C++中的I/O stream類

ios_base：頂層基類

basic_ios<>：派生自ios_base的template class 。具體定義：

template<class charT, class traits = char_traits<charT> >class basic_ios ：public class ios_base {};

basic_istream<> / basic_ostream<>：兩者虛擬派生自basic_ios<>的模版類。具體定義：

template<class charT, class traits = char_traits<charT> >class basic_istream ：virtual public class basic_ios <charT, traits> {};

template<class charT, class traits = char_traits<charT> >class basic_ostream ：virtual public class basic_ios <charT, traits> {};

basic_iostream<>：派生自basic_istream<>和basic_ostream<>的模版類。為了避免多重繼承中由多個父類共同的基類產生的二義性，所以basic_istream<> / basic_ostream<>需要虛擬派生自basic_ios<>。具體定義：

template<class _Elem,class _Traits>class basic_iostream: public basic_istream<_Elem, _Traits>,  public basic_ostream<_Elem, _Traits> ｛｝

basic_fstream<>：派生自basic_iostream<>的模版類。具體定義：

template<class _Elem, class _Traits>class basic_fstream    : public basic_iostream<_Elem, _Traits> {}

basic_ifstream<>：派生自basic_istream<>的模版類。具體定義：

template<class _Elem, class _Traits>class basic_ifstream    : public basic_istream<_Elem, _Traits> {}

basic_ofstream<>：派生自basic_ostream<>的模版類。具體定義：

template<class _Elem, class _Traits>class basic_ofstream    : public basic_ostream<_Elem, _Traits> {}

我們熟悉的iostream、istream、ostream、fstream、ifstream、ofstream、ios都是上述模版類的特例型別。具體定義：

typedef basic_ios<char, char_traits<char> > ios;typedef basic_istream<char, char_traits<char> > istream;typedef basic_ostream<char, char_traits<char> > ostream;typedef basic_iostream<char, char_traits<char> > iostream;typedef basic_ifstream<char, char_traits<char> > ifstream;typedef basic_ofstream<char, char_traits<char> > ofstream;typedef basic_fstream<char, char_traits<char> > fstream;

寫這些，主要就是為了理清c++中stream classes的整個繼承體系。