PHP functions are divided into four categories: built-in functions, user-defined functions, core functions and user-defined extension functions. Built-in functions can be used without loading, such as the echo function. User-defined functions are created by users, such as the greet function. Core functions are used for low-level system operations, such as the file_get_contents function. User-defined extension functions are provided by extensions, such as my_extension. Practical examples include using built-in functions to get the length of a string, using user-defined functions to format dates, and using core functions to read file contents.
In-depth classification of PHP functions and their practical cases
The functions in PHP are particularly rich, and they can be divided into the following categories :
1. Built-in functions
These functions come with PHP and can be used without additional loading. For example:
echo("Hello World!");
2. User-defined functions
These functions are created by users themselves and need to be defined using the function
keyword. For example:
function greet($name) { echo("Hello, $name!"); } greet("John Doe");
3. Core functions
These functions are part of the PHP core extension. They are usually used to handle low-level system operations such as file operations, error handling, etc. For example:
file_get_contents("file.txt");
4. User-defined extension functions
These functions are provided by user-created extensions and require the use of the extension_loaded()
function load. For example:
extension_loaded("my_extension");
Practical case
Example 1: Use built-in function to get the string length
$str = "Hello World!"; $length = strlen($str);
Example 2: Use user-defined function to format date
function format_date($date) { return date("Y-m-d H:i:s", $date); } echo format_date(time());
Example 3: Use core function to read file content
$content = file_get_contents("file.txt");
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