Function handling 函数
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PHP手册

func_get_arg

(PHP 4, PHP 5)

func_get_arg — Return an item from the argument list

说明

mixed func_get_arg ( int $arg_num )

Gets the specified argument from a user-defined function's argument list.

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

参数

arg_num

The argument offset. Function arguments are counted starting from zero.

返回值

Returns the specified argument, or FALSE on error.

更新日志

版本 说明
5.3.0 This function can now be used in parameter lists.
5.3.0 If this function is called from the outermost scope of a file which has been included by calling include or require from within a function in the calling file, it now generates a warning and returns FALSE.

错误/异常

Generates a warning if called from outside of a user-defined function, or if arg_num is greater than the number of arguments actually passed.

范例

Example #1 func_get_arg() example

<?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);
?>

Example #2 func_get_arg() example before and after PHP 5.3

test.php
<?php
function foo() {
    include './fga.inc';
}

foo('First arg', 'Second arg');
?>

fga.php
<?php

$arg = func_get_arg(1);
var_export($arg);

?>

Output previous to PHP 5.3: 

'Second arg'

Output in PHP 5.3 and later: 

Warning: func_get_arg():  Called from the global scope - no function
context in /home/torben/Desktop/code/ml/fga.inc on line 3
false

Example #3 func_get_arg() example of byref and byval arguments

<?php
function byVal($arg) {
    echo 'As passed     : ', var_export(func_get_arg(0)), PHP_EOL;
    $arg = 'baz';
    echo 'After change  : ', var_export(func_get_arg(0)), PHP_EOL;
}

function byRef(&$arg) {
    echo 'As passed     : ', var_export(func_get_arg(0)), PHP_EOL;
    $arg = 'baz';
    echo 'After change  : ', var_export(func_get_arg(0)), PHP_EOL;
}

$arg = 'bar';
byVal($arg);
byRef($arg);
?>

以上例程会输出：


As passed : 'bar'
After change : 'bar'
As passed : 'bar'
After change : 'baz'

注释

Note:

因为函数依赖于当前作用域以确定参数的细节， 所以在 5.3.0 以前的版本中不能用作函数的参数。如必须传递此值时，可将结果赋与一个变量，然后用此变量进行传递。

Note:

如果参数以引用方式传递, 函数对该参数的任何改变将在函数返回后保留。

Note: This function returns a copy of the passed arguments only, and does not account for default (non-passed) arguments.

参见

Function handling 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: Return an item from the argument list

用户评论:

beta3designs [at] gmail [dot] com (06-Jul-2009 02:34)

This functions seems so powerful... just when i saw it i thought about writing a fast average of n numbers function so here it is, it is very simple... example usage included.

<?php

//Calculate the average of the numbers given

function avg(){
    $sum = 0;
    for($i = 0; $i < func_num_args(); $i++){
        $sum += func_get_arg($i);
    }
    $avg = $sum / func_num_args();
    return $avg;
}

echo sprintf("%.2f",avg(2,1,2,1,3,4,5,1,3,6));
?>

wintermute (20-Sep-2007 07:11)

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.

Aries-Belgium (11-Jan-2007 06:44)

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();
?>

bishop (11-Dec-2004 05:58)

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 (07-Dec-2004 10:56)

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 (21-Oct-2004 10:54)

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:

<?php
  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 (14-Sep-2004 11:09)

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 02:16)

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.

(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?

anders at ingemann dot fakestuff dot de (30-Apr-2004 12:18)

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:

<?php
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.:

<?php whatever(3600); ?>

in that case $limit would be defined with 3600.

It doesn't matter if you do this:

<?php whatever(3600,false); ?>

or this:

<?php whatever(3600,"blaaah"); ?>

or this:

<?php 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 (12-Mar-2004 05:45)

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.