std:: partial_sort_copy

Sorts some of the elements in the range [ first , last ) in ascending order, storing the result in the range [ d_first , d_last ) .

At most d_last - d_first of the elements are placed sorted to the range [ d_first , d_first + n ) . n is the number of elements to sort ( std:: min ( std:: distance ( first, last ) , d_last - d_first ) ). The order of equal elements is not guaranteed to be preserved.

If * first is not writable to d_first , the program is ill-formed.

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

Parameters

Return value

An iterator to the element defining the upper boundary of the sorted range, i.e. d_first + std:: min ( std:: distance ( first, last ) , d_last - d_first ) .

Complexity

Given \(\scriptsize N\) N as std:: distance ( first, last ) , \(\scriptsize D\) D as d_last - d_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++ .

Example

#include <algorithm>
#include <functional>
#include <iostream>
#include <string_view>
#include <type_traits>
#include <vector>
 
void println(std::string_view rem, const auto& v)
{
    std::cout << rem;
    if constexpr (std::is_scalar_v<std::decay_t<decltype(v)>>)
        std::cout << v;
    else
        for (int e : v)
            std::cout << e << ' ';
    std::cout << '\n';
}
 
int main()
{
    const auto v0 = {4, 2, 5, 1, 3};
    std::vector<int> v1{10, 11, 12};
    std::vector<int> v2{10, 11, 12, 13, 14, 15, 16};
    std::vector<int>::iterator it;
 
    it = std::partial_sort_copy(v0.begin(), v0.end(), v1.begin(), v1.end());
    println("Writing to the smaller vector in ascending order gives: ", v1);
 
    if (it == v1.end())
        println("The return value is the end iterator", ' ');
 
    it = std::partial_sort_copy(v0.begin(), v0.end(), v2.begin(), v2.end(),
                                std::greater<int>());
 
    println("Writing to the larger vector in descending order gives: ", v2);
    println("The return value is the iterator to ", *it);
}

Writing to the smaller vector in ascending order gives: 1 2 3
The return value is the end iterator
Writing to the larger vector in descending order gives: 5 4 3 2 1 15 16
The return value is the iterator to 15

Defect reports

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

See also