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<H1><a name=
"Php"></a>24 SWIG and PHP4
</H1>
<li><a href=
"#Php_nn1">Generating PHP4 Extensions
</a>
<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 PHP4 Extensions
</a>
<li><a href=
"#Php_nn2">Basic PHP4 interface
</a>
<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>
<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>
<li><a href=
"#Php_nn2_7">PHP4 Pragmas, Startup and Shutdown code
</a>
<b>Caution: This chapter (and module!) is still under construction
</b>
In this chapter, we discuss SWIG's support of PHP4. The PHP4 module
has been extensively rewritten in release
1.3.26. Although it is
significantly more functional, it still does not implement all the
features available in other languages.
The examples and test cases have been developed with PHP4.
Support for PHP5 at this time is limited to wrapping C libraries or
C++ libraries while using the
<tt>-noproxy
</tt> flag. This deficiency
will be fixed in a subsequent release of SWIG.
In order to use this module, you will need to have a copy of the PHP
4.0 (or
above) include files to compile the SWIG generated files. You can find these
files by running
<tt>'php-config --includes'
</tt>. To test the modules you will
need either the php binary or the Apache php module. If you want to build your
extension into php directly (without having the overhead of loading it into
each script), you will need the complete PHP source tree available.
<H2><a name=
"Php_nn1"></a>24.1 Generating PHP4 Extensions
</H2>
To build a PHP4 extension, run swig using the
<tt>-php4
</tt> option as
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 PHP4 extension. The second file,
<tt>php_example.h
</tt> contains the header information needed to
statically link the extension into PHP. 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
Swig can generate PHP4 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
24.2.6</a>.
To finish building the extension, you have two choices. You can either build
the extension as a separate shared object file which will then have to be explicitly
loaded by each script. Or you can rebuild the entire php source tree and build
the extension into the php executable/library so it will be available in every
script. The first choice is the default, however it can be changed by passing
the '-phpfull' command line switch to select the second build method.
<H3><a name=
"Php_nn1_1"></a>24.1.1 Building a loadable extension
</H3>
There are two methods to build the extension as a dynamically loaded
module: using standard compilation utilities (make, gcc), or using
PHP4's
<em>phpize
</em> utility.
To build manually, use a compile string similar to this (different for each
cc -I.. $(PHPINC) -fpic -c example_wrap.c
cc -shared example_wrap.o -o libexample.so
The
<tt>-make
</tt> command line argument to swig will generate an
additional file Makefile. This Makefile can usually build the
extension itself (on unix platforms).
If you want to build your extension using the
<tt>phpize
</tt>utility, or if you want to build your module into PHP directly, you
can specify the
<tt>-phpfull
</tt> command line argument to swig.
The
<tt>-phpfull
</tt> will generate three additional files. The first
extra file,
<tt>config.m4
</tt> contains the shell code needed to
enable the extension as part of the PHP4 build process. The second
extra file,
<tt>Makefile.in
</tt> contains the information needed to
build the final Makefile after substitutions. The third and final
extra file,
<tt>CREDITS
</tt> should contain the credits for the
To build with phpize, after you have run swig you will need to run the
'phpize' command (installed as part of php) in the same
directory. This re-creates the php build environment in that
directory. It also creates a configure file which includes the shell
code from the config.m4 that was generated by SWIG, this configure
script will accept a command line argument to enable the extension to
be run ( by default the command line argument is --enable-modulename,
however you can edit the config.m4 file before running phpize to
accept --with-modulename. You can also add extra tests in config.m4 to
check that a correct library version is installed or correct header
files are included, etc, but you must edit this file before running
phpize. ) If you like SWIG can generate simple extra tests for
libraries and header files for you.
If you depend on source files not generated by SWIG, before generating
the configure file, you may need to edit the
<tt>Makefile.in
</tt>file. This contains the names of the source files to compile (just the
wrapper file by default) and any additional libraries needed to be
linked in. If there are extra C files to compile, you will need to add
them to the Makefile.in, or add the names of libraries if they are
needed. In simple cases SWIG is pretty good at generating a complete
Makefile.in and config.m4 which need no further editing.
You then run the configure script with the command line argument needed
to enable the extension. Then run make, which builds the extension.
The extension object file will be left in the modules sub directory, you can
move it to wherever it is convenient to call from your php script.
Both the
<tt>-make
</tt> and
<tt>-phpfull
</tt> arguments accept
additional optional arguments:
<li><tt>-withincs
"<files>"</tt> Adds include files to the config.m4 file.
<li><tt>-withlibs
"<files>"</tt> Links the libraries into the shared object.
<li><tt>-withc
"<files>"</tt> Compiles and links the named C files into the shared object.
<li><tt>-withcxx
"<files>"</tt> Compiles and links the named C++ files into the shared object,
<li><tt>-dlname
"<name>"</tt> Changes the name of the generated shared object.
<H3><a name=
"Php_nn1_2"></a>24.1.2 Building extensions into PHP
</H3>
This method, selected with the
<tt>-phpfull
</tt> command line switch, involves
rebuilding the entire php source tree. Whilst more complicated to build,
it does mean that the extension is then available without having to load it
After running swig with the -phpfull switch, you will be left with a shockingly
similar set of files to the previous build process. However you will then need
to move these files to a subdirectory within the php source tree, this subdirectory you will need to create under the ext directory, with the name of the extension ( e.g mkdir php-
4.0.6/ext/modulename .)
After moving the files into this directory, you will need to run the 'buildall'
script in the php source directory. This rebuilds the configure script
and includes the extra command line arguments from the module you have added.
Before running the generated configure file, you may need to edit the
<tt>Makefile.in
</tt>. This contains the names of the source files to compile (
just the wrapper file by default) and any additional libraries needed to
link in. If there are extra C files to compile you will need to add them
to the Makefile, or add the names of libraries if they are needed.
In most cases
<tt>Makefile.in
</tt> will be complete, especially if you
make use of
<tt>-withlibs
</tt> and
<tt>-withincs
</tt> swig -php4 -phpfull -withlibs
"xapian omquery" --withincs
"om.h"Will include in the config.m4 and Makefile.in search for libxapian.a or
libxapian.so and search for libomquery.a or libomquery.so as well as a
You then need to run the configure command and pass the necessary command
line arguments to enable your module ( by default this is --enable-modulename,
but this can be changed by editing the config.m4 file in the modules directory
before running the buildall script. In addition, extra tests can be added to
the config.m4 file to ensure the correct libraries and header files are
Once configure has completed, you can run make to build php. If this all
compiles correctly, you should end up with a php executable/library
which contains your new module. You can test it with a php script which
does not have the 'dl' command as used above.
<H3><a name=
"Php_nn1_3"></a>24.1.3 Using PHP4 Extensions
</H3>
To test the extension from a PHP script, you need to load it first. You do
this by putting the line,
dl(
"/path/to/modulename.so"); // Load the module
at the start of each PHP file. SWIG also generates a php module, which
attempts to do the
<tt>dl()
</tt> call for you:
<H2><a name=
"Php_nn2"></a>24.2 Basic PHP4 interface
</H2>
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.
<H3><a name=
"Php_nn2_1"></a>24.2.1 Constants
</H3>
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 file like this,
%constant int E =
2.71828you can access the constants in your php script like this,
echo
"PI = " . PI .
"\n";
There are two peculiarities with using constants in PHP4. 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,
#define EASY_TO_MISPELL
0accessed incorrectly in PHP,
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.
The second 'feature' is that although constants are case sensitive (by
default), you cannot declare a constant twice with alternative
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
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. )
<H3><a name=
"Php_nn2_2"></a>24.2.2 Global Variables
</H3>
Because PHP4 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.
zend_printf(
"seki is now %f\n",seki);
seki_set( seki_get() *
2); # The C variable is now
4.
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.
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
At this time SWIG does not support custom accessor methods.
<H3><a name=
"Php_nn2_3"></a>24.2.3 Functions
</H3>
C functions are converted into PHP functions. Default/optional arguments are
also allowed. An interface file like this :
double bar(double, double b =
3.0);
Will be accessed in PHP like this :
$c = bar(
3.5); # Use default argument for
2nd parameter
Because PHP4 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:
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
$s =
"2 A string representing two";
$a = foo($s); # invokes 'foo(
2)';
print $s; # The value of $s was not changed.
<H3><a name=
"Php_nn2_4"></a>24.2.4 Overloading
</H3>
Although PHP4 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
<ahref=
"TypemapsSWIGPlus.html#SWIGPlus_overloaded_methods">Wrapping
Overloaded Functions and Methods
</a>.
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:
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>.
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.
It should be noted that
<tt>SWIGTYPE
</tt> references and pointers will
not be silently converted. So these two functions:
void doit( const Vector
& );
Cause less confusion and
<tt>doit(
"2");
</tt> will invoke the function
taking the integer argument.
<H3><a name=
"Php_nn2_5"></a>24.2.5 Pointers and References
</H3>
Pointers to C/C++ objects are
<b>no longer
</b> represented as character
strings such as:
<tt>_523d3f4_Circle_p
</tt>, instead they are represented
as PHP resources, rather like MySQL connection handles.
There are multiple ways to wrap pointers to simple types. Given the
void add( int *in1, int *in2, int *result);
One can include
<b>cpointer.i
</b> to generate PHP wrappers to
<tt>int
%pointer_functions(int,intp)
void add( int *in1, int *in2, int *result);
This will result in the following usage in PHP:
add( $in1, $in2, $result );
echo
"The sum " . intp_value($in1) .
" + " . intp_value($in2) .
" = " . intp_value( $result) .
"\n";
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.
void add( int *INPUT, int *INPUT, int *OUTPUT);
This will result in the following usage in PHP:
$result= add($in1,$in2); # Note using variables for the input is unnecessary.
echo
"The sum $in1 + $in2 = $result\n";
Because PHP has a native concept of reference, it may seem more natural
to the PHP developer to use references to pass pointers. To enable
this, one needs to include
<b>phppointers.i
</b> which defines the
void add( int *REF, int *REF, int *REF);
This will result in the following usage in PHP:
add(
&$in1,
&$in2,
&$result);
echo
"The sum $in1 + $in2 = $result\n";
It is important to note that a php variable which is NULL when passed
by reference would end up passing a NULL pointer into the function.
In PHP, an unassigned variable (ie first reference is not assigned) is
NULL. In the above example, if any of the three variables had not
been assigned, a NULL pointer would have been passed into
<tt>add
</tt>. Depending on the implementation of the function, this
may or may not be a good thing.
We chose to allow passing NULL pointers into functions because that is
sometimes required in C libraries. A NULL pointer can be created in
PHP in a number of ways: by using
<tt>unset
</tt> on an existing
variable, or assigning
<tt>NULL
</tt> to a variable.
<H3><a name=
"Php_nn2_6"></a>24.2.6 Structures and C++ classes
</H3>
By default, SWIG represents structs and C++ classes using a PHP4
class. The PHP4 class is implemented entirely using the Zend C API so
no additional php code is generated.
Would be used in the following way:
echo
"Magnitude of ($v->x,$v->y,$v->z) = " . $v-
>magnitude() .
"\n";
$v = NULL; # destructor called.
# $c destructor called when $c goes out of scope.
Member variables and methods are accessed using the
<tt>-
></tt> operator.
<H4><a name=
"Php_nn2_6_1"></a>24.2.6.1 Using
<tt>-noproxy
</tt></H4>
The
<tt>-noproxy
</tt> option flattens the object structure and
generates collections of named functions. The above example results
in the following PHP functions:
<H4><a name=
"Php_nn2_6_2"></a>24.2.6.2 Constructors and Destructors
</H4>
The constructor is called when
<tt>new Object()
</tt> (or
<tt>new_Object()
</tt> if using
<tt>-noproxy
</tt>) is used to create an
instance of the object. If multiple constructors are defined for an
object, function overloading will be used to determine which
Because PHP4 uses reference counting to manage resources, simple
assignment of one variable to another such as:
causes the symbol
<tt>$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.
One can force execution of the copy constructor by using:
$o_copy = new Object($o);
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
<H4><a name=
"Php_nn2_6_3"></a>24.2.6.3 Static Member Variables
</H4>
Class variables are not supported in PHP. Static member variables are
therefore accessed using a class function with the same name, which
returns the current value of the class variable. For example
would be accessed in PHP as,
echo
"There has now been " . Ko::threats() .
" threats\n";
To set the static member variable, pass the value as the argument to the class function, e.g.
echo
"There has now been " . Ko::threats() .
" threats\n";
<H4><a name=
"Php_nn2_6_4"></a>24.2.6.4 Static Member Functions
</H4>
Class functions are supported in PHP using the
<tt>class::function()
</tt> syntax. For example
would be executed in PHP as,
<H3><a name=
"Php_nn2_7"></a>24.2.7 PHP4 Pragmas, Startup and Shutdown code
</H3>
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
# This code is inserted into example.php
echo \"example.php execution\\n\
";
Results in the following in
"example.php"# This code is inserted into example.php
echo
"example.php execution\n";
The
<b>include
</b> pragma is a short cut to add include statements to
%pragma(php)
include=
"include.php" // equivalent.
The
<b>phpinfo
</b> pragma inserts code in the
<tt>PHP_MINFO_FUNCTION
</tt> which is called from PHP's
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();
To insert code into the
<tt>PHP_MINIT_FUNCTION
</tt>, one can use
either
<tt>%init
</tt> or
<tt>%minit
</tt>.
zend_printf(
"Inserted into PHP_MINIT_FUNCTION\n");
zend_printf(
"Inserted into PHP_MINIT_FUNCTION\n");
To insert code into the
<tt>PHP_MSHUTDOWN_FUNCTION
</tt>, one can use
either
<tt>%init
</tt> or
<tt>%minit
</tt>.
zend_printf(
"Inserted into PHP_MSHUTDOWN_FUNCTION\n");
The
<tt>%rinit
</tt> and
<tt>%rshutdown
</tt> statements insert code
into the request init and shutdown code respectively.
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