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Difference between revisions of "cpp/algorithm/iter swap"

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< cpp‎ | algorithm
m (Text replace - "===Equivalent function===" to "===Possible implementation===")
(Wording update.)
 
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{{cpp/title|iter_swap}}
 
{{cpp/title|iter_swap}}
−
{{cpp/algorithm/sidebar}}
+
{{cpp/algorithm/navbar}}
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{{ddcl list begin}}
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{{ddcl|header=algorithm|notes={{mark constexpr since c++20}}|
−
{{ddcl list header | algorithm}}
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template< class ForwardIt1, class ForwardIt2 >
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{{ddcl list item |
+
void iter_swap( ForwardIt1 a, ForwardIt2 b );
−
template< class ForwardIterator1, class ForwardIterator2 >
+
−
void iter_swap( ForwardIterator1 a, ForwardIterator2 b );
+
 
}}
 
}}
−
{{ddcl list end}}
 
  
−
Swaps the values of the elements the given iterators are pointing to.  
+
Swaps the values of the elements the given iterators are pointing to.
 +
 
 +
If any of the following conditions is satisfied, the behavior is undefined:
 +
* {{c|a}} or {{c|b}} is not [[cpp/iterator#Dereferenceability and validity|dereferenceable]].
 +
* {{c|*a}} is not {{named req|Swappable}} with {{c|*b}}.
  
 
===Parameters===
 
===Parameters===
−
{{param list begin}}
+
{{par begin}}
−
{{param list item | a, b | iterators to the elements to swap}}
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{{par|a, b|iterators to the elements to swap}}
−
{{param list end}}
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{{par hreq}}
 +
{{par req named|ForwardIt1, ForwardIt2|ForwardIterator}}
 +
{{par end}}
  
 
===Return value===
 
===Return value===
Line 20: Line 23:
  
 
===Complexity===
 
===Complexity===
 +
Constant.
  
−
constant
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===Notes===
 +
This function template models the semantics of the swap operation given by {{named req|Swappable}}. That is, overloads of {{c|swap}} found by [[cpp/language/adl|ADL]] and the fall back of {{lc|std::swap}} are considered.
  
 
===Possible implementation===
 
===Possible implementation===
−
{{eq fun cpp | 1=
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{{eq fun|1=
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template<class ForwardIterator1, class ForwardIterator2>
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template<class ForwardIt1, class ForwardIt2>
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void iter_swap(ForwardIterator1 a, ForwardIterator2 b)
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constexpr //< since C++20
 +
void iter_swap(ForwardIt1 a, ForwardIt2 b)
 
{
 
{
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  std::swap(*a, *b);
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    using std::swap;
 +
    swap(*a, *b);
 
}
 
}
 
}}
 
}}
  
 
===Example===
 
===Example===
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{{example cpp
+
{{example
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| The following is an implementation of selection sort in C++
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|The following is an implementation of selection sort in C++.
−
| code=#include <random>
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|code=
−
#include <vector>
+
−
#include <iostream>
+
 
#include <algorithm>
 
#include <algorithm>
−
#include <functional>
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#include <iostream>
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#include <iterator>
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#include <random>
 +
#include <string_view>
 +
#include <vector>
  
−
template<class ForwardIterator>
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template<class ForwardIt>
−
void selection_sort(ForwardIterator begin, ForwardIterator end)
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void selection_sort(ForwardIt begin, ForwardIt end)
 
{
 
{
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     for(ForwardIterator i = begin; i != end; ++i)
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     for (ForwardIt it = begin; it != end; ++it)
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         std::iter_swap(i, std::min_element(i, end));
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         std::iter_swap(it, std::min_element(it, end));
 
}
 
}
  
−
int main()
+
void println(std::string_view rem, std::vector<int> const& v)
 
{
 
{
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     std::random_device rd;
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     std::cout << rem;
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     std::mt19937 gen(rd());
+
     for (int e : v)
−
    std::uniform_int_distribution<> dist(-10, 10);
+
        std::cout << e << ' ';
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     std::vector<int> v;
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     std::cout << '\n';
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    generate_n(back_inserter(v), 20, bind(dist, gen));
+
}
  
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     std::cout << "Before sort: ";
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template<int min, int max>
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    copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " "));
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int rand_int()
 +
{
 +
     static std::uniform_int_distribution dist(min, max);
 +
    static std::mt19937 gen(std::random_device{}());
 +
    return dist(gen);
 +
}
  
 +
int main()
 +
{
 +
    std::vector<int> v;
 +
    std::generate_n(std::back_inserter(v), 20, rand_int<-9, +9>);
 +
   
 +
    std::cout << std::showpos;
 +
    println("Before sort: ", v);
 
     selection_sort(v.begin(), v.end());
 
     selection_sort(v.begin(), v.end());
−
 
+
     println("After sort: ", v);
−
     std::cout << "\nAfter sort: ";
+
−
    copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " "));
+
−
    std::cout << '\n';
+
 
}
 
}
−
| output=Before sort: -7 6 2 4 -1 6 -9 -1 2 -5 10 -9 -5 -3 -5 -3 6 6 1 8
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|p=true
−
After sort: -9 -9 -7 -5 -5 -5 -3 -3 -1 -1 1 2 2 4 6 6 6 6 8 10
+
|output=
 +
Before sort: -9 -3 +2 -8 +0 -1 +8 -4 -5 +1 -4 -5 +4 -9 -8 -6 -6 +8 -4 -6
 +
After sort: -9 -9 -8 -8 -6 -6 -6 -5 -5 -4 -4 -4 -3 -1 +0 +1 +2 +4 +8 +8
 
}}
 
}}
 +
 +
===Defect reports===
 +
{{dr list begin}}
 +
{{dr list item|wg=lwg|dr=187|std=C++98|before=it was unspecified whether {{c|swap}} is used|after=the effect is equivalent to {{c|swap(*a, *b)}}}}
 +
{{dr list end}}
  
 
===See also===
 
===See also===
−
{{dcl list begin}}
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{{dsc begin}}
−
{{dcl list template | cpp/algorithm/dcl list swap}}
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{{dsc inc|cpp/algorithm/dsc swap}}
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{{dcl list template | cpp/algorithm/dcl list swap_ranges}}
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{{dsc inc|cpp/algorithm/dsc swap_ranges}}
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{{dcl list end}}
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{{dsc inc|cpp/iterator/adaptor/dsc iter_swap|reverse_iterator}}
 +
{{dsc inc|cpp/iterator/adaptor/dsc iter_swap|move_iterator}}
 +
{{dsc inc|cpp/iterator/ranges/dsc iter_swap}}
 +
{{dsc end}}
 +
 
 +
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Latest revision as of 23:49, 25 March 2024

 
C++
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
(C++11)
Swap operations
iter_swap
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
Defined in header <algorithm>
template< class ForwardIt1, class ForwardIt2 >
void iter_swap( ForwardIt1 a, ForwardIt2 b );
 (constexpr since C++20)

Swaps the values of the elements the given iterators are pointing to.

If any of the following conditions is satisfied, the behavior is undefined:

Contents

[edit] Parameters

a, b - iterators to the elements to swap
Type requirements
-
ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.

[edit] Return value

(none)

[edit] Complexity

Constant.

[edit] Notes

This function template models the semantics of the swap operation given by Swappable. That is, overloads of swap found by ADL and the fall back of std::swap are considered.

[edit] Possible implementation

template<class ForwardIt1, class ForwardIt2>
constexpr //< since C++20
void iter_swap(ForwardIt1 a, ForwardIt2 b)
{
    using std::swap;
    swap(*a, *b);
}

[edit] Example

The following is an implementation of selection sort in C++.

Run this code
#include <algorithm>
#include <iostream>
#include <random>
#include <string_view>
#include <vector>
 
template<class ForwardIt>
void selection_sort(ForwardIt begin, ForwardIt end)
{
    for (ForwardIt it = begin; it != end; ++it)
        std::iter_swap(it, std::min_element(it, end));
}
 
void println(std::string_view rem, std::vector<int> const& v)
{
    std::cout << rem;
    for (int e : v)
        std::cout << e << ' ';
    std::cout << '\n';
}
 
template<int min, int max>
int rand_int()
{
    static std::uniform_int_distribution dist(min, max);
    static std::mt19937 gen(std::random_device{}());
    return dist(gen);
}
 
int main()
{
    std::vector<int> v;
    std::generate_n(std::back_inserter(v), 20, rand_int<-9, +9>);
 
    std::cout << std::showpos;
    println("Before sort: ", v);
    selection_sort(v.begin(), v.end());
    println("After sort:  ", v);
}

Possible output: 

Before sort: -9 -3 +2 -8 +0 -1 +8 -4 -5 +1 -4 -5 +4 -9 -8 -6 -6 +8 -4 -6 
After sort:  -9 -9 -8 -8 -6 -6 -6 -5 -5 -4 -4 -4 -3 -1 +0 +1 +2 +4 +8 +8

[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
LWG 187 C++98 it was unspecified whether swap is used the effect is equivalent to swap(*a, *b)

[edit] See also

 swaps the values of two objects
(function template) [edit]
swaps two ranges of elements
(function template) [edit]
(C++20)
 swaps the objects pointed to by two adjusted underlying iterators
(function template) [edit]
(C++20)
 swaps the objects pointed to by two underlying iterators
(function template) [edit]
(C++20)
 swaps the values referenced by two dereferenceable objects
(customization point object)[edit]
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