cppdraft_translate/cppdraft/ifstream.md

[ifstream]

31 Input/output library [input.output]

31.10 File-based streams [file.streams]

31.10.4 Class template basic_ifstream [ifstream]

31.10.4.1 General [ifstream.general]

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namespace std {template<class charT, class traits = char_traits>class basic_ifstream : public basic_istream<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; // [ifstream.cons], constructors basic_ifstream(); explicit basic_ifstream(const char* s, ios_base::openmode mode = ios_base::in); explicit basic_ifstream(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in);// wide systems only; see [fstream.syn]explicit basic_ifstream(const string& s, ios_base::openmode mode = ios_base::in); templateexplicit basic_ifstream(const T& s, ios_base::openmode mode = ios_base::in); basic_ifstream(const basic_ifstream&) = delete; basic_ifstream(basic_ifstream&& rhs);

basic_ifstream& operator=(const basic_ifstream&) = delete; basic_ifstream& operator=(basic_ifstream&& rhs); // [ifstream.swap], swapvoid swap(basic_ifstream& rhs); // [ifstream.members], 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); void open(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in); // wide systems only; see [fstream.syn]void open(const string& s, ios_base::openmode mode = ios_base::in); void open(const filesystem::path& s, ios_base::openmode mode = ios_base::in); void close(); private: basic_filebuf<charT, traits> sb; // exposition only};}

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The classbasic_ifstream<charT, traits> supports reading from named files.

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

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

• (1.1)

sb, the filebuf object.

31.10.4.2 Constructors [ifstream.cons]

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basic_ifstream();

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Effects: Initializes the base class withbasic_istream<charT, traits>(addressof(sb)) ([istream.cons]) and sb withbasic_filebuf<charT, traits>() ([filebuf.cons]).

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

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Effects: Initializes the base class withbasic_istream<charT, traits>(addressof(sb)) ([istream.cons]) and sb withbasic_filebuf<charT, traits>() ([filebuf.cons]), then callsrdbuf()->open(s, mode | ios_base​::​in).

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

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explicit basic_ifstream(const string& s, ios_base::openmode mode = ios_base::in);

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

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

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

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

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basic_ifstream(basic_ifstream&& rhs);

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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.

31.10.4.3 Swap [ifstream.swap]

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void swap(basic_ifstream& rhs);

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Effects: Exchanges the state of this and rhs by callingbasic_istream<charT, traits>​::​swap(rhs) andsb*.swap(rhs.sb).

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

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Effects: Equivalent to x.swap(y).

31.10.4.4 Member functions [ifstream.members]

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

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

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native_handle_type native_handle() const noexcept;

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

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bool is_open() const;

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Returns: rdbuf()->is_open().

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

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Effects: Callsrdbuf()->open(s, mode | ios_base​::​in).

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

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

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

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void close();

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