Using functions from a plugin in your theme

I am a beginner to wordpress (and to php for that matter).

I am trying to understand some of the basics, and building a little e-commerce store using a plugin called “Jigoshop.”

I’m reading through the source files and seeing a bunch of useful functions- things like a “is_featured” function that returns true if the product has a product meta that marks it as featured; or a reference to all products that I can use without having to set up my own by querying the posts and filtering out those that are not products.

I have a custom-template file that I am using for the storefront (homepage), and I would like to access some of these functions to simplify the code I have to write, but it seems I don’t have access to them.

My questions is:

Are functions and objects defined in a plugin useable in my theme templates (or custom templates; I’m using a child theme right now)?

Yes, you can use functions from plugins in your theme. Please use the function_exists() function to make sure that the function does exit. I used the Breadcrumbs Plus in one of the themes like this:

<?php
if (function_exists('breadcrumbs_plus'))
{
    $breadcrumb_options = array(
            'prefix' => '<div id="breadcrumb">',
            'suffix' => '</div>',
            'title' => 'Du er her: ',
            'home' => 'Forside',
            'sep' => "https://wordpress.stackexchange.com/",
            'front_page' => false,
            'bold' => false,
            'blog' => __('Blog', 'rev'),
            'echo' => true
    );

    breadcrumbs_plus($breadcrumb_options);
}
?>