Understand the substr() function in PHP to intercept strings

Understand the substr() function in PHP for intercepting strings

In the PHP language, the substr() function is a very useful string processing function. It can be used to intercept a string fragment at a specified position and length. The substr() function accepts three parameters: the string to be intercepted, the starting position of the interception, and the length of the interception. Below we will introduce the use of the substr() function in detail and give specific code examples.

1. Basic usage of the substr() function

The basic usage of the substr() function is very simple. You only need to pass in the string to be intercepted and the starting position of the interception. and length. The following is the basic syntax format:

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

Among them, the string $string is the string to be intercepted, $start indicates the starting position of interception, and $length indicates the length of interception. After calling the substr() function, it will return the intercepted string fragment.

2. Examples of intercepting strings

The following are several specific code examples showing the use and effect of the substr() function.

(1) Intercept the first few characters of the string:

$str = "Hello, world!";
$substr = substr($str, 0, 5);
echo $substr;  // 输出 "Hello"

(2) Intercept the last few characters of the string:

$str = "Hello, world!";
$substr = substr($str, -6);
echo $substr;  // 输出 "world!"

(3) Intercept the string The middle part:

$str = "Hello, world!";
$substr = substr($str, 7, 5);
echo $substr;  // 输出 "world"

3. Notes

When using the substr() function, you need to pay attention to the following points:

(1) Start Both position and length are calculated starting from 0.

(2) If the starting position is a negative number, it means counting from the end of the string, and -1 means the first character from the last.

(3) If the intercepted length is a negative number or exceeds the string length, an empty string will be returned.

(4) If the intercepted length parameter is omitted, the substr() function will intercept all characters from the starting position to the end of the string.

4. Summary

The substr() function is a very useful string processing function in PHP, which can intercept fragments of a string as needed. Through the introduction of this article, we understand the basic usage and precautions of the substr() function, and give specific code examples. I hope this article can help readers better understand and use the substr() function.

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