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零基础学习PHP篇变量声明赋值超全局变量获取记录等

智云科技发布于 2022年8月19日评论(37)阅读(505)

变量

1.变量声明

变量以美元符 $ 开头，然后是变量名;

变量名由字母或下划线开头，由字母，下划线，数字组成;

变量名区分大小写;

php 是弱类型的语言，不需要事先声明变量的数据类型;

php可以不用显示的声明变量就直接使用，不过好的编码习惯：所有的变量在使用前应该进行声明;

例： $age = 25;

$color = ‘red’;

$sum = 12 + “15”; // $sum = 27 (“//” 为注释的意思)

2.变量赋值

(1). 值赋值：就是将赋值表达式的值复制到变量;

(2). 引用赋值：php4引入了引用赋值功能，创建的变量与另一个变量引用的内容相同。

例：

$val_1 = ‘hello’;

$val_2 = &$val_1; //把$val_1的内存空间地址赋值给$val_2，是同一个变量

$val_2 = ‘goodbye’;

$var_1 = ‘goodbye’;

3.变量的变量

$val_1 = ‘hello’;

$$val_1 = ‘world’;

echo $hello;

echo $val_1;

echo ${$val_1};

2.PHP的超 全局变量

php提供了很多有用的预定义变量，用于提供大量与环境有关的信息。

(1). $_SERVER 服务器变量

该全局变量包含着服务器和客户端配置及当前请求环境的有关信息

$_SERVER[‘SERVER_NAME’]; : 当前运行脚本所在的服务器的主机名

$_SERVER[‘REMOTE_ADDR’]: 客户端IP地址

$_SERVER[‘REQUEST_URI’]: URL的路径部份

$_SERVER[‘HTTP_USER_AGENT’] : 操作系统和浏览器的有关信息

(2). $_GET

该变量包含使用 GET 方法传递的参数的有关信息;

例：

url:

$id = $_GET[‘id’];

$page = $_GET[‘page’];

(3). $_POST

该变量包含使用 POST 方法传递的参数的有关信息;

例：html:

<form name=”reg” action=”test.php” method=”post”>

用户名：<input type=”text” name=”username” />

密码: <input type=”password” name=”passwd”/>

<input type=”submit” value=”提交” />

</form>

php部分:

$username = $_POST[‘username’];

$passwd = $_POST[‘passwd’];

(4). $_REQUEST

该变量记录着通过各种输入方法传递给脚本的变量，如GET POST,但不要用这个超级全局变量，因为它不安全而且速度比较慢;

(5). $_COOKIE cookie变量数组

(6). $_SESSION 会话变量数组

(7). $_FILES 与上传文件有关的变量数组

(8). $_ENV 环境变量 数组

(9). $GLOBALS 所有全局变量数组

下一节将讲到常量、数据类型等。

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文章来源：智云一二三科技

文章标题：零基础学习PHP篇变量声明赋值超全局变量获取记录等

文章地址：https://www.zhihuclub.com/79843.shtml

关于作者: 智云科技

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