php - preg_match_all 匹配数组

Question

我有这样的东西

$matches = array();
preg_match_all('/(`.+`)(\s+AS\s+`.+`)?/i', '`foo` AS `bar`', $matches);
print_r($matches);

结果是

Array
(
[0] => Array
    (
        [0] => `foo` AS `bar`
    )

[1] => Array
    (
        [0] => `foo` AS `bar`
    )

[2] => Array
    (
        [0] => 
    )

)

所以，问题是为什么我没有' AS `bar`' in $matches[2][0]？（如果我从正则表达式中删除“？”符号，我会得到它，但我需要“？”:)）

Answer 1

默认情况下，量词+是贪婪的，所以如果第一个可以匹配所有内容，它就会这样做。让它不贪婪应该可以完成这项工作：

preg_match_all('/(`.+?`)(\s+AS\s+`.+`)?/i', '`foo` AS `bar`', $matches);

顺便说一句，$matches = array();这不是必需的 - 变量仅由 by 写入，preg_match_all因此它不需要在之前进行初始化/定义。

php > preg_match_all('/(`.+?`)(\s+AS\s+`.+`)?/i', '`foo` AS `bar`', $matches);
php > print_r($matches);
Array
(
    [0] => Array
        (
            [0] => `foo` AS `bar`
        )

    [1] => Array
        (
            [0] => `foo`
        )

    [2] => Array
        (
            [0] =>  AS `bar`
        )

)