<?php
function add_some_extra(&$string) // 引入变量，使用同一个存储地址
{
    $string .= 'and something extra.';
}
$str = 'This is a string, ';
add_some_extra($str);
echo $str;    // outputs 'This is a string, and something extra.'
?> 

输出:
This is a string, and something extra.

如果没有这个&符号，

<?php
function add_some_extra($string) 
{
    $string .= 'and something extra.';
}
$str = 'This is a string, ';
add_some_extra($str);
echo $str;    // outputs 'This is a string, '
?> 

输出：
This is a string,

本文转自TBHacker博客园博客，原文链接：http://www.cnblogs.com/jiqing9006/p/5536856.html，如需转载请自行联系原作者