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basic_istream , istream , wistream , basic_iostream , iostream , wiostream , operator>> , ws - defines the template class that performs extractions
namespace std { template<class E, class T = char_traits<E> > class basic_istream; typedef basic_istream<char, char_traits<char> > istream; typedef basic_istream<wchar_t, char_traits<wchar_t> > wistream; template<class E, class T = char_traits<E> > class basic_iostream; typedef basic_iostream<char, char_traits<char> > iostream; typedef basic_iostream<wchar_t, char_traits<wchar_t> > wiostream; // EXTRACTORS template<class E, class T> basic_istream<E, T>& operator>>(basic_istream<E, T>& is, E *s); template<class E, class T> basic_istream<E, T>& operator>>(basic_istream<E, T>& is, E& c); template<class T> basic_istream<char, T>& operator>>(basic_istream<char, T>& is, signed char *s); template<class T> basic_istream<char, T>& operator>>(basic_istream<char, T>& is, signed char& c); template<class T> basic_istream<char, T>& operator>>(basic_istream<char, T>& is, unsigned char *s); template<class T> basic_istream<char, T>& operator>>(basic_istream<char, T>& is, unsigned char& c); // MANIPULATORS template class<E, T> basic_istream<E, T>& ws(basic_istream<E, T>& is); };
Include the iostreams
standard header <istream>
to define template class
basic_istream
,
which mediates extractions for the iostreams, and the template class.
basic_iostream
,
which mediates both insertions and extractions.
The header also defines a related
manipulator.
(This header is typically included for you by another
of the iostreams headers. You seldom have occasion to include it
directly.)
template <class E, class T = char_traits<E> > class basic_iostream : public basic_istream<E, T>, public basic_ostream<E, T> { public: explicit basic_iostream(basic_streambuf<E, T>& *sb); virtual ~basic_iostream(); };
The template class describes an object that controls
insertions, through its base object
basic_ostream<E, T>
,
and extractions, through its base object
basic_istream<E, T>
.
The two objects share a common virtual base object
basic_ios<E, T>
.
They also manage a common
stream buffer,
with elements of type E
, whose
character traits are determined
by the class T
. The constructor initializes its base objects
via basic_istream(sb)
and basic_ostream(sb)
.
basic_istream , gcount , get , getline , ignore , ipfx , isfx , operator>> , peek , putback , read , readsome , seekg , sentry , sync , tellg , unget
template <class E, class T = char_traits<E> > class basic_istream : virtual public basic_ios<E, T> { public: typedef typename basic_ios<E, T>::char_type char_type; typedef typename basic_ios<E, T>::traits_type traits_type; typedef typename basic_ios<E, T>::int_type int_type; typedef typename basic_ios<E, T>::pos_type pos_type; typedef typename basic_ios<E, T>::off_type off_type; explicit basic_istream(basic_streambuf<E, T> *sb); class sentry; virtual ~istream(); bool ipfx(bool noskip = false); void isfx(); basic_istream& operator>>( basic_istream& (*pf)(basic_istream&)); basic_istream& operator>>( ios_base& (*pf)(ios_base&)); basic_istream& operator>>( basic_ios<E, T>& (*pf)(basic_ios<E, T>&)); basic_istream& operator>>( basic_streambuf<E, T> *sb); basic_istream& operator>>(bool& n); basic_istream& operator>>(short& n); basic_istream& operator>>(unsigned short& n); basic_istream& operator>>(int& n); basic_istream& operator>>(unsigned int& n); basic_istream& operator>>(long& n); basic_istream& operator>>(unsigned long& n); basic_istream& operator>>(void *& n); basic_istream& operator>>(float& n); basic_istream& operator>>(double& n); basic_istream& operator>>(long double& n); streamsize gcount() const; int_type get(); basic_istream& get(char_type& c); basic_istream& get(char_type *s, streamsize n); basic_istream& get(char_type *s, streamsize n, char_type delim); basic_istream& get(basic_streambuf<char_type, T> *sb); basic_istream& get(basic_streambuf<E, T> *sb, char_type delim); basic_istream& getline(char_type *s, streamsize n); basic_istream& getline(char_type *s, streamsize n, char_type delim); basic_istream& ignore(streamsize n = 1, int_type delim = traits_type::eof()); int_type peek(); basic_istream& read(char_type *s, streamsize n); streamsize readsome(char_type *s, streamsize n); basic_istream& putback(char_type c); basic_istream& unget(); pos_type tellg(); basic_istream& seekg(pos_type pos); basic_istream& seekg(off_type off, ios_base::seek_dir way); int sync(); };
The template class describes an object that controls
extraction of elements and encoded objects from a
stream buffer
with elements of type E
, also known as
char_type
, whose
character traits are determined by the
class T
, also known as
traits_type
.
Most of the member functions that overload
operator>>
are formatted input functions.
They follow the pattern:
iostate state = goodbit; const sentry ok(*this); if (ok) {try {<extract elements and convert accumulate flags in state store a successful conversion>} catch (...) {try {setstate(badbit); } catch (...) {} if ((exceptions() & badbit) != 0) throw; }} setstate(state); return (*this);
Many other member functions are unformatted input functions. They follow the pattern:
iostate state = goodbit; count = 0; // the value returned by gcount const sentry ok(*this, true); if (ok) {try {<extract elements and deliver count extracted elements in count accumulate flags in state>} catch (...) {try {setstate(badbit); } catch (...) {} if ((exceptions() & badbit) != 0) throw; }} setstate(state);
Both groups of functions call
setstate(eofbit)
if they encounter end-of-file while extracting elements.
An object of class basic_istream<E, T>
stores:
basic_ios<E, T>
count
in the code above)explicit basic_istream(basic_streambuf<E, T> *sb);
The constructor initializes the base class by calling
init(sb)
.
It also stores zero in the
extraction count.
streamsize gcount() const;
The member function returns the extraction count.
int_type get(); basic_istream& get(char_type& c); basic_istream& get(char_type *s, streamsize n); basic_istream& get(char_type *s, streamsize n, char_type delim); basic_istream& get(basic_streambuf<E, T> *sb); basic_istream& get(basic_streambuf<E, T> *sb, char_type delim);
The first of these
unformatted input functions
extracts an element, if possible, as if by returning
rdbuf()->sbumpc()
.
Otherwise, it returns
traits_type::eof()
.
If the function extracts no element, it calls
setstate(failbit)
.
The second function extracts the
int_type
element
x
the same way. If x
compares equal to
traits_type::eof(x)
,
the function calls
setstate(failbit)
.
Otherwise, it stores
traits_type::to_char_type(x)
in c
. The function returns *this
.
The third function returns get(s, n, widen('\n'))
.
The fourth function extracts up to n - 1
elements
and stores them in the array beginning at s
. It always stores
char_type()
after
any extracted elements it stores. In order of testing, extraction stops:
delim
, in which case the element is put back
to the controlled sequencen - 1
elementsIf the function extracts no elements, it calls
setstate(failbit)
.
In any case, it returns *this
.
The fifth function returns get(sb, widen('\n'))
.
The sixth function extracts elements and inserts them in
sb
. Extraction stops on end-of-file or on an element
that compares equal to delim
(which is not extracted).
It also stops, without extracting the element in question,
if an insertion fails or throws an exception (which is caught
but not rethrown). If the function extracts no elements, it calls
setstate(failbit)
.
In any case, the function returns *this
.
basic_istream& getline(char_type *s, streamsize n); basic_istream& getline(char_type *s, streamsize n, char_type delim);
The first of these
unformatted input functions
returns getline(s, n, widen('\n'))
.
The second function extracts up to n - 1
elements
and stores them in the array beginning at s
. It always stores
char_type()
after
any extracted elements it stores. In order of testing, extraction stops:
delim
, in which case the element is neither put back nor
appended to the controlled sequencen - 1
elementsIf the function extracts no elements or n - 1
elements, it calls
setstate(failbit)
.
In any case, it returns *this
.
basic_istream& ignore(streamsize n = 1, int_type delim = traits_type::eof());
The unformatted input function
extracts up to n
elements and discards them.
If n
equals
numeric_limits<int>::max()
,
however, it is taken as arbitrarily large.
Extraction stops early on end-of-file or
on an element x
such that
traits_type::to_int_type(x)
compares equal to delim
(which is
also extracted).
The function returns *this
.
bool ipfx(bool noskip = false);
The member function prepares for
formatted or
unformatted input.
If good()
is true, the function:
tie->
flush()
if tie()
is not a null pointerws(*this)
if
flags() &
skipws
is nonzeroIf, after any such preparation,
good()
is false, the function calls
setstate(failbit)
.
In any case, the function returns good()
.
You should not call ipfx
directly.
It is called as needed by an object of class
sentry
.
void isfx();
The member function has no official duties, but an implementation
may depend on a call to isfx
by a
formatted or
unformatted input
function to tidy up after an extraction.
You should not call isfx
directly.
It is called as needed by an object of class
sentry
.
basic_istream& operator>>( basic_istream& (*pf)(basic_istream&)); basic_istream& operator>>( ios_base& (*pf)(ios_base&)); basic_istream& operator>>( basic_ios<E, T>& (*pf)(basic_ios<E, T>&)); basic_istream& operator>>( basic_streambuf<E, T> *sb); basic_istream& operator>>(bool& n); basic_istream& operator>>(short& n); basic_istream& operator>>(unsigned short& n); basic_istream& operator>>(int& n); basic_istream& operator>>(unsigned int& n); basic_istream& operator>>(long& n); basic_istream& operator>>(unsigned long& n); basic_istream& operator>>(void *& n); basic_istream& operator>>(float& n); basic_istream& operator>>(double& n); basic_istream& operator>>(long double& n);
The first member function ensures that an expression of the
form istr >> ws
calls
ws(istr)
, then returns *this
.
The second and third functions ensure that other
manipulators,
such as hex
behave
similarly. The remaining functions constitute the
formatted input functions.
The function:
basic_istream& operator>>( basic_streambuf<E, T> *sb);
extracts elements, if sb
is not a null pointer,
and inserts them in sb
. Extraction stops on end-of-file.
It also stops, without extracting the element in question,
if an insertion fails or throws an exception (which is caught
but not rethrown).
If the function extracts no elements, it calls
setstate(failbit)
.
In any case, the function returns *this
.
The function:
basic_istream& operator>>(bool& n);
extracts a field and converts it to a boolean value by calling
use_facet<num_get<E,
InIt>(getloc()).
get(InIt(
rdbuf()), Init(0), *this,
getloc(), n)
. Here, InIt
is defined as
istreambuf_iterator<E,
T>
.
The function returns *this
.
The functions:
basic_istream& operator>>(short& n); basic_istream& operator>>(unsigned short& n); basic_istream& operator>>(int& n); basic_istream& operator>>(unsigned int& n); basic_istream& operator>>(long& n); basic_istream& operator>>(unsigned long& n); basic_istream& operator>>(void *& n);
each extract a field and convert it to a numeric value by calling
use_facet<num_get<E,
InIt>(getloc()).
get(InIt(
rdbuf()), Init(0), *this,
getloc(), x)
. Here, InIt
is defined as
istreambuf_iterator<E,
T>
, and x
has type long,
unsigned long, or void * as needed.
If the converted value cannot
be represented as the type of n
, the function calls
setstate(failbit)
.
In any case, the function returns *this
.
The functions:
basic_istream& operator>>(float& n); basic_istream& operator>>(double& n); basic_istream& operator>>(long double& n);
each extract a field and convert it to a numeric value by calling
use_facet<num_get<E,
InIt>(getloc()).
get(InIt(
rdbuf()), Init(0), *this,
getloc(), x)
. Here, InIt
is defined as
istreambuf_iterator<E,
T>
, and x
has type double or
long double as needed.
If the converted value cannot
be represented as the type of n
, the function calls
setstate(failbit)
.
In any case, it returns *this
.
int_type peek();
The unformatted input function
extracts an element, if possible, as if by returning
rdbuf()->sgetc()
.
Otherwise, it returns
traits_type::eof()
.
basic_istream& putback(char_type c);
The unformatted input function
puts back c
, if possible, as if by calling
rdbuf()->sputbackc()
.
If rdbuf()
is a null pointer, or if the call to sputbackc
returns
traits_type::eof()
,
the function calls
setstate(badbit)
.
In any case, it returns *this
.
basic_istream& read(char_type *s, streamsize n);
The unformatted input function
extracts up to n
elements
and stores them in the array beginning at s
.
Extraction stops early on end-of-file, in which case the function calls
setstate(failbit)
.
In any case, it returns *this
.
streamsize readsome(char_type *s, streamsize n);
The member function extracts up to n
elements
and stores them in the array beginning at s
.
If rdbuf()
is
a null pointer, the function calls
setstate(failbit)
.
Otherwise, it assigns the value of
rdbuf()->in_avail()
to N
. if N < 0
, the function calls
setstate(eofbit)
.
Otherwise, it replaces the value stored in N
with
the smaller of n
and N
, then calls
read(s, N)
.
In any case, the function returns
gcount()
.
basic_istream& seekg(pos_type pos); basic_istream& seekg(off_type off, ios_base::seek_dir way);
If fail()
is false,
the first member function calls
rdbuf()->
pubseekpos(pos)
.
If fail()
is false, the second function calls
rdbuf()->
pubseekoff(off,
way)
. Both functions return *this
.
class sentry { public: explicit sentry(basic_istream& is, bool noskip = false); operator bool() const; };
The nested class describes an object whose declaration structures the
formatted input functions
and the
unformatted input functions.
The constructor effectively calls
is.ipfx(noskip)
and
stores the return value. operator bool()
delivers this
return value. The destructor effectively calls
is.isfx()
.
int sync();
If rdbuf()
is
a null pointer, the function returns -1. Otherwise, it calls
rdbuf()->pubsync()
.
If that returns -1, the function calls
setstate(badbit)
and returns -1. Otherwise, the function returns zero.
pos_type tellg();
If fail()
is false,
the member function returns
rdbuf()->
pubseekoff(0,
cur,
in)
.
Otherwise, it returns pos_type(-1)
.
basic_istream& unget();
The unformatted input function
puts back the previous element in the stream, if possible, as if by calling
rdbuf()->sungetc()
.
If rdbuf()
is a null pointer, or if the call to sungetc
returns
traits_type::eof()
,
the function calls
setstate(badbit)
.
In any case, it returns *this
.
typedef basic_iostream<char, char_traits<char> > iostream;
The type is a synonym for template class
basic_iostream
, specialized
for elements of type char with default
character traits.
typedef basic_istream<char, char_traits<char> > istream;
The type is a synonym for template class
basic_istream
, specialized
for elements of type char with default
character traits.
template<class E, class T> basic_istream<E, T>& operator>>(basic_istream<E, T>& is, E *s); template<class E, class T> basic_istream<E, T>& operator>>(basic_istream<E, T>& is, E& c); template<class T> basic_istream<char, T>& operator>>(basic_istream<char, T>& is, signed char *s); template<class T> basic_istream<char, T>& operator>>(basic_istream<char, T>& is, signed char& c); template<class T> basic_istream<char, T>& operator>>(basic_istream<char, T>& is, unsigned char *s); template<class T> basic_istream<char, T>& operator>>(basic_istream<char, T>& is, unsigned char& c);
The template function:
template<class E, class T> basic_istream<E, T>& operator>>(basic_istream<E, T>& is, E *s);
extracts up to n - 1
elements
and stores them in the array beginning at s
.
If is.width()
is greater
than zero, n
is is.width()
; otherwise it is
the largest array of E
that can be declared.
The function always stores
E()
after
any extracted elements it stores. Extraction stops early on end-of-file
or on any element (which is not extracted) that would be discarded by
ws
.
If the function extracts no elements, it calls
is.setstate(failbit)
.
In any case, it calls is.width(0)
and
returns is
.
The template function:
template<class E, class T> basic_istream<E, T>& operator>>(basic_istream<E, T>& is, char& c);
extracts an element, if possible, and stores it in c
.
Otherwise, it calls
is.setstate(failbit)
.
In any case, it returns is
.
The template function:
template<class T> basic_istream<char, T>& operator>>(basic_istream<char, T>& is, signed char *s);
returns is >> (char *)s
.
The template function:
template<class T> basic_istream<char, T>& operator>>(basic_istream<char, T>& is, signed char& c);
returns is >> (char&)c
.
The template function:
template<class T> basic_istream<char, T>& operator>>(basic_istream<char, T>& is, unsigned char *s);
returns is >> (char *)s
.
The template function:
template<class T> basic_istream<char, T>& operator>>(basic_istream<char, T>& is, unsigned char& c);
returns is >> (char&)c
.
typedef basic_iostream<wchar_t, char_traits<wchar_t> > wiostream;
The type is a synonym for template class
basic_iostream
, specialized
for elements of type wchar_t
with default
character traits.
typedef basic_istream<wchar_t, char_traits<wchar_t> > wistream;
The type is a synonym for template class
basic_istream
, specialized
for elements of type wchar_t
with default
character traits.
template class<E, T> basic_istream<E, T>& ws(basic_istream<E, T>& is);
The manipulator extracts and discards any elements
x
for which
use_facet<
ctype<E> >(
getloc()).
is(
ctype<E>::space, x)
is true.
The function calls
setstate(eofbit)
if it encounters end-of-file while extracting elements.
It returns is
.
Copyright © 1992-1996 by P.J. Plauger. Portions derived from work copyright © 1994 by Hewlett-Packard Company. All rights reserved.