Why is it empty for $ matches [0] because regular expressions are crazy? Write a regular expression, which can be matched normally, but I still need it to return the entire matched string.
The regular expression is as follows:
preg_match( '/^
/', $_content, $matches);
$ _ Content is
I know that only the first one can be matched, but according to the official document:
$ Matches [0] will contain the text matching the full mode
However, after a long test, I can only get the following results:
Array( [0] => [1] => header)
$ Matches [0] why is it empty? What about the matched text? (I originally thought that the value of $ matches [0] is )
There is another problem. I don't know why the assertion won't match,
preg_match( '/^
$/', $_content, $matches);
In this way, if a dollar sign is added at the end, nothing can be matched. Although this does not affect, I still want to know why and read the documents on the Internet, A bunch of terms are dizzy. I hope you can answer them. thank you.
Dizzy, how can I only give 100 points? I have 1000 points...
Reply to discussion (solution)
$_content =<<< HTML
HTML;preg_match( '/^
/', $_content, $matches);print_r($matches);
Array( [0] =>
[1] => header)No problem
You are confused by yourself.
$ Matches [0] is an html tag that can be viewed only in text mode.
$_content='
';preg_match_all('/
/', $_content, $matches);print_r($matches);/*Array( [0] => Array ( [0] =>
[1] =>
) [1] => Array ( [0] => header [1] => footer ))*/
$ Matches [0] will contain the text matching the full modeIt has the following sentence:
$ Matches [1] will contain the text matched by the first capture sub-group, and so on.
This means that it only contains your anti-capture (that is, the content enclosed in your parentheses), rather than the global matching, so preg_match_all is used to perform global matching.
In addition, your regular expression is prefixed with ^, which indicates that the matching string must start with the content after ^. Yes.
Similarly, $ indicates that the matched string must end with $. therefore, to match the content, $ _ content =' '; Or $ _ content =' '; Can be matched
$_content =<<< HTML
HTML;preg_match( '/^
/', $_content, $matches);print_r($matches);
Array( [0] =>
[1] => header)No problem
You are confused by yourself.
$ Matches [0] is an html tag that can be viewed only in text mode.
I got it !!! I forgot the HTML comment mark, dizzy, and really fainted for one night. thank you for reminding me.
$_content='
';preg_match_all('/
/', $_content, $matches);print_r($matches);/*Array( [0] => Array ( [0] =>
[1] =>
) [1] => Array ( [0] => header [1] => footer ))*/
$ Matches [0] will contain the text matching the full modeIt has the following sentence:
$ Matches [1] will contain the text matched by the first capture sub-group, and so on.
This means that it only contains your anti-capture (that is, the content enclosed in your parentheses), rather than the global matching, so preg_match_all is used to perform global matching.
In addition, your regular expression is prefixed with ^, which indicates that the matching string must start with the content after ^. Yes.
Similarly, $ indicates that the matched string must end with $. therefore, to match the content, $ _ content =' '; Or $ _ content =' '; Can be matched
I still don't quite understand. after ^ is used, can it be compared only from $ content [0? If the preceding strings are the same, match them. $ is the same?
There is another problem that we hope to solve.
A string exists.
$string = 'bbs/csdn/net/xxx';
If the string does not start with bbs, it will be matched.
For example
$string = 'www/csdn/net/xxx';
Because it does not start with bbs, continue matching
I think of a way to write
preg_match( '#((?!bbs/).)*#', 'www/csdn/net/xxx/', $matches);
However, I feel that the efficiency is a little low. I wonder if I can optimize it?
^ Is the starting position for matching the input string. if the string to be matched does not start with the content after ^, the matching will not be executed at all.
If it is just judgmentThe string does not start with bbs, This is faster
$ Str = '/bbs/www/csdn/net/xxx/'; if (strpos ($ str, 'bbs ')! = 0 | strpos ($ str, 'bbs ') = false) {// 0 indicates that the value starts with bbs. If no value is found, false is returned (all values are equal to false) echo 'exe ';}
^ Is the starting position for matching the input string. if the string to be matched does not start with the content after ^, the matching will not be executed at all.
If it is just judgmentThe string does not start with bbs, This is faster
$ Str = '/bbs/www/csdn/net/xxx/'; if (strpos ($ str, 'bbs ')! = 0 | strpos ($ str, 'bbs ') = false) {// 0 indicates that the value starts with bbs. If no value is found, false is returned (all values are equal to false) echo 'exe ';}
No. actually, I want to write a URL routing function similar to django. if the above method is used, the scalability is not strong enough, so I want to use regular expressions.
$ Str = 'www/bbs/net/xxx/'; if (preg_match ('/^ bbs. +? /', $ Str) {echo' starts with bbs ';} else {echo 'exe ';}
