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This article brings you an analysis of the problems caused by the use of the php trim method. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.
Scenario
The characters before and after intercepting the string in php include three methods: ltrim, rtrim, and trim.
In the following example, only the ltrim method is used as an example
In my previous understanding (of course I am very ignorant and have never seen this source code), if I want to delete empty strings, empty tabs, etc. on the left side of the string, then I will use ltrim directly. ($str)
If I want to delete specified characters, for example, there is a string helloworld now, and I want to intercept the h character at the head, directly var_dump(ltrim("helloworld", " h")); can get the result I expected and output elloworld
The above are all within the range I thought, and I have always used it this way, until one time we had a need to print on some strings Do openssl_encrypt encryption. After encryption, make a base64, and then splice it with our special string prefix KO:. After each encryption is completed, splice the KO: character. Similarly, before decryption, remove the KO: first and then decrypt it. The result is that the decryption result is No matter how I solved it, it failed. Later, I made a few breakpoints and found that the result was different from the expected result when ltrim was used.
Recurrence
<?php // 以下做一个简单的情景复现 $str = "abccabdefg"; $character_mask = “abc”; var_dump(ltrim($str, $character_mask)); // 输出结果为 bdefg,而不是只截取前三位的abc
Cause analysis
After the above small steps demo, you should know the reason. The simplest and most popular way is that it performs a rotation training on the previous $str, character by character, and checks whether it is included in the subsequent $character_mask. If so, proceed. Intercept, stop running if it is not there
Expression in the form of ltrim code:
<?php $str = "abcccabdecbag"; $res = ''; $character_mask = 'abc'; $arrStr = str_split($str); // 字符串转数组 for ($i=0; $i<=count($arrStr); $i++) { if(strpos($character_mask, $arrStr[$i]) !== false) { unset($arrStr[$i]); } else { break; } } echo ltrim($str, $character_mask); echo "\r\n"; echo implode($arrStr); echo "\r\n";
Solution
The solution is to use some string manipulation functions in php, adding more basic judgments
if (substr($str, 0, strlen($character_mask)) == $character_mask) { echo substr($str, strlen($character_mask)); }
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