[fstream] (original) (raw)

31 Input/output library [input.output]

31.10 File-based streams [file.streams]

31.10.6 Class template basic_fstream [fstream]

31.10.6.1 General [fstream.general]

namespace std { template<class charT, class traits = char_traits<charT>> class basic_fstream : public basic_iostream<charT, traits> { public: using char_type = charT;using int_type = typename traits::int_type;using pos_type = typename traits::pos_type;using off_type = typename traits::off_type;using traits_type = traits;using native_handle_type = typename basic_filebuf<charT, traits>::native_handle_type; basic_fstream();explicit basic_fstream( const char* s, ios_base::openmode mode = ios_base::in | ios_base::out);explicit basic_fstream( const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in | ios_base::out); explicit basic_fstream( const string& s, ios_base::openmode mode = ios_base::in | ios_base::out);template<class T> explicit basic_fstream(const T& s, ios_base::openmode mode = ios_base::in | ios_base::out); basic_fstream(const basic_fstream&) = delete; basic_fstream(basic_fstream&& rhs); basic_fstream& operator=(const basic_fstream&) = delete; basic_fstream& operator=(basic_fstream&& rhs);void swap(basic_fstream& rhs); basic_filebuf<charT, traits>* rdbuf() const; native_handle_type native_handle() const noexcept;bool is_open() const;void open( const char* s, ios_base::openmode mode = ios_base::in | ios_base::out);void open( const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in | ios_base::out); void open( const string& s, ios_base::openmode mode = ios_base::in | ios_base::out);void open( const filesystem::path& s, ios_base::openmode mode = ios_base::in | ios_base::out);void close();private: basic_filebuf<charT, traits> sb; };}

The class templatebasic_fstream<charT, traits>supports reading and writing from named files.

It uses abasic_filebuf<charT, traits>object to control the associated sequences.

For the sake of exposition, the maintained data is presented here as:

• sb, the basic_filebuf object.

31.10.6.2 Constructors [fstream.cons]

Effects: Initializes the base class withbasic_iostream<charT, traits>(addressof(sb)) ([iostream.cons]) and_sb_ with basic_filebuf<charT, traits>().

explicit basic_fstream( const char* s, ios_base::openmode mode = ios_base::in | ios_base::out);explicit basic_fstream( const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in | ios_base::out); // wide systems only; see [[fstream.syn]](fstream.syn "31.10.1 Header <fstream> synopsis")

Effects: Initializes the base class withbasic_iostream<charT, traits>(addressof(sb)) ([iostream.cons]) and_sb_ with basic_filebuf<charT, traits>().

Then callsrdbuf()->open(s, mode).

If that function returns a null pointer, callssetstate(failbit).

explicit basic_fstream( const string& s, ios_base::openmode mode = ios_base::in | ios_base::out);

Effects: Equivalent to basic_fstream(s.c_str(), mode).

template<class T> explicit basic_fstream(const T& s, ios_base::openmode mode = ios_base::in | ios_base::out);

Constraints: is_same_v<T, filesystem​::​path> is true.

Effects: Equivalent to basic_fstream(s.c_str(), mode).

basic_fstream(basic_fstream&& rhs);

Effects: Move constructs the base class, and the contained basic_filebuf.

Then calls basic_istream<charT, traits>​::​set_rdbuf(​addressof(sb))to install the contained basic_filebuf.

31.10.6.3 Swap [fstream.swap]

void swap(basic_fstream& rhs);

Effects: Exchanges the state of *thisand rhs by callingbasic_iostream<charT,traits>​::​swap(rhs) and_sb_.swap(rhs.sb).

template<class charT, class traits> void swap(basic_fstream<charT, traits>& x, basic_fstream<charT, traits>& y);

Effects: Equivalent to x.swap(y).

31.10.6.4 Member functions [fstream.members]

basic_filebuf<charT, traits>* rdbuf() const;

Returns: const_cast<basic_filebuf<charT, traits>*>(addressof(sb)).

native_handle_type native_handle() const noexcept;

Effects: Equivalent to: return rdbuf()->native_handle();

Returns: rdbuf()->is_open().

void open( const char* s, ios_base::openmode mode = ios_base::in | ios_base::out);void open( const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in | ios_base::out); // wide systems only; see [[fstream.syn]](fstream.syn "31.10.1 Header <fstream> synopsis")

Effects: Callsrdbuf()->open(s, mode).

If that function does not return a null pointer calls clear(), otherwise callssetstate(failbit)(which may throwios_base​::​failure) ([iostate.flags]).

void open( const string& s, ios_base::openmode mode = ios_base::in | ios_base::out);void open( const filesystem::path& s, ios_base::openmode mode = ios_base::in | ios_base::out);

Effects: Calls open(s.c_str(), mode).

Effects: Callsrdbuf()->close()and, if that function returns a null pointer, callssetstate(failbit)(which may throwios_base​::​failure) ([iostate.flags]).