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<h1>Constants</h1>
<p>
In PHP scripts you can define constants - both global constants and
class level constants. This can also be done with PHP-CPP. If you want
to expose constants to user space PHP code, you can do that by adding
the constants to the Php::Extension object inside the get_module()
call.
</p>
<p>
<pre class="language-c++"><code>
#include <phpcpp.h>
/**
* Switch to C context so that the get_module() function can be
* called by C programs (which the Zend engine is)
*/
extern "C" {
/**
* Startup function for the extension
* @return void*
*/
PHPCPP_EXPORT void *get_module() {
static Php::Extension myExtension("my_extension", "1.0");
// add integer constants
myExtension.add(Php::Constant("MY_CONSTANT_1", 1));
myExtension.add(Php::Constant("MY_CONSTANT_2", 2));
// floating point constants
myExtension.add(Php::Constant("MY_CONSTANT_3", 3.1415927));
myExtension.add(Php::Constant("MY_CONSTANT_4", 4.932843));
// string constants
myExtension.add(Php::Constant("MY_CONSTANT_5", "This is a constant value"));
myExtension.add(Php::Constant("MY_CONSTANT_6", "Another constant value"));
// null constants
myExtension.add(Php::Constant("MY_CONSTANT_7", nullptr));
// return the extension
return myExtension;
}
}
</code></pre>
</p>
<p>
It is all very straight forward. Using the constants in a PHP script is
just as easy:
</p>
<p>
<pre class="language-php"><code>
<?php
echo(MY_CONSTANT_1."\n");
echo(MY_CONSTANT_2."\n");
echo(MY_CONSTANT_3."\n");
echo(MY_CONSTANT_4."\n");
echo(MY_CONSTANT_5."\n");
echo(MY_CONSTANT_6."\n");
echo(MY_CONSTANT_7."\n");
?>
</code></pre>
</p>
<p>
PHP also supports the concept of class level constants. Internally, in
the Zend engine, class level constants are implemented as regular class
members, but instead of a "public" or "private" flag, a constant property
is marked with a "constant" flag. PHP-CPP exposes this too. You can
register class properties with a Php::Const flag.
</p>
<p>
Besides this, a Php::Class instance also has a "constant" method, and
you can add instances of Php::Constant to the class. Semantically, all
these three ways to create class level constants are identical.
</p>
<p>
<pre class="language-c++"><code>
/**
* The C++ class that we're going to expose
*
* (For this example we use a completely empty class, as only examples
* are given on how to use constants)
*/
class Dummy : public Php::Base
{
};
/**
* Switch to C context so that the get_module() function can be
* called by C programs (which the Zend engine is)
*/
extern "C" {
/**
* Startup function for the extension
* @return void*
*/
PHPCPP_EXPORT void *get_module() {
static Php::Extension myExtension("my_extension", "1.0");
// create a class objects
Php::Class<Dummy> dummy("Dummy");
// there are many different ways to add constants, but semantically,
// they're all the same
dummy.property("MY_CONSTANT_1", 1, Php::Const);
dummy.property("MY_CONSTANT_2", "abcd", Php::Const);
dummy.constant("MY_CONSTANT_3", "xyz");
dummy.constant("MY_CONSTANT_4", 3.1415);
dummy.add(Php::Constant("MY_CONSTANT_5", "constant string"));
dummy.add(Php::Constant("MY_CONSTANT_5", true));
// add the class to the extension
myExtension.add(std::move(dummy));
// return the extension
return myExtension;
}
}
</code></pre>
</p>
<h2>Runtime constants</h2>
<p>
If you want to find out the value of a user space constant at runtime
from your C++ code, or when you want to find out if a constant is
defined or not, you can simply use the Php::constant() or Php::defined()
functions. To define constants at runtime, use Php::define():
</p>
<p>
<pre class="language-c++"><code>
/**
* Function that can be called from a PHP script
*/
void example_function()
{
// check if a certain user space constant is defined
if (Php::defined("USER_SPACE_CONSTANT"))
{
// retrieve the value of a constant
Php::Value constant = Php::constant("ANOTHER_CONSTANT");
// define other constants at runtime
Php::define("DYNAMIC_CONSTANT", 12345);
}
}
/**
* Switch to C context so that the get_module() function can be
* called by C programs (which the Zend engine is)
*/
extern "C" {
/**
* Startup function for the extension
* @return void*
*/
PHPCPP_EXPORT void *get_module() {
static Php::Extension myExtension("my_extension", "1.0");
// add a function to the extension
extension.add("example_function", example_function);
// return the extension
return myExtension;
}
}
</code></pre>
</p>
|
