What is the difference between hook_menu(), hook_menu_alter(), and hook_menu_link_alter()?

Question

So, I am fairly new to Drupal (about 8 months in) and I am using Profile2 with 3 different profile types. Everything is working excellent, except for I wish I could wrap my head around how I can override the Profile2 view button when you click on, let's say Main Profile. So, if you are familiar with profile2, you know that it comes with a default profile as soon as it's activated, and when you click on it within the User Menu, you are presented with a screen with the local menu tabs called View, and Edit.

All I want to do is keep the View button, but change the path to either a panel page or an actual Views page.

I've explored hook_menu(), hook_menu_alter(), hook_menu_link_alter(), and to tell you the truth, I just don't get how those work. I believe hook_menu actually adds new "nodes" or paths to the system with their own page?

I think I have a lot to learn when it comes to these three functions (hook_menu(), hook_menu_alter(), and hook_menu_link_alter()) I just need a savior to explain these to me.

As a sub question, along with the View, and Edit button, how would I go about adding an extra local menu button to this row? Like upgrade my account, or view your bill?

Any light would be appreciated, and I do have the Devel module installed, as well as the theme developer tool. I tried making a custom module, and running a DPM on those functions above, but it's not even outputting anything.

Answer 1

hook_menu() -> Define menu items and page callbacks.

hook_menu_alter() -> Alter the data being saved to the {menu_router} table after hook_menu is invoked.

hook_menu_link_alter() -> Alter the data being saved to the {menu_links} table

Answer 2

To get result from those functions you will have to clear your caches. Use the admin_menu module which has a direct link for clearing caches.

There are a lot of examples available on how to use hook_menu. This is a comprehensive step step example: How should I implement hook_menu()? or another example on how to create tabs: create tabs with hook_menu() for custom module

Answer 3

I was investigating this more and finally came to a solution on how to add a local task menu to a profile2 page. It's kind of dirty, but it will do for now.

I basically added this to my site's glue module to modify the local task items.

function ch_glue_menu_local_tasks_alter(&$data, $router_item, $root_path) {
global $user;

foreach($user->roles as $k=>$v){
    if(preg_match('/paid1|paid2|paid3/i', $v)){
        $is_paid_member = true;
    }
}

if(preg_match('/profile/i', $root_path) && !$is_paid_member){
        // Add a tab linking to node/add to all pages.
        $data['tabs'][0]['output'][] = array(
            '#theme' => 'menu_local_task',
            '#link' => array(
                'title' => t('Upgrade Account'),
                'href' => 'node/3',
                'localized_options' => array(
                    'attributes' => array(
                        'title' => t('Add new content'),
                    ),
                ),
            ),
        );
}
}

Thanks for explaining the menu functions, but it seems like I have A LOT to learn when it comes to the drupal menu system. I'm just glad this will work for right now.