[ifstream] (original) (raw)
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]
namespace std { template<class charT, class traits = char_traits<charT>> 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; 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);explicit basic_ifstream(const string& s, ios_base::openmode mode = ios_base::in);template<class T> explicit 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);void swap(basic_ifstream& 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);void open(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in); 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; };}
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:
- sb, the filebuf object.
31.10.4.2 Constructors [ifstream.cons]
Effects: Initializes the base class withbasic_istream<charT, traits>(addressof(sb)) ([istream.cons]) and sb withbasic_filebuf<charT, traits>() ([filebuf.cons]).
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")
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).
explicit basic_ifstream(const string& s, ios_base::openmode mode = ios_base::in);
Effects: Equivalent to basic_ifstream(s.c_str(), mode).
template<class T> explicit basic_ifstream(const T& s, ios_base::openmode mode = ios_base::in);
Constraints: is_same_v<T, filesystem::path> is true.
Effects: Equivalent to basic_ifstream(s.c_str(), mode).
basic_ifstream(basic_ifstream&& 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.
31.10.4.3 Swap [ifstream.swap]
void swap(basic_ifstream& rhs);
Effects: Exchanges the state of *thisand rhs by callingbasic_istream<charT, traits>::swap(rhs) and_sb_.swap(rhs.sb).
template<class charT, class traits> void swap(basic_ifstream<charT, traits>& x, basic_ifstream<charT, traits>& y);
Effects: Equivalent to x.swap(y).
31.10.4.4 Member functions [ifstream.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);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")
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]).
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);
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]).