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Difference between revisions of "cpp/algorithm/sort"

From cppreference.com
< cpp‎ | algorithm
m (→‎See also: + std::ranges version; langlinks.)
m (→‎Example: reduce boilerplate printing; "cast" C++ comments into output strings)
Line 77: Line 77:
 
int main()
 
int main()
 
{
 
{
−
     std::array<int, 10> s = {5, 7, 4, 2, 8, 6, 1, 9, 0, 3};  
+
     std::array<int, 10> s = {5, 7, 4, 2, 8, 6, 1, 9, 0, 3};
 +
 
 +
    auto print = [&s](auto const rem) {
 +
        for (auto a : s) {
 +
            std::cout << a << ' ';
 +
        }
 +
        std::cout << ": " << rem << '\n';
 +
    };
  
−
    // sort using the default operator<
 
 
     std::sort(s.begin(), s.end());
 
     std::sort(s.begin(), s.end());
−
     for (auto a : s) {
+
     print("sort using the default operator<");
−
        std::cout << a << " ";
+
−
    } 
+
−
    std::cout << '\n';
+
  
−
    // sort using a standard library compare function object
 
 
     std::sort(s.begin(), s.end(), std::greater<int>());
 
     std::sort(s.begin(), s.end(), std::greater<int>());
−
     for (auto a : s) {
+
     print("sort using a standard library compare function object");
−
        std::cout << a << " ";
+
−
    } 
+
−
    std::cout << '\n';
+
  
−
    // sort using a custom function object
 
 
     struct {
 
     struct {
−
         bool operator()(int a, int b) const
+
         bool operator()(int a, int b) const { return a < b; }
−
        {  
+
−
            return a < b;
+
−
        }  
+
 
     } customLess;
 
     } customLess;
 
     std::sort(s.begin(), s.end(), customLess);
 
     std::sort(s.begin(), s.end(), customLess);
−
     for (auto a : s) {
+
     print("sort using a custom function object");
−
        std::cout << a << " ";
+
−
    } 
+
−
    std::cout << '\n';
+
  
−
    // sort using a lambda expression
 
 
     std::sort(s.begin(), s.end(), [](int a, int b) {
 
     std::sort(s.begin(), s.end(), [](int a, int b) {
−
         return a > b;  
+
         return a > b;
 
     });
 
     });
−
     for (auto a : s) {
+
     print("sort using a lambda expression");
−
        std::cout << a << " ";
+
−
    }
+
−
    std::cout << '\n';
+
 
}  
 
}  
 
  | output=
 
  | output=
−
0 1 2 3 4 5 6 7 8 9  
+
0 1 2 3 4 5 6 7 8 9 : sort using the default operator<
−
9 8 7 6 5 4 3 2 1 0  
+
9 8 7 6 5 4 3 2 1 0 : sort using a standard library compare function object
−
0 1 2 3 4 5 6 7 8 9  
+
0 1 2 3 4 5 6 7 8 9 : sort using a custom function object
−
9 8 7 6 5 4 3 2 1 0  
+
9 8 7 6 5 4 3 2 1 0 : sort using a lambda expression
 
}}
 
}}
  

Revision as of 11:18, 9 January 2021

 
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
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>
(1)
template< class RandomIt >
void sort( RandomIt first, RandomIt last );
 (until C++20)
template< class RandomIt >
constexpr void sort( RandomIt first, RandomIt last );
 (since C++20)
template< class ExecutionPolicy, class RandomIt >
void sort( ExecutionPolicy&& policy, RandomIt first, RandomIt last );
 (2) (since C++17)
(3)
template< class RandomIt, class Compare >
void sort( RandomIt first, RandomIt last, Compare comp );
 (until C++20)
template< class RandomIt, class Compare >
constexpr void sort( RandomIt first, RandomIt last, Compare comp );
 (since C++20)
template< class ExecutionPolicy, class RandomIt, class Compare >
void sort( ExecutionPolicy&& policy, RandomIt first, RandomIt last, Compare comp );
 (4) (since C++17)

Sorts the elements in the range [first, last) in non-descending order. The order of equal elements is not guaranteed to be preserved.

A sequence is sorted with respect to a comparator comp if for any iterator it pointing to the sequence and any non-negative integer n such that it + n is a valid iterator pointing to an element of the sequence, comp(*(it + n), *it) (or *(it + n) < *it) evaluates to false.

1) Elements are compared using operator<.
3) Elements are compared using the given binary comparison function comp.
2,4) Same as (1,3), but executed according to policy. These overloads participate in overload resolution only if

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

(until C++20)

std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.

(since C++20)

Contents

Parameters

first, last - the range of elements to sort
policy - the execution policy to use. See execution policy for details.
comp - comparison function object (i.e. an object that satisfies the requirements of Compare) which returns ​true if the first argument is less than (i.e. is ordered before) the second.

The signature of the comparison function should be equivalent to the following:

bool cmp(const Type1& a, const Type2& b);

While the signature does not need to have const&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 regardless of value category (thus, Type1& is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy(since C++11)).
The types Type1 and Type2 must be such that an object of type RandomIt can be dereferenced and then implicitly converted to both of them. ​

Type requirements
-
RandomIt must meet the requirements of ValueSwappable and LegacyRandomAccessIterator.
-
The type of dereferenced RandomIt must meet the requirements of MoveAssignable and MoveConstructible.
-
Compare must meet the requirements of Compare.

Return value

(none)

Complexity

O(N·log(N)), where N = std::distance(first, last) comparisons on average.

(until C++11)

O(N·log(N)), where N = std::distance(first, last) comparisons.

(since C++11)

Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

  • If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation

See also the implementations in libstdc++ and libc++.

Example

Run this code
#include <algorithm>
#include <functional>
#include <array>
#include <iostream>
 
int main()
{
    std::array<int, 10> s = {5, 7, 4, 2, 8, 6, 1, 9, 0, 3};
 
    auto print = [&s](auto const rem) {
        for (auto a : s) {
            std::cout << a << ' ';
        }
        std::cout << ": " << rem << '\n';
    };
 
    std::sort(s.begin(), s.end());
    print("sort using the default operator<");
 
    std::sort(s.begin(), s.end(), std::greater<int>());
    print("sort using a standard library compare function object");
 
    struct {
        bool operator()(int a, int b) const { return a < b; }
    } customLess;
    std::sort(s.begin(), s.end(), customLess);
    print("sort using a custom function object");
 
    std::sort(s.begin(), s.end(), [](int a, int b) {
        return a > b;
    });
    print("sort using a lambda expression");
}

Output: 

0 1 2 3 4 5 6 7 8 9 : sort using the default operator<
9 8 7 6 5 4 3 2 1 0 : sort using a standard library compare function object
0 1 2 3 4 5 6 7 8 9 : sort using a custom function object
9 8 7 6 5 4 3 2 1 0 : sort using a lambda expression

See also

 sorts the first N elements of a range
(function template) [edit]
sorts a range of elements while preserving order between equal elements
(function template) [edit]
(C++20)
 sorts a range into ascending order
(niebloid)[edit]
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