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Nullstream implementation - comments?

Ben Sizer · 2002-10-21T13:40:03

Basically I thought it would be handy to have an istream and ostream that effectively did nothing. Why? So that I can write a function that takes a stream as a parameter - as a logfile, for example - and be able to turn off that stream without having to do any checking inside the functions, or to rewrite the interface. So to turn off logging, I pass a nullostream instead of an ofstream or whatever. I thought I''d post these here so that anyone can use them, but more importantly for anyone to suggest corrections or amendments, as I''ve never done this sort of thing before. They seem to work, but by their very nature, are hard to test. I also haven''t done a nulliostream yet, because I''m not quite sure (a) whether I''ll ever need one, and (b) how it affects the implementation. Please also excuse the slightly erroneously-named namespace and my grouping of 4 classes in 2 files instead of 4 files. // nulloutbuf.h --------------------------------------- #include <streambuf> #include <locale> namespace KyloSTL { // MSVC 6 (or at least, my version of it) will NOT allow you to specify // these explicitly, but will compile happily with these using statements. // Hopefully this namespace pollution is confined to this namespace, // but who knows what MSVC decides. using std::char_traits; using std::basic_streambuf; using std::basic_ostream; // Null output stream buffer ----------------------------------------- template <class charT, class traits = char_traits<charT> > class basic_nulloutbuf : public basic_streambuf<charT, traits> { protected: virtual int_type overflow(int_type c) { // Return not_eof, as we never need to stop writing return traits::not_eof(c); } }; typedef basic_nulloutbuf<char> nulloutbuf; typedef basic_nulloutbuf<wchar_t> wnulloutbuf; // Null output stream ---------------------------------------------------- template <class charT, class traits = char_traits<charT> > class basic_nullostream : public basic_ostream<charT, traits> { protected: basic_nulloutbuf<charT, traits> buf; public: basic_nullostream() : basic_ostream<charT, traits>(&buf) {} }; typedef basic_nullostream<char> nullostream; typedef basic_nullostream<wchar_t> wnullostream; } // end KyloSTL namespace // nullinbuf.h ------------------------------------ #include <streambuf> #include <locale> namespace KyloSTL { // MSVC 6 (or at least, my version of it) will NOT allow you to specify // these explicitly, but will compile happily with these using statements. // Hopefully this namespace pollution is confined to this namespace, // but who knows what MSVC decides. using std::char_traits; using std::basic_streambuf; using std::basic_istream; // Null input stream buffer ------------------------------------------ template <class charT, class traits = char_traits<charT> > class basic_nullinbuf : public basic_streambuf<charT, traits> { private: // This is what will be ''read'' each time int_type theValue; protected: // Always the same character... virtual int_type underflow() { return theValue; } // No buffer, so we get this direct from underflow and don''t // need all the traits conversion trickery to change it to an // int_type virtual int_type uflow() { return underflow(); } public: basic_nullinbuf(int_type v) : theValue(v) {} }; typedef basic_nullinbuf<char> nullinbuf; typedef basic_nullinbuf<wchar_t> wnullinbuf; // Null input stream ----------------------------------------------------- template <class charT, class traits = char_traits<charT> > class basic_nullistream : public basic_istream<charT, traits> { protected: basic_nullinbuf<charT, traits> buf; public: // Hmm... initialisation order issue? Dunno... basic_nullistream(int_type v = 0) : buf(v), basic_istream<charT, traits>(&buf) {}; }; typedef basic_nullistream<char> nullistream; typedef basic_nullistream<wchar_t> wnullistream; } // end KyloSTL namespace [ MSVC Fixes | STL | SDL | Game AI | Sockets | C++ Faq Lite | Boost | Asking Questions | Organising code files | My stuff ]