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Neil Watkiss


Inline::CPP - Write Perl subroutines and classes in C++.


   use Inline CPP;

   print "9 + 16 = ", add(9, 16), "\n";
   print "9 - 16 = ", subtract(9, 16), "\n";


   int add(int x, int y) { 
      return x + y;

   int subtract(int x, int y) {
      return x - y;


The Inline::CPP module allows you to put C++ source code directly "inline" in a Perl script or module. You code classes or functions in C++, and you can use them as if they were written in Perl.

Choosing a C++ Compiler

Inline::CPP just parses your C++ code and creates bindings to it. Like Inline::C, you will need a suitable compiler the first time you run the script. Choosing a C++ compiler can prove difficult, because Perl is written in C, not C++.

Here's the rule: use any C++ compiler that's compatible with the compiler which built perl. For instance, if perl was built with gcc, use g++. If you're on a Sun or an IRIX box and the system C compiler cc built perl, then use the system C++ compiler, CC.

Some compilers actually compile both C and C++ with the same compiler. Microsoft's cl.exe is one such compiler -- you pass it the <-TP> flag to convince it that you want C++ mode.

Using Inline::CPP

Inline::CPP is very similar to Inline::C. It uses a grammar to parse your C++ code, and binds to functions or classes which are recognized. If a function is recognized, it will be available from Perl space. If the function's signature is not recognized, it will not be available from Perl space, but will be available from other functions in C++.

For more information about the grammar used to parse C++ code, see the section called "Grammar".

The following example shows how C++ snippets map into the Perl namespace:

Example 1:

   use Inline CPP => <<'END';

   int doodle() { }

   class Foo {

       int get_data() { return data; }
       void set_data(int a) { data = a; }
       int data;

   Foo::Foo() { cout << "creating a Foo()" << endl; }
   Foo::~Foo() { cout << "deleting a Foo()" << endl; }


After running the code above, Perl's namespace would look similar to if following code had been run:

   sub main::doodle { }

   package main::Foo;

   sub new { print "creating a Foo()\n"; bless {}, shift }
   sub DESTROY { print "deleting a Foo()\n" }

   sub get_data { my $o=shift; $o->{data} }
   sub set_data { my $o=shift; $o->{data} = shift }

The difference, of course, is that in the latter, Perl does the work. In the Inline::CPP example, all function calls get sent off to your C++ code. That means that things like this won't work:

   my $obj = new Foo;
   $obj->{extrafield} = 10;

It doesn't work because $obj is not a blessed hash. It's a blessed reference to a C++ object (and anyway, C++ wouldn't let you do that either, since extrafield wasn't defined).

C++ Configuration Options

For information on how to specify Inline configuration options, see Inline. This section describes each of the configuration options available for C. Most of the options correspond either the MakeMaker or XS options of the same name. See ExtUtils::MakeMaker and perlxs.


Adds a new entry to the end of the list of alternative libraries to bind with. MakeMaker will search through this list and use the first entry where all the libraries are found.

   use Inline Config => ALTLIBS => '-L/my/other/lib -lfoo';

See also the LIBS config option, which appends to the last entry in the list.


Specifies extra statements to be automatically included. They will be added on to the defaults. A newline char will automatically be added.

   use Inline Config => AUTO_INCLUDE => '#include "something.h"';


Specifies code to be run when your code is loaded. May not contain any blank lines. See perlxs for more information.

   use Inline Config => BOOT => 'foo();';


Specifies which compiler to use.


Specifies extra compiler flags. Corresponds to the MakeMaker option.


Specifies one (or more, in an array ref) filter which is to be applied to the code just prior to parsing. The filters are executed one after another, each operating on the output of the previous one. You can pass in a code reference or the name of a prepackaged filter.

   use Inline Config => FILTERS => [Strip_POD => \&myfilter];

The filter may do anything. The code is passed as the first argument, and it returns the filtered code.


Specifies extra include directories. Corresponds to the MakeMaker parameter.

   use Inline Config => INC => '-I/my/path';


Specifies the linker to use.


Specifies which linker flags to use.

NOTE: These flags will completely override the existing flags, instead of just adding to them. So if you need to use those too, you must respecify them here.


Specifies external libraries that should be linked into your code. Corresponds to the MakeMaker parameter.

   use Inline Config => LIBS => '-L/your/path -lyourlib';

Unlike the LIBS configuration parameter used in Inline::C, successive calls to LIBS append to the previous calls. For example,

   use Inline Config => LIBS => '-L/my/path', LIBS => '-lyourlib';

will work correctly. If you want to add a new element to the list of possible libraries to link with, use the Inline::CPP configuration ALTLIBS.


Specifies the name of the 'make' utility to use.


Specifies a user compiled object that should be linked in. Corresponds to the MakeMaker parameter.

   use Inline Config => MYEXTLIB => '/your/path/something.o';


Specifies a prefix that will automatically be stripped from C++ functions when they are bound to Perl. Less useful than in C, because C++ mangles its function names so they don't conflict with C functions of the same name.

   use Inline Config => PREFIX => 'ZLIB_';

This only affects C++ function names, not C++ class names or methods.


By default, Inline::CPP replaces ... in bound functions with three spaces, since the arguments are always passed on the Perl Stack, not on the C stack. This is usually desired, since it allows functions with no fixed arguments (most compilers require at least one fixed argument).

   use Inline Config => PRESERVE_ELLIPSIS => 1;
   use Inline Config => ENABLE => PRESERVE_ELLIPSIS;

For an example of why PRESERVE_ELLIPSIS is normally not needed, see the examples section, below.


By default, Inline::CPP includes iostream.h at the top of your code. This option makes it include iostream instead, which is the ANSI-compliant version of the header. Usually, these include files are not compatible with one another.

   use Inline CPP => Config => ENABLE => STD_IOSTREAM;


Specifies whether to bind C structs into Perl using Inline::Struct. NOTE: Support for this option is experimental. Inline::CPP already binds to structs defined in your code. Structs and classes are treated as the same construct, except that a struct's initial scope is public, not private. Inline::Struct provides autogenerated get/set methods, an overloaded constructor, and several other features not available in Inline::CPP.

You can invoke STRUCTS in several ways:

   use Inline Config => STRUCTS => 'Foo';
   use Inline Config => STRUCTS => ['Bar', 'Baz'];

Binds the named structs to Perl. Emits warnings if a struct was requested but could not be bound for some reason.

   use Inline Config => ENABLE => 'STRUCTS';
   use Inline Config => STRUCTS => 1;

Enables binding structs to Perl. All structs which can be bound, will. This parameter overrides all requests for particular structs.

   use Inline Config => DISABLE => 'STRUCTS';
   use Inline Config => STRUCTS => 0;

Disables binding structs to Perl. Overrides any other settings.

See Inline::Struct for more details about how Inline::Struct binds C structs to Perl.


Specifies extra typemap files to use. These types will modify the behaviour of C++ parsing. Corresponds to the MakeMaker parameter.

   use Inline Config => TYPEMAPS => '/your/path/typemap';

C++-Perl Bindings

This section describes how the Perl variables get mapped to C++ variables and back again.

Perl uses a stack to pass arguments back and forth to subroutines. When a sub is called, it pops off all its arguments from the stack; when it's done, it pushes its return values back onto the stack.

XS (Perl's language for creating C or C++ extensions for Perl) uses "typemaps" to turn SVs into C types and back again. This is done through various XS macro calls, casts, and the Perl API. XS also allows you to define your own mappings.

Inline::CPP uses a much simpler approach. It parses the system's typemap files and only binds to functions with supported types. You can tell Inline::CPP about custom typemap files too.

If you have very complicated data structures in either C++ or Perl, you should just pass them as an SV* and do the conversion yourself in your C++ function.

In C++, a struct is a class whose default scope is public, not private. Inline::CPP binds to structs with this in mind -- get/set methods are not yet auto-generated (although they are scheduled to land in an upcoming release).

If you have a C struct, you can use Inline::Struct to allow Perl complete access to the internals of the struct. You can create and modify structs from inside Perl, as well as pass structs into C++ functions and return them from functions. Please note that Inline::Struct does not understand any C++ features, so constructors and member functions are not supported. See Inline::Struct for more details.


Here are some examples.

Example 1 - Farmer Bob

This example illustrates how to use a simple class (Farmer) from Perl. One of the new features in Inline::CPP is binding to classes with inline method definitions:

   use Inline CPP;

   my $farmer = new Farmer("Ingy", 42);
   my $slavedriver = 1;
   while($farmer->how_tired < 420) {
     $slavedriver <<= 1;

   print "Wow! The farmer worked ", $farmer->how_long, " hours!\n";


   class Farmer {
     Farmer(char *name, int age);

     int how_tired() { return tiredness; }
     int how_long() { return howlong; }
     void do_chores(int howlong);

     char *name;
     int age;
     int tiredness;
     int howlong;

   Farmer::Farmer(char *name, int age) {
     this->name = strdup(name);
     this->age = age;
     tiredness = 0;
     howlong = 0;

   Farmer::~Farmer() {

   void Farmer::do_chores(int hl) {
     howlong += hl;
     tiredness += (age * hl);

Example 2 - Plane and Simple

This example demonstrates some new features of Inline::CPP: support for inheritance and abstract classes. The defined methods of the abstract class Object are bound to Perl, but there is no constructor or destructor, meaning you cannot instantiate an Object.

The Airplane is a fully-bound class which can be created and manipulated from Perl.

   use Inline CPP;

   my $plane = new Airplane;
   if ($plane->isa("Object")) { print "Plane is an Object!\n"; }
   unless ($plane->can("fly")) { print "This plane sucks!\n"; }


   /* Abstract class (interface) */
   class Object {
     virtual void print() { cout << "Object (" << this << ")" << endl; }
     virtual void info() = 0;
     virtual bool isa(char *klass) = 0;
     virtual bool can(char *method) = 0;

   class Airplane : public Object {
     Airplane() {}
     ~Airplane() {}

     virtual void info() { print(); }
     virtual bool isa(char *klass) { return strcmp(klass, "Object")==0; }
     virtual bool can(char *method) { 
       bool yes = false;
       yes |= strcmp(method, "print")==0;
       yes |= strcmp(method, "info")==0;
       yes |= strcmp(method, "isa")==0;
       yes |= strcmp(method, "can")==0;
       return yes;

Example 3 - The Ellipsis Abridged

One of the big advantages of Perl over C or C++ is the ability to pass an arbitrary number of arguments to a subroutine. You can do it in C, but it's messy and difficult to get it right. All of this mess is necessary because C doesn't give the programmer access to the stack. Perl, on the other hand, gives you access to everything.

Here's a useful function written in Perl that is relatively slow:

   sub average { 
      my $average = 0;
      for (my $i=0; $i<@_; $i++) {
         $average *= $i;
         $average += $_[$i];
         $average /= $i + 1;
      return $average;

Here's the same function written in C:

   double average() {
      double avg = 0.0;
      for (int i=0; i<Inline_Stack_Items; i++) {
         avg *= i;
         avg += SvNV(Inline_Stack_Item(i));
         avg /= i + 1;
      return avg;

Here's a benchmark program that tests which is faster:

   use Inline CPP;
   my @numbers = map { rand } (1 .. 10000);
   my ($a, $stop);
   $stop = 200;
   if (@ARGV) {
      $a = avg(@numbers) while $stop--;
   else {
      $a = average(@numbers) while $stop--;
   print "The average of 10000 random numbers is: ", $a, "\n";

   sub average {
       my $average = 0;
       for (my $i=0; $i<@_; $i++) {
           $average *= $i;
           $average += $_[$i];
           $average /= $i + 1;
       return $average;


   double avg(...) {
       double avg = 0.0;
       for (int i=0; i<items; i++) {
           avg *= i;
           avg += SvNV(ST(i));
           avg /= i + 1;
       return avg;

The perl sub runs in 14.18 seconds, an average of 0.0709s per call. The C function runs in 1.52 seconds, an average of 0.0076s per call. Mind you, those both include the time taken to initialize the array with random numbers. And by varying the number of elements in the array and the number of repetitions of the function, we can change this number a lot.

What's the point? Of course C or C++ is faster than Perl. Well..., actually, that wasn't really the point; that was an aside. Look at the function declaration:

   double avg(...)

Why didn't we need to use varargs macros to get at the arguments? Why didn't the compiler complain that there were no required arguments? Because Inline::C++ actually compiled this:

   double avg(   )

When it bound to the function, it noticed the ellipsis and decided to get rid of it. Any function bound to Perl that has an ellipsis in it will have its arguments passed via the Perl stack, not the C stack. That means if you write a function like this:

   void myprintf(char *format, ...);

then you'd better be reading things from the Perl stack. If you aren't, then specify the PRESERVE_ELLIPSIS option in your script. That will leave the ellipsis in the code for the compiler to whine about. :)

Example 4 - Stacks and Queues

Everyone who learns C++ writes a stack and queue class sooner or later. I might as well try it from Inline. But why reinvent the wheel? Perl has a perfectly good Array type, which can easily implement both a Queue and a Stack.

This example implements a Queue and a Stack class, and shows off just a few more new features of Inline::CPP: default values to arguments,

   use Inline CPP;

   my $q = new Queue;
   $q->q("Where am I?");
   $q->q("In a queue.");
   print "There are ", $q->size, " items in the queue\n";
   while($q->size) {
     print "About to dequeue:  ", $q->peek, "\n";
     print "Actually dequeued: ", $q->dq, "\n";

   my $s = new Stack;
   print "There are ", $s->size, " items on the stack\n";
   while($s->size) {
     print "About to pop:    ", $s->peek, "\n";
     print "Actually popped: ", $s->pop, "\n";


   class Queue {
     Queue(int sz=0) { q = newAV(); if (sz) av_extend(q, sz-1); }
     ~Queue() { av_undef(q); }

     int size() {return av_len(q) + 1; }

     int q(SV *item) { av_push(q, SvREFCNT_inc(item)); return av_len(q)+1; }
     SV *dq() { return av_shift(q); }
     SV *peek() { return size() ? SvREFCNT_inc(*av_fetch(q,0,0)): &PL_sv_undef;}

     AV *q;

   class Stack {
     Stack(int sz=0) { s = newAV(); if (sz) av_extend(s, sz-1); }
     ~Stack() { av_undef(s); }

     int size() { return av_len(s) + 1; }

     int push(SV *i) { av_push(s, SvREFCNT_inc(i)); return av_len(s)+1; }
     SV *pop() { return av_pop(s); }
     SV *peek() { return size() ? SvREFCNT_inc(*av_fetch(s,size()-1,0)) : &PL_sv_undef; }

     AV *s;

Grammar Details

Perl 5.6.0 is recommended for Inline::CPP, and is required to get all the new features. If you are using Perl 5.005_03 the package will build and run, but you will have problems in certain circumstances:

Inline function definitions

For the purposes of this discussion, inline function definitions are best described by this example:

   class Foo {
       Foo() { /* Do something */ }

This example shows a class with a constructor defined inline. Inline::CPP can parse this example with 5.005. But this example requires Perl 5.6.0:

   class Foo {
       Foo() { if(1) { /* Do something */ } }

Here's what happened: Inline::CPP saw a class, saw the method, then noticed it was an inline method. So it grabbed this text:

   "{ if(1) { /* Do something */ }"

And then it tried to match another part of the class. But it failed because the next part of the string is this (with newlines trimmed):

   "} };"

The remaining text doesn't parse right. There are two solutions:


Use Perl version 5.6.0 or better; or,


Move the definition outside the class.

Complex default parameters

Again, default parameters are best described by example:

   int root(double number, int whatroot=2);

This function takes one or two arguments. If the second is missing, C++ gives it the value 2. Inline::CPP can parse this simple example regardless of your perl version. But the following example requires 5.6.0:

   int root(double number, int whatroot=((2)));

That's because if you're using 5.005, your arguments are parsed with a regular expression that looks for only one closing parenthesis. Any more than that, and you get a parse error.

Again, there are two solutions:


Use Perl version 5.6.0 or better; or,


Make the strange expression a constant or macro and use that.

Rant: Perl 5.005 is for Dummies

I'm going to take the opportunity to rant. Everything in the rest of this section can be ignored if you don't want to hear it.

Perl 5.6.0 has been out for a long time. It's proven, stable, and people use it all the time. Perl 5.6.1 is the latest stable release. Unless you depend on one of the few modules which are only available for the ancient versions of Perl, there is absolutely no reason not to upgrade today!


For general information about how Inline binds code to Perl, see Inline.

For information on using C with Perl, see Inline::C and Inline::C-Cookbook. For WMTYEWTK, see perlxs, perlxstut, perlapi, and perlguts.

For information on using C and C++ structs with Perl, see Inline::Struct.


When reporting a bug, please do the following:

 - Put "use Inline REPORTBUG;" at the top of your code, or 
   use the command line option "perl -MInline=REPORTBUG ...".
 - Run your code.
 - Follow the printed instructions.

Here are some things to watch out for:

  1. The grammar used for parsing C++ is still quite simple, and does not allow several features of C++:




    operator overloading


    function overloading

    Other grammar problems will probably be noticed quickly.

  2. In order of relative importance, improvements planned in the near future are:


    support for overloaded functions and methods


    binding to constants and constant #defines


    binding to unions


    autogenerated get/set methods on public members


Neil Watkiss <NEILW@cpan.org>

Brian Ingerson <INGY@cpan.org> is the author of Inline, Inline::C and Inline::CPR. He is known in the innermost Inline circles as "Batman". ;)


Copyright (c) 2000 - 2001, Neil Watkiss.

All Rights Reserved. This module is free software. It may be used, redistributed and/or modified under the same terms as Perl itself.

See http://www.perl.com/perl/misc/Artistic.html