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PHP中许多预定义的变量都是“超全局的”，这意味着他们在一个脚本的全部作用域中都可用。在函数或方法中无需执行global $variable;也可以访问他们

这些超全局变量为:

.GLOBALS
._SERVER
._REQUEST
._POST
._GET
._FILES
._ENV
._COOKIE
._SESSION

1.$GLOBALS-引用全局作用域中可用的全部变量

$GLOBALS这种全局变量用于在PHP脚本中的任意位置访问全局变量 PHP在名为$ GLOBALS[index]的数组中存储了所有全局变量。变量的名字就是数组的键

实例如下

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
</head>
<body>
<?php
    $x = 2;
    $y = 3;

    function addition()
    {
        $GLOBALS['z'] = $GLOBALS['x'] + $GLOBALS['y'];
    }
    addition();
    echo $z;
?>
</body>
</html>

2.$GLOBALS-引用全局作用域中可用的全部变量

$_SERVER这种超全局变量保存关于报头，路劲和脚本位置信息

展示如何使用$_SERVER中的某些值

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
</head>
<body>
<?php
    echo $_SERVER['PHP_SELF'];
    echo "<br>";
    echo $_SERVER['SERVER_NAME'];
    echo "<br>";
    echo $_SERVER['HTTP_HOST'];
    echo "<br>";
    echo $_SERVER['HTTP_REFERER'];
    echo "<br>";
    echo $_SERVER['HTTP_USER_AGENT'];
    echo "<br>";
    echo $_SERVER['SCRIPT_NAME'];

?>
</body>
</html>

3.$_REQUEST-收集HTML表单提交数据

简单实例

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
</head>
<body>

<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
    Name:<input type="text" name="fname">
    <input type="submit">
</form>

<?php
    $name = $_REQUEST['fname'];
    echo $name;
?>
</body>
</html>

4.$_POST-获取表单数据

如下实例中，当用户点击提交之后，表单数据会被发送到标签的action属性中指定的文件中

实例如下

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
</head>
<body>

<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
    Name:<input type="text" name="fname">
    <input type="submit">
</form>

<?php
    $name = $_POST['fname'];
    echo $name;
?>
</body>
</html>

5.$_GET-提交表单数据

带超链接

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <a href="one.php?name1=苗帅&name2=jesse">点我</a>
</body>
</html>

获取页面

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
</head>
<body>

<?php
    echo $_GET['name1'] . " is " . $_GET['name2'];
?>
</body>
</html>