merge(3C++) - merge(3C++)
Standard C++ Library Copyright 1998, Rogue Wave Software, Inc.
NAMEmerge
- Merges two sorted sequences into a third sequence.
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 con‐
tain 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 per‐
formed.
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 Output1 2 3 41 2 3 41 1 2 2 3 3 4 41 1 2 2 3 3 4 411 12 13 14 15 16 17 1811 12 13 14 15 16 17 181 1 2 2 3 3 4 41 1 2 2 3 3 4 4WARNINGS
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
Rogue Wave Software 02 Apr 1998 merge(3C++)
