std::basic_const_iterator
std::basic_const_iterator
(C++23)(C++23)(C++23)(C++23)
std::basic_const_iterator is an iterator adaptor which behaves exactly like the underlying iterator (which must be at least an LegacyInputIterator or model input_iterator), except that dereferencing converts the value returned by the underlying iterator as immutable. Specializations of std::basic_const_iterator are constant iterators, that is, the iterator can never be used as an output iterator because modifying elements is not allowed.
[edit] Member types
Member type
Definition
iterator_category(conditionally present)
If Iter models forward_iterator:
Otherwise, there is no member iterator_category.
[edit] Member objects
Member name
Definition
current (private)
the underlying iterator from which
base() copies or moves
(exposition-only member object*)
[edit] Member functions
constructs a new
basic_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]
[edit] Non-member functions
compares
basic_const_iterator with non-
basic_const_iterator (function template) [edit]
advances or decrements the iterator
(function template) [edit]
computes the distance between two iterator adaptors
(function template) [edit]
casts the result of dereferencing the underlying iterator to its associated rvalue reference type
(function) [edit]
[edit] Helper classes
determines the common type of an iterator and an adapted
basic_const_iterator type
(class template specialization) [edit]
[edit] Helper alias templates
If I models constant-iterator (an exposition-only concept), then const_iterator<I> denotes a type I. Otherwise, basic_const_iterator<I>.
If S models input_iterator, then const_sentinel<S> denotes a type const_iterator<S>. Otherwise, S.
[edit] Helper function templates
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)
[edit] Example
#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 object
assert (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 writable
assert (*ci == 42); // OK, underlying location v[0] was modified
}
[edit] Defect reports
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
|