Detailed explanation and usage of substr() function in php

Syntax:

string substr(string $string, int $start [, int $length]), which can be used in a longer string# Find matching strings or characters in ##, $string is the string to be processed, $start is the starting position to be selected, $length is the length to be selected.

$length is positive data from left Read characters from the right. When

$length is a negative number, read characters from right to left.

string Required, specifies that a part of the string should be returned.

start Required , specifies where to start in the string.

charlist Optional, specifies the length of the string to be returned, the default is until the end of the string.

Positive number - specified in the string Position start

Negative number - Start at the specified position from the end of the string

0 - Start at the first character in the string

PHP example code is as follows:

$rest_1 = substr("abcdef", 2); // returns "cdef" 
$rest_2 = substr("abcdef", -2); // returns "ef" 
 
$rest1 = substr("abcdef", 0, 0); // returns "" 
$rest2 = substr("abcdef", 0, 2); // returns "ab" 
$rest3 = substr("abcdef", 0, -1); // returns "abcde" 
$rest4 = substr("abcdef", 2,0); // returns "" 
$rest5 = substr("abcdef", 2,2); // returns "cd" 
$rest6 = substr("abcdef", 2, -1); // returns "cde" 
$rest7 = substr("abcdef", -2,0); // returns "" 
$rest8 = substr("abcdef", -2,2); // returns "ef" 
$rest9 = substr("abcdef", -2,-1); // returns "e"

PHP substr()

Function can split text, but if the text to be split includes Chinese characters, you will often encounter problems. In this case, you can use mb_substr()/ The usage of mb_strcut function, mb_substr()/mb_strcut is similar to substr(), except that one more parameter is added at the end of mb_substr()/mb_strcut to set the encoding of the string, but most servers do not open php_mbstring.dll. You need to open php_mbstring.dll in php.ini.

<?php
echo mb_substr(&#39;我们都是好孩子hehe&#39;,0,9);
?>

Output: We are all

Now we add the

character setutf-8

<?php
echo mb_substr(&#39;我们都是好孩子hehe&#39;,0,9,&#39;utf-8&#39;);
?>

Output: We are all good kids he

The first one is to use three bytes as one Chinese character. This is the characteristic of utf-8 encoding. The description of the utf-8 character set is added below, so it is intercepted in units of one word.

The following is the function in ecshop to intercept strings encoded in UTF-8

function sub_str($str, $length = 0, $append = true)
{
    $str = trim($str);
    $strlength = strlen($str);
    if ($length == 0 || $length >= $strlength)
    {
        return $str;  //截取长度等于0或大于等于本字符串的长度，返回字符串本身
    }
    elseif ($length < 0)  //如果截取长度为负数
    {
        $length = $strlength + $length;//那么截取长度就等于字符串长度减去截取长度
        if ($length < 0)
        {
            $length = $strlength;//如果截取长度的绝对值大于字符串本身长度，则截取长度取字符串本身的长度
        }
    }
    if (function_exists(&#39;mb_substr&#39;))
    {
        $newstr = mb_substr($str, 0, $length, EC_CHARSET);
    }
    elseif (function_exists(&#39;iconv_substr&#39;))
    {
        $newstr = iconv_substr($str, 0, $length, EC_CHARSET);
    }
    else
    {
        //$newstr = trim_right(substr($str, 0, $length));
        $newstr = substr($str, 0, $length);
    }
    if ($append && $str != $newstr)
    {
        $newstr .= &#39;...&#39;;
    }
    return $newstr;
}

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