流的初体验（未完成）

Typical constructor：

strstream( char* pch, int nLength, int nMode );

fstream( const char* szName, int nMode, int nProt = filebuf::openprot );

stdiostream( FILE* fp );

strstreambuf( char* pch, int n, char* pstart = 0 );

Iostream_init constructor that initializes cin, cout, cerr, and clog. For internal use only.