class member function in function?

So i have this class that includes some custom functions named class.php I have another file called config.php that includes

require('engine.class.php');
$engine = new engine;

config.php also requires 开发者_运维知识库functions.php to run like:

require('functions.php');

i have a function in functions.php that uses $engine eg:

function login($username, $password){
    return $engine->mysql_query('SELECT `user_id` WH...', 'array);//this is custom function in class.php
}

but when i run the page that reuires config.php i get some error like:

Fatal error: Call to a member function mysql_query() on a non-object in ../somedir/functions.php on line 3

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Global variables are indisputably evil. Any one who tells you to use them does not have scope experience in dealing w/ code that uses them. Unfortunately, there are far more PHP coders using globals than any other language, in my experience, largely due to ignorance.

Virtually every class should be self-consistent, meaning that it shouldn't matter how many times you substantiate it into an object via new. The only exception is the Singleton pattern, but real-world instances where singletons are desirable are so rare that virtually every use of those is also an uncalled design flaw that just tightly couples code, which is also a very bad thing.

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PHP caches DB connections, so you can have an unlimited mysql_connect()s in the same program and it will only connect once per page load (unless you manually close it). So remove the $engine from your config.php immediately and rewrite all your code to this:

function login($username, $password)
{
    $engine = new Engine;
    //this is custom function in class.php
    return $engine->mysql_query('SELECT `user_id` WH...', 'array);
}

I'll happily elucidate more, if you need it.

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You will need to refer to Variables scope. As you cannot access $engine without it being global or defining / declaring it (singleton design pattern comes to mind) inside the function.

EDIT

You could also pass it as a parameter to the function (previously forgot to mention this).