Merge operations empower you to merge sorted ranges in a new sorted range. The algorithm requires that the ranges and the algorithm use the same sorting criterion. If not, the program is undefined. Per default the predefined sorting criterion
std::less is used. If you use your sorting criterion, it has to obey the strict weak ordering. If not, the program is undefined.
You can merge two sorted ranges with
std::merge. You can check with
std::includes if one sorted range is in another sorted range. You can merge with
std::set_union two sorted ranges in a new sorted range.
Merges in place two sorted sub ranges
[first, mid) and