深入了解PHP：从入门到精通

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引言：
php是一种广泛应用于web开发的服务器端脚本语言，它简单易学，适用于初学者，也提供了丰富的功能和扩展性，能够满足复杂的开发需求。本文将从入门到精通，通过具体的代码示例，带您逐步了解PHP的各个方面。

一、基础知识

1. 变量声明和输出

   $name = "John";
   $age = 25;
   echo "My name is " . $name . " and I am " . $age . " years old.";
   

   条件语句

   $score = 90;
   if ($score >= 60) {
    echo "You passed the exam!";
   } else {
    echo "You failed the exam.";
   }
   

   循环语句

   for ($i = 0; $i < 5; $i++) {
    echo $i;
   }
   

   函数的定义和调用

   function sayHello($name) {
    echo "Hello, " . $name . "!";
   }
   sayHello("Tom");
   

   二、数组和字符串

   1. 数组的声明和遍历

   $fruits = ["apple", "banana", "orange"];
   foreach ($fruits as $fruit) {
    echo $fruit;
   }
   

   字符串操作

   $str = "Hello, PHP!";
   echo strlen($str);  // 输出：12
   echo strtoupper($str);  // 输出：HELLO, PHP!
   echo substr($str, 7);  // 输出：PHP!
   

   三、数据库操作

   1. 连接数据库

   $servername = "localhost";
   $username = "root";
   $password = "123456";
   $dbname = "myDB";
   $conn = mysqli_connect($servername, $username, $password, $dbname);
   if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
   }
   

   查询数据

   $sql = "SELECT * FROM users";
   $result = mysqli_query($conn, $sql);
   if (mysqli_num_rows($result) > 0) {
    while ($row = mysqli_fetch_assoc($result)) {
        echo "Name: " . $row['name'] . ", Age: " . $row['age'];
    }
   } else {
    echo "No results found.";
   }
   

   插入数据

   $sql = "INSERT INTO users (name, age) VALUES ('John', 25)";
   if (mysqli_query($conn, $sql)) {
    echo "Data inserted successfully.";
   } else {
    echo "Error: " . mysqli_error($conn);
   }
   

   四、面向对象编程

   1. 类的定义和实例化

   class Car {
    public $color;
    public function drive() {
        echo "Driving...";
    }
   }
   $car = new Car();
   $car->color = "red";
   $car->drive();
   

   继承和多态

   class SportsCar extends Car {
    public function drive() {
        echo "Driving at high speed!";
    }
   }
   $sportsCar = new SportsCar();
   $sportsCar->color = "blue";
   $sportsCar->drive();
   

   五、常见应用

   1. 文件上传

   <form action="upload.php" method="POST" enctype="multipart/form-data">
    <input type="file" name="file">
    <input type="submit" value="Upload">
   </form>
   

   $targetDir = "uploads/";
   $targetFile = $targetDir . basename($_FILES["file"]["name"]);
   if (move_uploaded_file($_FILES["file"]["tmp_name"], $targetFile)) {
    echo "File uploaded successfully.";
   } else {
    echo "Error uploading file.";
   }
   

   用户注册与登录

   $hashedPassword = password_hash($password, PASSWORD_DEFAULT);
   $sql = "INSERT INTO users (username, password) VALUES ('$username', '$hashedPassword')";
   if (mysqli_query($conn, $sql)) {
    echo "Registration successful. You can now login.";
   } else {
    echo "Error: " . mysqli_error($conn);
   }
   

   $hashedPassword = password_hash($password, PASSWORD_DEFAULT);
   $sql = "INSERT INTO users (username, password) VALUES ('$username', '$hashedPassword')";
   if (mysqli_query($conn, $sql)) {
    echo "Registration successful. You can now login.";
   } else {
    echo "Error: " . mysqli_error($conn);
   }
   

   结语：
   通过本文的介绍和实例代码，希望读者能够从PHP的基础知识开始，逐步深入了解PHP的各个方面，从而掌握PHP的高级应用技巧，提升自己的开发能力。同时，也欢迎读者在实践中探索更多有趣和创新的PHP应用。