libinline-c-perl 0.78-1 / usr / share / perl5 / Inline / C / Cookbook.pod

=pod

=for comment
DO NOT EDIT. This Pod was generated by Swim v0.1.46.
See http://github.com/ingydotnet/swim-pm#readme

=encoding utf8

=head1 NAME

Inline::C::Cookbook - A Cornucopia of Inline C Recipes

=head1 DESCRIPTION

It's a lot easier for most of us to cook a meal from a recipe, rather than
just throwing things into a pot until something edible forms. So it is with
programming as well. C<Inline.pm> makes C programming for Perl as easy as
possible. Having a set of easy to understand samples, makes it simpler yet.

This Cookbook is intended to be an evergrowing repository of small yet
complete coding examples; each showing how to accomplish a particular task
with Inline. Each example is followed by a short discussion, explaining in
detail the particular features that are being demonstrated.

Many of these recipes are adapted from email discussions I have had with
Inline users around the world. It has been my experience so far, that Inline
provides an elegant solution to almost all problems involving Perl and C.

Bon Appetit!

=head1 APPETIZERS

=head2 Hello, world

=over

=item Problem


=back

It seems that the first thing any programmer wants to do when he learns a new
programming technique is to use it to greet the Earth. How can I do this
using Inline?

=over

=item Solution

    use Inline C => <<'...';

    void greet() {
      printf("Hello, world\n");
    }
    ...

    greet;

=item Discussion

Nothing too fancy here. We define a single C function C<greet()> which prints
a message to STDOUT. One thing to note is that since the Inline code comes
before the function call to C<greet>, we can call it as a bareword (no
parentheses).

=item See Also

See L<Inline> and L<Inline::C> for basic info about C<Inline.pm>.

=item Credits

=over

=item * Brian Kernigan

=item * Dennis Ritchie

=back

=back

=head2 One Liner

=over

=item Problem

A concept is valid in Perl only if it can be shown to work in one line. Can
Inline reduce the complexities of Perl/C interaction to a one-liner?

=item Solution

    perl -e 'use Inline C=>q{void greet(){printf("Hello, world\n");}};greet'

=item Discussion

Try doing that in XS :-)

=item See Also

My email signature of late is:

    perl -le 'use Inline C=>q{SV*JAxH(char*x){return newSVpvf("Just Another %s Hacker",x);}};print JAxH+Perl'

A bit fancier but a few bytes too long to qualify as a true one liner :-(

=item Credits

"Eli the Bearded" <elijah@workspot.net> gave me the idea that I should have an
Inline one-liner as a signature.

=back

=head1 MEAT & POTATOES

=head2 Data Types

=over

=item Problem

How do I pass different types of data to and from Inline C functions; like
strings, numbers and integers?

=item Solution

    # vowels.pl
    use Inline C;

    $filename = $ARGV[0];
    die "Usage: perl vowels.pl filename\n" unless -f $filename;

    $text = join '', <>;           # slurp input file
    $vp = vowel_scan($text);       # call our function
    $vp = sprintf("%03.1f", $vp * 100);  # format for printing
    print "The letters in $filename are $vp% vowels.\n";

    __END__
    __C__

    /* Find percentage of vowels to letters */
    double vowel_scan(char* str) {
      int letters = 0;
      int vowels = 0;
      int i = 0;
      char c;
      char normalize = 'a' ^ 'A';
      /* normalize forces lower case in ASCII; upper in EBCDIC */
      char A = normalize | 'a';
      char E = normalize | 'e';
      char I = normalize | 'i';
      char O = normalize | 'o';
      char U = normalize | 'u';
      char Z = normalize | 'z';

      while(c = str[i++]) {
        c |= normalize;
        if (c >= A && c <= Z) {
           letters++;
           if (c == A || c == E || c == I || c == O || c == U)
             vowels++;
        }
      }

      return letters ? ((double) vowels / letters) : 0.0;
    }

=item Discussion

This script takes a file name from the command line and prints the ratio of
vowels to letters in that file. C<vowels.pl> uses an Inline C function called
C<vowel_scan>, that takes a string argument, and returns the percentage of
vowels as a floating point number between 0 and 1. It handles upper and lower
case letters, and works with ASCII and EBCDIC. It is also quite fast.

Running this script produces:

    > perl vowels.pl /usr/share/dict/words
    The letters in /usr/share/dict/words are 37.5% vowels.

It is very important to note that the examples in this cookbook use C<char *>
to mean a string. Internally Perl has various mechanisms to deal with strings
that contain characters with code points above 255, using Unicode. This means
that naively treating strings as C<char *>, an array of 8-bit characters, can
lead to problems. You need to be aware of this and consider using a UTF-8
library to deal with strings.

=item See Also

The Perl Journal vol #19 has an article about Inline which uses this example.

=item Credits

This example was reprinted by permission of The Perl Journal. It was edited to
work with Inline v0.30 and higher.

=back

=head2 Variable Argument Lists

=over

=item Problem


=back

How do I pass a variable-sized list of arguments to an Inline C function?

=over

=item Solution

    greet(qw(Sarathy Jan Sparky Murray Mike));

    use Inline C => <<'END_OF_C_CODE';

    void greet(SV* name1, ...) {
      Inline_Stack_Vars;
      int i;

      for (i = 0; i < Inline_Stack_Items; i++)
        printf("Hello %s!\n", SvPV(Inline_Stack_Item(i), PL_na));

      Inline_Stack_Void;
    }

    END_OF_C_CODE

=item Discussion

This little program greets a group of people, such as my coworkers. We use the
C<C> ellipsis syntax: "C<...>", since the list can be of any size.

Since there are no types or names associated with each argument, we can't
expect XS to handle the conversions for us. We'll need to pop them off the
B<Stack> ourselves. Luckily there are two functions (macros) that make this a
very easy task.

First, we need to begin our function with a "C<Inline_Stack_Vars>" statement.
This defines a few internal variables that we need to access the B<Stack>. Now
we can use "C<Inline_Stack_Items>", which returns an integer containing the
number of arguments passed to us from Perl.

B<NOTE:> It is important to I<only> use "C<Inline_Stack_>" macros when there
is an ellipsis (C<...>) in the argument list, I<or> the function has a return
type of void.

Second, we use the C<Inline_Stack_Item(x)> function to access each argument
where "0 <= x < items".

B<NOTE:> When using a variable length argument list, you have to specify at
least one argument before the ellipsis. (On my compiler, anyway.) When XS does
it's argument checking, it will complain if you pass in less than the number
of I<defined> arguments. Therefore, there is currently no way to pass an empty
list when a variable length list is expected.

=item See Also


=item Credits


=back

=head2 Multiple Return Values

=over

=item Problem

How do I return a list of values from a C function?

=item Solution

    print map {"$_\n"} get_localtime(time);

    use Inline C => <<'END_OF_C_CODE';

    #include <time.h>

    void get_localtime(SV * utc) {
      const time_t utc_ = (time_t)SvIV(utc);
      struct tm *ltime = localtime(&utc_);
      Inline_Stack_Vars;

      Inline_Stack_Reset;
      Inline_Stack_Push(sv_2mortal(newSViv(ltime->tm_year)));
      Inline_Stack_Push(sv_2mortal(newSViv(ltime->tm_mon)));
      Inline_Stack_Push(sv_2mortal(newSViv(ltime->tm_mday)));
      Inline_Stack_Push(sv_2mortal(newSViv(ltime->tm_hour)));
      Inline_Stack_Push(sv_2mortal(newSViv(ltime->tm_min)));
      Inline_Stack_Push(sv_2mortal(newSViv(ltime->tm_sec)));
      Inline_Stack_Push(sv_2mortal(newSViv(ltime->tm_isdst)));
      Inline_Stack_Done;
    }
    END_OF_C_CODE

=item Discussion

Perl is a language where it is common to return a list of values from a
subroutine call instead of just a single value. C is not such a language. In
order to accomplish this in C we need to manipulate the Perl call stack by
hand. Luckily, Inline provides macros to make this easy.

This example calls the system C<localtime>, and returns each of the parts of
the time struct; much like the perl builtin C<localtime()>. On each stack
push, we are creating a new Perl integer (SVIV) and mortalizing it. The
sv_2mortal() call makes sure that the reference count is set properly. Without
it, the program would leak memory.

NOTE: The C<#include> statement is not really needed, because Inline
      automatically includes the Perl headers which include almost all
      standard system calls.

=item See Also

For more information on the Inline stack macros, see L<Inline::C>.

=item Credits

Richard Anderson <starfire@zipcon.net> contributed the original idea for
this snippet.

=back

=head2 Multiple Return Values (Another Way)

=over

=item Problem

How can I pass back more than one value without using the Perl Stack?

=item Solution

    use Inline::Files;
    use Inline C;

    my ($foo, $bar);
    change($foo, $bar);

    print "\$foo = $foo\n";
    print "\$bar = $bar\n";

    __C__

    int change(SV* var1, SV* var2) {
      sv_setpvn(var1, "Perl Rocks!", 11);
      sv_setpvn(var2, "Inline Rules!", 13);
      return 1;
    }

=item Discussion

Most perl function interfaces return values as a list of one or more scalars.
Very few like C<chomp>, will modify an input scalar in place. On the other
hand, in C you do this quite often. Values are passed in by reference and
modified in place by the called function.

It turns out that we can do that with Inline as well. The secret is to use a
type of 'C<SV*>' for each argument that is to be modified. This ensures
passing by reference, because no typemapping is needed.

The function can then use the Perl5 API to operate on that argument. When
control returns to Perl, the argument will retain the value set by the C
function. In this example we passed in 2 empty scalars and assigned values
directly to them.

=item See Also


=item Credits

Ned Konz <ned@bike-nomad.com> brought this behavior to my attention. He also
pointed out that he is not the world famous computer cyclist Steve Roberts
(L<http://www.microship.com),> but he is close (L<http://bike-nomad.com).>
Thanks Ned.

=back

=head2 Using Memory

=over

=item Problem

How should I allocate buffers in my Inline C code?

=item Solution

    print greeting('Ingy');

    use Inline C => <<'END_OF_C_CODE';

    SV* greeting(SV* sv_name) {
      return (newSVpvf("Hello %s!\n", SvPV(sv_name, PL_na)));
    }

    END_OF_C_CODE

=item Discussion

In this example we will return the greeting to the caller, rather than
printing it. This would seem mighty easy, except for the fact that we need to
allocate a small buffer to create the greeting.

I would urge you to stay away from C<malloc>ing your own buffer. Just use
Perl's built in memory management. In other words, just create a new Perl
string scalar. The function C<newSVpv> does just that. And C<newSVpvf>
includes C<sprintf> functionality.

The other problem is getting rid of this new scalar. How will the ref count
get decremented after we pass the scalar back? Perl also provides a function
called C<sv_2mortal>. Mortal variables die when the context goes out of scope.
In other words, Perl will wait until the new scalar gets passed back and then
decrement the ref count for you, thereby making it eligible for garbage
collection. See C<perldoc perlguts>.

In this example the C<sv_2mortal> call gets done under the hood by XS, because
we declared the return type to be C<SV*>.

To view the generated XS code, run the command "C<perl -
MInline=INFO,FORCE,NOCLEAN example004.pl>". This will leave the build
directory intact and tell you where to find it.

=item See Also


=item Credits


=back

=head2 Direct Access to Perl variables

=over

=item Problem

Can I write an Inline C function that can access a Perl variable directly
without having to pass it as an argument?

=item Solution

    use strict;
    use warnings;
    use Inline C => "DATA";

    our $mesh_data = "MESH-POINTS 0.0 0.0 0.5 0.25 1.0 0.5 1.5 0.75";
    CalcSurfaceHeights();

    __DATA__
    __C__
    #define N_MP 4

    void CalcSurfaceHeights() {
       double x[N_MP], y[N_MP], z;
       int    ix;
       char   *mesh_data = SvPV_nolen(get_sv("main::mesh_data", 0));

       sscanf(mesh_data, "MESH-POINTS %lf%lf%lf%lf%lf%lf%lf%lf",
                         x, y, x+1, y+1, x+2, y+2, x+3, y+3);

       for (ix=0; ix < N_MP; ix++) {
          z = 0.5*( sin(x[ix]) + sin(y[ix]) );

          printf("Surface-Height: %6.3f Mesh-Point: %6.2f, %6.2f\n",
                 z, x[ix], y[ix]);
       }
    }

=item Discussion

There are really only two points that need an explanation to understand why
the above code works. In the Perl section, you will notice the declaration

    our $mesh_data = "...";

For Perl variables to be directly accessible from Inline::C functions, they
must be declared as package variables. Lexical variables, those declared with
B<my>, cannot be accessed this way.

In the C code section of the example, the following line is what makes direct
access to the Perl variable work;

    char *mesh_data = SvPV_nolen(get_sv("main::mesh_data", 0))

Here SvPV_nolen() returns a pointer to the C string contained in the
scalar variable. The "_nolen" variation ignores the length of the C
string. Hence, the function takes only a single argument, which is the SV*
of the scalar variable.

We could have used the usual two-argument form of B<SvPV()> and, since we
don't care about the string length, specified B<PL_na> for the second
argument. The function call would then change to,

    SvPV(get_sv("main::mesh_data", 0), PL_na)

The function B<get_sv()> returns the SV* of a named scalar package variable.
It takes a C string, containing the fully qualified name of the variable, as
the first argument. The second argument contains flag values related to data
type. Since we are only reading the scalar variable, in our example, a value
of 0 can be used.

=item See Also

=over

=item * perldoc perlguts

=item * perldoc perlapi

=back

=item Credits

The code example and description were inspired by a discussion thread on the
Inline mailing list (inline@perl.org).

=back

=head1 FAST FOOD

=head2 Inline CGI

=over

=item Problem

How do I use Inline securely in a CGI environment?

=item Solution

    #!/usr/bin/perl

    use CGI qw(:standard);
    use Inline Config =>
      DIRECTORY => '/usr/local/apache/Inline';

    print
      header,
      start_html('Inline CGI Example'),
      h1(JAxH('Inline')),
      end_html;

    use Inline C => <<END;
    SV* JAxH(char* x) {
      return newSVpvf("Just Another %s Hacker", x);
    }
    END

=item Discussion

The problem with running Inline code from a CGI script is that Inline
B<writes> to a build area on your disk whenever it compiles code. Most CGI
scripts don't (and shouldn't) be able to create a directory and write into it.

The solution is to explicitly tell Inline which directory to use with the 'use
Inline Config => DIRECTORY => ...' line. Then you need to give write access to
that directory from the web server (CGI script).

If you see this as a security hole, then there is another option. Give write
access to yourself, but read-only access to the CGI script. Then run the
script once by hand (from the command line). This will cause Inline to
precompile the C code. That way the CGI will only need read access to the
build directory (to load in the shared library from there).

Just remember that whenever you change the C code, you need to
precompile it again.

=item See Also

See L<CGI> for more information on using the C<CGI.pm> module.

=item Credits


=back

=head2 mod_perl

=over

=item Problem


=back

How do I use Inline with mod_perl?

=over

=item Solution

    package Factorial;
    use strict;
    use Inline Config =>
               DIRECTORY => '/usr/local/apache/Inline',
               enable => 'UNTAINT';
    use Inline 'C';
    Inline->init;

    sub handler {
      my $r = shift;
      $r->send_http_header('text/plain');
      printf "%3d! = %10d\n", $_, factorial($_) for 1..100;
      return Apache::Constants::OK;
    }

    1;
    __DATA__
    __C__
    double factorial(double x) {
      if (x < 2) return 1;
      return x * factorial(x - 1)
    }

=item Discussion

This is a fully functional mod_perl handler that prints out the factorial
values for the numbers 1 to 100. Since we are using Inline under mod_perl,
there are a few considerations to , um, consider.

First, mod_perl handlers are usually run with C<-T> taint detection.
Therefore, we need to enable the UNTAINT option. The next thing to deal with
is the fact that this handler will most likely be loaded after Perl's compile
time. Since we are using the DATA section, we need to use the special
C<init()> call. And of course we need to specify a DIRECTORY that mod_perl can
compile into. I<See the above CGI example for more info.>

Other than that, this is a pretty straightforward mod_perl handler, tuned for
even more speed!

=item See Also

See Stas Bekman's upcoming O'Reilly book on mod_perl to which this example was
contributed.

=back

=head2 Object Oriented Inline

=over

=item Problem


=back

How do I implement Object Oriented programming in Perl using C objects?

=over

=item Solution

    my $obj1 = Soldier->new('Benjamin', 'Private', 11111);
    my $obj2 = Soldier->new('Sanders', 'Colonel', 22222);
    my $obj3 = Soldier->new('Matt', 'Sergeant', 33333);

    for my $obj ($obj1, $obj2, $obj3) {
      print $obj->get_serial, ") ",
            $obj->get_name, " is a ",
            $obj->get_rank, "\n";
    }

    #---------------------------------------------------------

    package Soldier;

    use Inline C => <<'END';

    /*
    Allocate memory with Newx if it's
    available - if it's an older perl
    that doesn't have Newx then we
    resort to using New.
    */
    #ifndef Newx
    #  define Newx(v,n,t) New(0,v,n,t)
    #endif

    typedef struct {
      char* name;
      char* rank;
      long  serial;
    } Soldier;

    SV* new(const char * classname, const char * name,
            const char * rank, long serial) {
      Soldier * soldier;
      SV      * obj;
      SV      * obj_ref;

      Newx(soldier, 1, Soldier);
      soldier->name = savepv(name);
      soldier->rank = savepv(rank);
      soldier->serial = serial;

      obj = newSViv((IV)soldier);
      obj_ref = newRV_noinc(obj);
      sv_bless(obj_ref, gv_stashpv(classname, GV_ADD));
      SvREADONLY_on(obj);

      return obj_ref;
    }

    char* get_name(SV* obj) {
      return ((Soldier*)SvIV(SvRV(obj)))->name;
    }

    char* get_rank(SV* obj) {
      return ((Soldier*)SvIV(SvRV(obj)))->rank;
    }

    long get_serial(SV* obj) {
      return ((Soldier*)SvIV(SvRV(obj)))->serial;
    }

    void DESTROY(SV* obj) {
      Soldier* soldier = (Soldier*)SvIV(SvRV(obj));
      Safefree(soldier->name);
      Safefree(soldier->rank);
      Safefree(soldier);
    }

    END

=item Discussion


=back

Damian Conway has given us myriad ways of implementing OOP in Perl. This is
one he might not have thought of.

The interesting thing about this example is that it uses Perl for all the OO
bindings while using C for the attributes and methods.

If you examine the Perl code everything looks exactly like a regular OO
example. There is a C<new> method and several accessor methods. The familiar
'arrow syntax' is used to invoke them.

In the class definition (second part) the Perl C<package> statement is used to
name the object class or namespace. But that's where the similarities end
Inline takes over.

The idea is that we call a C subroutine called C<new()> which returns a
blessed scalar. The scalar contains a readonly integer which is a C pointer to
a Soldier struct. This is our object.

The C<new()> function needs to malloc the memory for the struct and then copy
the initial values into it using C<savepv()>. This also allocates more memory
(which we have to keep track of).

The accessor methods are pretty straightforward. They return the current value
of their attribute.

The last method C<DESTROY()> is called automatically by Perl whenever an
object goes out of scope. This is where we can free all the memory used by
the object.

That's it. It's a very simplistic example. It doesn't show off any advanced OO
features, but it is pretty cool to see how easy the implementation can be. The
important Perl call is C<newSVrv()> which creates a blessed scalar.

=over

=item See Also


=back

Read "Object Oriented Perl" by Damian Conway, for more useful ways of doing
OOP in Perl.

You can learn more Perl calls in L<perlapi>. If you don't have Perl 5.6.0 or
higher, visit L<http://www.perldoc.com/perl5.6/pod/perlapi.html>

=head1 THE MAIN COURSE

=head2 Exposing Shared Libraries

=over

=item Problem

You have this great C library and you want to be able to access parts of it
with Perl.

=item Solution

    print get('http://www.axkit.org');

    use Inline C => Config =>
               LIBS => '-lghttp';
    use Inline C => <<'END_OF_C_CODE';

    #include <ghttp.h>

    char *get(SV* uri) {
      SV* buffer;
      ghttp_request* request;

      buffer = NEWSV(0,0);
      request = ghttp_request_new();
      ghttp_set_uri(request, SvPV(uri, PL_na));

      ghttp_set_header(request, http_hdr_Connection, "close");

      ghttp_prepare(request);
      ghttp_process(request);

      sv_catpv(buffer, ghttp_get_body(request));

      ghttp_request_destroy(request);

      return SvPV(buffer, PL_na);
    }

    END_OF_C_CODE

=item Discussion

This example fetches and prints the HTML from
L<http://www.axkit.org> Itrequires the GNOME http libraries. L<http://www.gnome.org>

One of the most common questions I get is "How can I use Inline to make use of
some shared library?". Although it has always been possible to do so, the
configuration was ugly, and there were no specific examples.

With version 0.30 and higher, you can specify the use of shared libraries
easily with something like this:

    use Inline C => Config => LIBS => '-lghttp';
    use Inline C => "code ...";

or

    use Inline C => "code ...", LIBS => '-lghttp';

To specify a specific library path, use:

    use Inline C => "code ...", LIBS => '-L/your/lib/path -lyourlib';

To specify an include path use:

    use Inline C => "code ...",
               LIBS => '-lghttp',
               INC => '-I/your/inc/path';

=item See Also

The C<LIBS> and C<INC> configuration options are formatted and passed into
MakeMaker. For more info see L<ExtUtils::MakeMaker>. For more options see
L<Inline::C>.

=item Credits

This code was written by Matt Sergeant <matt@sergeant.org>, author of many
CPAN modules. The configuration syntax has been modified for use with
Inline v0.30.

=back

=head2 Automatic Function Wrappers

=over

=item Problem

You have some functions in a C library that you want to access from Perl
exactly as you would from C.

=item Solution

The error function C<erf()> is probably defined in your standard math library.
Annoyingly, Perl does not let you access it. To print out a small table of its
values, just say:

    perl -le 'use Inline C => q{ double erf(double); }, enable => "autowrap"; print "$_ @{[erf($_)]}" for (0..10)'

The excellent C<Term::ReadLine::Gnu> implements Term::ReadLine using the
GNU ReadLine library. Here is an easy way to access just C<readline()> from
that library:

    package MyTerm;

    use Inline C => Config =>
               enable => autowrap =>
               LIBS => "-lreadline -lncurses -lterminfo -ltermcap ";
    use Inline C => q{ char * readline(char *); };

    package main;
    my $x = MyTerm::readline("xyz: ");

Note however that it fails to C<free()> the memory returned by readline, and
that C<Term::ReadLine::Gnu> offers a much richer interface.

=item Discussion

We access existing functions by merely showing Inline their declarations,
rather than a full definition. Of course the function declared must exist,
either in a library already linked to Perl or in a library specified using the
C<LIBS> option.

The first example wraps a function from the standard math library, so Inline
requires no additional C<LIBS> directive. The second uses the Config option to
specify the libraries that contain the actual compiled C code.

This behavior is always disabled by default. You must enable the C<autowrap>
option to make it work.

=item See Also

=over

=item * C<readline>

=item * C<Term::ReadLine::Gnu>

=back

=item Credits

GNU ReadLine was written by Brian Fox <bfox@ai.mit.edu> and Chet Ramey
<chet@ins.cwru.edu>. Term::ReadLine::Gnu was written by Hiroo Hayashi
<hiroo.hayashi@computer.org>. Both are far richer than the slim interface
given here!

The idea of producing wrapper code given only a function declaration is taken
from Swig by David M. Beazley <beazley@cs.uchicago.edu>.

Ingy's inline editorial insight:

This entire entry was contributed by Ariel Scolnicov <ariels@compugen.co.il>.
Ariel also first suggested the idea for Inline to support function declaration
processing.

=back

=head2 Replacing h2xs

=over

=item Problem

You have a complete C library that you want to access from Perl exactly as you
would from C.

=item Solution

Just say:

    use IO::All;
    use Inline C => sub { io('allheaders.h')->all =~ s/LEPT_DLL extern//gr },
      enable => "autowrap",
      libs => '-lleptonica';

=item Discussion

In principle, you can use h2xs to wrap a C library into an XS module. One
problem with this is that the C parser code is a little out of date. Also,
since it works by generating a number of files, maintaining it when the C
library changes is a certain amount of work. Using Inline to do the work is
much easier.

If the header file needs some processing, like removing some text that a full
C compiler can deal with, but the Inline::C parser cannot, as in the example
above? Well, Perl is good at text-processing.

=back

=head2 Complex Data

=over

=item Problem


=back

How do I deal with complex data types like hashes in Inline C?

=over

=item Solution

    use Inline C => <<'END_OF_C_CODE';

    void dump_hash(SV* hash_ref) {
      HV* hash;
      HE* hash_entry;
      int num_keys, i;
      SV* sv_key;
      SV* sv_val;

      if (! SvROK(hash_ref))
        croak("hash_ref is not a reference");

      hash = (HV*)SvRV(hash_ref);
      num_keys = hv_iterinit(hash);
      for (i = 0; i < num_keys; i++) {
        hash_entry = hv_iternext(hash);
        sv_key = hv_iterkeysv(hash_entry);
        sv_val = hv_iterval(hash, hash_entry);
        printf("%s => %s\n", SvPV(sv_key, PL_na), SvPV(sv_val, PL_na));
      }
      return;
    }

    END_OF_C_CODE

    my %hash = (
      Author => "Ingy döt Net",
      Nickname => "INGY",
      Module => "Inline.pm",
      Version => "0.30",
      Language => "C",
    );

    dump_hash(\%hash);

=item Discussion

The world is not made of scalars alone, although they are definitely the
easiest creatures to deal with, when doing Inline stuff. Sometimes we need to
deal with arrays, hashes, and code references, among other things.

Since Perl subroutine calls only pass scalars as arguments, we'll need to use
the argument type C<SV*> and pass references to more complex types.

The above program dumps the key/value pairs of a hash. To figure it out, just
curl up with L<perlapi> for a couple hours. Actually, its fairly straight
forward once you are familiar with the calls.

Note the C<croak> function call. This is the proper way to die from your C
extensions.

=item See Also

See L<perlapi> for information about the Perl5 internal API.

=item Credits


=back

=head2 Hash of Lists

=over

=item Problem


=back

How do I create a Hash of Lists from C?

=over

=item Solution

    use Inline C;
    use Data::Dumper;

    $hash_ref = load_data("./cartoon.txt");
    print Dumper $hash_ref;

    __END__
    __C__

    static int next_word(char**, char*);

    SV* load_data(char* file_name) {
      char buffer[100], word[100], * pos;
      AV* array;
      HV* hash = newHV();
      FILE* fh = fopen(file_name, "r");

      while (fgets(pos = buffer, sizeof(buffer), fh)) {
        if (next_word(&pos, word)) {
          array = newAV();
          hv_store(hash, word, strlen(word),
            newRV_noinc((SV*)array), 0);
          while (next_word(&pos, word))
            av_push(array, newSVpvf("%s", word));
        }
      }
      fclose(fh);
      return newRV_noinc((SV*) hash);
    }

    static int next_word(char** text_ptr, char* word) {
      char* text = *text_ptr;
      while(*text != '\0' &&
            *text <= ' ')
        text++;
      if (*text <= ' ')
        return 0;
      while(*text != '\0' &&
            *text > ' ') {
        *word++ = *text++;
      }
      *word = '\0';
      *text_ptr = text;
      return 1;
    }

=item Discussion

This is one of the larger recipes. But when you consider the number of
calories it has, it's not so bad. The function C<load_data> takes the name of
a file as it's input. The file C<cartoon.text> might look like:

    flintstones fred barney
    jetsons     george jane elroy
    simpsons    homer marge bart

The function will read the file, parsing each line into words. Then it will
create a new hash, whereby the first word in a line becomes a hash key and the
remaining words are put into an array whose reference becomes the hash value.
The output looks like this:

    $VAR1 = {
              'flintstones' => [
                                 'fred',
                                 'barney'
                               ],
              'simpsons' => [
                              'homer',
                              'marge',
                              'bart'
                            ],
              'jetsons' => [
                             'george',
                             'jane',
                             'elroy'
                           ]
            };

=item See Also

See L<perlapi> for information about the Perl5 internal API.

=item Credits

Al Danial <alnd@pacbell.net> requested a solution to this on
comp.lang.perl.misc. He borrowed the idea from the "Hash of Lists" example in
the Camel book.

=back

=head1 JUST DESSERTS

=head2 Win32

=over

=item Problem

How do I access Win32 DLL-s using Inline?

=item Solution

    use Inline C => DATA =>
               LIBS => '-luser32';

    $text = "@ARGV" || 'Inline.pm works with MSWin32. Scary...';

    WinBox('Inline Text Box', $text);

    __END__
    __C__

    #include <windows.h>

    int WinBox(char* Caption, char* Text) {
      return MessageBoxA(0, Text, Caption, 0);
    }

=item Discussion

This example runs on MS Windows. It makes a text box appear on the screen
which contains a message of your choice.

The important thing is that its proof that you can use Inline to interact with
Windows DLL-s. Very scary indeed. 8-o

To use Inline on Windows with ActivePerl (
L<http://www.ActiveState.com> )you'll need MS Visual Studio. You can also use the Cygwin environment,available at L<http://www.cygwin.com>
.

=item See Also

See L<Inline-Support> for more info on MSWin32 programming with Inline.

=item Credits

This example was adapted from some sample code written by Garrett Goebel
<garrett@scriptpro.com>

=back

=head2 Embedding Perl in C

=over

=item Problem

How do I use Perl from a regular C program?

=item Solution

    #!/usr/bin/cpr

    int main(void) {
      printf("Using Perl version %s from a C program!\n\n",
             CPR_eval("use Config; $Config{version};"));

      CPR_eval("use Data::Dumper;");
      CPR_eval("print Dumper \\%INC;");

      return 0;
    }

=item Discussion

By using CPR. (C Perl Run)

This example uses another Inline module, C<Inline::CPR>, available separately
on CPAN. When you install this module it also installs a binary interpreter
called C</usr/bin/cpr>. (The path may be different on your system)

When you feed a C program to the CPR interpreter, it automatically compiles
and runs your code using Inline. This gives you full access to the Perl
internals. CPR also provides a set of easy to use C macros for calling Perl
internals.

This means that you can effectively "run" C source code by putting a CPR
hashbang as the first line of your C program.

=item See Also

See L<Inline::CPR> for more information on using CPR.

C<Inline::CPR> can be obtained from
L<http://search.cpan.org/search?dist=Inline-CPR>

=item Credits

Randal Schwartz <merlyn@stonehenge.com>, Randolph Bentson
<bentson@grieg.holmsjoen.com>, Richard Anderson <starfire@zipcon.net>, and Tim
Maher <tim@consultix-inc.com> helped me figure out how to write a program that
would work as a hashbang.

=back

=head1 ENTERTAINING GUESTS

As of version 0.30, Inline has the ability to work in cooperation with other
modules that want to expose a C API of their own. The general syntax for
doing this is:

    use Inline with => 'Module';
    use Inline C => ... ;

This tells C<Module> to pass configuration options to Inline. Options like
typemaps, include paths, and external libraries, are all resolved
automatically so you can just concentrate on writing the functions.

=head2 Event handling with Event.pm

=over

=item Problem

You need to write a C callback for the C<Event.pm> module. Can this be done
more easily with Inline?

=item Solution

    use Inline with => 'Event';

    Event->timer(desc     => 'Timer #1',
                 interval => 2,
                 cb       => \&my_callback,
                );

    Event->timer(desc     => 'Timer #2',
                 interval => 3,
                 cb       => \&my_callback,
                );

    print "Starting...\n";
    Event::loop;

    use Inline C => <<'END';
    void my_callback(pe_event* event) {
      pe_timer * watcher = event->up;

      printf("%s\n\tEvent priority = %d\n\tWatcher priority = %d\n\n",
             SvPVX(watcher->base.desc),
             event->prio,
             watcher->base.prio
            );
    }
    END

=item Discussion

The first line tells Inline to load the C<Event.pm> module. Inline then
queries C<Event> for configuration information. It gets the name and location
of Event's header files, typemaps and shared objects. The parameters that
C<Event> returns look like:

    INC => "-I $path/Event",
    TYPEMAPS => "$path/Event/typemap",
    MYEXTLIB => "$path/auto/Event/Event.$so",
    AUTO_INCLUDE => '#include "EventAPI.h"',
    BOOT => 'I_EVENT_API("Inline");',

Doing all of this automatically allows you, the programmer, to simply write a
function that receives a pointer of type C<'pe_event*'>. This gives you access
to the C<Event> structure that was passed to you.

In this example, I simply print values out of the structure. The Perl code
defines 2 timer events which each invoke the same callback. The first one,
every two seconds, and the second one, every three seconds.

As of this writing, C<Event.pm> is the only CPAN module that works in
cooperation with Inline.

=item See Also

Read the C<Event.pm> documentation for more information. It contains a
tutorial showing several examples of using Inline with C<Event>.

=item Credits

Jochen Stenzel <perl@jochen-stenzel.de> originally came up with the idea of
mixing Inline and C<Event>. He also authored the C<Event> tutorial.

Joshua Pritikin <joshua.pritikin@db.com> is the author of C<Event.pm>.

=back

=head1 FOOD FOR THOUGHT

=head2 Calling C from both Perl and C

=over

=item Problem

I'd like to be able to call the same C function from both Perl and C.
Also I like to define a C function that B<doesn't> get bound to Perl. How
do I do that?

=item Solution

    print "9 + 5 = ", add(9, 5), "\n";
    print "SQRT(9^2 + 5^2) = ", pyth(9, 5), "\n";
    print "9 * 5 = ", mult(9, 5), "\n";

    use Inline C => <<'END_C';
    int add(int x, int y) {
      return x + y;
    }
    static int mult(int x, int y) {
      return x * y;
    }
    double pyth(int x, int y) {
      return sqrt(add(mult(x, x), mult(y, y)));
    }
    END_C

=item Discussion

The program produces:

    9 + 5 = 14
    SQRT(9^2 + 5^2) = 10.295630140987
    Can't locate auto/main/mult.al in @INC ...

Every Inline function that is bound to Perl is also callable by C. You don't
have to do anything special. Inline arranges it so that all the typemap code
gets done by XS and is out of sight. By the time the C function receives
control, everything has been converted from Perl to C.

Of course if your function manipulates the Perl Stack, you probably don't want
to call it from C (unless you I<really> know what you're doing).

If you declare a function as C<static>, Inline won't bind it to Perl. That's
why we were able to call C<mult()> from C but the call failed from Perl.

=back

=head2 Calling Perl from C

=over

=item Problem

So now that I can call C from Perl, how do I call a Perl subroutine from an
Inline C function.

=item Solution

    use Inline C;

    for(1..5) {
      c_func_1('This is the first line');
      c_func_2('This is the second line');
      print "\n";
    }

    sub perl_sub_1 {
      print map "$_\n", @_;
    }

    __DATA__
    __C__

    void c_func_2(SV* text) {
      dSP;

      ENTER;
      SAVETMPS;

      XPUSHs(sv_2mortal(newSVpvf("Plus an extra line")));
      PUTBACK;

      call_pv("perl_sub_1", G_DISCARD);

      FREETMPS;
      LEAVE;
    }

    void c_func_1(SV* text) {
      c_func_2(text);
    }

=item Discussion

This demo previously made use of Inline Stack macros only - but that's not the
correct way to do it. Instead, base the callbacks on the perlcall
documentation (as we're now doing).

Actually, this program demonstrates calling a C function which calls another C
function which in turn calls a Perl subroutine.

The nice thing about Inline C functions is that you can call them from both
Perl-space B<and> C-space. That's because Inline creates a wrapper function
around each C function. When you use Perl to call C you're actually calling
that function's wrapper. The wrapper handles typemapping and Stack management,
and then calls your C function.

The first time we call C<c_func_1> which calls C<c_func_2>. The second time we
call C<c_func_2> directly. C<c_func_2> calls the Perl subroutine
(C<perl_sub_1>) using the internal C<perl_call_pv> function. It has to put
arguments on the stack by hand. Since there is already one argument on the
stack when we enter the function, the C<XPUSHs> ( which is equivalent to an
C<Inline_Stack_Push> ) adds a second argument.

We iterate through a 'for' loop 5 times just to demonstrate that things still
work correctly when we do that. (This was where the previous rendition, making
use solely of Inline Stack macros, fell down.)

=item See Also

See L<Inline::C> for more information about Stack macros.

See L<perlapi> for more information about the Perl5 internal API.

=back

=head2 Evaling C

=over

=item Problem

I've totally lost my marbles and I want to generate C code at run time, and
C<eval> it into Perl. How do I do this?

=item Solution

    use Inline;
    use Code::Generator;

    my $c_code = generate('foo_function');

    Inline->bind(C => $c_code);

    foo_function(1, 2, 3);

=item Discussion

I can't think of a real life application where you would want to generate C
code on the fly, but at least I know how I would do it. :)

The C<bind()> function of Inline let's you bind (compileI<load>execute) C
functions at run time. It takes all of the same arguments as C<< use Inline C
=> ... >>.

The nice thing is that once a particular snippet is compiled, it remains
cached so that it doesn't need to be compiled again. I can imagine that
someday a mad scientist will dream up a self generating modeling system that
would run faster and faster over time.

If you know such a person, have them drop me a line.

=back

=head2 Providing a pure perl alternative

=over

=item Problem

I want to write a script that will use a C subroutine if Inline::C is
installed, but will otherwise use an equivalent pure perl subroutine if
Inline::C is not already installed. How do I do this?

=item Solution

    use strict;
    use warnings;

    eval {
      require Inline;
      Inline->import (C => Config =>
                      BUILD_NOISY => 1);
      Inline->import (C =><<'EOC');

      int foo() {
        warn("Using Inline\n");
        return 42;
      }

    EOC
    };

    if ($@) {
      *foo =\&bar;
    }

    sub bar {
      warn("Using Pure Perl Implementation\n");
      return 42;
    }

    my $x = foo();
    print "$x\n";

=item Discussion

If Inline::C is installed and functioning properly, the C sub foo is called by
the perl code. Otherwise, $@ gets set, and the equivalent pure perl function
bar is instead called.

Note, too, that the pure perl sub bar can still be explicitly called even if
Inline::C is available.

=back

=head2 Accessing Fortran subs using Inline::C

=over

=item Problem

I've been given a neat little sub written in fortran that takes, as its args,
two integers and returns their product. And I would like to use that sub as is
from Inline::C. By way of example, let's say that the fortran source file is
named 'prod.f', and that it looks like this:

    integer function sqarea(r,s)
    integer r, s
    sqarea = r*s
    return
    end

=item Solution

We can't access that code directly, but we can compile it into a library which
we B<can> then access from Inline::C. Using gcc we could run:

    gfortran -c prod.f -o prod.o
    ar cru libprod.a prod.o

The function is then accessible as follows:

    use warnings;

    use Inline C => Config =>
      LIBS => '-L/full/path/to/libprod_location -lprod -lgfortran';

    use Inline C => <<'  EOC';

    int wrap_sqarea(int a, int b) {
      return sqarea_(&a, &b);
    }

    EOC

    $x = 15;
    $y = $x + 3;
    $ret = wrap_sqarea($x, $y);
    print "Product of $x and $y is $ret\n";

=item Discussion

Note firstly that, although the function is specified as 'sqarea' in the
source file, gfortran appends an underscore to the name when the source is
compiled. (I don't know if B<all> fortran compilers do this.) Therefore
Inline::C needs to call the function as 'sqarea_'.

Secondly, because fortran subs pass args by reference, we need to pass the
B<addresses> of the two integer args to sqarea() when we call it from our
Inline::C sub.

If using g77 instead of gfortran, the only necessary change is that we specify
'-lg2c' instead of '-lgfortran' in our 'LIBS' setting.

=back

=head1 SEE ALSO

For generic information about Inline, see L<Inline>.

For information about using Inline with C see L<Inline::C>.

For information on supported languages and platforms see L<Inline-Support>.

For information on writing your own Inline language support module, see
L<Inline-API>.

Inline's mailing list is inline@perl.org

To subscribe, send email to inline-subscribe@perl.org

=head1 AUTHORS

Ingy döt Net <ingy@cpan.org>

Sisyphus <sisyphus@cpan.org>

=head1 COPYRIGHT AND LICENSE

Copyright 2000-2017. Ingy döt Net.

Copyright 2008, 2010-2014. Sisyphus.

This program is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.

See L<http://www.perl.com/perl/misc/Artistic.html>

=cut