数组 函数
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compact

(PHP 4, PHP 5)

compact — 建立一个数组，包括变量名和它们的值

说明

array compact ( mixed $varname [, mixed $... ] )

compact() 接受可变的参数数目。每个参数可以是一个包括变量名的字符串或者是一个包含变量名的数组，该数组中还可以包含其它单元内容为变量名的数组， compact() 可以递归处理。

对每个参数，compact() 在当前的符号表中查找该变量名并将它添加到输出的数组中，变量名成为键名而变量的内容成为该键的值。简单说，它做的事和 extract() 正好相反。返回将所有变量添加进去后的数组。

任何没有变量名与之对应的字符串都被略过。

Note: Gotcha

因为可变变量也许不能在函数内部用于 PHP 的超全局数组，此时不能将超全局数组传递入 compact() 中。

Example #1 compact() 例子

<?php
$city  = "San Francisco";
$state = "CA";
$event = "SIGGRAPH";

$location_vars = array("city", "state");

$result = compact("event", "nothing_here", $location_vars);
?>

经过处理后，$result 为： 

Array
(
    [event] => SIGGRAPH
    [city] => San Francisco
    [state] => CA
)

参见 extract()。

数组 函数
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PHP手册
PHP手册 - N: 建立一个数组，包括变量名和它们的值

用户评论:

piedone at pyrocenter dot hu (15-Apr-2011 02:00)

A quick way of compacting all local variables:

<?php
$localVariables = compact(array_keys(get_defined_vars()));
?>

This is useful if you want to return all local variables from a function/method or you want to pass all local variables to one. A valid example would be to use this with application hooks/events (if you want the called hook to be able to modify everything in the caller), but otherwise use with care (as methods should be used through their declared interface).

Robc (19-Jan-2011 11:16)

The description says that compact is the opposite of extract() but it is important to understand that it does not completely reverse extract().  In particluar compact() does not unset() the argument variables given to it (and that extract() may have created).  If you want the individual variables to be unset after they are combined into an array then you have to do that yourself.

tatarynowicz at gmail dot com (10-Jan-2011 11:17)

Please note that compact() will _not_ issue a warning if the specified variable name is undefined.

Anonymous (06-Apr-2009 11:41)

Compact does not work with references, but there is a short way to resolve this:

<?php
//$foo=array();
foreach( array('apple','banana') as $v) $foo[$v] = &$v;
?>

packard_bell_nec at hotmail dot com (31-Jan-2008 05:46)

You can check whether a variable is defined by using array_key_exists()!
First, you may ask that no reserved array (would be called $LOCALS) is predefined in function scope (contrast to reserved array $GLOBALS in global scope. To solve it, you can use compact().
Then, you may ask that why property_exists() cannot be used. This is because no reserved function is predefined to create OBJECT containing variables and their values, and no reserved function is predefined to import variables into the current symbol table from an OBJECT. In addition, property_exists() breaks the naming convention of reserved function.
Finally, I show how to check whether a variable is defined by using array_key_exists():
<?php
function too(){
$roo = array_key_exists('foo', compact('foo'));
echo ($roo?'1':'0').'<br/>';
$foo = null;
$roo = array_key_exists('foo', compact('foo'));
echo ($roo?'1':'0').'<br/>';
}
too();
?>
The output will be:
0<br/>
1<br/>

M Spreij (24-May-2007 02:10)

Can also handy for debugging, to quickly show a bunch of variables and their values:

<?php
print_r(compact(explode(' ', 'count acw cols coldepth')));
?>

gives

Array
(
    [count] => 70
    [acw] => 9
    [cols] => 7
    [coldepth] => 10
)

mijllirg at wearethedotin dot com (17-Nov-2005 07:38)

You might could think of it as ${$var}.  So, if you variable is not accessible with the ${$var} it will not working with this function.  Examples being inside of function or class where you variable is not present.

<?php
$foo = 'bar';

function blah()
{
    // this will no work since the $foo is not in scope
    $somthin = compact('foo'); // you get empty array
}
?>

PS: Sorry for my poor english...

hericklr at gmail dot com (13-Jun-2005 04:43)

The compact function doesn't work inside the classes or functions.
I think its escope is local...
Above it is a code to help about it.
Comments & Suggestions are welcome.
PS: Sorry for my poor english...

<?php

    function x_compact()
    {    if(func_num_args()==0)
        {    return false; }
        $m=array();

        function attach($val)
        {    global $m;
            if((!is_numeric($val)) && array_key_exists($val,$GLOBALS))
            {    $m[$val]=$GLOBALS[$val];}
        }

        function sub($par)
        {    global $m;
            if(is_array($par))
            {    foreach($par as $cel)
                {    if(is_array($cel))
                    {    sub($cel); }
                    else
                    {    attach($cel); }
                }
            }
            else
            {    attach($par); }
            return $m;
        }

        for($i=0;$i<func_num_args();$i++)
        {    $arg=func_get_arg($i);
            sub($arg);
        }

        return sub($arg);
    }
?>

pillepop2003 at yahoo dot de (22-Nov-2004 08:26)

Use the following piece of code if you want to insert a value into an array at a path that is extracted from a string.

Example:
You have a syntax like 'a|b|c|d' which represents the array structure, and you want to insert a value X into the array at the position $array['a']['b']['c']['d'] = X.

<?
    function array_path_insert(&$array, $path, $value)
    {
        $path_el = split('\|', $path);
       
        $arr_ref =& $array;
       
        for($i = 0; $i < sizeof($path_el); $i++)
        {
            $arr_ref =& $arr_ref[$path_el[$i]];
        }
       
        $arr_ref = $value;
    }

    $array['a']['b']['f'] = 4;
    $path  = 'a|b|d|e';
    $value = 'hallo';
   
    array_path_insert($array, $path, $value);

    /* var_dump($array) returns:

    array(1) {
      ["a"]=>
      &array(1) {
        ["b"]=>
        &array(2) {
          ["f"]=>
          int(4)
          ["d"]=>
          &array(1) {
            ["e"]=>
            string(5) "hallo"
          }
        }
      }
    */

?>

Rock on
Philipp