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    <p><strong>Shared ownership:</strong><br> The <code>shared_ptr</code> and <code>weak_ptr</code> the standard adopted are pretty much the same as their <a href="http://www.boost.org/doc/libs/1_49_0/libs/smart_ptr/shared_ptr.htm" rel="noreferrer">Boost counterparts</a>. Use them when you need to share a resource and don't know which one will be the last to be alive. Use <code>weak_ptr</code> to observe the shared resource without influencing its lifetime, not to break cycles. Cycles with <code>shared_ptr</code> shouldn't normally happen - two resources can't own each other.</p> <p>Note that Boost additionally offers <a href="http://www.boost.org/doc/libs/1_49_0/libs/smart_ptr/shared_array.htm" rel="noreferrer"><code>shared_array</code></a>, which might be a suitable alternative to <code>shared_ptr&lt;std::vector&lt;T&gt; const&gt;</code>.</p> <p>Next, Boost offers <a href="http://www.boost.org/doc/libs/1_49_0/libs/smart_ptr/intrusive_ptr.html" rel="noreferrer"><code>intrusive_ptr</code></a>, which are a lightweight solution if your resource offers reference-counted management already and you want to adopt it to the RAII principle. This one was not adopted by the standard.</p> <p><strong>Unique ownership:</strong><br> Boost also has a <a href="http://www.boost.org/doc/libs/1_49_0/libs/smart_ptr/scoped_ptr.htm" rel="noreferrer"><code>scoped_ptr</code></a>, which is not copyable and for which you can not specify a deleter. <code>std::unique_ptr</code> is <code>boost::scoped_ptr</code> on steroids and should be your <strong>default choice when you need a smart pointer</strong>. It allows you to specify a deleter in its template arguments and is <em>movable</em>, unlike <code>boost::scoped_ptr</code>. It is also fully usable in STL containers as long as you don't use operations that need copyable types (obviously).</p> <p>Note again, that Boost has an array version: <a href="http://www.boost.org/doc/libs/1_49_0/libs/smart_ptr/scoped_array.htm" rel="noreferrer"><code>scoped_array</code></a>, which the standard unified by requiring <code>std::unique_ptr&lt;T[]&gt;</code> partial specialization that will <code>delete[]</code> the pointer instead of <code>delete</code>ing it (with the <code>default_delete</code>r). <code>std::unique_ptr&lt;T[]&gt;</code> also offers <code>operator[]</code> instead of <code>operator*</code> and <code>operator-&gt;</code>.</p> <p>Note that <code>std::auto_ptr</code> is still in the standard, but it is <em>deprecated</em>. <code>§D.10 [depr.auto.ptr]</code></p> <blockquote> <p>The class template <code>auto_ptr</code> is deprecated. [ <em>Note:</em> The class template <code>unique_ptr</code> (20.7.1) provides a better solution. <em>—end note</em> ]</p> </blockquote> <p><strong>No ownership:</strong><br> Use dumb pointers (raw pointers) or references for <strong>non-owning references</strong> to resources and when you know that the <strong>resource will outlive</strong> the referencing object / scope. Prefer references and use raw pointers when you need either nullability or resettability.</p> <p>If you want a non-owning reference to a resource, but you don't know if the resource will outlive the object that references it, pack the resource in a <code>shared_ptr</code> and use a <code>weak_ptr</code> - you can test if the parent <code>shared_ptr</code> is alive with <code>lock</code>, which will return a <code>shared_ptr</code> that is non-null if the resource still exists. If want to test whether the resource is dead, use <code>expired</code>. The two may sound similar, but are very different in the face of concurrent execution, as <code>expired</code> only guarantees its return value for that single statement. A seemingly innocent test like</p> <pre><code>if(!wptr.expired()) something_assuming_the_resource_is_still_alive(); </code></pre> <p>is a potential race condition.</p>
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    1. POWhich kind of pointer do I use when?
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    1. COIn the case of no ownership, you should probably prefer references to pointers unless you need no ownership *and* resettability where references won't cut it, even then you might want to consider rewriting the original object to be a `shared_ptr` and the non owning pointer to be a `weak_ptr`...
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      1. USDavid Rodríguez - dribeas
    2. CO@Davig: References to pointers are not a good idea. What if they don't get set through the actual owning ptr but through a local or parameter to a function?
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    3. COI did not mean *reference to pointer*, but rather reference *instead of* pointer. If there is no ownership, unless you need resettability (or nullability, but nullability without being able to reset would be quite limited) you can use a plain reference rather than a pointer in the first place.
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      1. USDavid Rodríguez - dribeas
 

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