std::forward_list<T,Allocator>:: merge

The function does nothing if other refers to the same object as * this .

Otherwise, merges other into * this . Both lists should be sorted. No elements are copied, and the container other becomes empty after the merge. This operation is stable: for equivalent elements in the two lists, the elements from * this always precede the elements from other , and the order of equivalent elements of * this and other does not change.

No iterators or references become invalidated. The pointers and references to the elements moved from * this , as well as the iterators referring to these elements, will refer to the same elements of * this , instead of other .

If * this or other is not sorted with respected to the corresponding comparator, or get_allocator ( ) ! = other. get_allocator ( ) , the behavior is undefined.

Parameters

Return value

(none)

Exceptions

If an exception is thrown for any reason, these functions have no effect ( strong exception safety guarantee ). Except if the exception comes from a comparison.

Complexity

If other refers to the same object as * this , no comparisons are performed.

Otherwise, given \(\scriptsize N\) N as std:: distance ( begin ( ) , end ( ) ) and \(\scriptsize R\) R as std:: distance ( other. begin ( ) , other. end ( ) ) :

Example

#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> list1 = {5, 9, 1, 3, 3};
    std::forward_list<int> list2 = {8, 7, 2, 3, 4, 4};
 
    list1.sort();
    list2.sort();
    std::cout << "list1: " << list1 << '\n';
    std::cout << "list2: " << list2 << '\n';
 
    list1.merge(list2);
    std::cout << "merged:" << list1 << '\n';
}

list1:  1 3 3 5 9
list2:  2 3 4 4 7 8
merged: 1 2 3 3 3 4 4 5 7 8 9

Defect reports

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

See also