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Difference between revisions of "cpp/iterator/reverse iterator/base"

From cppreference.com
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{{cpp/iterator/reverse_iterator/title| base}}
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{{cpp/iterator/reverse_iterator/title|base}}
 
{{cpp/iterator/reverse_iterator/navbar}}
 
{{cpp/iterator/reverse_iterator/navbar}}
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{{dcl begin}}
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{{ddcla|constexpr=c++17|
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{{dcl |  
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iterator_type base() const;
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Iterator base() const;
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}}
 
}}
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{{dcl end}}
 
  
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Returns the underlying base iterator.
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Returns the underlying iterator.
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The base iterator refers to the element that is next to the element the {{tt|reverse_iterator}} is currently pointing to. That is {{c|std::reverse_iterator(it).base() {{==}} std::next(it)}}.
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===Parameters===
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(none)
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===Return value===
 
===Return value===
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The underlying iterator.
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{{box|{{rlpst|/#current}}}}
  
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===Exceptions===
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===Notes===
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(none)
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The base iterator refers to the element that is next (from the {{tt|iterator_type}} perspective) to the element the {{tt|reverse_iterator}} is currently pointing to. That is {{c|1=&*(this->base() - 1) == &*(*this)}}.
  
 
===Example===
 
===Example===
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{{example |
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{{example
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| code=
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|code=
 
#include <iostream>
 
#include <iostream>
 
#include <iterator>
 
#include <iterator>
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int main()
 
int main()
 
{
 
{
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     std::vector<int> v = { 0, 1, 2, 3, 4, 5 };
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     std::vector<int> v = {0, 1, 2, 3, 4, 5};
 
      
 
      
 
     using RevIt = std::reverse_iterator<std::vector<int>::iterator>;
 
     using RevIt = std::reverse_iterator<std::vector<int>::iterator>;
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     RevIt r_end(v.begin());
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     RevIt r_begin(v.end());
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    const auto it = v.begin() + 3;
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     RevIt r_it{it};
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     for (auto it = r_end.base(); it != r_begin.base(); ++it) {
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         std::cout << *it << " ";
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    std::cout << "*it == " << *it << '\n'
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     }
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              << "*r_it == " << *r_it << '\n'
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     std::cout << "\n";
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              << "*r_it.base() == " << *r_it.base() << '\n'
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              << "*(r_it.base() - 1) == " << *(r_it.base() - 1) << '\n';
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    RevIt r_end{v.begin()};
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     RevIt r_begin{v.end()};
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 +
     for (auto it = r_end.base(); it != r_begin.base(); ++it)
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         std::cout << *it << ' ';
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     std::cout << '\n';
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    for (auto it = r_begin; it != r_end; ++it)
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        std::cout << *it << ' ';
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    std::cout << '\n';
 
}
 
}
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| output=
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|output=
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*it == 3
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*r_it == 2
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*r_it.base() == 3
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*(r_it.base() - 1) == 2
 
0 1 2 3 4 5
 
0 1 2 3 4 5
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5 4 3 2 1 0
 
}}
 
}}
  
 
===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
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{{dsc inc | cpp/iterator/adaptor/dsc operator*|reverse_iterator}}
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{{dsc inc|cpp/iterator/adaptor/dsc operator*|reverse_iterator}}
 
{{dsc end}}
 
{{dsc end}}
  
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{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
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[[de:cpp/iterator/reverse iterator/base]]
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[[es:cpp/iterator/reverse iterator/base]]
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[[fr:cpp/iterator/reverse iterator/base]]
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[[it:cpp/iterator/reverse iterator/base]]
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[[ja:cpp/iterator/reverse iterator/base]]
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[[pt:cpp/iterator/reverse iterator/base]]
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[[ru:cpp/iterator/reverse iterator/base]]
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[[zh:cpp/iterator/reverse iterator/base]]
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Latest revision as of 19:24, 30 October 2024

 
C++
 
Iterator library
Iterator concepts
Iterator primitives
Algorithm concepts and utilities
Indirect callable concepts
Common algorithm requirements
(C++20)
(C++20)
(C++20)
Utilities
(C++20)
Iterator adaptors
Range access
(C++11)(C++14)
(C++14)(C++14)  
(C++11)(C++14)
(C++14)(C++14)  
(C++17)(C++20)
(C++17)
(C++17)
 
std::reverse_iterator
 
iterator_type base() const;
 (constexpr since C++17)

Returns the underlying iterator.

Contents

[edit] Return value

current

[edit] Notes

The base iterator refers to the element that is next (from the iterator_type perspective) to the element the reverse_iterator is currently pointing to. That is &*(this->base() - 1) == &*(*this).

[edit] Example

Run this code
#include <iostream>
#include <iterator>
#include <vector>
 
int main()
{
    std::vector<int> v = {0, 1, 2, 3, 4, 5};
 
    using RevIt = std::reverse_iterator<std::vector<int>::iterator>;
 
    const auto it = v.begin() + 3;
    RevIt r_it{it};
 
    std::cout << "*it == " << *it << '\n'
              << "*r_it == " << *r_it << '\n'
              << "*r_it.base() == " << *r_it.base() << '\n'
              << "*(r_it.base() - 1) == " << *(r_it.base() - 1) << '\n';
 
    RevIt r_end{v.begin()};
    RevIt r_begin{v.end()};
 
    for (auto it = r_end.base(); it != r_begin.base(); ++it)
        std::cout << *it << ' ';
    std::cout << '\n';
 
    for (auto it = r_begin; it != r_end; ++it)
        std::cout << *it << ' ';
    std::cout << '\n';
}

Output: 

*it == 3
*r_it == 2
*r_it.base() == 3
*(r_it.base() - 1) == 2
0 1 2 3 4 5
5 4 3 2 1 0

[edit] See also

 accesses the pointed-to element
(public member function) [edit]
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