Application of PHP string processing function substr()

PHP is a programming language widely used in web development. It has many string processing functions, one of which is widely recognized as the substr() function. This article will delve into the application and use of the substr() function to help you better process strings.

1. Substr() function introduction

The substr() function is used to intercept a part of characters from a string. Its syntax is:

substr(string $string, int $start, ?int $length);

Among them,

• $string: required parameter, original string;
• $start: required parameter, The position to start interception can be a negative number. A negative number means counting from the end of the string. -1 means the first character from the last, -2 means the second character from the last, and so on;
• $length : Optional parameter, the length to be intercepted. The default is from $start to the end of the string. If it is a negative number, it means the last few characters to be intercepted.

2. Application scenarios of the substr() function

1. Interception of strings

The most common application scenario of the substr() function is interception string. By passing in different parameters, we can intercept different string lengths and positions. The following are some basic applications:

$original_string = "Hello, World!";
echo substr($original_string, 0, 5); // Output "Hello"
echo substr($original_string , 7, 5); // Output "World"
echo substr($original_string, -6); // Output "World!"

2. Replace part of the string

In addition to intercepting strings, the substr() function can also be used to replace part of a string. The following is an example:

$original_string = "Hello, World!";
$new_string = substr_replace($original_string, "Bob", 0, 5);
echo $new_string; // Output "Bob, World!"

In this example, we replace "Hello" in the $original_string string with "Bob". The first parameter is the original string, the second parameter is the content to be replaced, the third parameter is the starting position to be replaced, and the fourth parameter is the length to be replaced.

3. Get the file suffix name

The substr() function can also be used to get the file suffix name. We can determine the position of the suffix name and return it by passing in the file name string and the position of ".". Here is an example:

$file_name = "example.jpg";
$ext = substr($file_name, strrpos($file_name, '.') 1);
echo $ext; // Output "jpg"

In this example, we use PHP's built-in strrpos() function to get the position of the last occurrence of "." in the file name string, and then use the substr() function Intercept the suffix part of the file name.

3. Summary

The substr() function is one of the basic functions of PHP string processing. Through its simple syntax and multiple parameter passing methods, we can easily intercept and process strings, making it convenient for us to perform string operations in web development. Of course, in practical applications, we can also combine other string functions to perform more complex string operations. I hope this article can help you and make you more proficient in using the substr() function.

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