php中的静态变量不保存值

发布于 2025-01-14 06:42:32 字数 1921 浏览 4 评论 0原文

我编写了一个演示程序来描述我在 php 中使用静态变量时遇到的问题。我有一个单例类 History.php，它包含一个静态 $idx 变量，最初设置为 -1。 History 类中的 incIdx() 函数递增 $idx。该演示首先调用index.php，它获取History 的实例，重复调用incIdx() 并显示$idx 最终值。然后，单击按钮时，将调用 test.php，获取 History 实例，重复调用 incIdx()，并显示最终值。我不明白的是，index.php 创建的值不是 test.php 的起始值。也就是说，index.php 和 test.php 都以初始值 = -1 开始。代码如下：

<?php
class History {
    private static int $idx;
    private static $instance = null;
    
    private function __construct() {
        $this::$idx = -1;
    }
    
    public static function getHistory() {
        if (self::$instance === null) {
            self::$instance = new History();
        } 
        return self::$instance;
    }
    
    public function incIdx() {
        $this::$idx++;
    }
    
    public function getIdx(): int {
        return $this::$idx;
    }
}

<?php
require_once "History.php";

$instance = History::getHistory();
for ($i = 0; $i < 5; $i++) {
    $instance->incIdx();
}
$value = $instance->getIdx();
?>
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Test Static</title>
    </head>
    <body>
        <h1>In index.php</h1>
        <h2>Current idx = "<?php echo $value; ?>"</h2>
        <button type="button"><a href="test.php">Click to continue</a></button>
    </body>
</html>

<?php
require_once "History.php";

$instance = History::getHistory();
for ($i = 0; $i < 5; $i++) {
    $instance->incIdx();
}
$value = $instance->getIdx();
?>
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Test Static</title>
    </head>
    <body>
        <h1>In test.php</h1>
        <h2>Current idx = "<?php echo $value; ?>"</h2>
    </body>
</html>```

原文

I have written a demo program to describe a problem I'm having with static variables in php. I have a singleton class, History.php, that contains a static $idx variable intially set to -1. An incIdx() function in the History class increments $idx. The demo starts by calling index.php which gets an instance of History, repeatedly calls incIdx() and displays the $idx final value. Then, on clicking a button, test.php is called which gets the History instance, repeatedly calls incIdx(), and displays the final value. What I don't understand is, the value created by index.php is not the starting value for the test.php. That is, index.php and test.php both start with the initial value = -1.
The code follows:

<?php
class History {
    private static int $idx;
    private static $instance = null;
    
    private function __construct() {
        $this::$idx = -1;
    }
    
    public static function getHistory() {
        if (self::$instance === null) {
            self::$instance = new History();
        } 
        return self::$instance;
    }
    
    public function incIdx() {
        $this::$idx++;
    }
    
    public function getIdx(): int {
        return $this::$idx;
    }
}

<?php
require_once "History.php";

$instance = History::getHistory();
for ($i = 0; $i < 5; $i++) {
    $instance->incIdx();
}
$value = $instance->getIdx();
?>
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Test Static</title>
    </head>
    <body>
        <h1>In index.php</h1>
        <h2>Current idx = "<?php echo $value; ?>"</h2>
        <button type="button"><a href="test.php">Click to continue</a></button>
    </body>
</html>

<?php
require_once "History.php";

$instance = History::getHistory();
for ($i = 0; $i < 5; $i++) {
    $instance->incIdx();
}
$value = $instance->getIdx();
?>
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Test Static</title>
    </head>
    <body>
        <h1>In test.php</h1>
        <h2>Current idx = "<?php echo $value; ?>"</h2>
    </body>
</html>```

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