php preg match中的“ *”和“？”有什么区别？

Question

使用“ *”或“？”之间有区别吗？ 在php preg_match中？ 还是有一个例子？

<?php

// the string to match against
$string = 'The cat sat on the matthew';

// matches the letter "a" followed by zero or more "t" characters
echo preg_match("/at*/", $string);

// matches the letter "a" followed by a "t" character that may or may not be present
echo preg_match("/at?/", $string);

Answer 1

*匹配0或更多

? 匹配0或1

在您的特定测试中，您无法分辨出差异，因为*和? 匹配不固定或后面没有任何内容-它们都将匹配包含a任何字符串，无论后面是否跟着t 。

如果您在匹配字符之后有其他内容，则区别很重要，例如：

echo preg_match("/at*z/", "attz"); // true
echo preg_match("/at?z/", "attz"); // false - too many "t"s

而与您的：

echo preg_match("/at*/", "attz"); // true - 0 or more
echo preg_match("/at?/", "attz"); // true - but it stopped after the
                                  // first "t" and ignored the second

Answer 2

// matches the letter "a" followed by zero or more "t" characters

// matches the letter "a" followed by a "t" character that may or may not be present

资料来源： 您