AWS SDK for PHP won't work in multiple directories
===

I have AWS SDK for PHP installed into */usr/share/php/*

When I execute sample files from this directory, it works fine.   

My web root directory is */var/www/*

When I execute sample files from this directory, they do not work.

Here is a sample file */var/www/test_sdk.php*:

    <?php

    require_once 'sdk.class.php';

    $s3 = new AmazonS3();  

    $bucket = 'test_bucket' . time();

    $response = $s3->create_bucket($bucket, AmazonS3::REGION_US_W1, AmazonS3::ACL_PUBLIC);

    if ((int) $response->isOK()) {
    echo 'Created Bucket';
    }else {
    echo (string) $response->body->Message;
    }
    ?> 

I think the problem is in my 'require_once' statement.  I have tried:
 
    "require_once '/usr/share/php/AWSSDKforPHP/sdk.class.php'"

It didn't work

Any help is greatly appreciated!!