正则表达式加与星号的区别? [英] Regex plus vs star difference?
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问题描述
What is the difference between:
(.+?)
and
(.*?)
when I use it in my php preg_match
regex?
解决方案
They are called quantifiers.
*
0 or more of the preceding expression
+
1 or more of the preceding expression
Per default a quantifier is greedy, that means it matches as many characters as possible.
The ?
after a quantifier changes the behaviour to make this quantifier "ungreedy", means it will match as little as possible.
Example greedy/ungreedy
For example on the string "abab"
a.*b
will match "abab" (preg_match_all will return one match, the "abab")
while a.*?b
will match only the starting "ab" (preg_match_all will return two matches, "ab")
You can test your regexes online e.g. on Regexr, see the greedy example here
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