我想创建一个网页，所有的图片都在我的网站上列出标题和替代表示.
我已经编写了一个小程序来查找和加载所有HTML文件，但现在我陷入了如何从这个HTML中提取src、title和alt的困境:
<img src="/image/fluffybunny.jpg" title="Harvey the bunny" alt="a cute little fluffy bunny" />我想这应该用一些正则表达式来完成，但是由于标签的顺序可能会有所不同，而且我需要所有标签，我真的不知道如何以优雅的方式解析它(我可以用硬字符逐个字符的方式来解析，但这很痛苦).
使用regexp来解决这类问题的成本是a bad idea%，并且可能会导致无法维护和不可靠的代码.最好用HTML parser.
在这种情况下，最好将流程分为两部分:
我假设你的文档不是严格的xHTML，所以你不能使用XML解析器.例如，使用此网页源代码:
/* preg_match_all match the regexp in all the $html string and output everything as
an array in $result. "i" option is used to make it case insensitive */
preg_match_all('/<img[^>]+>/i',$html, $result);
print_r($result);
Array
(
[0] => Array
(
[0] => <img src="/Content/Img/stackoverflow-logo-250.png" width="250" height="70" alt="logo link to homepage" />
[1] => <img class="vote-up" src="/content/img/vote-arrow-up.png" alt="vote up" title="This was helpful (click again to undo)" />
[2] => <img class="vote-down" src="/content/img/vote-arrow-down.png" alt="vote down" title="This was not helpful (click again to undo)" />
[3] => <img src="http://www.gravatar.com/avatar/df299babc56f0a79678e567e87a09c31?s=32&d=identicon&r=PG" height=32 width=32 alt="gravatar image" />
[4] => <img class="vote-up" src="/content/img/vote-arrow-up.png" alt="vote up" title="This was helpful (click again to undo)" />
[...]
)
)
然后我们通过循环获得所有img标签属性:
$img = array();
foreach( $result as $img_tag)
{
preg_match_all('/(alt|title|src)=("[^"]*")/i',$img_tag, $img[$img_tag]);
}
print_r($img);
Array
(
[<img src="/Content/Img/stackoverflow-logo-250.png" width="250" height="70" alt="logo link to homepage" />] => Array
(
[0] => Array
(
[0] => src="/Content/Img/stackoverflow-logo-250.png"
[1] => alt="logo link to homepage"
)
[1] => Array
(
[0] => src
[1] => alt
)
[2] => Array
(
[0] => "/Content/Img/stackoverflow-logo-250.png"
[1] => "logo link to homepage"
)
)
[<img class="vote-up" src="/content/img/vote-arrow-up.png" alt="vote up" title="This was helpful (click again to undo)" />] => Array
(
[0] => Array
(
[0] => src="/content/img/vote-arrow-up.png"
[1] => alt="vote up"
[2] => title="This was helpful (click again to undo)"
)
[1] => Array
(
[0] => src
[1] => alt
[2] => title
)
[2] => Array
(
[0] => "/content/img/vote-arrow-up.png"
[1] => "vote up"
[2] => "This was helpful (click again to undo)"
)
)
[<img class="vote-down" src="/content/img/vote-arrow-down.png" alt="vote down" title="This was not helpful (click again to undo)" />] => Array
(
[0] => Array
(
[0] => src="/content/img/vote-arrow-down.png"
[1] => alt="vote down"
[2] => title="This was not helpful (click again to undo)"
)
[1] => Array
(
[0] => src
[1] => alt
[2] => title
)
[2] => Array
(
[0] => "/content/img/vote-arrow-down.png"
[1] => "vote down"
[2] => "This was not helpful (click again to undo)"
)
)
[<img src="http://www.gravatar.com/avatar/df299babc56f0a79678e567e87a09c31?s=32&d=identicon&r=PG" height=32 width=32 alt="gravatar image" />] => Array
(
[0] => Array
(
[0] => src="http://www.gravatar.com/avatar/df299babc56f0a79678e567e87a09c31?s=32&d=identicon&r=PG"
[1] => alt="gravatar image"
)
[1] => Array
(
[0] => src
[1] => alt
)
[2] => Array
(
[0] => "http://www.gravatar.com/avatar/df299babc56f0a79678e567e87a09c31?s=32&d=identicon&r=PG"
[1] => "gravatar image"
)
)
[..]
)
)
regexp是CPU密集型的，因此您可能需要缓存此页面.如果你没有缓存系统，你可以通过使用ob_start和从文本文件加载/保存来调整自己的缓存系统.
首先，我们使用preg_ match_ all，这个函数获取与模式匹配的每个字符串，并将其输出到第三个参数中.
正则表达式:
<img[^>]+>
We apply it on all html web pages. It can be read as every string that starts with "<img", contains non ">" char and ends with a >.
(alt|title|src)=("[^"]*")
我们在每个img标签上依次应用它.可以理解为every string starting with "alt", "title" or "src", then a "=", then a ' " ', a bunch of stuff that are not ' " ' and ends with a ' " '. Isolate the sub-strings between ().
最后，每当您想要处理regexp时，使用好的工具来快速测试它们是很方便的.判断这个online regexp tester.
编辑:回答第一条 comments .
的确，我没有考虑到(希望是少数)使用单引号的人.
好吧，如果你只使用'，只需替换所有的"by".
如果你两者都混合的话.首先你应该打自己一巴掌:-)，然后试着用("|‘)或者"和[^ø]来代替[^"].