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In this article, the editor introduces in detail "php how to retain only the English alphabet". The content is detailed, the steps are clear, and the details are handled properly. I hope this article "php how to retain only the English alphabet" can help you solve your doubts.

In php, you can use preg_match_all () with regular expressions to filter strings, leaving only English letters; syntax "preg_match_all (" / [a-zA-Z] / u "," $str ", $arr)", letters are stored in an array, and you can use join () to convert an array into a string.

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

Php retains only the English alphabet

You can use the preg_match_all () function with regular expressions to filter strings, leaving only the English alphabet

The preg_match_all () function stores the matching characters (reserved alphabets) in an array (specified by the third argument).

As you can see, the result is a two-dimensional array.

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

Join ('', $arr [0])

Description: preg_match_all ()-performs global regular expression matching

The preg_match_all () function searches for all results in a string that match a regular expression, in the following syntax format:

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

The parameters are described as follows:

$pattern: the pattern to search for, that is, the defined regular expression

$subject: string to search for

$matches: optional parameter (multi-dimensional array) to store all matching results. Array sorting is specified by $flags

$flags: optional parameter that can be used in combination with the following tags (note that PREG_PATTERN_ORDER and PREG_SET_ORDER cannot be used at the same time):

PREG_PATTERN_ORDER: the result is sorted as $matches [0] to save all matches for the complete pattern, $matches [1] to save all matches for the first subgroup, and so on.

PREG_SET_ORDER: the order of the result is $matches [0] containing all matches (including subgroups) from the first match, $matches [1] is an array containing all matches (including subgroups) from the second match, and so on.

PREG_OFFSET_CAPTURE: if this tag is passed, each found match returns with an increase in its offset from the target string. Note that this changes each matching result string element in $matches so that the 0th element is the matching result string, and the first element is the offset of the matching result string in the subject.

$offset: optional parameter, $offset is used to start the search (in bytes) from the location specified in the target string.

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

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