正则表达式中的捕获组不输出

Question

<?php
    $string = 'This is my regular expression';
    $array = array();
    preg_match('/^.*((my)? regular (expression)?)$/i', $string, $array);
    var_dump($array);
?>

执行此脚本后，我有：

array (size=4)
    0 => string 'This is my regular expression' (length=29)
    1 => string ' regular expression' (length=19)
    2 => string '' (length=0)
    3 => string 'expression' (length=10)

为什么它不输出捕获组（我的）？

Answer 1

那是因为你之前有一个贪婪的量词.*。您应该使用非贪心量词.*?。

请改为：

<?php
    $string = 'This is my regular expression';
    $array = array();
    preg_match('/^.*?((my)? regular (expression)?)$/i', $string, $array);
    var_dump($array);
?>

DEMO

[OUTPUT]

array (size=4)
0 => string 'This is my regular expression' (length=29)
1 => string 'my regular expression' (length=21)
2 => string 'my' (length=2)
3 => string 'expression' (length=10)