User permission - triggering code on user role (Wordpress)

I'm developing a custom plugin in PHP so existing plugins are not usable. What I want to achieve is that I want to display different url within a post for some users . For users that are registered in wordpress, contacted me and are 'approved'. I want to set up this extra user profile field so I can use this field in a condition. So guests and users without this 开发者_开发知识库field or without the right value in this field will get url1 but the other ones url2.

requirements

• only users with admin role
• can create/edit extra user profile field
• for all other users

I know how I can add extra user profile field in Wordpress (see the links below), but I don't know how to restrict editing that field to users in a given role and how user with admin role can create/edit this filed for all users. It seems to me that I have to add new code under wordpress dashboard/users/new user and/or dashboard/users/authors & users.

I did some google search and found few sites on how to add extra user profile field

• Adding and using custom user profile fields
• User Contact Fields in WordPress 2.9
• Add Data to User Field in WordPress

It seems to me that Adding and using custom user profile fields is almost what I want to do but I still do not know how to manage the "only admin' can do that.

How about this:

$ID="2";
$user = new WP_User($ID);
if ($user->wp_capabilities['administrator']==1) {
    //code here
}

see this link about user capabilities for wordpress

So with the above, and that link you gave, maybe something like this:

function my_show_extra_profile_fields( $user ) {
    if ($user->wp_capabilities['administrator']!=1) {
        return false;
    } ?>
    <h3>Extra profile information</h3>

    <table class="form-table">

        <tr>
            <th><label for="twitter">Twitter</label></th>

            <td>
                <input type="text" name="twitter" id="twitter" value="<?php echo esc_attr( get_the_author_meta( 'twitter', $user->ID ) ); ?>" class="regular-text" /><br />
                <span class="description">Please enter your Twitter username.</span>
            </td>
        </tr>

    </table>
<?php }