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    <p>In "place1", you need a reference. <code>Object1</code> isn't fully defined, so you can't take it by value. That said, you wouldn't want to pass by value; when you take the address of it, you'd be getting the address of the copy, not the actual object.</p> <p>Since you only want a pointer to a <code>BaseClass</code>, it might make more sense to only place that restriction on the parameter. (Of course, if you really need an <code>Object1</code>, reflect that in the type of <code>link</code>: <code>Object1* link;</code>).</p> <p>Also consider using an initialization list:</p> <pre><code>Object1(int a) : i(a), link(0) /* &lt;- important! */ { } Object1(int a, BaseClass&amp; o) : i(a), link(&amp;o) { } </code></pre> <p>Always use an initialize list.</p> <p>"place2" creates an unnamed instance of <code>Object1</code> using a constructor. It has <strike>no storage(?)</strike> <code>auto</code> storage, and <a href="https://stackoverflow.com/questions/2298781/why-do-un-named-c-objects-destruct-before-the-scope-block-ends/2298796"><em>dies at the end of the expression</em></a>.</p> <p>That is, once you've hit the semicolon in <code>Object1 a(1, /*place2*/ Object1(2));</code>, it ceases to exist and you have a pointer to an non-existent object! This results in undefined behavior.</p> <p>Give it a lifetime beyond the expression:</p> <pre><code>Object1 x(2); Object1 a(1, x); </code></pre> <p>Always make sure that when you refer an object, it will live the entire time you refer to it.</p> <hr> <p>Your new compile error is because you can't have a reference to a temporary variable. You <em>can</em> have one with a const-reference, though. The thing is, your pointer needs to point to a <code>const BaseClass</code> now, which may dampen what you want.</p> <p>Again, your design needs reworking, unfortunately. </p>
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    1. POC++ syntax of constructors " 'Object1 a (1, Object1(2))''
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    1. COI can change code before place1 to BaseClass. Will it help me?
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    2. CO@osgx: That would work too, and is probably preferred. since you only need a pointer to a `BaseClass`, may as well take a reference to one. (Not by value! You'll slice it. http://en.wikipedia.org/wiki/Object_slicing)
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    3. COYou can't pass it by value no matter what type you decide to use, because then you'll store the address of the copy, which is certainly not what is desired.
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      1. USDennis Zickefoose
 

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