C-Cookbook(3) User Contributed Perl Documentation C-Cookbook(3)NAME
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 apdapted 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.
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(int 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");
}
#---------------------------------------------------------
use Inline C => <<'END';
typedef struct {
char* name;
char* rank;
long serial;
} Soldier;
SV* new(char* class, char* name, char* rank, long serial) {
Soldier* soldier;
SV* obj_ref = newSViv(0);
SV* obj = newSVrv(obj_ref, class);
New(42, soldier, 1, Soldier);
soldier->name = savepv(name);
soldier->rank = savepv(rank);
soldier->serial = serial;
sv_setiv(obj, (IV)soldier);
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 "strdup()". 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 => "Brian Ingerson",
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
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
Brian Ingerson <INGY@cpan.org>
COPYRIGHT
Copyright (c) 2001, 2002. Brian Ingerson.
Copyright (c) 2008, 2010, 2011. Sisyphus.
All Rights Reserved. This module is free software. It may be used,
redistributed and/or modified under the terms of the Perl Artistic
License.
See http://www.perl.com/perl/misc/Artistic.html
perl v5.12.5 2011-01-29 C-Cookbook(3)