PHP学习笔记--有关php中的变量_PHP教程

php中文网

发布时间：2016-07-20 11:13:48

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来源于php中文网

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PHP中的可变变量(更多请自行参考php手册):

　　php中的可变变量说白了，就是拿一个变量的值解析成一个变量名，去读那个变量名的值。实例：

<?<span php><span> = "China";  <span><span>
    <span> = "a";       <span><span>
    <span> = "I'm Chinese !"; <span><span>
    <span> = "b";  <span><span>
    
    <span echo> <span>."<br />";  <span><span china>
    <span echo> $<span>."<br />"; <span><span i chinese>
    <span> = "f";  <span><span>
    <span echo> $<span>."<br />"; <span><span b>
    <span> = "b"; <span><span>
    <span echo> $<span>."<br /><br />"; <span><span a>
    
    <span echo> <span>."<br />"; <span><span a>
    <span echo> $<span>."<br />"; <span><span b>
    <span echo> $$<span>."<br /><br />"; <span><span a>
    
    <span echo> <span>."<br />"; <span><span b>
    <span echo> $<span>."<br />"; <span><span a>
    <span echo> $$<span>."<br />"; <span><span b>
    <span echo> $$$<span>."<br /><br />"; <span><span a>
<span><span> = "China"; <span><span>
    <span echo> <span>."<br />"; <span><span china>
    <span echo> $<span>; <span><span i chinese>
?></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>

注意：可变变量不能应用于$this和超全局变量 (php变量的作用域和其他高级编程语言有所不同。看代码)

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<?<span php><span> = 'man'<span><span> = 'abc'; <span><span>
    $$<span> = 'def'<span><span echo> <span>."<br />"; <span><span>
    <span echo> <span>; <span><span>
    
    <span echo> "<br /> <hr />"<span><span function><span show><span global> <span>; <span><span>
        <span echo> <span>."<br />";  <span><span>
<span><span function><span showtwo><span><span global>
        <span echo> <span>['name']; <span><span>
<span show showtwo>?></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>

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变量函数:

<?<span php><span function><span b><span echo> "这是B"<span><span function> c(<span> = "China") <span><span>
<span><span echo> "这是<span>"<span><span> = 'b'<span><span>(); <span><span>
         <span> = 'c'<span><span><span></span> </span>?></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>

可变变量的一个典型应用:

<!DOCTYPE html <span public> "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head>

<body>
    
    <div>
        <form action="#" method="post">
            <label>name: </label>
            <input type="text" name="name" /><br />
            <label>pwd : </label>
            <input type="text" name="pwd" /><br />
            <label>tag : </label>
            <input type="text" name="tag" /><br />
            <input type="submit" value="提交" />
        </form>
    </div>
    <?<span php><span foreach>(<span> <span as> <span>=><span><span><span><span print_r>
            $<span> = <span><span><span><span extract>
        <span echo> <span>."<br />"<span><span echo> <span>."<br />"<span><span echo> <span>."<br />"<span>?>
</body>
</html></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>

　　补充：

　　变量的特性。如果一个变量事先没有声明，那么如果你要对一个变量赋值，此时PHP在后台的一个操作就是，当你给这个未声明的变量进行赋值时，后台就已经帮你申明了这个变量了。直接看例子：

<?<span php><span class><span a><span public> <span function><span show><span><span>
        <span echo> (<span isset>(<span>->name)?"true":"false")." -- "<span><span echo> <span>-><span name><span> = <span new> A(); <span><span>
<span>->show();  <span><span>
<span>->name = "我有输出了。这个变量被声明了!"<span><span echo> "<br />"<span><span>->show(); <span><span>
?></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>

小结：看了上面的示例后，你们以后再看到别人封装的代码里，如果有那种没有声明变量就直接用的，不要感到奇怪。那是叫你自己去设置呢。你直接赋值用就行了。。。（PS：其实本人一开始也感到迷糊，因为以前在搞.NET的在C#里是绝对不会允许这种情况发生的。强型语言用惯了。。。在看这种弱类型的语言，确实一开始不会很适应）