swig/Doc/Manual/Php.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<!-- Hand crafted HTML -->
<html>
<head>
<title>SWIG and PHP</title>
<link rel="stylesheet" type="text/css" href="style.css">
</head>

<body bgcolor="#ffffff">
<H1><a name="Php"></a>28 SWIG and PHP</H1>
<!-- INDEX -->
<div class="sectiontoc">
<ul>
<li><a href="#Php_nn1">Generating PHP Extensions</a>
<ul>
<li><a href="#Php_nn1_1">Building a loadable extension</a>
<li><a href="#Php_nn1_2">Building extensions into PHP</a>
<li><a href="#Php_nn1_3">Using PHP Extensions</a>
</ul>
<li><a href="#Php_nn2">Basic PHP interface</a>
<ul>
<li><a href="#Php_nn2_1">Constants</a>
<li><a href="#Php_nn2_2">Global Variables</a>
<li><a href="#Php_nn2_3">Functions</a>
<li><a href="#Php_nn2_4">Overloading</a>
<li><a href="#Php_nn2_5">Pointers and References</a>
<li><a href="#Php_nn2_6">Structures and C++ classes</a>
<ul>
<li><a href="#Php_nn2_6_1">Using <tt>-noproxy</tt></a>
<li><a href="#Php_nn2_6_2">Constructors and Destructors</a>
<li><a href="#Php_nn2_6_3">Static Member Variables</a>
<li><a href="#Php_nn2_6_4">Static Member Functions</a>
</ul>
<li><a href="#Php_nn2_7">PHP Pragmas, Startup and Shutdown code</a>
</ul>
</ul>
</div>
<!-- INDEX -->


<p>
<b>Caution: This chapter (and module!) is still under construction</b>
</p>

<p>
SWIG supports generating wrappers for PHP5.  Support for PHP4 has been removed
as of SWIG 1.3.37.  The PHP developers are no longer making new PHP4 releases,
and won't even be patching critical security issues after 2008-08-08, so it
doesn't make much sense for SWIG to continue to support PHP4 at this point.
If you need to continue to use PHP4, stick with SWIG 1.3.36.
</p>

<p>
In this chapter, we discuss SWIG's support of PHP.  The PHP module
was extensively rewritten in release 1.3.26, and support for generating
OO wrappers for PHP5 was added in 1.3.30.  The PHP module works fairly
well, but currently does not implement all the
features available in some of the other languages.
</p>

<p>
In order to use this module, you will need to have a copy of the PHP5
include files to compile the SWIG generated files.  If you installed
PHP from a binary package, you may need to install a "php-dev" or "php-devel"
package for these to be installed.  You can find out where these files are
by running <tt>php-config --includes</tt>.  To use the built PHP module you
will need either the php binary or the Apache php module. If you want to build
your extension into php directly, you will need the complete PHP source tree
available.
</p>

<H2><a name="Php_nn1"></a>28.1 Generating PHP Extensions</H2>


<p>
To build a PHP extension, run swig using the <tt>-php</tt> option as
follows:
</p>

<div class="code"><pre>
swig -php example.i
</pre></div>

<p>
This will produce 3 files example_wrap.c, php_example.h and
example.php. The first file, <tt>example_wrap.c</tt> contains all of
the C code needed to build a PHP extension. The second file,
<tt>php_example.h</tt> contains the header information needed if
you wish to statically link the extension into the php interpreter.
The third file,
<tt>example.php</tt> can be included by PHP scripts.  It attempts to
dynamically load the extension and contains extra php code specified
in the interface file.  If wrapping C++ code with PHP classes, it will
also contain PHP5 class wrappers.
</p>

<p>
Swig can generate PHP extensions from C++ libraries as well when
given the <tt>-c++</tt> option.  The support for C++ is discussed in
more detail in <a href="#Php_nn2_6">section 27.2.6</a>.
</p>

<p>
The usual (and recommended) way is to build the extension as a separate
dynamically loaded module (which is supported by all modern operating
systems).  You can then specify that this be loaded
automatically in <tt>php.ini</tt> or load it explicitly for any script which
needs it.
</p>

<p>
It is also possible to rebuild PHP from source so that your module is
statically linked into the php executable/library.  This is a lot more
work, and also requires a full rebuild of PHP to update your module,
and it doesn't play nicely with package system.  We don't recommend
this approach, or provide explicit support for it.
</p>

<H3><a name="Php_nn1_1"></a>28.1.1 Building a loadable extension</H3>

<p>
To build your module as a dynamically loadable extension, use compilation
commands like these (if you aren't using GCC, the commands will be different,
and there may be some variation between platforms - these commands should at
least work for Linux though):
</p>

<div class="code"><pre>
	gcc `php-config --includes` -fpic -c example_wrap.c
	gcc -shared example_wrap.o -o example.so
</pre></div>

<H3><a name="Php_nn1_3"></a>28.1.3 Using PHP Extensions</H3>

<p>
To test the extension from a PHP script, you need to load it first. You
can load it for every script by adding this line the <tt>[PHP]</tt> section of
<tt>php.ini</tt>:
</p>

<div class="code"><pre>
	extension=/path/to/modulename.so
</pre></div>

<p>
Alternatively, you can load it explicitly only for scripts which need it
by adding this line:
</p>

<div class="code"><pre>
	dl("/path/to/modulename.so");	// Load the module
</pre></div>

<p>
to the start of each PHP file.  SWIG also generates a php module, which
attempts to do the <tt>dl()</tt> call for you:
</p>

<div class="code"><pre>
	include("example.php");
</pre></div>

<H2><a name="Php_nn2"></a>28.2 Basic PHP interface</H2>


<p>
It is important to understand that PHP uses a single global namespace
into which all symbols from extension modules are loaded.  It is quite
possible for names of symbols in one extension module to clash with
other symbols unless care is taken to <tt>%rename</tt> them.
</p>

<H3><a name="Php_nn2_1"></a>28.2.1 Constants</H3>


<p>
These work in much the same way as in C/C++, constants can be defined
by using either the normal C pre-processor declarations, or the
<tt>%constant</tt> SWIG directive.  These will then be available from
your PHP script as a PHP constant, (i.e. no dollar sign is needed to
access them.) For example, with a swig interface file like this,
</p>

<div class="code"><pre>
%module example

#define PI 3.14159

%constant int E  = 2.71828
</pre>
</div>

<p>
you can access the constants in your php script like this,
</p>

<div class="code"><pre>
include("example.php");

echo "PI = " . PI . "\n";

echo "E = " . E . "\n";

</pre>
</div>

<p>
There are two peculiarities with using constants in PHP. The first is that
if you try to use an undeclared constant, it will evaluate to a string
set to the constant's name. For example,
</p>

<div class="code"><pre>
%module example

#define EASY_TO_MISPELL	0
</pre>
</div>

<p>
accessed incorrectly in PHP,
</p>

<div class="code">
<pre>
include("example.php");

if(EASY_TO_MISPEL) {
	....
} else {
	....
}

</pre>
</div>

<p>
will issue a warning about the undeclared constant, but will then
evaluate it and turn it into a string ('EASY_TO_MISPEL'), which
evaluates to true, rather than the value of the constant which would
be false. This is a feature!
</p>

<p>
The second 'feature' is that although constants are case sensitive (by
default), you cannot declare a constant twice with alternative
cases. E.g.,
</p>

<div class="code">
<pre>
%module example

#define TEST	Hello
#define Test	World
</pre>
</div>

<p>
accessed from PHP,
</p>

<div class="code">
<pre>
include("example.php");

echo TEST, Test;
</pre>
</div>

<p>
will output "Hello Test" rather than "Hello World". This is because
internally, all constants are stored in a hash table by their lower
case name, so 'TEST' and 'Test' will map to the same hash element
('Test'). But, because we declared them case sensitive, the Zend
engine will test if the case matches with the case the constant was
declared with first.
</p>

<p>
So, in the example above, the TEST constant was declared first, and
will be stored under the hash element 'test'. The 'Test' constant will
also map to the same hash element 'test', but will not overwrite
it. When called from the script, the TEST constant will again be
mapped to the hash element 'test' so the constant will be
retrieved. The case will then be checked, and will match up, so the
value ('Hello') will be returned. When 'Test' is evaluated, it will
also map to the same hash element 'test'. The same constant will be
retrieved, this time though the case check will fail as 'Test' !=
'TEST'. So PHP will assume that Test is a undeclared constant, and as
explained above, will return it as a string set to the constant name
('Test'). Hence the script above will print 'Hello Test'. If they were
declared non-case sensitive, the output would be 'Hello Hello', as
both point to the same value, without the case test taking place.  (
Apologies, this paragraph needs rewriting to make some sense. )
</p>

<H3><a name="Php_nn2_2"></a>28.2.2 Global Variables</H3>


<p>
Because PHP does not provide a mechanism to intercept access and
assignment of global variables, global variables are supported through
the use of automatically generated accessor functions.
</p>

<div class="code"><pre>
%module example;

%inline %{
  double seki = 2;
  void print_seki() {
    zend_printf("seki is now %f\n",seki);
  }
%}
</pre></div>

<p>
is accessed as follows:
</p>

<div class="code"><pre>
include("example.php");
print seki_get();
seki_set( seki_get() * 2);	# The C variable is now 4.
print seki_get();
</pre></div>

<p>
SWIG supports global variables of all C datatypes including pointers
and complex objects.  Additional types can be supported by using the
<tt>varinit</tt> typemap.
</p>

<p>
SWIG honors the <tt>%immutable</tt> modifier by not generating code
for the <tt>_set</tt> method.  This provides read-only access to the
variable from the php script.  Attempting to access the <tt>_set</tt>
method will result in a php fatal error because the function is
undefined.
</p>

<p>
At this time SWIG does not support custom accessor methods.
</p>

<H3><a name="Php_nn2_3"></a>28.2.3 Functions</H3>


<p>
C functions are converted into PHP functions. Default/optional arguments are
also allowed. An interface file like this :
</p>

<div class="code"><pre>
%module example
int foo(int a);
double bar(double, double b = 3.0);
...
</pre></div>

<p>
Will be accessed in PHP like this :
</p>

<div class="code"><pre>
include("example.php");
$a = foo(2);
$b = bar(3.5, -1.5);
$c = bar(3.5);		# Use default argument for 2nd parameter

</pre></div>

<!-- This isn't correct for 1.3.30 and needs rewriting to reflect reality
<p>
Because PHP is a dynamically typed language, the default typemaps
used for simple types will attempt to coerce the arguments into the appropriate type.  That is the following invocations are equivalent:
</p>

<div class="code"><pre>
$a = foo(2);
$a = foo("2");
$a = foo(2.0);
</pre></div>

<p>
Functions are invoked using pass by value semantics like all of PHP.
This means the conversion which automatically takes place when
invoking a swig wrapped method does not change the native type of the
argument variable.
</p>
<div class="code"><pre>
$s = "2 A string representing two";
$a = foo($s);  # invokes 'foo(2)';
print $s;      # The value of $s was not changed.
</pre></div>
-->


<H3><a name="Php_nn2_4"></a>28.2.4 Overloading</H3>


<p>
Although PHP does not support overloading functions natively, swig
will generate dispatch functions which will use <tt>%typecheck</tt>
typemaps to allow overloading.  This dispatch function's operation and
precedence is described in <a
href="TypemapsSWIGPlus.html#SWIGPlus_overloaded_methods">Wrapping
Overloaded Functions and Methods</a>.
</p>

<!-- This isn't correct for 1.3.30 and needs rewriting to reflect reality
<p>
Because PHP4 is a dynamically typed language, simple values can be
silently converted from one type to another.  For example, integers,
doubles and strings silently convert to each other depending on
context.  This situation make overloading slightly problematic because
given the following function:
</p>

<div class="code"><pre>
void doit( int i );
void doit( double i );
</pre></div>

<p>
it is questionable which to invoke when <tt>doit("2");</tt> is used in
PHP.  The string <tt>"2"</tt> simultaneously represents the integer
<tt>2</tt> and the double <tt>2.0</tt>.
</p>

<p>
In order to provide the most natural experience to PHP programmers,
the default <tt>%typecheck</tt> implemented in <tt>php4.swg</tt>
allows any simple type (integer, double, string) in PHP to be used for
any simple C type (int, double, char *).  The function selected then
depends only on the argument type precedence defined by SWIG.
</p>

<p>
It should be noted that <tt>SWIGTYPE</tt> references and pointers will
not be silently converted.  So these two functions:
</p>

<div class="code"><pre>
void doit( const Vector &amp; );
void doit( int i );
</pre></div>

<p>
Cause less confusion and <tt>doit("2");</tt> will invoke the function
taking the integer argument.
</p>
-->

<H3><a name="Php_nn2_5"></a>28.2.5 Pointers and References</H3>


<p>
Pointers to C/C++ objects are represented
as PHP resources, rather like MySQL connection handles.
</p>

<p>
There are multiple ways to wrap pointers to simple types.  Given the
following C method:
</p>

<div class="code"><pre>
  void add( int *in1, int *in2, int *result);
</pre></div>

<p>
One can include <b>cpointer.i</b> to generate PHP wrappers to <tt>int
*</tt>.
</p>

<div class="code"><pre>
%module example
%include cpointer.i
%pointer_functions(int,intp)

void add( int *in1, int *in2, int *result);
</pre></div>

<p>
This will result in the following usage in PHP:
</p>

<div class="code"><pre>
&lt;?php

include("example.php");

$in1=copy_intp(3);
$in2=copy_intp(5);
$result=new_intp();

add( $in1, $in2, $result );

echo "The sum " . intp_value($in1) . " + " . intp_value($in2) . " = " . intp_value( $result) . "\n";
?&gt;
</pre></div>

<p>
An alternative would be to use the include <b>typemaps.i</b> which
defines named typemaps for INPUT, OUTPUT and INOUT variables.  One
needs to either <tt>%apply</tt> the appropriate typemap or adjust the
parameter names as appropriate.
</p>

<div class="code"><pre>
%module example
%include typemaps.i

void add( int *INPUT, int *INPUT, int *OUTPUT);

</pre></div>

<p>
This will result in the following usage in PHP:
</p>

<div class="code"><pre>
&lt;?php

include("example.php");

$in1 = 3;
$in2 = 5;
$result= add($in1,$in2);  # Note using variables for the input is unnecessary.

echo "The sum $in1 + $in2 = $result\n";
?&gt;
</pre></div>

<p>
Because PHP has a native concept of reference, it may seem more natural
to the PHP developer to use references to pass pointers.  To enable
this, one needs to include <b>phppointers.i</b> which defines the
named typemap REFERENCE.
</p>

<div class="code"><pre>
%module example
%include phppointers.i

void add( int *REF, int *REF, int *REF);

</pre></div>

<p>
This will result in the following usage in PHP:
</p>

<div class="code"><pre>
&lt;?php

include("example.php");

$in1 = 3;
$in2 = 5;
$result = 0;
add(&amp;$in1,&amp;$in2,&amp;$result);

echo "The sum $in1 + $in2 = $result\n";
?&gt;
</pre></div>

<p>
It is important to note that a php variable which is NULL when passed
by reference would end up passing a NULL pointer into the function.
In PHP, an unassigned variable (i.e. where the first reference to the
variable is not an assignment) is
NULL.  In the above example, if any of the three variables had not
been assigned, a NULL pointer would have been passed into
<tt>add</tt>.  Depending on the implementation of the function, this
may or may not be a good thing.
</p>

<p>
We chose to allow passing NULL pointers into functions because that is
sometimes required in C libraries.  A NULL pointer can be created in
PHP in a number of ways: by using <tt>unset</tt> on an existing
variable, or assigning <tt>NULL</tt> to a variable.
</p>

<H3><a name="Php_nn2_6"></a>28.2.6 Structures and C++ classes</H3>


<p>
SWIG defaults to wrapping C++ structs and classes with PHP classes
unless "-noproxy" is specified.  For PHP5, a PHP wrapper
class is generated which calls a set of flat functions wrapping the C++ class.
</p>

<p>
This interface file
</p>

<div class="code"><pre>
%module vector

class Vector {
public:
	double x,y,z;
	Vector();
	~Vector();
	double magnitude();
};

struct Complex {
 double re, im;
};
</pre></div>

<p>
Would be used in the following way from PHP5:
</p>

<div class="code"><pre>
&lt;?php
  require "vector.php";

  $v = new Vector();
  $v-&gt;x = 3;
  $v-&gt;y = 4;
  $v-&gt;z = 5;

  echo "Magnitude of ($v-&gt;x,$v-&gt;y,$v-&gt;z) = " . $v-&gt;magnitude() . "\n";

  $v = NULL;   # destructor called.

  $c = new Complex();

  $c-&gt;re = 0;
  $c-&gt;im = 0;

  # $c destructor called when $c goes out of scope.
?&gt;
</pre></div>

<p>
Member variables and methods are accessed using the <tt>-&gt;</tt> operator.
</p>

<H4><a name="Php_nn2_6_1"></a>28.2.6.1 Using <tt>-noproxy</tt></H4>


<p>
The <tt>-noproxy</tt> option flattens the object structure and
generates collections of named functions (these are the functions
which the PHP5 class wrappers call).  The above example results
in the following PHP functions:
</p>

<div class="code"><pre>
new_Vector();
Vector_x_set($obj,$d);
Vector_x_get($obj);
Vector_y_set($obj,$d);
Vector_y_get($obj);
Vector_z_set($obj,$d);
Vector_z_get($obj);
Vector_magnitude($obj);
new_Complex();
Complex_re_set($obj,$d);
Complex_re_get($obj);
Complex_im_set($obj,$d);
Complex_im_get($obj);
</pre></div>

<H4><a name="Php_nn2_6_2"></a>28.2.6.2 Constructors and Destructors</H4>


<p>
The constructor is called when <tt>new Object()</tt> (or
<tt>new_Object()</tt> if using <tt>-noproxy</tt>) is used to create an
instance of the object. If multiple constructors are defined for an
object, function overloading will be used to determine which
constructor to execute.
</p>

<p>
Because PHP uses reference counting to manage resources, simple
assignment of one variable to another such as:
</p>

<div class="code"><pre>
$ref = $v;
</pre></div>

<p>
causes the symbol <tt>$ref</tt> to refer to the same underlying object
as <tt>$v</tt>.  This does not result in a call to the C++ copy
constructor or copy assignment operator.
</p>

<p>
One can force execution of the copy constructor by using:
</p>
<div class="code"><pre>
$o_copy = new Object($o);
</pre></div>

<p>
Destructors are automatically called when all variables referencing
the instance are reassigned or go out of scope.  The destructor is not
available to be called manually.  To force a destructor to be called
the programmer can either reassign the variable or call
<tt>unset($v)</tt>
</p>

<H4><a name="Php_nn2_6_3"></a>28.2.6.3 Static Member Variables</H4>


<p>
Static member variables in C++ are not wrapped as such in PHP
as it does not appear to be possible to intercept accesses to such variables.
Therefore, static member variables are
wrapped using a class function with the same name, which
returns the current value of the class variable. For example
</p>

<div class="code"><pre>
%module example

class Ko {
	static int threats;
};

</pre></div>

<p>
would be accessed in PHP as,
</p>

<div class="code"><pre>
include("example.php");

echo "There has now been " . Ko::threats() . " threats\n";

</pre></div>

<p>
To set the static member variable, pass the value as the argument to the class
function, e.g.
</p>

<div class="code"><pre>

Ko::threats(10);

echo "There has now been " . Ko::threats() . " threats\n";

</pre></div>
<H4><a name="Php_nn2_6_4"></a>28.2.6.4 Static Member Functions</H4>


<p>
Static member functions are supported in PHP using the
<tt>class::function()</tt> syntax.  For example
</p>

<div class="code"><pre>
%module example
class Ko {
  static void threats();
};
</pre></div>

would be executed in PHP as,
<div class="code"><pre>
include("example.php");
Ko::threats();
</pre></div>


<H3><a name="Php_nn2_7"></a>28.2.7 PHP Pragmas, Startup and Shutdown code</H3>


<p>
Note: Currently pragmas for PHP need to be specified using
<tt>%pragma(php4)</tt> but also apply for PHP5!  This is just a historical
oddity because SWIG's PHP support predates PHP5.
</p>

<p>
To place PHP code in the generated "example.php" file one can use the
<b>code</b> pragma. The code is inserted after loading the shared
object.
</p>

<div class="code"><pre>
%module example
%pragma(php4) code="
# This code is inserted into example.php
echo \"example.php execution\\n\";
"
</pre></div>

<p>
Results in the following in "example.php"
</p>

<div class="code"><pre>
# This code is inserted into example.php
echo "example.php execution\n";
</pre></div>

<p>
The <b>include</b> pragma is a short cut to add include statements to
the example.php file.
</p>

<div class="code"><pre>
%module example
%pragma(php4) code="
include \"include.php\";
"
%pragma(php) include="include.php"   // equivalent.
</pre></div>

<p>
The <b>phpinfo</b> pragma inserts code in the
<tt>PHP_MINFO_FUNCTION</tt> which is called from PHP's
phpinfo() function.
</p>

<div class="code"><pre>
%module example;
%pragma(php4) phpinfo="
  zend_printf("An example of PHP support through SWIG\n");
  php_info_print_table_start();
  php_info_print_table_header(2, \"Directive\", \"Value\");
  php_info_print_table_row(2, \"Example support\", \"enabled\");
  php_info_print_table_end();
"
</pre></div>

<p>
To insert code into the <tt>PHP_MINIT_FUNCTION</tt>, one can use
either <tt>%init</tt> or <tt>%minit</tt>.
</p>

<div class="code"><pre>
%module example;
%init {
  zend_printf("Inserted into PHP_MINIT_FUNCTION\n");
}
%minit {
  zend_printf("Inserted into PHP_MINIT_FUNCTION\n");
}
</pre></div>

<p>
To insert code into the <tt>PHP_MSHUTDOWN_FUNCTION</tt>, one can use
either <tt>%init</tt> or <tt>%minit</tt>.
</p>

<div class="code"><pre>
%module example;
%mshutdown {
  zend_printf("Inserted into PHP_MSHUTDOWN_FUNCTION\n");
}
</pre></div>

<p>
The <tt>%rinit</tt> and <tt>%rshutdown</tt> statements insert code
into the request init and shutdown code respectively.
</p>

</body>
</html>