std:: sort

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

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

Parameters

Complexity

Given \(\scriptsize N\) N as last - first :

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++ .

Notes

Before LWG713 , the complexity requirement allowed sort() to be implemented using only Quicksort , which may need \(\scriptsize O(N^2)\) O(N 2 ) comparisons in the worst case.

Introsort can handle all cases with \(\scriptsize O(N \cdot \log(N))\) O(N·log(N)) comparisons (without incurring additional overhead in the average case), and thus is usually used for implementing sort() .

libc++ has not implemented the corrected time complexity requirement until LLVM 14 .

Example

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

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

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also