namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_filebuf;
using filebuf = basic_filebuf<char>;
using wfilebuf = basic_filebuf<wchar_t>;
template <class charT, class traits = char_traits<charT>>
class basic_ifstream;
using ifstream = basic_ifstream<char>;
using wifstream = basic_ifstream<wchar_t>;
template <class charT, class traits = char_traits<charT>>
class basic_ofstream;
using ofstream = basic_ofstream<char>;
using wofstream = basic_ofstream<wchar_t>;
template <class charT, class traits = char_traits<charT>>
class basic_fstream;
using fstream = basic_fstream<char>;
using wfstream = basic_fstream<wchar_t>;
}The header <fstream> defines four class templates and eight types that associate stream buffers with files and assist reading and writing files.
[ Note: The class template basic_filebuf treats a file as a source or sink of bytes. In an environment that uses a large character set, the file typically holds multibyte character sequences and the basic_filebuf object converts those multibyte sequences into wide character sequences. — end note ]
In this subclause, member functions taking arguments of const filesystem::path::value_type* are only be provided on systems where filesystem::path::value_type ([fs.class.path]) is not char. [ Note: These functions enable class path support for systems with a wide native path character type, such as wchar_t. — end note ]