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& rhs) = delete;
basic_istream(basic_istream&& rhs);
// [istream.assign], assign and swap
basic_istream& operator=(const basic_istream& rhs) = 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>
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*);
}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.
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.
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.
If one of these called functions throws an exception, then unless explicitly noted otherwise, the input function sets badbit in error state. If badbit is on 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.
explicit basic_istream(basic_streambuf<charT, traits>* sb);
Effects: Constructs an object of class basic_istream, initializing the base class subobject with basic_ios::init(sb) ([basic.ios.cons]).
basic_istream(basic_istream&& rhs);
Effects: Move constructs from the rvalue rhs. This is accomplished by default constructing the base class, copying the gcount() from rhs, calling basic_ios<charT, traits>::move(rhs) to initialize the base class, and setting the gcount() for rhs to 0.
virtual ~basic_istream();
basic_istream& operator=(basic_istream&& rhs);
void swap(basic_istream& rhs);
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_istream<charT, traits>::sentry {
using traits_type = traits;
bool ok_; // exposition only
public:
explicit sentry(basic_istream<charT, traits>& is, bool noskipws = false);
~sentry();
explicit operator bool() const { return ok_; }
sentry(const sentry&) = delete;
sentry& operator=(const sentry&) = delete;
};
}The class sentry defines a class that is responsible for doing exception safe prefix and suffix operations.
explicit sentry(basic_istream<charT, traits>& is, bool noskipws = false);
Effects: If is.good() is false, calls is.setstate(failbit). Otherwise, prepares for formatted or unformatted input. First, if is.tie() is not a null pointer, the function calls is.tie()->flush() to synchronize the output sequence with any associated external C stream. Except that this call can be suppressed if the put area of is.tie() is empty. Further an implementation is allowed to defer the call to flush until a call of is.rdbuf()->underflow() occurs. If no such call occurs before the sentry object is destroyed, the call to flush may be eliminated entirely.305 If noskipws is zero and is.flags() & ios_base::skipws is nonzero, the function extracts and discards each character as long as the next available input character c is a whitespace character. If is.rdbuf()->sbumpc() or is.rdbuf()->sgetc() returns traits::eof(), the function calls setstate(failbit | eofbit) (which may throw ios_base::failure).
Remarks: The constructor
explicit sentry(basic_istream<charT, traits>& is, bool noskipws = false)
uses the currently imbued locale in is, to determine whether the next input character is whitespace or not.
To decide if the character c is a whitespace character, the constructor performs as if it executes the following code fragment:
const ctype<charT>& ctype = use_facet<ctype<charT>>(is.getloc());
if (ctype.is(ctype.space, c) != 0)
// c is a whitespace character.
If, after any preparation is completed, is.good() is true, ok_ != false otherwise, ok_ == false. During preparation, the constructor may call setstate(failbit) (which may throw ios_base::failure ([iostate.flags]))306
~sentry();
explicit operator bool() const;
This will be possible only in functions that are part of the library. The semantics of the constructor used in user code is as specified.