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std::forward_list::sort

void sort();
 (1) (since C++11) 
template< class Compare > 
void sort( Compare comp );
 (2) (since C++11)

Sorts the elements in ascending order. The order of equal elements is preserved. The first version uses operator< to compare the elements, the second version uses the given comparison function comp.

If an exception is thrown, the order of elements in *this is unspecified.

Parameters

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);

The signature does not need to have const &, but the function object must not modify the objects passed to it.
The types Type1 and Type2 must be such that an object of type forward_list<T,Allocator>::const_iterator can be dereferenced and then implicitly converted to both of them. ​

Return value

(none).

Complexity

Approximately N log N comparisons, where N is the number of elements in the list.

Notes

std::sort requires random access iterators and so cannot be used with forward_list . This function also differs from std::sort in that it does not require the element type of the forward_list to be swappable, preserves the values of all iterators, and performs a stable sort.

Example

#include <iostream>
#include <functional>
#include <forward_list>
 
std::ostream& operator<<(std::ostream& ostr, const std::forward_list<int>& list)
{
    for (auto &i : list) {
        ostr << " " << i;
    }
    return ostr;
}
 
int main()
{
    std::forward_list<int> list = { 8,7,5,9,0,1,3,2,6,4 };
 
    std::cout << "before:     " << list << "\n";
    list.sort();
    std::cout << "ascending:  " << list << "\n";
    list.sort(std::greater<int>());
    std::cout << "descending: " << list << "\n";
}

Output:

before:      8 7 5 9 0 1 3 2 6 4
ascending:   0 1 2 3 4 5 6 7 8 9
descending:  9 8 7 6 5 4 3 2 1 0

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