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POC++ Decorate basic_stream::underflow()
 

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  1. POC++ Decorate basic_stream::underflow()
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    <p>I want to extend the behavior of a basic_streambuf object by using the decorator pattern. That`s what I currently got:</p> <pre><code>template&lt;typename char_type, class traits_type&gt; class forwarding_basic_streambuf : boost::noncopyable, public std::basic_streambuf&lt;char_type, traits_type&gt; { public: typedef std::basic_streambuf&lt;char_type, traits_type&gt; forwarded_type; forwarding_basic_streambuf(forwarded_type&amp; fwd_buf) : m_fwd(&amp;fwd_buf) { } virtual ~forwarding_basic_streambuf() { } // locales: // std::locale pubimbue(std::locale const&amp; loc); // =&gt; Calls: imbue(loc) | Returns: Previous value of getloc(); // std::locale getloc () const; // =&gt; Returns: If pubimbue() has ever been called, then the last value of loc supplied, otherwise the // current global locale, locale(), in effect at the time of construction. If called after // pubimbue() has been called but before pubimbue has returned (i.e., from within the call // of imbue()) then it returns the previous value. // buffer management and positioning: // forwarded_type* pubsetbuf (char_type* s, std::streamsize n); =&gt; Returns: setbuf(s, n) // pos_type pubseekoff(off_type off, std::ios_base::seekdir way, // std::ios_base::openmode which = std::ios_base::in | std::ios_base::out); // =&gt; Returns seekoff(off, way, which) // pos_type pubseekpos(pos_type sp, // std::ios_base::openmode which = std::ios_base::in | std::ios_base::out); // =&gt; Returns: seekpos(sp, which) // int pubsync (); =&gt; Returns: sync() // get and put areas: // get area: // std::streamsize sgetn (char_type* s, std::streamsize n); =&gt; Returns: xsgetn(s, n) // put area: // std::streamsize sputn(char_type const* s, std::streamsize n); =&gt; Returns: xsputn(s, n) protected: // virtual functions: // locales: virtual void imbue(std::locale const&amp; loc) { this-&gt;m_fwd-&gt;pubimbue(loc); } // buffer management and positioning: virtual forwarded_type* setbuf (char_type* s, std::streamsize n) { return this-&gt;m_fwd-&gt;pubsetbuf(s, n); } virtual pos_type seekoff(off_type off, std::ios_base::seekdir way, std::ios_base::openmode which = std::ios_base::in | std::ios_base::out) { return this-&gt;m_fwd-&gt;pubseekoff(off, way); } virtual pos_type seekpos(pos_type sp, std::ios_base::openmode which = std::ios_base::in | std::ios_base::out) { return this-&gt;m_fwd-&gt;pubseekpos(sp, which); } virtual int sync () { return this-&gt;m_fwd-&gt;pubsync(); } // get and put areas: // get area: virtual std::streamsize xsgetn(char_type* s, std::streamsize n) { return this-&gt;m_fwd-&gt;sgetn(s, n); } virtual int_type uflow() { if (traits_type::eq_int_type(this-&gt;underflow(), traits_type::eof())) return traits_type::eof(); return this-&gt;m_fwd-&gt;sgetc(); } // put area: virtual std::streamsize xsputn (char_type const* s, std::streamsize n) { return this-&gt;m_fwd-&gt;sputn(s, n); } virtual int_type overflow(int_type c = traits_type::eof()) { if (traits_type::eq_int_type(c, traits_type::eof())) return traits_type::not_eof(c); return this-&gt;m_fwd-&gt;sputc(traits_type::to_char_type(c)); } private: forwarded_type* m_fwd; }; </code></pre> <p>The basic goal (as a first step) would be to simply forward each functionality to the decorated object. Thus, it should be possible to use this decorater even with a pointer to it`s base class.</p> <p>That all works fine for writing methods, but I don`t know how to deal with the underflow() function, which is called from uflow() and sgetc().</p>
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    1. COWhy don't you just forwarding the virtual functions to the forwarded type, why re-implement them? There's no point in hiding the base class versions of the non-virtual functions as they won't be use by anyone using a pointer or reference to your base class: `std::basic_streambuf`.
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    2. CO@Charles Bailes - Sorry for that. Fixed it.
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