How to keep only English letters in php

In PHP, you can use preg_match_all() with regular expressions to filter strings and only retain English letters; the syntax is "preg_match_all("/[a-zA-Z]/u","$str", $arr)", the letters will be stored in the array, and join() can be used to convert the array into a string.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

php only retains English The letters

can be used with the preg_match_all() function in conjunction with regular expressions to filter strings and only retain English letters

The preg_match_all() function will match the characters (reserved English letters) are stored in the array one by one (the array is specified by the third parameter).

<?php
header("Content-type:text/html;charset=utf-8");
$str = "php.cn23v457zblog,?#$%^&())*(&^";
preg_match_all("/[a-zA-Z]/u","$str",$arr);
var_dump($arr);
?>

It can be seen that the result is a two-dimensional array.

If you want to use the join() function to splice the result value into a string, you need to use the following statement

join('',$arr[0])

Instructions: preg_match_all()--Perform global regular expression matching

preg_match_all() function can search for all results in the string that can match the regular expression. The syntax format is as follows:

preg_match_all($pattern, $subject [, &$matches [, $flags = PREG_PATTERN_ORDER [, $offset = 0 ]]])

Parameter description as follows:

• $pattern: The pattern to be searched, which is the defined regular expression;
• $subject: the string to be searched;
• $matches: Optional parameter (multidimensional array), used to store all matching results. Array sorting is specified by $flags;
• $flags: optional parameters, can be used in combination with the following flags (note that PREG_PATTERN_ORDER and PREG_SET_ORDER cannot be used at the same time):
  • PREG_PATTERN_ORDER: The results are ordered so that $matches[0] holds all matches for the complete pattern, $matches[1] holds all matches for the first subgroup, and so on.
  • PREG_SET_ORDER: The results are sorted as $matches[0] contains all matches (including subgroups) obtained by the first match, $matches[1] is an array containing all matches (including subgroups) obtained by the second match, so that analogy.
  • PREG_OFFSET_CAPTURE: If this flag is passed, each found match is returned with its offset relative to the target string increased. Note that this will change each match string element in $matches to be one where the 0th element is the match string and the 1st element is the offset of the match string within the subject.
• $offset: Optional parameter, $offset is used to start searching from the specified position in the target string (unit is byte).

The preg_match_all() function can return the number of matches for $pattern (possibly 0), or FALSE if an error occurs.

Recommended learning: "PHP Video Tutorial"

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