Let's talk about the correct usage of substr and substring in PHP and the introduction of related parameters

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 it does have a substr function.
If you don’t believe it, you can test it yourself. A correct piece of code is given below.

<&#63;
$a="me";
echo(substr($a,,));//输出me
&#63;>
下面又给出一段错误的代码
<&#63;
$a="me";
echo(subString($a,,));
&#63;>

substr() function returns a part of a string.

substr(string,start,length)

string: The string to be intercepted

start:

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

length:

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

Detailed explanation of the usage of PHP substr()

Definition and usage

substr() function returns a part of the string. Using the substr() function to intercept Chinese may cause garbled characters. It is recommended to use the mb_substr() function to intercept Chinese.

Syntax

substr(string,start,length)

Parameters	Description
string	Required. Specifies a part of the string to be returned.
start	Required. Specifies where in the string to begin. 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 first character in the string
length	Optional. Specifies the length of the string to be returned. The default is until the end of the string. Positive number - returned from the position of the start parameter Negative number - returned from the end of the string

Tips and Notes

Note: If start is a negative number and length is less than or equal to start, then length is 0.

Example

<&#63;php
$str = 'hello world!';
echo substr($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
&#63;>

The above has introduced the correct usage of substr and substring in PHP and the introduction of related parameters, including the content. I hope it will be helpful to friends who are interested in PHP tutorials.