global
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variables and we've simplified our code as well.
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=head2 Performing Perl pattern matches and substitutions from your C program
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The I<eval_sv()> function lets us evaluate strings of Perl code, so we can
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define some functions that use it to "specialize" in matches and
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substitutions: I<match()>, I<substitute()>, and I<matches()>.
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I32 match(SV *string, char *pattern);
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Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which
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in your C program might appear as "/\\b\\w*\\b/"), match()
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returns 1 if the string matches the pattern and 0 otherwise.
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int substitute(SV **string, char *pattern);
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Given a pointer to an C<SV> and an C<=~> operation (e.g.,
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C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string
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within the C<SV> as according to the operation, returning the number of
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substitutions made.
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SSize_t matches(SV *string, char *pattern, AV **matches);
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Given an C<SV>, a pattern, and a pointer to an empty C<AV>,
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matches() evaluates C<$string =~ $pattern> in a list context, and
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fills in I<matches> with the array elements, returning the number of matches
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found.
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Here's a sample program, I<match.c>, that uses all three (long lines have
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been wrapped here):
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#include <EXTERN.h>
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#include <perl.h>
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static PerlInterpreter *my_perl;
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/** my_eval_sv(code, error_check)
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** kinda like eval_sv(),
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** but we pop the return value off the stack
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**/
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SV* my_eval_sv(SV *sv, I32 croak_on_error)
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{
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dSP;
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SV* retval;
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PUSHMARK(SP);
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eval_sv(sv, G_SCALAR);
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SPAGAIN;
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retval = POPs;
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PUTBACK;
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if (croak_on_error && SvTRUE(ERRSV))
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croak_sv(ERRSV);
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return retval;
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}
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/** match(string, pattern)
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**
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** Used for matches in a scalar context.
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**
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** Returns 1 if the match was successful; 0 otherwise.
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**/
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I32 match(SV *string, char *pattern)
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{
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SV *command = newSV(0), *retval;
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sv_setpvf(command, "my $string = '%s'; $string =~ %s",
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SvPV_nolen(string), pattern);
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retval = my_eval_sv(command, TRUE);
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SvREFCNT_dec(command);
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return SvIV(retval);
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}
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/** substitute(string, pattern)
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**
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** Used for =~ operations that
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** modify their left-hand side (s/// and tr///)
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**
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** Returns the number of successful matches, and
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** modifies the input string if there were any.
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**/
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I32 substitute(SV **string, char *pattern)
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{
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SV *command = newSV(0), *retval;
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sv_setpvf(command, "$string = '%s'; ($string =~ %s)",
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SvPV_nolen(*string), pattern);
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retval = my_eval_sv(command, TRUE);
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SvREFCNT_dec(command);
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*string = get_sv("string", 0);
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return SvIV(retval);
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}
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/** matches(string, pattern, matches)
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**
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** Used for matches in a list context.
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**
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** Returns the number of matches,
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** and fills in **matches with the matching substrings
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**/
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SSize_t matches(SV *string, char *pattern, AV **match_list)
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{
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SV *command = newSV(0);
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SSize_t num_matches;
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sv_setpvf(command, "my $string = '%s'; @array = ($string =~ %s)",
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SvPV_nolen(string), pattern);
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my_eval_sv(command, TRUE);
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SvREFCNT_dec(command);
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*match_list = get_av("array", 0);
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num_matches = av_top_index(*match_list) + 1;
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return num_matches;
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}
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main (int argc, char **argv, char **env)
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{
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char *embedding[] = { "", "-e", "0", NULL };
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AV *match_list;
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I32 num_matches, i;
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SV *text;
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PERL_SYS_INIT3(&argc,&argv,&env);
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my_perl = perl_alloc();
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perl_construct(my_perl);
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perl_parse(my_perl, NULL, 3, embedding, NULL);
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PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
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text = newSV(0);
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sv_setpv(text, "When he is at a convenience store and the "
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"bill comes to some amount like 76 cents, Maynard is "
|
|
"aware that there is something he *should* do, something "
|
|
"that will enable him to get back a quarter, but he has "
|
|
"no idea *what*. He fumbles through his red squeezey "
|
|
"changepurse and gives the boy three extra pennies with "
|
|
"his dollar, hoping that he might luck into the correct "
|
|
"amount. The boy gives him back two of his own pennies "
|
|
"and then the big shiny quarter that is his prize. "
|
|
"-RICHH");
|
|
|
|
if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
|
|
printf("match: Text contains the word 'quarter'.\n\n");
|
|
else
|
|
printf("match: Text doesn't contain the word 'quarter'.\n\n");
|
|
|
|
if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
|
|
printf("match: Text contains the word 'eighth'.\n\n");
|
|
else
|
|
printf("match: Text doesn't contain the word 'eighth'.\n\n");
|
|
|
|
/** Match all occurrences of /wi../ **/
|
|
num_matches = matches(text, "m/(wi..)/g", &match_list);
|
|
printf("matches: m/(wi..)/g found %d matches...\n", num_matches);
|
|
|
|
for (i = 0; i < num_matches; i++)
|
|
printf("match: %s\n",
|
|
SvPV_nolen(*av_fetch(match_list, i, FALSE)));
|
|
printf("\n");
|
|
|
|
/** Remove all vowels from text **/
|
|
num_matches = substitute(&text, "s/[aeiou]//gi");
|
|
if (num_matches) {
|
|
printf("substitute: s/[aeiou]//gi...%lu substitutions made.\n",
|
|
(unsigned long)num_matches);
|
|
printf("Now text is: %s\n\n", SvPV_nolen(text));
|
|
}
|
|
|
|
/** Attempt a substitution **/
|
|
if (!substitute(&text, "s/Perl/C/")) {
|
|
printf("substitute: s/Perl/C...No substitution made.\n\n");
|
|
}
|
|
|
|
SvREFCNT_dec(text);
|
|
PL_perl_destruct_level = 1;
|
|
perl_destruct(my_perl);
|
|
perl_free(my_perl);
|
|
PERL_SYS_TERM();
|
|
}
|
|
|
|
which produces the output (again, long lines have been wrapped here)
|
|
|
|
match: Text contains the word 'quarter'.
|
|
|
|
match: Text doesn't contain the word 'eighth'.
|
|
|
|
matches: m/(wi..)/g found 2 matches...
|
|
match: will
|
|
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,
|
|
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
|
|
|
|
substitute: s/Perl/C...No substitution made.
|
|
|
|
=head2 Fiddling with the Perl stack from your C program
|
|
|
|
When trying to explain stacks, most computer science textbooks mumble
|
|
something about spring-loaded columns of cafeteria plates: the last
|
|
thing you pushed on the stack is the first thing you pop off. That'll
|
|
do for our purposes: your C program will push some arguments onto "the Perl
|
|
stack", shut its eyes while some magic happens, and then pop the
|
|
results--the return value of your Perl subroutine--off the stack.
|
|
|
|
First you'll need to know how to convert between C types and Perl
|
|
types, with newSViv() and sv_setnv() and newAV() and all their
|
|
friends. They're described in L<perlguts> and L<perlapi>.
|
|
|
|
Then you'll need to know how to manipulate the Perl stack. That's
|
|
described in L<perlcall>.
|
|
|
|
Once you've understood those, embedding Perl in C is easy.
|
|
|
|
Because C has no 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>:
|
|
|
|
sub expo {
|
|
my ($a, $b) = @_;
|
|
return $a ** $b;
|
|
}
|
|
|
|
Now I'll create a C program, I<power.c>, with a function
|
|
I<PerlPower()> that contains all the perlguts necessary to push the
|
|
two arguments into I<expo()> and to pop the return value out. Take a
|
|
deep breath...
|
|
|
|
#include <EXTERN.h>
|
|
#include <perl.h>
|
|
|
|
static PerlInterpreter *my_perl;
|
|
|
|
static void
|
|
PerlPower(int a, int b)
|
|
{
|
|
dSP; /* initialize stack pointer */
|
|
ENTER; /* everything created after here */
|
|
SAVETMPS; /* ...is a temporary variable. */
|
|
PUSHMARK(SP); /* remember the stack pointer */
|
|
XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */
|
|
XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */
|
|
PUTBACK; /* make local stack pointer global */
|
|
call_pv("expo", G_SCALAR); /* call the function */
|
|
SPAGAIN; /* refresh stack pointer */
|
|
/* pop the return value from stack */
|
|
printf ("%d to the %dth power is %d.\n", a, b, POPi);
|
|
PUTBACK;
|
|
FREETMPS; /* free that return value */
|
|
LEAVE; /* ...and the XPUSHed "mortal" args.*/
|
|
}
|
|
|
|
int main (int argc, char **argv, char **env)
|
|
{
|
|
char *my_argv[] = { "", "power.pl", NULL };
|
|
|
|
PERL_SYS_INIT3(&argc,&argv,&env);
|
|
my_perl = perl_alloc();
|
|
perl_construct( my_perl );
|
|
|
|
perl_parse(my_perl, NULL, 2, my_argv, (char **)NULL);
|
|
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
|
|
perl_run(my_perl);
|
|
|
|
PerlPower(3, 4); /*** Compute 3 ** 4 ***/
|
|
|
|
perl_destruct(my_perl);
|
|
perl_free(my_perl);
|
|
PERL_SYS_TERM();
|
|
exit(EXIT_SUCCESS);
|
|
}
|
|
|
|
|
|
|
|
Compile and run:
|
|
|
|
% cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
|
|
|
|
% 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<perlapi/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
|
|
|
|
#define BUFFER_SIZE 1024
|
|
|
|
static PerlInterpreter *my_perl = NULL;
|
|
|
|
int
|
|
main(int argc, char **argv, char **env)
|
|
{
|
|
char *embedding[] = { "", "persistent.pl", NULL };
|
|
char *args[] = { "", DO_CLEAN, NULL };
|
|
char filename[BUFFER_SIZE];
|
|
int failing, exitstatus;
|
|
|
|
PERL_SYS_INIT3(&argc,&argv,&env);
|
|
if((my_perl = perl_alloc()) == NULL) {
|
|
fprintf(stderr, "no memory!");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
perl_construct(my_perl);
|
|
|
|
PL_origalen = 1; /* don't let $0 assignment update the
|
|
proctitle or embedding[0] */
|
|
failing = perl_parse(my_perl, NULL, 2, embedding, NULL);
|
|
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
|
|
if(!failing)
|
|
failing = perl_run(my_perl);
|
|
if(!failing) {
|
|
while(printf("Enter file name: ") &&
|
|
fgets(filename, BUFFER_SIZE, stdin)) {
|
|
|
|
filename[strlen(filename)-1] = '\0'; /* strip \n */
|
|
/* call the subroutine,
|
|
passing it the filename as an argument */
|
|
args[0] = filename;
|
|
call_argv("Embed::Persistent::eval_file",
|
|
G_DISCARD | G_EVAL, args);
|
|
|
|
/* check $@ */
|
|
if(SvTRUE(ERRSV))
|
|
fprintf(stderr, "eval error: %s\n", SvPV_nolen(ERRSV));
|
|
}
|
|
}
|
|
|
|
PL_perl_destruct_level = 0;
|
|
exitstatus = perl_destruct(my_perl);
|
|
perl_free(my_perl);
|
|
PERL_SYS_TERM();
|
|
exit(exitstatus);
|
|
}
|
|
|
|
Now compile:
|
|
|
|
% cc -o persistent persistent.c \
|
|
`perl -MExtUtils::Embed -e ccopts -e ldopts`
|
|
|
|
Here's an 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 Execution of END blocks
|
|
|
|
Traditionally END blocks have been executed at the end of the perl_run.
|
|
This causes problems for applications that never call perl_run. Since
|
|
perl 5.7.2 you can specify C<PL_exit_flags |= PERL_EXIT_DESTRUCT_END>
|
|
to get the new behaviour. This also enables the running of END blocks if
|
|
the perl_parse fails and C<perl_destruct> will return the exit value.
|
|
|
|
=head2 $0 assignments
|
|
|
|
When a perl script assigns a value to $0 then the perl runtime will
|
|
try to make this value show up as the program name reported by "ps" by
|
|
updating the memory pointed to by the argv passed to perl_parse() and
|
|
also calling API functions like setproctitle() where available. This
|
|
behaviour might not be appropriate when embedding perl and can be
|
|
disabled by assigning the value C<1> to the variable C<PL_origalen>
|
|
before perl_parse() is called.
|
|
|
|
The F<persistent.c> example above is for instance likely to segfault
|
|
when $0 is assigned to if the C<PL_origalen = 1;> assignment is
|
|
removed. This because perl will try to write to the read only memory
|
|
of the C<embedding[]> strings.
|
|
|
|
=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, when perl is not
|
|
built with any special options, the global variable
|
|
C<PL_perl_destruct_level> is set to C<0>, since extra cleaning isn't
|
|
usually needed when a program only ever creates a single interpreter
|
|
in its entire lifetime.
|
|
|
|
Setting C<PL_perl_destruct_level> to C<1> makes everything squeaky clean:
|
|
|
|
while(1) {
|
|
...
|
|
/* reset global variables here with PL_perl_destruct_level = 1 */
|
|
PL_perl_destruct_level = 1;
|
|
perl_construct(my_perl);
|
|
...
|
|
/* clean and reset _everything_ during perl_destruct */
|
|
PL_perl_destruct_level = 1;
|
|
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. The
|
|
second assignment to C<PL_perl_destruct_level> is needed because
|
|
perl_construct resets it to C<0>.
|
|
|
|
Now suppose we have more than one interpreter instance running at the
|
|
same time. This is feasible, but only if you used the Configure option
|
|
C<-Dusemultiplicity> or the options C<-Dusethreads -Duseithreads> when
|
|
building perl. By default, enabling one of these Configure options
|
|
sets the per-interpreter global variable C<PL_perl_destruct_level> to
|
|
C<1>, so that thorough cleaning is automatic and interpreter variables
|
|
are initialized correctly. Even if you don't intend to run two or
|
|
more interpreters at the same time, but to run them sequentially, like
|
|
in the above example, it is recommended to build perl with the
|
|
C<-Dusemultiplicity> option otherwise some interpreter variables may
|
|
not be initialized correctly between consecutive runs and your
|
|
application may crash.
|
|
|
|
See also L<perlxs/Thread-aware system interfaces>.
|
|
|
|
Using C<-Dusethreads -Duseithreads> rather than C<-Dusemultiplicity>
|
|
is more appropriate if you intend to run multiple interpreters
|
|
concurrently in different threads, because it enables support for
|
|
linking in the thread libraries of your system with the interpreter.
|
|
|
|
Let's give it a try:
|
|
|
|
|
|
#include <EXTERN.h>
|
|
#include <perl.h>
|
|
|
|
/* 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, *two_perl;
|
|
char *one_args[] = { "one_perl", SAY_HELLO, NULL };
|
|
char *two_args[] = { "two_perl", SAY_HELLO, NULL };
|
|
|
|
PERL_SYS_INIT3(&argc,&argv,&env);
|
|
one_perl = perl_alloc();
|
|
two_perl = perl_alloc();
|
|
|
|
PERL_SET_CONTEXT(one_perl);
|
|
perl_construct(one_perl);
|
|
PERL_SET_CONTEXT(two_perl);
|
|
perl_construct(two_perl);
|
|
|
|
PERL_SET_CONTEXT(one_perl);
|
|
perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
|
|
PERL_SET_CONTEXT(two_perl);
|
|
perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
|
|
|
|
PERL_SET_CONTEXT(one_perl);
|
|
perl_run(one_perl);
|
|
PERL_SET_CONTEXT(two_perl);
|
|
perl_run(two_perl);
|
|
|
|
PERL_SET_CONTEXT(one_perl);
|
|
perl_destruct(one_perl);
|
|
PERL_SET_CONTEXT(two_perl);
|
|
perl_destruct(two_perl);
|
|
|
|
PERL_SET_CONTEXT(one_perl);
|
|
perl_free(one_perl);
|
|
PERL_SET_CONTEXT(two_perl);
|
|
perl_free(two_perl);
|
|
PERL_SYS_TERM();
|
|
exit(EXIT_SUCCESS);
|
|
}
|
|
|
|
Note the calls to PERL_SET_CONTEXT(). These are necessary to initialize
|
|
the global state that tracks which interpreter is the "current" one on
|
|
the particular process or thread that may be running it. It should
|
|
always be used if you have more than one interpreter and are making
|
|
perl API calls on both interpreters in an interleaved fashion.
|
|
|
|
PERL_SET_CONTEXT(interp) should also be called whenever C<interp> is
|
|
used by a thread that did not create it (using either perl_alloc(), or
|
|
the more esoteric perl_clone()).
|
|
|
|
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
|
|
that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++
|
|
library, this probably happened:
|
|
|
|
|
|
Can't load module Socket, dynamic loading not available in this perl.
|
|
(You may need to build a new perl executable which either supports
|
|
dynamic loading or has the Socket module statically linked into it.)
|
|
|
|
|
|
What's wrong?
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|
|
|
Your interpreter doesn't know how to communicate with these extensions
|
|
on its own. A little glue will help. Up until now you've been
|
|
calling I<perl_parse()>, handing it NULL for the second argument:
|
|
|
|
perl_parse(my_perl, NULL, argc, my_argv, NULL);
|
|
|
|
That's where the glue code can be inserted to create the initial contact
|
|
between Perl and linked C/C++ routines. Let's take a look some pieces of
|
|
I<perlmain.c> to see how Perl does this:
|
|
|
|
static void xs_init (pTHX);
|
|
|
|
EXTERN_C void boot_DynaLoader (pTHX_ CV* cv);
|
|
EXTERN_C void boot_Socket (pTHX_ CV* cv);
|
|
|
|
|
|
EXTERN_C void
|
|
xs_init(pTHX)
|
|
{
|
|
char *file = __FILE__;
|
|
/* DynaLoader is a special case */
|
|
newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
|
|
newXS("Socket::bootstrap", boot_Socket, file);
|
|
}
|
|
|
|
Simply put: for each extension linked with your Perl executable
|
|
(determined during its initial configuration on your
|
|
computer or when adding a new extension),
|
|
a Perl subroutine is created to incorporate the extension's
|
|
routines. Normally, that subroutine is named
|
|
I<Module::bootstrap()> and is invoked when you say I<use Module>. In
|
|
turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl
|
|
counterpart for each of the extension's XSUBs. Don't worry about this
|
|
part; leave that to the I<xsubpp> and extension authors. If your
|
|
extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()>
|
|
for you on the fly. In fact, if you have a working DynaLoader then there
|
|
is rarely any need to link in any other extensions statically.
|
|
|
|
|
|
Once you have this code, slap it into the second argument of I<perl_parse()>:
|
|
|
|
|
|
perl_parse(my_perl, xs_init, argc, my_argv, NULL);
|
|
|
|
|
|
Then compile:
|
|
|
|
% cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
|
|
|
|
% interp
|
|
use Socket;
|
|
use SomeDynamicallyLoadedModule;
|
|
|
|
print "Now I can use extensions!\n"'
|
|
|
|
B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code.
|
|
|
|
% perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c
|
|
% cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts`
|
|
% cc -c interp.c `perl -MExtUtils::Embed -e ccopts`
|
|
% cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts`
|
|
|
|
Consult L<perlxs>, L<perlguts>, and L<perlapi> for more details.
|
|
|
|
=head2 Using embedded Perl with POSIX locales
|
|
|
|
(See L<perllocale> for information about these.)
|
|
When a Perl interpreter normally starts up, it tells the system it wants
|
|
to use the system's default locale. This is often, but not necessarily,
|
|
the "C" or "POSIX" locale. Absent a S<C<"use locale">> within the perl
|
|
code, this mostly has no effect (but see L<perllocale/Not within the
|
|
scope of "use locale">). Also, there is not a problem if the
|
|
locale you want to use in your embedded perl is the same as the system
|
|
default. However, this doesn't work if you have set up and want to use
|
|
a locale that isn't the system default one. Starting in Perl v5.20, you
|
|
can tell the embedded Perl interpreter that the locale is already
|
|
properly set up, and to skip doing its own normal initialization. It
|
|
skips if the environment variable C<PERL_SKIP_LOCALE_INIT> is set (even
|
|
if set to 0 or C<"">). A perl that has this capability will define the
|
|
C pre-processor symbol C<HAS_SKIP_LOCALE_INIT>. This allows code that
|
|
has to work with multiple Perl versions to do some sort of work-around
|
|
when confronted with an earlier Perl.
|
|
|
|
If your program is using the POSIX 2008 multi-thread locale
|
|
functionality, you should switch into the global locale and set that up
|
|
properly before starting the Perl interpreter. It will then properly
|
|
switch back to using the thread-safe functions.
|
|
|
|
=head1 Hiding Perl_
|
|
|
|
If you completely hide the short forms of the Perl public API,
|
|
add -DPERL_NO_SHORT_NAMES to the compilation flags. This means that
|
|
for example instead of writing
|
|
|
|
warn("%d bottles of beer on the wall", bottlecount);
|
|
|
|
you will have to write the explicit full form
|
|
|
|
Perl_warn(aTHX_ "%d bottles of beer on the wall", bottlecount);
|
|
|
|
(See L<perlguts/"Background and PERL_IMPLICIT_CONTEXT"> for the explanation
|
|
of the C<aTHX_>. ) Hiding the short forms is very useful for avoiding
|
|
all sorts of nasty (C preprocessor or otherwise) conflicts with other
|
|
software packages (Perl defines about 2400 APIs with these short names,
|
|
take or leave few hundred, so there certainly is room for conflict.)
|
|
|
|
=head1 MORAL
|
|
|
|
You can sometimes I<write faster code> in C, but
|
|
you can always I<write code faster> in Perl. Because you can use
|
|
each from the other, combine them as you wish.
|
|
|
|
|
|
=head1 AUTHOR
|
|
|
|
Jon Orwant <F<orwant@media.mit.edu>> and Doug MacEachern
|
|
<F<dougm@covalent.net>>, with small contributions from Tim Bunce, Tom
|
|
Christiansen, Guy Decoux, Hallvard Furuseth, Dov Grobgeld, and Ilya
|
|
Zakharevich.
|
|
|
|
Doug MacEachern has an article on embedding in Volume 1, Issue 4 of
|
|
The Perl Journal ( L<http://www.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.
|
|
|
|
=head1 COPYRIGHT
|
|
|
|
Copyright (C) 1995, 1996, 1997, 1998 Doug MacEachern and Jon Orwant. All
|
|
Rights Reserved.
|
|
|
|
This document may be distributed under the same terms as Perl itself.
|