29 Input/output library [input.output]

29.7 Formatting and manipulators [iostream.format]

29.7.4 Input streams [input.streams]

29.7.4.2 Class template basic_­istream [istream]

29.7.4.2.1 General [istream.general]

namespace std { template<class charT, class traits = char_traits<charT>> class basic_istream : virtual public basic_ios<charT, traits> { public: // types (inherited from basic_­ios) 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; // [istream.cons], constructor/destructor explicit basic_istream(basic_streambuf<charT, traits>* sb); virtual ~basic_istream(); // [istream.sentry], prefix/suffix class sentry; // [istream.formatted], formatted input basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& (*pf)(basic_istream<charT, traits>&)); basic_istream<charT, traits>& operator>>(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&)); basic_istream<charT, traits>& operator>>(ios_base& (*pf)(ios_base&)); basic_istream<charT, traits>& operator>>(bool& n); basic_istream<charT, traits>& operator>>(short& n); basic_istream<charT, traits>& operator>>(unsigned short& n); basic_istream<charT, traits>& operator>>(int& n); basic_istream<charT, traits>& operator>>(unsigned int& n); basic_istream<charT, traits>& operator>>(long& n); basic_istream<charT, traits>& operator>>(unsigned long& n); basic_istream<charT, traits>& operator>>(long long& n); basic_istream<charT, traits>& operator>>(unsigned long long& n); basic_istream<charT, traits>& operator>>(float& f); basic_istream<charT, traits>& operator>>(double& f); basic_istream<charT, traits>& operator>>(long double& f); basic_istream<charT, traits>& operator>>(void*& p); basic_istream<charT, traits>& operator>>(basic_streambuf<char_type, traits>* sb); // [istream.unformatted], unformatted input streamsize gcount() const; int_type get(); basic_istream<charT, traits>& get(char_type& c); basic_istream<charT, traits>& get(char_type* s, streamsize n); basic_istream<charT, traits>& get(char_type* s, streamsize n, char_type delim); basic_istream<charT, traits>& get(basic_streambuf<char_type, traits>& sb); basic_istream<charT, traits>& get(basic_streambuf<char_type, traits>& sb, char_type delim); basic_istream<charT, traits>& getline(char_type* s, streamsize n); basic_istream<charT, traits>& getline(char_type* s, streamsize n, char_type delim); basic_istream<charT, traits>& ignore(streamsize n = 1, int_type delim = traits::eof()); int_type peek(); basic_istream<charT, traits>& read (char_type* s, streamsize n); streamsize readsome(char_type* s, streamsize n); basic_istream<charT, traits>& putback(char_type c); basic_istream<charT, traits>& unget(); int sync(); pos_type tellg(); basic_istream<charT, traits>& seekg(pos_type); basic_istream<charT, traits>& seekg(off_type, ios_base::seekdir); protected: // [istream.cons], copy/move constructor basic_istream(const basic_istream&) = delete; basic_istream(basic_istream&& rhs); // [istream.assign], assign and swap basic_istream& operator=(const basic_istream&) = delete; basic_istream& operator=(basic_istream&& rhs); void swap(basic_istream& rhs); }; // [istream.extractors], character extraction templates template<class charT, class traits> basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>&, charT&); template<class traits> basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, unsigned char&); template<class traits> basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, signed char&); template<class charT, class traits, size_t N> basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>&, charT(&)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, unsigned char(&)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, signed char(&)[N]); }
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The class template basic_­istream defines a number of member function signatures that assist in reading and interpreting input from sequences controlled by a stream buffer.
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Two groups of member function signatures share common properties: the formatted input functions (or extractors) and the unformatted input functions. Both groups of input functions are described as if they obtain (or extract) input characters by calling rdbuf()->sbumpc() or rdbuf()->sgetc().
They may use other public members of istream.
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If rdbuf()->sbumpc() or rdbuf()->sgetc() returns traits​::​eof(), then the input function, except as explicitly noted otherwise, completes its actions and does setstate(eofbit), which may throw ios_­base​::​failure ([iostate.flags]), before returning.
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If one of these called functions throws an exception, then unless explicitly noted otherwise, the input function sets badbit in the error state.
If badbit is set in exceptions(), the input function rethrows the exception without completing its actions, otherwise it does not throw anything and proceeds as if the called function had returned a failure indication.