composer 自动载入的问题 ?报错

最近开始学习composer的自动加载, 做了一个小例子。

目录结构：

index.php

include "./vendor/autoload.php";
\core\Bootstrap::run();

composer.json

{
    "name": "manbudezhu/demo",
    "description": "composer test",
    "type": "project",
    "require": {},
    "license": "yxg",
    "authors": [
        {
            "name": "xiaog",
            "email": "manbudezhu@163.com"
        }
    ],
    "autoload":{
        "files":["core/functions.php"],
        "psr-4":{
            "core\\":"core",
            "web\\":"web"
        }
    }

}

bootstrap.php

namespace core;
class Bootstrap{
	public static function run(){
		self::parseUrl();
	}

	public static function parseUrl(){
		echo 'abcd';
		\dd('abc');
	}
}

functions.php

	function dd($data){
		echo "<pre>".print_r($data,true)."</pre>";		
	}

bootstrap.php中的\dd('abc');语句报错,提示: Call to undefined function dd().我哪块有问题了,为啥functions.php的dd函数没有被载入.
还有composer的自动载入本地的文件,需不需要网络支持了?