PHP函数的范围 [英] Scope of PHP function

问题描述

我有一个文件将我的可重用函数集成到一个文件中（ functions.php ）。它在每个需要它的页面上都是 include_once（）'d。当我的自定义函数试图访问自己范围之外的MySQL连接时，出现错误。源代码有点像这样：

 <？php 
 // functions.php 
 $ connect = mysql_connect（localhost，user，pass）或死（MySQL说：.mysql_error（））; 
 mysql_select_db（database，$ connect）或死（MySQL说：.mysql_error（））; //没有错误
 
 / * ... * / 
 
函数getmotd（$ user）{
 $ query =SELECT cid FROM`users` 
 WHERE id =。$ user; 
 $ query = mysql_query（$ query，$ connect）; //错误发生在这里，$ connect不是一个有效的MySQL链接资源
 / * ... * / 
} 
？> 
  

为什么我的函数访问变量不能在其范围之上声明？我可以通过在函数中复制 $ connect 的声明来获得成功的连接。

解决方案

使用 global 关键字。

示例

 函数getmotd（$ user）{
 global $连接; 
 $ query =SELECT cid FROM`users` 
 WHERE id =。$ user; 
 $ query = mysql_query（$ query，$ connect）; //错误发生在这里，$ connect不是有效的MySQL链接资源
 / * ... * / 
} 
  

你也可以这样做

 函数getmotd（$ user）{
 $ query =SELECT cid FROM`users` 
 WHERE id =。$ user; 
 $ query = mysql_query（$ query，$ GLOBALS ['connect']）; //错误发生在这里，$ connect不是有效的MySQL链接资源
 / * ... * / 
} 
  

如果您想制作可重复使用的代码，那么使用OOP可能会更好。为数据库创建一个类，然后为数据库信息添加一些属性，并使用 this 关键字从函数中访问它们。

I have a file that corrals my re-usable functions into one file (functions.php). It's include_once()'d on every page that needs it. I'm getting an error when my custom functions are trying to access a MySQL connection outside their own scope. The source is a bit like this:

<?php
    // functions.php
    $connect = mysql_connect("localhost", "user", "pass") or die("MySQL said: ".mysql_error());
    mysql_select_db("database", $connect) or die("MySQL said: ".mysql_error()); // no error

    /* ... */

    function getmotd($user) {           
        $query = "SELECT cid FROM `users`
        WHERE id = ".$user;
        $query = mysql_query($query, $connect); // error occurs here, $connect is not a valid MySQL link-resource
        /* ... */
    }
?>

Why can't my function access variables declared above it's scope? I can get a successful connection by reproducing $connect's declaration within the function.

Any insight into how I can work around this or what I'm doing wrong here?

解决方案

Use the global keyword.

Example

function getmotd($user) {  
     global $connect;
    $query = "SELECT cid FROM `users`
    WHERE id = ".$user;
    $query = mysql_query($query, $connect); // error occurs here, $connect is not a valid MySQL link-resource
    /* ... */
}

You can also do it like this

function getmotd($user) {  
    $query = "SELECT cid FROM `users`
    WHERE id = ".$user;
    $query = mysql_query($query, $GLOBALS['connect']); // error occurs here, $connect is not a valid MySQL link-resource
    /* ... */
}

If you want to make re-usable codes, you'd probably be better off with OOP. Create a class for the database, and add some properties for the database info, and access them from the functions by using the this keyword.

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