preg_quote()

<?php
/*
    preg_quote($str) 平时不常用
    正则运算符转义
    . \ + * ? ^ [ ] $ ( ) { } = ! < > | : -
*/
    header('content-type: text/html;charset = utf-8');

    $str = 'qwer{asdf}[1234]';

    $str = preg_quote($str);

    show($str);

    // 对输出做个判断，选择合适的输出方式
    function show($var = null){
        if(empty($var)){
            echo 'null';
        }elseif(is_array($var) || is_object($var)){
            //array, object
            echo '<pre>';
            print_r($var);
            echo '</pre>';
        }else{
            //string, int, float...
            echo $var;
        }
    }