被PHP的正则挫败了。

被PHP的正则打败了。。。
我简单的匹配abba 这样的4个连续的数字，里面使用了子表达式和反向引用，结果没有捕获到，真不知道为什么，我哪里写错了？

<?php<br />header("Content-type:text/html;charset=utf-8");<br />$str="fdsafsdafsgfdag1223fa1551sdfassd3265";<br />$mypreg="/(\d)(\d)\2\1/";//匹配abba式的数字，即上面的1551<br />$mycon="这是数字";<br />$str=preg_replace($mypreg,$mycon,$str);<br />echo $str."<br/>";<br />

分享到：

------解决方案--------------------
嗯，是双引号的问题
在双引号中字符的转义符生效了

$a = "/(\d)(\d)\2\1/";<br />$b = '/(\d)(\d)\2\1/';<br />var_dump($a == $b);<br />var_dump($a, $b);

bool(false) string(12) "/(\d)(\d)
/" string(14) "/(\d)(\d)\2\1/"

要这样

$a = "/(\d)(\d)\\2\\1/";<br />$b = '/(\d)(\d)\2\1/';<br />var_dump($a == $b);<br />var_dump($a, $b);

bool(true) string(14) "/(\d)(\d)\2\1/" string(14) "/(\d)(\d)\2\1/"

所以你会看到一些正则表达式中会有一连串的 \
\\\、\\\\....
总之是不对就加一个
------解决方案--------------------

引用:

我简单的匹配abba 这样的4个连续的数字，里面使用了子表达式和反向引用，结果没有捕获到，真不知道为什么，我哪里写错了？

<?php<br />header("Content-type:text/html;charset=utf-8");<br />$str="fdsafsdafsgfdag1223fa1551sdfassd3265";<br />$mypreg="/(\d)(\d)\2\1/";//匹配abba式的数字，即上面的1551<br />$mycon="这是数字";<br />$str=preg_replace($mypreg,$mycon,$str);<br />echo $str."<br/>";<br />

PHP中使用正则建议使用单引号，即：

$str="fasdgasgdfgfduuuuuu1221uuuuufasdfsdfsdaf4444";<br />$mypreg='/(\d)\1{3}/i';<br />$mycon="这是数字";<br />echo $str."<br/>";        <br />$str=preg_replace($mypreg,$mycon,$str);<br />echo $str."<br/>";

因为PHP的\在双引号中会起转义作用

Related labels：

nbsp str string

source：php.cn

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