• php
• c++
• PHP-CPP

Constants

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.

#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;
    }
}

 It is all very straight forward. Using the constants in a PHP script is just as easy:

<?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");
?>

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.

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.

/**
 *  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;
    }
}

Runtime constants

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():

/**
 *  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;
    }
}