Inline::C::Cookbook
===================

A Cornucopia of Inline C Recipes

= 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. `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!

= Appetizers

== Hello, world

- Problem

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?

- Solution

    use Inline C => <<'END_C';

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

    greet;

- Discussion

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

- See Also

  See [Inline] and [Inline::C] for basic info about `Inline.pm`.

- Credits

  * Brian Kernigan
  * Dennis Ritchie

== One Liner

- 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?

- Solution

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

- Discussion

  Try doing that in XS :-)

- 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 :-(

- Credits

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

= Meat & Potatoes

== Data Types

- Problem

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

- 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;
    }

- Discussion

  This script takes a file name from the command line and prints the ratio of
  vowels to letters in that file. `vowels.pl` uses an Inline C function called
  `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/dict/words
    The letters in /usr/dict/words are 37.5% vowels.

  It is very important to note that the examples in this cookbook use
  `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 `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.

- See Also

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

- Credits

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

== Variable Argument Lists

- Problem

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

- 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


- Discussion

  This little program greets a group of people, such as my coworkers. We use
  the `C` ellipsis syntax: "`...`", 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
  *Stack* ourselves. Luckily there are two functions (macros) that make this a
  very easy task.

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

  *NOTE:* It is important to /only/ use "`Inline_Stack_`" macros when there is
  an ellipsis (`...`) in the argument list, /or/ the function has a return type
  of void.

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

  *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 /defined/ arguments. Therefore, there is currently no way to pass
  an empty list when a variable length list is expected.

- See Also

- Credits

== Multiple Return Values

- Problem

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

- 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

- 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 `localtime`, and returns each of the parts of
  the time struct; much like the perl builtin `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 `#include` statement is not really needed, because Inline
  automatically includes the Perl headers which include almost all standard
  system calls.

- See Also

  For more information on the Inline stack macros, see [Inline::C].

- Credits

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

== Multiple Return Values (Another Way)

- Problem

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

- 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;
    }

- Discussion

  Most perl function interfaces return values as a list of one or more scalars.
  Very few like `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 '`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.

- See Also

- 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
  (http://www.microship.com), but he is close (http://bike-nomad.com). Thanks
  Ned.

== Using Memory

- Problem

  How should I allocate buffers in my Inline C code?

- 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

- 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 `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 `newSVpv` does just that. And `newSVpvf` includes
  `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 `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 `perldoc perlguts`.

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

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

- See Also

- Credits

= Fast Food

== Inline CGI

- Problem

  How do I use Inline securely in a CGI environment?

- 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

- Discussion

  The problem with running Inline code from a CGI script is that Inline
  *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.

- See Also

  See [CGI] for more information on using the `CGI.pm` module.

- Credits

== mod_perl

- Problem

How do I use Inline with mod_perl?

- 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)
    }

- 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 `-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
  `init()` call. And of course we need to specify a DIRECTORY that mod_perl can
  compile into. /See the above CGI example for more info./

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

- See Also

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

- Credits

== Object Oriented Inline

- Problem

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

- 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

- Discussion

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 `new` method and several accessor methods. The familiar
'arrow syntax' is used to invoke them.

In the class definition (second part) the Perl `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 `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 `new()` function needs to malloc the memory for the struct and then copy
the initial values into it using `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 `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 `newSVrv()` which creates a blessed scalar.

- See Also

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

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

- Credits

= The Main Course

== Exposing Shared Libraries

- Problem

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

- 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

- Discussion

  This example fetches and prints the HTML from http://www.axkit.org It
  requires the GNOME http libraries. 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';

- See Also

  The `LIBS` and `INC` configuration options are formatted and passed into
  MakeMaker. For more info see [ExtUtils::MakeMaker]. For more options see
  [Inline::C].

- 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.

== Automatic Function Wrappers

- Problem

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

- Solution

  The error function `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 `Term::ReadLine::Gnu` implements Term::ReadLine using the GNU
  ReadLine library. Here is an easy way to access just `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 `free()` the memory returned by readline, and
  that `Term::ReadLine::Gnu` offers a much richer interface.

- 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 `LIBS` option.

  The first example wraps a function from the standard math library, so Inline
  requires no additional `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 `AUTOWRAP`
  option to make it work.

- See Also

  `readline`, `Term::ReadLine::Gnu`

- 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.

== Complex Data

- Problem

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

- 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);

- 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 `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 [perlapi] for a couple hours. Actually, its fairly straight
  forward once you are familiar with the calls.

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

- See Also

  See [perlapi] for information about the Perl5 internal API.

- Credits

== Hash of Lists

- Problem

How do I create a Hash of Lists from C?

- 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)) {
                hv_store(hash, word, strlen(word),
                        newRV_noinc((SV*)array = newAV()), 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;
    }

- 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 `load_data` takes the name of
  a file as it's input. The file `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'
                           ]
            };

- See Also

  See [perlapi] for information about the Perl5 internal API.

- 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.

= Just Desserts

== Win32

- Problem

  How do I access Win32 DLL-s using Inline?

- 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);
    }

- 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 ( http://www.ActiveState.com )
  you'll need MS Visual Studio. You can also use the Cygwin environment,
  available at http://www.cygwin.com .

- See Also

  See [Inline-Support] for more info on MSWin32 programming with Inline.

- Credits

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

== Embedding Perl in C

- Problem

  How do I use Perl from a regular C program?

- 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;

    }

- Discussion

  By using CPR. (C Perl Run)

  This example uses another Inline module, `Inline::CPR`, available separately
  on CPAN. When you install this module it also installs a binary interpreter
  called `/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.

- See Also

  See [Inline::CPR] for more information on using CPR.

  `Inline::CPR` can be obtained from
  http://search.cpan.org/search?dist=Inline-CPR

- 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.

= 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 `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.

== Event handling with Event.pm

- Problem

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

- 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

- Discussion

  The first line tells Inline to load the `Event.pm` module. Inline then
  queries `Event` for configuration information. It gets the name and location
  of Event's header files, typemaps and shared objects. The parameters that
  `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 `'pe_event*'`. This gives you access
  to the `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, `Event.pm` is the only CPAN module that works in
  cooperation with Inline.

- See Also

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

- Credits

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

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

= Food for Thought

== Calling C from both Perl and C

- 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 *doesn't* get bound to Perl.  How do I do
  that?

- 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

- 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 /really/ know what you're doing).

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

- See Also

- Credits

== Calling Perl from C

- Problem

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

- 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);
    }


- 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 *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_func_1` which calls `c_func_2`. The second time we
  call `c_func_2` directly. `c_func_2` calls the Perl subroutine (`perl_sub_1`)
  using the internal `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 `XPUSHs` ( which is equivalent to an `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.)

- See Also

  See [Inline::C] for more information about Stack macros.

  See [perlapi] for more information about the Perl5 internal API.

- Credits

== Evaling C

- Problem

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

- Solution

    use Inline;
    use Code::Generator;

    my $c_code = generate('foo_function');

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

    foo_function(1, 2, 3);

- 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 `bind()` function of Inline let's you bind (compile/load/execute) C
  functions at run time. It takes all of the same arguments as '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.

- See Also

- Credits

== Providing a pure perl alternative

- 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?

- 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";

- 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.

== Accessing Fortran subs using Inline::C

- 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

- Solution

  We can't access that code directly, but we can compile it into a
  library which we *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";

- 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 *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
  *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.

= See Also

For generic information about Inline, see [Inline].

For information about using Inline with C see [Inline::C].

For information on supported languages and platforms see [Inline-Support].

For information on writing your own Inline language support module, see
[Inline-API].

Inline's mailing list is inline@perl.org

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

= Author

Ingy döt Net <ingy@cpan.org>

= Copyright

Copyright 2000-2014. 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 http://www.perl.com/perl/misc/Artistic.html
