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PHP : Function Reference : Function Handling Functions : func_get_arg

func_get_arg

Return an item from the argument list (PHP 4, PHP 5)
mixed func_get_arg ( int arg_num )

Example 758. func_get_arg() example

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<?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);
?>

Related Examples ( Source code ) » func_get_arg

Examples ( Source code ) » A Function to Format Debugging Messages

Code Examples / Notes » func_get_arg

26-may-2004 05:29
very clever unless you need to specify at least two parameters of the same type - which is which? Obviously, you may decide on some defaults, but then the whole thing gets ugly. What if you need a string ONLY if a boolean was also supplied? The type-checking becomes the main focus of your function, shit. For the sake of clean code you should specify a clean interface to your functions, and decide on what and where is passed as an argument. Yes, you can always code a do_absolutely_everything() function, but is there any sense?

martin
This function whilst elegant doesn't in itself avoid the problem of generating warning messages where variables are not set, unless of course you switched warnings off:
error_reporting(E_ERROR);
The answer for those of who like to see necessary warnings?
Call it like this:
@allSet($w, $x, $y, $z)
(Martin Francis)

bishop
Regarding a "deferment" operator for dvogel at ssc dot wisc dot edu, pick your poison:
<?php
// using ternary operators
function pick($a,$b) { return (isset($a) ? $a : $b); }
$a = (pick($b,$c) ? pick($c,$d) : null);
?>
<?php
// using varargs function
function pick($a) {
   $argc = func_num_args();
   for ($i = 0; $i < $argc; $i++) {
       $arg = func_get_arg($i);
       if (! is_null($arg)) {
           return $arg;
       }
   }
   return null;
}
$a = pick($b, $c, $d);
?>

dvogel
I've always wants a deferment or cascade operator so that I could use this expression:
 $a = $b ## $c ## $d;
and everything to the right of the assignment operator would evaluate to the left-most value that is not null. It is essentially a collapsed version of this:
 if ($b) {
   $a=$b;
 } else {
   if($c) {
     $a=$c;
   } else {
     if ($d) {
       $a = $d;
     } else {
       $a = null;
     }
   }
 }
In leiu of this, I'm trying to make a function that takes a variable number of arguments and returns the first that is not null. I wan't to use this on some large-ish arrays, so I'd like to pass these by reference. However, call-time reference passing is disabled (and should be, imo) in newer versions of PHP. I'd like suggestions on how to pass both references and values to this function.
The only solution I can think of is setting variables to the reference of the array first. e.g.
$a = array( ... );
$b = 0;
$c = &a;
first_not_null($a, $b);
Does anyone know a better solution?

aries-belgium
I was just thinking about a way to create a singleton where you only need to run the instance() function only one time with an argument. And I came up with this solution: (maybe it's useful for other users)
<?php
class Singleton {
     private $arg = "";
     
     private function __construct($arg) {
             $this->arg = $arg;
     }
     
     public static function instance() {
            static $_instance = null;
            if(func_num_args() == 0 && $_instance == null) {
                   $_instance = new Singleton(func_get_arg(0));
            }
     }
}
// first time
$singleton = Singleton::instance("foobar");
// later in your code (in other class and/or function)
$singleton = Singleton::instance();
?>

anders
I actually think that there is need for such "do absolutely everything" functions. I use them mostly as tools for rapid prototyping.
And there is a method with which you may be able to pass several strings to a function: ereg();
Another use for such functions is to create little code snippets for other people out there. They won't have to edit the function any longer if they do not use a parameter. They just don't name it when calling the function.
This results in allrounder functions that are very robust in their use.Normally you just have a little code snippet (e.g. ip-blocking snippets). Through this type of programming you have whole functions.

mightye
func_get_arg() returns a *copy* of the argument, to my knowledge there is no way to retrieve references to a variable number of arguments.
I have a module system in my game at http://lotgd.net where I'd like to be able to pass a variable number of arguments to functions in a module, and pass them by reference if the module asks for it by reference, but you can't accept optional parameters as references, nor can you retrieve the reference on a variable number of arguments.  Looks like my modules will have to do with out the ability to accept parameters to their functions by reference.

mw atto lanfear dotto com
func_get_arg() does not appear to be allowed to be used as a function argument itself within class constructors in PHP 5.0.2 (wonk-ay!!!):
<?php
class ABC
{
   function __construct()
   {
       foreach (func_get_args() as $name => $value)
       {
   echo <<<EOT
   <br/>
   $name : $value <br/>
   <br/>
EOT;
       }
   }
}
class DEF extends ABC
{
   function __construct()
   {
       parent::__construct(func_get_arg(0),
                                   func_get_arg(1),
                                   func_get_arg(2));
   }
}
$def = new DEF(123123, "asdfasdf", "blahblahblah");
?>
The above script generates:
Fatal error: func_get_arg(): Can't be used as a function parameter in c:\Inetpub\wwwroot\phpwasrc\chapter10\xxx.php on line 23
There are, however, no problems when passing these as parameters to regular functions.

harald
func_get_arg is useful, if you know the exact order of the arguments, or if the order doesn't matter. i use this function (or func_get_args) for example to create own sprintf wrappers.
if you want to pass a variable number of arguments to a function it's in my opinion better, to submit it as a key/value array e.g.:
<?php
functioncall(array("param1" => "...",...));
?>
and 'extract' the array inside the function. you don't need to do tricks like type-checking for parameter-recognition, in this case.

wintermute
Bishop: Your ternary example is flawed:
<?php
// using ternary operators
function pick($a,$b) { return (isset($a) ? $a : $b); }
$a = (pick($b,$c) ? pick($c,$d) : null);
?>
If $b is not null, it will evaluate pick($c, $d) and return $c if that is not null. If $b and $c are both null, it will not evaluate pick($c, $d) and will return null regardless of the value of $d. I'm not sure how you'd save this.
Another option would be to use an array:
<?PHP
function pick($array)
{
 foreach ($array as $element)
 {
   if ($element != null)
   {
     return($element)
   }
 }
 return(null);
}
$a = pick(array($b, $c, $d, $e))
?>
I don't know that there's any real difference between this and the variable-argument form, but some people might prefer it, so it's worth noting.

anders
A pretty cool thing for user defined functions is only to submit the needed parameters. If you call a function that has three optional parameters you have to define the two first ones (even if they should stay like the defined standard in the function) before your are able to tell the function what the third important parameter is. Instead you might as well just find out by the pattern or the type of the submitted parameter which variable it should be assigned to.
like this:
<?
function whatever()
{
for($i=0;$i<func_num_args();$i++)
{
if(is_bool(func_get_arg($i))) $log_ip=func_get_arg($i);
if(is_int(func_get_arg($i))) $limit=func_get_arg($i);
if(is_string(func_get_arg($i))) $name=func_get_arg($i);
}
}
?>
Now you can call the function with any parameter you want.
e.g.:
<? whatever(3600); ?>
in that case $limit would be defined with 3600.
It doesn't matter if you do this:
<? whatever(3600,false); ?>
or this:
<? whatever(3600,"blaaah"); ?>
or this:
<? whatever("blaaah",true,3600); ?>
You may also use ereg(). Through that you're able to use more than one parameter as a string.
hmm probably ereg() is the best solution...
never mind.
just check it out ;-)

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func_get_arg
func_get_args
func_num_args
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