What are the methods to intercept strings in php

php interception method: 1. Use substr() to intercept, you can intercept a certain length of characters from the specified position of the string; 2. Use mb_substr() to intercept, this function can intercept the specified characters from a string Part of it is not only valid for English characters, but also valid for Chinese characters.

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

1. Use substr() to intercept String

substr() function can intercept characters of a certain length from the specified position of the string. This intercepted character can be called a "substring" or "substring". Its syntax The format is as follows:

substr($string, $start [, $length])

Parameter description is as follows:

• $string: The string that needs to be intercepted, the string contains at least one character;
• $start: Interception The starting position of the string;
  • If $start is a non-negative number, the string will be intercepted from the $start character of $string, and $start starts counting from 0. For example, in the string "abcdef", the character at position 0 is "a", the character at position 2 is "c", etc.;
  • If $start is a negative number, the string will start from $ The end of string starts at the $start character forward, and $start starts counting from -1. For example, in the string "abcdef", the character at position -1 is "f", the character at position -3 is "d", etc.;
  • If the length of $string is less than $start, it will be returned FALSE.
• $length: Optional parameter, indicating the length of the intercepted string.
  • If $length is a positive number, then the string will be truncated up to $length characters from the $start position;
  • If $length is a negative number, then $length characters from the end of $string Characters will be omitted (if $start is a negative number, it will be counted from the end of the string);
  • If the value of $length is 0, FALSE or NULL, an empty string will be returned;
  • If $length is not provided, the returned substring will start from the $start position until the end of the string.

Example: Using start and length parameters with different positive and negative numbers

<?php
echo substr("Hello world",0,10)."<br>";
echo substr("Hello world",1,8)."<br>";
echo substr("Hello world",0,5)."<br>";
echo substr("Hello world",6,6)."<br>";
 
echo substr("Hello world",0,-1)."<br>";
echo substr("Hello world",-10,-2)."<br>";
echo substr("Hello world",0,-6)."<br>";
echo substr("Hello world",-2-3)."<br>";
?>

Output:

Hello worl
ello wor
Hello
world
Hello worl
ello wor
Hello
world

2. Use mb_substr() to intercept Chinese strings

The mb_substr() function can intercept a specified part of a string. Unlike the substr() function, the mb_substr() function not only English characters are valid, and Chinese characters are also valid. The syntax format is as follows:

mb_substr($str , $start [, $length = NULL [, $encoding = mb_internal_encoding()]])

Parameter description is as follows:

• $str: The string to be intercepted, the string contains at least one Character;
• $start: intercept the starting position of the string;
  • If $start is a non-negative number, the string will be intercepted starting from the $start character position of $str;
  • If $start is a negative number, the string will be intercepted from the end of $str, starting from the position of the $start character forward.
• $length: Optional parameter, indicating the length of the intercepted string;
  • If $length is a positive number, the string will be intercepted backwards from the $start position Up to $length characters;
  • If $length is a negative number, then $length characters at the end of $string will be omitted (if $start is a negative number, it will be counted from the end of the string);
  • If the value of $length is NULL or $length is omitted, it will be cut to the end of the string.
• $encoding: Optional parameter, indicating the character encoding of $str. If omitted, the internal character encoding is used.

Example: Use the mb_substr() function to intercept a Chinese string of specified length

<?php
    $str = &#39;欢迎访问PHP中文网，一个在线学习编程的网站。&#39;;
    echo mb_substr($str, 4).&#39;<br>&#39;;
    echo mb_substr($str, -19).&#39;<br>&#39;;
    echo mb_substr($str, 4, 6).&#39;<br>&#39;;
    echo mb_substr($str, 4, -16).&#39;<br>&#39;;
    echo mb_substr($str, -19, -13).&#39;<br>&#39;;
    echo mb_substr($str, -19, 6).&#39;<br>&#39;;
    var_dump(mb_substr($str, 40));
    echo &#39;<br>&#39;;
    var_dump(mb_substr($str, 4, null));
?>

The running results are as follows:

PHP中文网，一个在线学习编程的网站。
PHP中文网，一个在线学习编程的网站。
PHP中文网
PHP
PHP中文网
PHP中文网
string(0) ""
string(55) "PHP中文网，一个在线学习编程的网站。"

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