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Home Backend Development PHP Tutorial 正则捕获的疑问?

正则捕获的疑问?

Jun 23, 2016 pm 02:15 PM

$str="a1234a";
$preg="/(\d){4}/i";

上面能够匹配4个连续的数,
那么里面的子表达式捕获的



是1(一个子表达式)?
还是1324(一个子表达式)?
还是1、2、3、4(四个子表达式)?


回复讨论(解决方案)

看一下就知道了

$str = "a1234a";$preg = "/(\d){4}/i";preg_match_all($preg, $str, $res);print_r($res);
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Array
(
    [0] => Array
        (
            [0] => 1234
        )

    [1] => Array
        (
            [0] => 4
        )

)

$str="a1234a";
$preg="/(\d){4}/i";

上面能够匹配4个连续的数,
那么里面的子表达式捕获的



是1(一个子表达式)?
还是1324(一个子表达式)?
还是1、2、3、4(四个子表达式)?
一般是第一个值就是整个表达式获取到的部分
然后接着就是一个括号一个值

就像你这个正则表达式
第一个值是:1234
第二个值是:4
如果用数组$arr来表示
就是$arr[0] == 1234
$arr[1] == 4

你使用的(\d){4}代表的意思是:单个数字字符为子组,重复4次,所以执行后应该是
\d匹配1 子组为1
\d匹配2 相同子组,覆盖之前的值,子组为2
\d匹配3 相同子组,覆盖之前的值,子组为3
\d匹配4 相同子组,覆盖之前的值,子组为4

如果是(\d{4})则和之前明显不同,意思为4个连续的数字字符为子组

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