25 Iterators library [iterators]

25.6 Stream iterators [stream.iterators]

25.6.4 Class template istreambuf_­iterator [istreambuf.iterator]

25.6.4.1 General [istreambuf.iterator.general]

The class template istreambuf_­iterator defines an input iterator that reads successive characters from the streambuf for which it was constructed.
operator* provides access to the current input character, if any.
Each time operator++ is evaluated, the iterator advances to the next input character.
If the end of stream is reached (streambuf_­type​::​sgetc() returns traits​::​eof()), the iterator becomes equal to the end-of-stream iterator value.
The default constructor istreambuf_­iterator() and the constructor istreambuf_­iterator(nullptr) both construct an end-of-stream iterator object suitable for use as an end-of-range.
All specializations of istreambuf_­iterator shall have a trivial copy constructor, a constexpr default constructor, and a trivial destructor.
The result of operator*() on an end-of-stream iterator is undefined.
For any other iterator value a char_­type value is returned.
It is impossible to assign a character via an input iterator.
namespace std { template<class charT, class traits = char_traits<charT>> class istreambuf_iterator { public: using iterator_category = input_iterator_tag; using value_type = charT; using difference_type = typename traits::off_type; using pointer = unspecified; using reference = charT; using char_type = charT; using traits_type = traits; using int_type = typename traits::int_type; using streambuf_type = basic_streambuf<charT,traits>; using istream_type = basic_istream<charT,traits>; // [istreambuf.iterator.proxy], class istreambuf_­iterator​::​proxy class proxy; // exposition only constexpr istreambuf_iterator() noexcept; constexpr istreambuf_iterator(default_sentinel_t) noexcept; istreambuf_iterator(const istreambuf_iterator&) noexcept = default; ~istreambuf_iterator() = default; istreambuf_iterator(istream_type& s) noexcept; istreambuf_iterator(streambuf_type* s) noexcept; istreambuf_iterator(const proxy& p) noexcept; istreambuf_iterator& operator=(const istreambuf_iterator&) noexcept = default; charT operator*() const; istreambuf_iterator& operator++(); proxy operator++(int); bool equal(const istreambuf_iterator& b) const; friend bool operator==(const istreambuf_iterator& i, default_sentinel_t s); private: streambuf_type* sbuf_; // exposition only }; }

25.6.4.2 Class istreambuf_­iterator​::​proxy [istreambuf.iterator.proxy]

Class istreambuf_­iterator<charT,traits>​::​proxy is for exposition only.
An implementation is permitted to provide equivalent functionality without providing a class with this name.
Class istreambuf_­iterator<charT, traits>​::​proxy provides a temporary placeholder as the return value of the post-increment operator (operator++).
It keeps the character pointed to by the previous value of the iterator for some possible future access to get the character.
namespace std { template<class charT, class traits> class istreambuf_iterator<charT, traits>::proxy { // exposition only charT keep_; basic_streambuf<charT,traits>* sbuf_; proxy(charT c, basic_streambuf<charT,traits>* sbuf) : keep_(c), sbuf_(sbuf) { } public: charT operator*() { return keep_; } }; }

25.6.4.3 Constructors [istreambuf.iterator.cons]

For each istreambuf_­iterator constructor in this subclause, an end-of-stream iterator is constructed if and only if the exposition-only member sbuf_­ is initialized with a null pointer value.
constexpr istreambuf_iterator() noexcept; constexpr istreambuf_iterator(default_sentinel_t) noexcept;
Effects: Initializes sbuf_­ with nullptr.
istreambuf_iterator(istream_type& s) noexcept;
Effects: Initializes sbuf_­ with s.rdbuf().
istreambuf_iterator(streambuf_type* s) noexcept;
Effects: Initializes sbuf_­ with s.
istreambuf_iterator(const proxy& p) noexcept;
Effects: Initializes sbuf_­ with p.sbuf_­.

25.6.4.4 Operations [istreambuf.iterator.ops]

charT operator*() const;
Returns: The character obtained via the streambuf member sbuf_­->sgetc().
istreambuf_iterator& operator++();
Effects: As if by sbuf_­->sbumpc().
Returns: *this.
proxy operator++(int);
Returns: proxy(sbuf_­->sbumpc(), sbuf_­).
bool equal(const istreambuf_iterator& b) const;
Returns: true if and only if both iterators are at end-of-stream, or neither is at end-of-stream, regardless of what streambuf object they use.
template<class charT, class traits> bool operator==(const istreambuf_iterator<charT,traits>& a, const istreambuf_iterator<charT,traits>& b);
Returns: a.equal(b).
friend bool operator==(const istreambuf_iterator& i, default_sentinel_t s);
Returns: i.equal(s).