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std::forward_list<T,Allocator>::sort - cppreference.com

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void sort();

 (1) (since C++11)

template< class Compare > void sort( Compare comp );

 (2) (since C++11)

Sorts the elements and preserves the order of equivalent elements. No references or iterators become invalidated.

1) Elements are compared using operator<.

2) Elements are compared using 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);

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 forward_list<T,Allocator>::const_iterator can be dereferenced and then implicitly converted to both of them. ​

Type requirements
-Compare must meet the requirements of Compare.

Return value

(none)

Complexity

Given N as std::distance(begin(), end()):

1) Approximately N·log(N) comparisons using operator<.

2) Approximately N·log(N) applications of the comparison function comp.

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 <functional>
#include <iostream>
#include <forward_list>

std::ostream& operator<<(std::ostream& ostr, const std::forward_list<int>& list)
{
    for (const int 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 << "initially: " << list << '\n';
    
    list.sort();
    std::cout << "ascending: " << list << '\n';
    
    list.sort(std::greater<int>());
    std::cout << "descending:" << list << '\n';
}

Output: 

initially:  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

See also

reverses the order of the elements
(public member function) [edit]