# std::forward_list<T,Allocator>::sort

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< cpp‎ | container‎ | forward list

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);

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. ​

### 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

Run this code

    #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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