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  1. PO
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    <p>It's quite simple. Say I have a vector:</p> <pre><code>std::vector&lt;int&gt; vec; </code></pre> <p>I fill it with some data. Then I want to get some iterators to it. Maybe pass them around. Maybe to <code>std::for_each</code>:</p> <pre><code>std::for_each(vec.begin(), vec.end(), SomeFunctor()); </code></pre> <p>In C++03, <code>SomeFunctor</code> was free to be able to <em>modify</em> the parameter it gets. Sure, <code>SomeFunctor</code> could take its parameter by value or by <code>const&amp;</code>, but there's no way to <em>ensure</em> that it does. Not without doing something silly like this:</p> <pre><code>const std::vector&lt;int&gt; &amp;vec_ref = vec; std::for_each(vec_ref.begin(), vec_ref.end(), SomeFunctor()); </code></pre> <p>Now, we introduce <code>cbegin/cend</code>:</p> <pre><code>std::for_each(vec.cbegin(), vec.cend(), SomeFunctor()); </code></pre> <p>Now, we have syntactic assurances that <code>SomeFunctor</code> cannot modify the elements of the vector (without a const-cast, of course). We explicitly get <code>const_iterator</code>s, and therefore <code>SomeFunctor::operator()</code> will be called with <code>const int &amp;</code>. If it takes it's parameters as <code>int &amp;</code>, C++ will issue a compiler error.</p> <hr> <p>C++17 has a more elegant solution to this problem: <a href="http://en.cppreference.com/w/cpp/utility/as_const" rel="noreferrer"><code>std::as_const</code></a>. Well, at least it's elegant when using range-based <code>for</code>:</p> <pre><code>for(auto &amp;item : std::as_const(vec)) </code></pre> <p>This simply returns a <code>const&amp;</code> to the object it is provided. </p>
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    1. POWhat is the reason behind cbegin/cend?
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    1. USNicol Bolas
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    1. POWhat is the reason behind cbegin/cend?
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    1. COI thought the new protocol was cbegin(vec) rather than vec.cbegin().
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      1. USKaz Dragon
    2. CO@Kaz: There are no `std::cbegin/cend` free functions the way that `std::begin/std::end` exist. It was an oversight by the committee. If those functions did exist, that would generally be the way to use them.
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    3. COApparently, `std::cbegin/cend` will be added in C++14. See http://en.cppreference.com/w/cpp/iterator/begin
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      1. USAdi Shavit
 

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