## merge

    Algorithm

- Summary
- Data Type and Member Function Indexes
- Synopsis
- Description
- Complexity
- Example
- Warnings
- See Also

### Summary

Merges two sorted sequences into a third sequence.

### Data Type and Member Function Indexes
(exclusive of constructors and destructors)

None

### Synopsis

    #include <algorithm>
    template <class InputIterator1, class InputIterator2,
              class OutputIterator>
      OutputIterator
      merge(InputIterator first1, InputIterator1 last1,
            InputIterator2 first2, InputIterator last2,
            OutputIterator result);

    template <class InputIterator1, class InputIterator2,
              class OutputIterator, class Compare>
      OutputIterator
      merge(InputIterator1 first1, InputIterator1 last1,
            InputIterator2 first2, InputIterator last2,
            OutputIterator result, Compare comp);

### Description

The merge algorithm merges two sorted sequences, specified by `[first1, last1)` and `[first2, last2)`, into the sequence specified by `[result, result + (last1 - first1) + (last2 - first2))`. The first version of the merge algorithm uses the less than operator (`<`) to compare elements in the two sequences. The second version uses the comparison function included in the function call. If a comparison function is included, merge assumes that both sequences were sorted using that comparison function.

The merge is stable. This means that if the two original sequences contain equivalent elements, the elements from the first sequence always precede the matching elements from the second in the resulting sequence. The size of the result of a merge is equal to the sum of the sizes of the two argument sequences. merge returns an iterator that points to the end of the resulting sequence (in other words, `result + (last1 - first1) + (last2 -first2)`). The result of merge is undefined if the resulting range overlaps with either of the original ranges.

merge assumes that there are at least `(last1 - first1) + (last2 -` `first2)` elements following `result`, unless `result` has been adapted by an insert iterator.

### Complexity

At most `(last - first1) + (last2 - first2) - 1` comparisons are performed.

### Example

    //
    // merge.cpp
    //
     #include <algorithm>
     #include <vector>
     #include <iostream>
     using namespace std;

     int main()
     {
       int d1[4] = {1,2,3,4};
       int d2[8] = {11,13,15,17,12,14,16,18};

       // Set up two vectors
       vector<int> v1(d1,d1 + 4), v2(d1,d1 + 4);
       // Set up four destination vectors
       vector<int> v3(d2,d2 + 8),v4(d2,d2 + 8),
                   v5(d2,d2 + 8),v6(d2,d2 + 8);
       // Set up one empty vector
       vector<int> v7;

       // Merge v1 with v2
       merge(v1.begin(),v1.end(),v2.begin(),v2.end(),
             v3.begin());
       // Now use comparator
       merge(v1.begin(),v1.end(),v2.begin(),v2.end(),v4.begin(),
             less<int>());

       // In place merge v5
       vector<int>::iterator mid = v5.begin();
       advance(mid,4);
       inplace_merge(v5.begin(),mid,v5.end());
       // Now use a comparator on v6
       mid = v6.begin();
       advance(mid,4);
       inplace_merge(v6.begin(),mid,v6.end(),less<int>());

       // Merge v1 and v2 to empty vector using insert iterator
       merge(v1.begin(),v1.end(),v2.begin(),v2.end(),
             back_inserter(v7));

       // Copy all cout
       ostream_iterator<int,char> out(cout," ");
       copy(v1.begin(),v1.end(),out);
       cout << endl;
       copy(v2.begin(),v2.end(),out);
       cout << endl;
       copy(v3.begin(),v3.end(),out);
       cout << endl;
       copy(v4.begin(),v4.end(),out);
       cout << endl;
       copy(v5.begin(),v5.end(),out);
       cout << endl;
       copy(v6.begin(),v6.end(),out);
       cout << endl;
       copy(v7.begin(),v7.end(),out);
       cout << endl;

       // Merge v1 and v2 to cout
       merge(v1.begin(),v1.end(),v2.begin(),v2.end(),
             ostream_iterator<int,char>(cout," "));
       cout << endl;

       return 0;
     }

Program Output

    1 2 3 4
    1 2 3 4
    1 1 2 2 3 3 4 4
    1 1 2 2 3 3 4 4
    11 12 13 14 15 16 17 18
    11 12 13 14 15 16 17 18
    1 1 2 2 3 3 4 4
    1 1 2 2 3 3 4 4

### Warnings

If your compiler does not support default template parameters, then you always need to supply the `Allocator` template argument. For instance, you have to write:

`vector<int,allocator<int> >`

instead of:

`vector<int>`

If your compiler does not support namespaces, then you do not need the using declaration for `std`.

### See Also

Containers, inplace_merge

Copyright (c) 1998, Rogue Wave Software, Inc.
Send mail to report errors or comment on the documentation.
OEM Release, June 1998