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    <p>Since <code>std::vector</code> are dynamically sized, they can't possibly stores their elements as members or as a member array. Remember that the size of an object is known at compile-time.</p> <p>Even then, there is <em>still</em> something to be said about not using pointer members. Consider this type:</p> <pre><code>struct fat { array&lt;double, 30&gt; data; array&lt;long, 30&gt; more_data; array&lt;char, 30&gt; too_much_data; }; </code></pre> <p>where <code>array</code> can be <code>std::array</code>, <code>std::tr1::array</code> or <code>boost::array</code>; it's here just used as a stand-in for a large type. You are correct that <code>fat</code> objects will be, well, large. Changing the members to pointers (or dynamic arrays or any kind of moral equivalent) is still premature: first use the objects as-is, and then if it's too big or otherwise problematic you can dynamically allocate <em>them</em> instead of the members:</p> <pre><code>fat* so_much_stuff = new fat[30](); // Better: std::vector&lt;fat&gt; get_rid_of_it_already(30); </code></pre> <p>Value semantics just make things easier; it's only until it's too much copying or size or whatever (measure first) <em>but not before</em> that you should use (dynamic) containers and smart pointers (that themselves follow value semantics).</p> <p><strong>EDIT</strong></p> <p><code>std::vector</code> is not 'bad' in general (as a member or not), see the discussion with Tony in the comments.</p>
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    1. POUsage of objects or pointers to objects as class members and memory allocation
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    1. USLuc Danton
    1. USLuc Danton
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    1. CONice that you've been thinking about this and write well, but your reasoning is flawed by 2 oversights: 1) dynamic allocation using `vector<>` has the compelling benefit of resizing and continuing to run, whereas compile-time array sizing wastes memory when there are fewer elements, then fails totally. 2) `vector` *does* have value semantics (that C++ lets you create user-defined types with value semantics is a critical and very deliberate language feature), and `vector`s are therefore automatically handled properly by default-generated destructors and copy constructors.
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      1. USTony Delroy
    2. CO@Tony You are correct, I am not advocating using `std::array` over `std::array`. I am advising against prematurely using `std::vector` over `std::array` *as a member* solely on the grounds that it would make a leaner object. Choosing between `std::array` or `std::vector` (as a member or not) is another discussion altogether, and you already provided some arguments on the subject.
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      1. USLuc Danton
    3. CO@Luc: if your "leaner object" caveat is warning that say a `vector` with size N will not be as "lean" as an array of size N that's certainly true, but vectors definitely come into their own when the populated size is significantly less than the capacity N, and in resizing beyond the current capacity on demand. `vector`s value semantics make them well-behaved members, and they should be selected in preference to arrays in general use. Using `array` habitually would be the "premature" choice, as it's normally hard to choose a good capacity. I'm still not sure if you're agreeing or not? :-)
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