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    <p><code>char_traits</code> is indeed a hopelessly awful wastebin of random traits. Should every string pre-specify the largest supported file size, case-sensitivity, and (ugh) state type of the encoding mechanism itself? NO.</p> <p>However, what you ask is impossible even with well-designed traits. <code>string</code> and <code>wstring</code> are meaningfully different because the size of the internal character type differs. To run any kind of algorithm, you will need to query the object for <code>char_t</code>. That requires RTTI or virtual functions because <code>basic_string</code> doesn't (and shouldn't) maintain that info at runtime.</p> <blockquote> <p>One -possible- solution is to construct each library class as a template that manages the value_type, traits and allocators specified by the user. But that's overkill and makes abstract base classes (interfaces) impossible.</p> </blockquote> <p>This is the only complete solution. Templates actually <em>do</em> play well with abstract base classes: a number of templates can derive from a non-template abstract base, or the base can also be templated. However, it is difficult if not untenable because of the sensitivity and tedium of writing perfectly generic code.</p> <blockquote> <p>Another solution is to just specify one type (e.g. u32string) as default, every user must pass data using this type. But now think about a project which uses 3 libraries, and the first lib uses u32string, the second lib u16string and the thirth lib wstring -> HELL.</p> </blockquote> <p>This is why I'm scared by C++11's "improved" Unicode support. It simplifies direct interaction with file data and discourages abstraction to a <em>common</em> <code>wchar_t</code> internal format. It would have been better to require specific codecvts for UTF-16 and UTF-32 and specify that <code>wchar_t</code> must be at least 21 bits. Whereas before there were only "dumb" <code>char</code> and "smart" <code>wchar_t</code> libraries among clean C++ interfaces, we may have to contend with additional widths — and <code>char16_t</code> is just an instant red flag.</p> <p>But, that's down the road.</p> <p>If you really end up using a number of incompatible libraries, and the problem is shuttling data between functions requiring different formats, then write a <a href="http://drdobbs.com/cpp/184403758" rel="nofollow">ScopeGuard-style</a> utility to convert from and back to your chosen common format, such as <code>wstring</code>. This utility can be a template with an explicit specialization for each incompatible format you need, or a non-templated set of classes.</p>
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