douzhaishan5462
2014-02-28 14:31
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计算字符串中不带反斜杠的引号数

I'm using the following expression to find the number of occurences of ' and " in a string I don't want the count to include \' or \".

$subStr = 'asdf"asdf""a\\"sdf\'asdf\'\'a\\\'sdf';
preg_match_all('/[^\\\\]\'|[^\\\\]\"/', $subStr, $matches);
echo count($matches[0]);

I expect it to return 6 but it only returns 4. I think this is because the strings "" and '' are only count once.

This is what $matches contain:

Array
(
    [0] => Array
        (
            [0] => f"
            [1] => f"
            [2] => f'
            [3] => f'
        )

)

Is there any way I can get the count of 6? Note that I also need to exclude the \" and \'.

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我正在使用以下表达式查找'和<的出现次数 代码>“在一个字符串中我不希望计数包含 \'或 \”。 

   $ subStr ='asdf“asdf”“a \\”sdf \'asdf \'\'a \\\'sdf'; 
 npreg_match_all（'/ [^ \\\\] \'| [^ \  \\\] \“/'，$ subStr，$ matches）; 
echo count（$ matches [0]）; 
   
 
 
我希望它返回6 但它只返回 4 。我认为这是因为字符串“”和''只计算一次。 
  
 
这是 $ matches 包含： 
 
 
  Array 
（
 [0] =＆gt; Array 
（\  n [0] =＆gt; f“
 [1] =＆gt; f”
 [2] =＆gt; f'
 [3] =＆gt; f'
）
 
）
 <  / code>  
 
 
有什么方法可以得到 6 的数量吗？注意我还需要排除 \“ 和 \'。
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4条回答 默认 最新

  • dongzhuo6137 2014-02-28 14:33
    已采纳

    Why doesn't it work

    You can't use a character class to match a character not preceded by another character. This is because a character class (negated or not) must still match a character. For example, [^a]b does not mean "b not preceded by a". It means: "a character that's not a followed by b".

    The Solution

    If you want to match a single-quote or double-quote character not preceded by a backslash, then you'll have to use a lookaround expression (a negative lookbehind, specifically).

    The regex you're looking for is (?<!\\\\)[\'"].

    Autopsy:

    • (?<! - start of the lookbehind expression
      • \\\\ - match a literal backslash character
    • ) - end of the lookbehind expression
    • [\'"] - character class that matches a single character from the list "'

    Visual Representation:

    Visual Representation of the regex

    This effectively matches any single-quote / double-quote character that is not preceded by a literal backslash character.

    Using the above expression with preg_match_all is simple:

    $subStr = 'asdf"asdf""a\\"sdf\'asdf\'\'a\\\'sdf';
preg_match_all('/(?<!\\\\)[\'"]/', $subStr, $matches);
echo count($matches[0]); // => 6

    Demo

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