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    <p><strong>The risk is deallocating through a pointer to the base class</strong> (<em>delete</em>, <em>delete[]</em>, and potentially other deallocation methods). Since these classes (<em>deque</em>, <em>map</em>, <em>string</em>, etc.) don't have virtual dtors, it's impossible to clean them up properly with only a pointer to those classes:</p> <pre><code>struct BadExample : vector&lt;int&gt; {}; int main() { vector&lt;int&gt;* p = new BadExample(); delete p; // this is Undefined Behavior return 0; } </code></pre> <p>That said, <em>if</em> you're willing to make sure you never accidentally do this, there's little major drawback to inheriting them&mdash;but in some cases that's a big if. Other drawbacks include clashing with implementation specifics and extensions (some of which may not use reserved identifiers) and dealing with bloated interfaces (<em>string</em> in particular). However, inheritance is intended in some cases, as container adapters like <em>stack</em> have a protected member <em>c</em> (the underlying container they adapt), and it's almost only accessible from a derived class instance.</p> <p>Instead of either inheritance or composition, <strong>consider writing free functions</strong> which take either an iterator pair or a container reference, and operate on that. Practically all of &lt;algorithm&gt; is an example of this; and <em>make_heap</em>, <em>pop_heap</em>, and <em>push_heap</em>, in particular, are an example of using free functions instead of a domain-specific container.</p> <p>So, use the container classes for your data types, and still call the free functions for your domain-specific logic. But you can still achieve some modularity using a typedef, which allows you to both simplify declaring them and provides a single point if part of them needs to change:</p> <pre><code>typedef std::deque&lt;int, MyAllocator&gt; Example; // ... Example c (42); example_algorithm(c); example_algorithm2(c.begin() + 5, c.end() - 5); Example::iterator i; // nested types are especially easier </code></pre> <p>Notice the value_type and allocator can change without affecting later code using the typedef, and even the container can change from a <em>deque</em> to a <em>vector</em>.</p>
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