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    <p>You seem to have a basic OOP problem at hand. Here's some questions that may lead you in the right direction.</p> <p><strong>How many instances of each class do you need for your program?</strong></p> <p>This depends on what problem you are trying to solve, so only you can give the proper answer.</p> <ol> <li><p>If you need exactly one instance of both classes, then make them <a href="http://en.wikipedia.org/wiki/Singleton_pattern" rel="nofollow">singleton</a> and both will have access to each other, by simply retrieving the singleton instance.</p></li> <li><p>If you need, say, one display instance and multiple job instances, you will want to store the <code>Job</code> instances in a container to which the one <code>Display</code> instance has access. You will want to make the <code>Display</code> a <a href="http://en.wikipedia.org/wiki/Singleton_pattern" rel="nofollow">singleton</a> so that it can be accessed at will.</p></li> <li><p>If you need several instances of both, then you will need to explicitly <em>associate</em> those which need to work together, by passing an already created object to the constructor of the other.</p></li> </ol> <p>Think of this:</p> <pre><code>Display d1, d2; Job j1(&amp;d1), j2(&amp;d2); // make sure not to copy the displays! </code></pre> <p>and in the <code>Job</code> constructor:</p> <pre><code>Job(Display *display): display(display) { display-&gt;setJob(this); } </code></pre> <p>If there need to be multiple displays per job, you will have to replace the single <code>display</code> pointer in Job with a collection of <code>Display</code> pointers and manually add the appropriate displays to that collection.</p> <hr> <p>If this doesn't help, you will need to explain to us what problem you are solving, and we may help further.</p>
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    1. POC++ New Objects with Mulitple Classes
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    1. CO"If you need exactly one instance" is a _bad_ reason to use singleton. A singleton is just another way to have a global variable and should be avoided for the same reason. If you only need one instance of a class then only make one instance, don't hard code that into the class.
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    2. COIn a very simple use-case, I would agree. But not knowing the OP's code and problem, how will he make sure he doesn't instantiate the object accidentally? As soon as you introduce a lazy-init factory function (`friend` of class or static member) for initializing the global variable, it's become a singleton pattern, more or less.
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    3. COIn more complicated cases it's even more important to avoid singletons, just like a global variable isn't so bad in a small program. In this case I think Remy Lebeau has it right: Make one Display at the top level, and pass the objects that need to know about each other around.
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