Correct usage of substr and substring in PHP

Everyone knows that there are functions substr and substring for string interception in js. What about php? PHP does not have a directly available substring function, but there is a substr function.
If you don’t believe it, you can test it yourself. A correct piece of code is given below.

<?$a="me";echo(substr($a,,));//输出me?>下面又给出一段错误的代码<?$a="me";echo(subString($a,,));?>
substr() 函数返回字符串的一部分。
substr(string,start,length)
string:要截取的字符串

start:

Positive number - starts at the specified position in the string
Negative number - starts at the specified position from the end of the string
0 - starts at the specified position in the string Starts at one character

length:

Optional. Specifies the length of the string to be returned. The default is until the end of the string.
Positive number - Return from the position of the start parameter
Negative number - Return from the end of the string

Detailed explanation of the usage of PHP substr()

Definition and usage

substr(string,start,length)

<?php
$str = &#39;hello world!&#39;;
echo substr($str, 4); // o world! 左起第4开始向右截取到末尾
echo substr($str, 4, 5); // o wor 左起第4开始向右取5位
echo substr($str, 4, -1); // o world 左起第4与右起第1之间的字符
echo substr($str, -8, 4); // o wo 右起第8开始向右截取4位
echo substr($str, -8,-2); // o worl 右起第8与右起第2之间的字符

Analysis on usage of string interception of substr function in PHP, phpsubstr_PHP tutorial

Analysis of usage of string interception of substr function in PHP , phpsubstr

The method of substr_count() function in PHP to obtain the number of occurrences of a substring

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