What are the classifications of PHP functions?

PHP functions are divided into three main categories: core functions (built into the language, no extension required), extension functions (added through extensions, such as PDO), and user-defined functions (created by developers). Understanding these classifications is essential for efficient PHP programming, such as using the PDO extension to connect to a MySQL database.

PHP Function Classification Guide

PHP functions are predefined blocks of code that perform specific tasks. They are an important part of PHP programming and help simplify your code and make it more efficient. PHP functions can be divided into the following categories:

Core functions

Core functions are functions built into the PHP language that can be used without using any extensions or libraries. They include functions for working with strings, numbers, arrays, and other data types, as well as functions for performing I/O operations, file processing, and date/time operations.

Extension functions

Extension functions are added through PHP extensions that provide additional functionality. For example, the PDO (PHP Data Objects) extension provides functions for interacting with databases, while the GD extension provides image processing functions.

User-defined functions

User-defined functions are functions created by developers to encapsulate repetitive tasks or implement specific functions. They can be defined anywhere in the program and called as many times as necessary.

Practical case: Using PDO extension

The following code shows how to use PDO extension to connect to the MySQL database and retrieve data:

<?php
// 包含 PDO 库
require_once 'path/to/PDO.php';

// 创建 PDO 对象
$db = new PDO('mysql:host=localhost;dbname=test', 'root', '');

// 准备 SQL 查询
$sql = "SELECT * FROM users";

// 执行查询并获取结果
$stmt = $db->prepare($sql);
$stmt->execute();
$result = $stmt->fetchAll();

// 打印结果
foreach ($result as $row) {
    echo $row['name'] . "\n";
}
?>

It can be seen that , PHP functions are divided into core functions, extension functions and user-defined functions, each type has its specific purpose. Understanding these classifications is crucial to building robust and efficient PHP applications.

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