PHP通过引用传递参数用法分析

<?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.'
?>

This is a string, and something extra.

<?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, '
?>

This is a string,