cppdraft_translate/cppdraft/fstream.md

[fstream]

# 31 Input/output library [[input.output]](./#input.output)

## 31.10 File-based streams [[file.streams]](file.streams#fstream)

### 31.10.6 Class template basic_fstream [fstream]

#### [31.10.6.1](#general) General [[fstream.general]](fstream.general)

[🔗](#lib:basic_fstream)

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; // [[fstream.cons]](#cons "31.10.6.2 Constructors"), constructors 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); // wide systems only; see [[fstream.syn]](fstream.syn "31.10.1 Header <fstream> synopsis")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); // [[fstream.swap]](#swap "31.10.6.3 Swap"), swapvoid swap(basic_fstream& rhs); // [[fstream.members]](#members "31.10.6.4 Member functions"), members 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); // wide systems only; see [[fstream.syn]](fstream.syn "31.10.1 Header <fstream> synopsis")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*; // *exposition only*};}

[1](#general-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12347)

The
class templatebasic_fstream<charT, traits> supports reading and writing from named files[.](#general-1.sentence-1)

It uses abasic_filebuf<charT, traits> object to control the associated sequences[.](#general-1.sentence-2)

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

- [(1.1)](#general-1.1)

*sb*, the basic_filebuf object[.](#general-1.sentence-3)

#### [31.10.6.2](#cons) Constructors [[fstream.cons]](fstream.cons)

[🔗](#lib:basic_fstream,constructor)

`basic_fstream();
`

[1](#cons-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12369)

*Effects*: Initializes the base class withbasic_iostream<charT, traits>(addressof(*sb*)) ([[iostream.cons]](iostream.cons "31.7.5.7.2 Constructors"))
and*sb* with basic_filebuf<charT, traits>()[.](#cons-1.sentence-1)

[🔗](#lib:basic_fstream,constructor_)

`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")
`

[2](#cons-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12388)

*Effects*: Initializes the base class withbasic_iostream<charT, traits>(addressof(*sb*)) ([[iostream.cons]](iostream.cons "31.7.5.7.2 Constructors"))
and*sb* with basic_filebuf<charT, traits>()[.](#cons-2.sentence-1)

Then callsrdbuf()->open(s, mode)[.](#cons-2.sentence-2)

If that function returns a null pointer, callssetstate(failbit)[.](#cons-2.sentence-3)

[🔗](#lib:basic_fstream,constructor__)

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

[3](#cons-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12408)

*Effects*: Equivalent to basic_fstream(s.c_str(), mode)[.](#cons-3.sentence-1)

[🔗](#lib:basic_fstream,constructor___)

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

[4](#cons-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12420)

*Constraints*: is_same_v<T, filesystem​::​path> is true[.](#cons-4.sentence-1)

[5](#cons-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12424)

*Effects*: Equivalent to basic_fstream(s.c_str(), mode)[.](#cons-5.sentence-1)

[🔗](#lib:basic_fstream,constructor____)

`basic_fstream(basic_fstream&& rhs);
`

[6](#cons-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12435)

*Effects*: Move constructs the base class, and the contained basic_filebuf[.](#cons-6.sentence-1)

Then calls basic_istream<charT, traits>​::​set_rdbuf(​addressof(*sb*)) to install the contained basic_filebuf[.](#cons-6.sentence-2)

#### [31.10.6.3](#swap) Swap [[fstream.swap]](fstream.swap)

[🔗](#lib:swap,basic_fstream)

`void swap(basic_fstream& rhs);
`

[1](#swap-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12450)

*Effects*: Exchanges the state of *this and rhs by callingbasic_iostream<charT,traits>​::​swap(rhs) and*sb*.swap(rhs.*sb*)[.](#swap-1.sentence-1)

[🔗](#lib:swap,basic_fstream_)

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

[2](#swap-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12466)

*Effects*: Equivalent to x.swap(y)[.](#swap-2.sentence-1)

#### [31.10.6.4](#members) Member functions [[fstream.members]](fstream.members)

[🔗](#lib:rdbuf,basic_fstream)

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

[1](#members-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12479)

*Returns*: const_cast<basic_filebuf<charT, traits>*>(addressof(*sb*))[.](#members-1.sentence-1)

[🔗](#lib:native_handle,basic_fstream)

`native_handle_type native_handle() const noexcept;
`

[2](#members-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12490)

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

[🔗](#lib:is_open,basic_fstream)

`bool is_open() const;
`

[3](#members-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12501)

*Returns*: rdbuf()->is_open()[.](#members-3.sentence-1)

[🔗](#lib:open,basic_fstream)

`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")
`

[4](#members-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12517)

*Effects*: Callsrdbuf()->open(s, mode)[.](#members-4.sentence-1)

If that function does not return a null pointer calls clear(),
otherwise callssetstate(failbit) (which may throwios_base​::​failure) ([[iostate.flags]](iostate.flags "31.5.4.4 Flags functions"))[.](#members-4.sentence-2)

[🔗](#lib:open,basic_fstream_)

`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);
`

[5](#members-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12539)

*Effects*: Calls open(s.c_str(), mode)[.](#members-5.sentence-1)

[🔗](#lib:close,basic_fstream)

`void close();
`

[6](#members-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12550)

*Effects*: Callsrdbuf()->close() and, if that function
returns a null pointer,
callssetstate(failbit) (which may throwios_base​::​failure) ([[iostate.flags]](iostate.flags "31.5.4.4 Flags functions"))[.](#members-6.sentence-1)