( ! ) Fatal error: Cannot redeclare class Google_OAuth2 - php

Question

I want sign up with google plus in codeigniter. I have include files which are required for the php script but I'm getting error
(( ! ) Fatal error: Cannot redeclare class Google_OAuth2 in
D:\wamp\www\Surecash_back\application\libraries\google-plus-api-client-master\src\auth\Google_OAuth2.php
on line 453)

Answer 1

The error message tells you a very simple thing:
You are trying to load\include the same class file more then once
(which results in re-declaring a class name of an already declared class).
The fastest way to check this, will be:
If you are using an autoloader - check your autoloader folder tree for the existance of a file named Google_OAuth2.php
Run a project-wide (all files in your project) search for the string "Google_OAuth2.php" and another search for "class Google_OAuth2", look for any duplicate include(), include_once() or require_once().
(in phpStorm you click Cmd+Shift+F to open the path search, and in the options tab select "Whole project" in Scope.)
See where and if you are including\requiring\autoloading the Google_OAuth2 class file more then one time.
Finally, remove the duplicate.
Hope it helps a bit!