| Iterator concepts | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Iterator primitives | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Algorithm concepts and utilities | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Indirect callable concepts | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Common algorithm requirements | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Utilities | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Iterator adaptors | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Member functions | ||||
| Non-member functions | ||||
(C++23)(C++23)(C++23)(C++23) | ||||
(C++23) | ||||
(C++23) | ||||
| Helper classes | ||||
Defined in header <iterator> | ||
template<std::input_iterator Iter> class basic_const_iterator; | (since C++23) | |
std::basic_const_iterator is an iterator adaptor which behaves exactly like the underlying iterator (which must be at least anLegacyInputIterator or modelinput_iterator), except that dereferencing converts the value returned by the underlying iterator as immutable. Specializations ofstd::basic_const_iterator are constant iterators, that is, the iterator can never be used as an output iterator because modifying elements is not allowed.
Contents |
| Member type | Definition |
iterator_category(conditionally present) | If
Otherwise, there is no member |
iterator_concept |
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value_type | std::iter_value_t<Iter> |
difference_type | std::iter_difference_t<Iter> |
reference(private) | std::iter_const_reference_t<Iter> (exposition-only member type*) |
| Member name | Definition |
current(private) | the underlying iterator from whichbase() copies or moves(exposition-only member object*) |
constructs a newbasic_const_iterator(public member function)[edit] | |
| accesses the underlying iterator (public member function)[edit] | |
| accesses the pointed-to element (public member function)[edit] | |
| accesses an element by index (public member function)[edit] | |
| advances or decrements the iterator (public member function)[edit] | |
| converts into any constant iterator to which an underlying iterator can be convertible (public member function)[edit] | |
| compares the underlying iterators (public member function)[edit] |
comparesbasic_const_iterator with non-basic_const_iterator(function template)[edit] | |
(C++23) | advances or decrements the iterator (function template)[edit] |
(C++23) | computes the distance between two iterator adaptors (function template)[edit] |
(C++23) | casts the result of dereferencing the underlying iterator to its associated rvalue reference type (function)[edit] |
determines the common type of an iterator and an adaptedbasic_const_iterator type(class template specialization)[edit] |
template<std::input_iterator I> using const_iterator=/* see description */; | (since C++23) | |
IfI modelsconstant-iterator (an exposition-only concept), thenconst_iterator<I> denotes a typeI. Otherwise,basic_const_iterator<I>.
template<std::semiregular S> using const_sentinel=/* see description */; | (since C++23) | |
IfS modelsinput_iterator, thenconst_sentinel<S> denotes a typeconst_iterator<S>. Otherwise,S.
template<std::input_iterator T> constexpr const_iterator<T> make_const_iterator( I it){return it;} | (since C++23) | |
template<std::semiregular S> constexpr const_sentinel<S> make_const_sentinel( S s){return s;} | (since C++23) | |
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_ranges_as_const | 202207L | (C++23) | std::basic_const_iterator |
202311L | (C++23) (DR) | std::basic_const_iterator should follow its underlying type's convertibility |
#include <cassert>#include <iterator>#include <vector> int main(){std::vector v{1,2,3};std::vector<int>::iterator i= v.begin();*i=4;// OK, v[0] == 4 now i[1]=4;// OK, the same as *(i + 1) = 4; auto ci=std::make_const_iterator(i);assert(*ci==4);// OK, can read the underlying objectassert(ci[0]==4);// OK, ditto// *ci = 13; // Error: location is read-only// ci[0] = 13; // Error: ditto ci.base()[0]=42;// OK, underlying iterator is writableassert(*ci==42);// OK, underlying location v[0] was modified}
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| P2836R1 | C++23 | basic_const_iterator doesn't follow its underlying type's convertibility | conversion operator provided |
