func_get

Description

mixed func_get_arg ( int arg_num )

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.

注: 因为本函数依赖于当前域来决定参数细节，因此不能用作函数参数。如果必须要传递这个值，将结果赋给一个变量，然后传递该变量。


<?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.

add a note User Contributed Notes

bishop
11-Dec-2004 01:58


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);

?>

mw atto lanfear dotto com
08-Dec-2004 06:56


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.

dvogel at ssc dot wisc dot edu
22-Oct-2004 05:54


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?

harald at triptop dot org
15-Sep-2004 06:09


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.

anders at ingemann dot fakestuff dot de
04-Jun-2004 09:16


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.

27-May-2004 12:29


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?

anders at ingemann dot fakestuff dot de
30-Apr-2004 07:18


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 ;-)

mightye (at) mightye (dot) org
13-Mar-2004 01:45


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.

martin at classaxe dot com
08-Jun-2002 01:55


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)

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