[istreambuf.iterator] # 24 Iterators library [[iterators]](./#iterators) ## 24.6 Stream iterators [[stream.iterators]](stream.iterators#istreambuf.iterator) ### 24.6.4 Class template istreambuf_iterator [istreambuf.iterator] #### [24.6.4.1](#general) General [[istreambuf.iterator.general]](istreambuf.iterator.general) [1](#general-1) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L6844) The class templateistreambuf_iterator defines an [input iterator](input.iterators "24.3.5.3 Input iterators [input.iterators]") that reads successive*characters* from the streambuf for which it was constructed[.](#general-1.sentence-1) operator* provides access to the current input character, if any[.](#general-1.sentence-2) Each timeoperator++ is evaluated, the iterator advances to the next input character[.](#general-1.sentence-3) If the end of stream is reached (streambuf_type​::​sgetc() returnstraits​::​eof()), the iterator becomes equal to the[*end-of-stream*](#def:end-of-stream) iterator value[.](#general-1.sentence-4) The default constructoristreambuf_iterator() and the constructoristreambuf_iterator(nullptr) both construct an end-of-stream iterator object suitable for use as an end-of-range[.](#general-1.sentence-5) All specializations of istreambuf_iterator shall have a trivial copy constructor, a constexpr default constructor, and a trivial destructor[.](#general-1.sentence-6) [2](#general-2) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L6871) The result ofoperator*() on an end-of-stream iterator is undefined[.](#general-2.sentence-1) For any other iterator value achar_type value is returned[.](#general-2.sentence-2) It is impossible to assign a character via an input iterator[.](#general-2.sentence-3) [🔗](#lib:istreambuf_iterator) namespace std {template>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; using istream_type = basic_istream; // [[istreambuf.iterator.proxy]](#proxy "24.6.4.2 Class 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*};} #### [24.6.4.2](#proxy) Class istreambuf_iterator​::​*proxy* [[istreambuf.iterator.proxy]](istreambuf.iterator.proxy) [1](#proxy-1) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L6924) Classistreambuf_iterator​::​*proxy* is for exposition only[.](#proxy-1.sentence-1) An implementation is permitted to provide equivalent functionality without providing a class with this name[.](#proxy-1.sentence-2) Classistreambuf_iterator​::​*proxy* provides a temporary placeholder as the return value of the post-increment operator (operator++)[.](#proxy-1.sentence-3) It keeps the character pointed to by the previous value of the iterator for some possible future access to get the character[.](#proxy-1.sentence-4) [🔗](#lib:proxy,istreambuf_iterator) namespace std {templateclass istreambuf_iterator::*proxy* { // *exposition only* charT keep_; basic_streambuf* sbuf_; *proxy*(charT c, basic_streambuf* sbuf): keep_(c), sbuf_(sbuf) { }public: charT operator*() { return keep_; }};} #### [24.6.4.3](#cons) Constructors [[istreambuf.iterator.cons]](istreambuf.iterator.cons) [1](#cons-1) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L6955) 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[.](#cons-1.sentence-1) [🔗](#lib:istreambuf_iterator,constructor) `constexpr istreambuf_iterator() noexcept; constexpr istreambuf_iterator(default_sentinel_t) noexcept; ` [2](#cons-2) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L6968) *Effects*: Initializes sbuf_ with nullptr[.](#cons-2.sentence-1) [🔗](#lib:istreambuf_iterator,constructor_) `istreambuf_iterator(istream_type& s) noexcept; ` [3](#cons-3) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L6979) *Effects*: Initializes sbuf_ with s.rdbuf()[.](#cons-3.sentence-1) [🔗](#lib:istreambuf_iterator,constructor__) `istreambuf_iterator(streambuf_type* s) noexcept; ` [4](#cons-4) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L6990) *Effects*: Initializes sbuf_ with s[.](#cons-4.sentence-1) [🔗](#lib:istreambuf_iterator,constructor___) `istreambuf_iterator(const proxy& p) noexcept; ` [5](#cons-5) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L7001) *Effects*: Initializes sbuf_ with p.sbuf_[.](#cons-5.sentence-1) #### [24.6.4.4](#ops) Operations [[istreambuf.iterator.ops]](istreambuf.iterator.ops) [🔗](#lib:operator*,istreambuf_iterator) `charT operator*() const; ` [1](#ops-1) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L7014) *Returns*: The character obtained via thestreambuf membersbuf_->sgetc()[.](#ops-1.sentence-1) [🔗](#lib:operator++,istreambuf_iterator) `istreambuf_iterator& operator++(); ` [2](#ops-2) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L7028) *Effects*: As if by sbuf_->sbumpc()[.](#ops-2.sentence-1) [3](#ops-3) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L7032) *Returns*: *this[.](#ops-3.sentence-1) [🔗](#lib:operator++,istreambuf_iterator_) `proxy operator++(int); ` [4](#ops-4) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L7043) *Returns*: *proxy*(sbuf_->sbumpc(), sbuf_)[.](#ops-4.sentence-1) [🔗](#lib:equal,istreambuf_iterator) `bool equal(const istreambuf_iterator& b) const; ` [5](#ops-5) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L7054) *Returns*: true if and only if both iterators are at end-of-stream, or neither is at end-of-stream, regardless of whatstreambuf object they use[.](#ops-5.sentence-1) [🔗](#lib:operator==,istreambuf_iterator) `template bool operator==(const istreambuf_iterator& a, const istreambuf_iterator& b); ` [6](#ops-6) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L7071) *Returns*: a.equal(b)[.](#ops-6.sentence-1) [🔗](#lib:operator==,istreambuf_iterator_) `friend bool operator==(const istreambuf_iterator& i, default_sentinel_t s); ` [7](#ops-7) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L7082) *Returns*: i.equal(s)[.](#ops-7.sentence-1)