PHP Function Handling Functions

senraj · #1 (**permalink**) 04-03-2008, 06:04 AM

Hi,

I want to know more on Function Handling functions in php. Can anyone explain me?

Jeyaseelansarc · #2 (**permalink**) 04-03-2008, 11:54 PM

Hi Senraj,
These functions all handle various operations involved in working with functions.

Jeyaseelansarc · #3 (**permalink**) 04-08-2008, 10:55 PM

call_user_func_array()
call_user_func_array() call a user defined function given by function, with the parameters in param_arr.

example

PHP Code:

  <?php

function debug($var, $val) 

{

    echo "***DEBUGGING\nVARIABLE: $var\nVALUE:";

    if (is_array($val) || is_object($val) || is_resource($val)) {

        print_r($val);

    } else {

        echo "\n$val\n";

    }

    echo "***\n";

}

 
$c = mysql_connect();

$host = $_SERVER["SERVER_NAME"];

 
call_user_func_array('debug', array("host", $host));

call_user_func_array('debug', array("c", $c));

call_user_func_array('debug', array("_POST", $_POST));

?>

Jeyaseelansarc · #4 (**permalink**) 04-08-2008, 10:56 PM

call_user_func()

call_user_func() Call a user defined function given by the function parameter.

example

PHP Code:

  <?php

function barber($type) 

{

    echo "You wanted a $type haircut, no problem";

}

call_user_func('barber', "mushroom");

call_user_func('barber', "shave");

?>

Jeyaseelansarc · #5 (**permalink**) 04-08-2008, 10:57 PM

Object methods may also be invoked statically using this function by passing array($objectname, $methodname) to the function parameter.

PHP Code:

  <?php

class myclass {

    function say_hello() 

    {

        echo "Hello!\n";

    }

}

 
$classname = "myclass";

 
call_user_func(array($classname, 'say_hello'));

?>

Jeyaseelansarc · #6 (**permalink**) 04-08-2008, 10:58 PM

the parameters for call_user_func() are not passed by reference.

PHP Code:

  <?php

function increment(&$var)

{

    $var++;

}

 
$a = 0;

call_user_func('increment', $a);

echo $a; // 0

 
call_user_func_array('increment', array(&$a)); // You can use this instead

echo $a; // 1

?>

Jeyaseelansarc · #7 (**permalink**) 04-08-2008, 10:59 PM

Some functions like call_user_func() or usort() accept user defined callback functions as a parameter. Callback functions can not only be simple functions but also object methods including static class methods.

A PHP function is simply passed by its name as a string. You can pass any builtin or user defined function with the exception of array(), echo(), empty(), eval(), exit(), isset(), list(), print() and unset().

A method of an instantiated object is passed as an array containing an object as the element with index 0 and a method name as the element with index 1.

Static class methods can also be passed without instantiating an object of that class by passing the class name instead of an object as the element with index 0.

Jeyaseelansarc · #8 (**permalink**) 04-08-2008, 10:59 PM

Callback function examples

PHP Code:

  <?php 

// An example callback function

function my_callback_function() {

    echo 'hello world!';

}

 
// An example callback method

class MyClass {

    function myCallbackMethod() {

        echo 'Hello World!';

    }

}

 
// Type 1: Simple callback

call_user_func('my_callback_function'); 

 
// Type 2: Static class method call

call_user_func(array('MyClass', 'myCallbackMethod')); 

 
// Type 3: Object method call

$obj = new MyClass();

call_user_func(array(&$obj, 'myCallbackMethod'));

?>

Jeyaseelansarc · #9 (**permalink**) 04-11-2008, 02:20 AM

create_function() creates an anonymous function from the parameters passed, and returns a unique name for it. Usually the args will be passed as a single quote delimited string, and this is also recommended for the code. The reason for using single quoted strings, is to protect the variable names from parsing, otherwise, if you use double quotes there will be a need to escape the variable names, e.g. \$avar.

You can use this function, to (for example) create a function from information gathered at run time

Jeyaseelansarc · #10 (**permalink**) 04-11-2008, 10:47 PM

func_get_arg() returns the argument which is at the arg_num'th offset into a user-defined function's argument list. Function arguments are counted starting from zero. func_get_arg() will generate a warning if called from outside of a function definition. This function cannot be used directly as a function parameter. Instead, its result may be assigned to a variable, which can then be passed to the function.

If arg_num is greater than the number of arguments actually passed, a warning will be generated and func_get_arg() will return FALSE.

Jeyaseelansarc · #11 (**permalink**) 04-11-2008, 10:48 PM

For example

PHP Code:

  <?php

function foo() 

{

     $numargs = func_num_args();

     echo "Number of arguments: $numargs<br />\n";

     if ($numargs >= 2) {

     echo "Second argument is: " . func_get_arg(1) . "<br />\n";

     }

} 

 
foo (1, 2, 3);

?>

func_get_arg() may be used in conjunction with func_num_args() and func_get_args() to allow user-defined functions to accept variable-length argument lists.

Jeyaseelansarc · #12 (**permalink**) 04-11-2008, 10:49 PM

Because this function depends on the current scope to determine parameter details, it cannot be used as a function parameter. If you must pass this value, assign the results to a variable, and pass the variable.

Jeyaseelansarc · #13 (**permalink**) 04-11-2008, 10:50 PM

In the previous example func_num_args () returns the number of arguments passed into the current user-defined function. func_num_args() will generate a warning if called from outside of a user-defined function. This function cannot be used directly as a function parameter. Instead, its result may be assigned to a variable, which can then be passed to the function.

Jeyaseelansarc · #14 (**permalink**) 04-14-2008, 05:08 AM

func_get_args() returns a copy of the passed arguments only, and does not account for default (non-passed) arguments. Because this function depends on the current scope to determine parameter details, it cannot be used as a function parameter. If you must pass this value, assign the results to a variable, and pass the variable.

Jeyaseelansarc · #15 (**permalink**) 04-14-2008, 05:09 AM

Here the example of calling func_get_args()

PHP Code:

  <?php

function foo() 

{

    $numargs = func_num_args();

    echo "Number of arguments: $numargs<br />\n";

    if ($numargs >= 2) {

        echo "Second argument is: " . func_get_arg(1) . "<br />\n";

    }

    $arg_list = func_get_args();

    for ($i = 0; $i < $numargs; $i++) {

        echo "Argument $i is: " . $arg_list[$i] . "<br />\n";

    }

} 

 
foo(1, 2, 3);

?>

func_get_args() may be used in conjunction with func_num_args() and func_get_arg() to allow user-defined functions to accept variable-length argument lists.

Jeyaseelansarc · #16 (**permalink**) 04-14-2008, 05:10 AM

func_num_args() returns the number of arguments passed into the current user-defined function. func_num_args() will generate a warning if called from outside of a user-defined function. This function cannot be used directly as a function parameter. Instead, its result may be assigned to a variable, which can then be passed to the function.

Because this function depends on the current scope to determine parameter details, it cannot be used as a function parameter. If you must pass this value, assign the results to a variable, and pass the variable.

Jeyaseelansarc · #17 (**permalink**) 04-14-2008, 05:11 AM

example for the above function is

PHP Code:

  <?php

function foo() 

{

    $numargs = func_num_args();

    echo "Number of arguments: $numargs\n";

} 

 
foo(1, 2, 3);    // Prints 'Number of arguments: 3'

?>

Jeyaseelansarc · #18 (**permalink**) 04-17-2008, 07:28 AM

function_exists() checks the list of defined functions, both built-in (internal) and user-defined, for function_name.

example

PHP Code:

  <?php

if (function_exists('imap_open')) {

    echo "IMAP functions are available.<br />\n";

} else {

    echo "IMAP functions are not available.<br />\n";

}

?>

Jeyaseelansarc · #19 (**permalink**) 04-17-2008, 07:30 AM

Note that a function name may exist even if the function itself is unusable due to configuration or compiling options (with the image functions being an example). Also note that function_exists() will return FALSE for constructs, such as include_once() and echo().

Jeyaseelansarc · #20 (**permalink**) 04-17-2008, 07:31 AM

register_shutdown_function() registers the function named by function to be executed when script processing is complete.