# merge

**Visual Studio 2008**

Combines all of the elements from two sorted source ranges into a single, sorted destination range, where the ordering criterion may be specified by a binary predicate.

template<class InputIterator1, class InputIterator2, class OutputIterator> OutputIterator merge( InputIterator1 _First1, InputIterator1 _Last1, InputIterator2 _First2, InputIterator2 _Last2, OutputIterator _Result ); template<class InputIterator1, class InputIterator2, class OutputIterator, class BinaryPredicate> OutputIterator merge( InputIterator1 _First1, InputIterator1 _Last1, InputIterator2 _First2, InputIterator2 _Last2, OutputIterator _Result BinaryPredicate _Comp );

The sorted source ranges referenced must be valid; all pointers must be dereferenceable and within each sequence the last position must be reachable from the first by incrementation.

The destination range should not overlap either of the source ranges and should be large enough to contain the destination range.

The sorted source ranges must each be arranged as a precondition to the application of the **merge** algorithm in accordance with the same ordering as is to be used by the algorithm to sort the combined ranges.

The operation is stable as the relative order of elements within each range is preserved in the destination range. The source ranges are not modified by the algorithm **merge**.

The value types of the input iterators need be less-than comparable to be ordered, so that, given two elements, it may be determined either that they are equivalent (in the sense that neither is less than the other) or that one is less than the other. This results in an ordering between the nonequivalent elements. When there are equivalent elements in both source ranges, the elements in the first range precede the elements from the second source range in the destination range.

The complexity of the algorithm is linear with at most (*_Last1 – _First1*) – (*_Last2 – _First2*) – 1 comparisons.

The list class provides a member function merge to merge the elements of two lists.

**merge** has two related forms:

For information on how these functions behave, see Checked Iterators.

// alg_merge.cpp // compile with: /EHsc #include <vector> #include <algorithm> #include <functional> // For greater<int>( ) #include <iostream> // Return whether modulus of elem1 is less than modulus of elem2 bool mod_lesser ( int elem1, int elem2 ) { if (elem1 < 0) elem1 = - elem1; if (elem2 < 0) elem2 = - elem2; return elem1 < elem2; } int main() { using namespace std; vector <int> v1a, v1b, v1 ( 12 ); vector <int>::iterator Iter1a, Iter1b, Iter1; // Constructing vector v1a and v1b with default less than ordering int i; for ( i = 0 ; i <= 5 ; i++ ) v1a.push_back( i ); int ii; for ( ii =-5 ; ii <= 0 ; ii++ ) v1b.push_back( ii ); cout << "Original vector v1a with range sorted by the\n " << "binary predicate less than is v1a = ( " ; for ( Iter1a = v1a.begin( ) ; Iter1a != v1a.end( ) ; Iter1a++ ) cout << *Iter1a << " "; cout << ")." << endl; cout << "Original vector v1b with range sorted by the\n " << "binary predicate less than is v1b = ( " ; for ( Iter1b = v1b.begin ( ) ; Iter1b != v1b.end ( ) ; Iter1b++ ) cout << *Iter1b << " "; cout << ")." << endl; // Constructing vector v2 with ranges sorted by greater vector <int> v2a ( v1a ) , v2b ( v1b ) , v2 ( v1 ); vector <int>::iterator Iter2a, Iter2b, Iter2; sort ( v2a.begin ( ) , v2a.end ( ) , greater<int> ( ) ); sort ( v2b.begin ( ) , v2b.end ( ) , greater<int> ( ) ); cout << "Original vector v2a with range sorted by the\n " << "binary predicate greater is v2a = ( " ; for ( Iter2a = v2a.begin ( ) ; Iter2a != v2a.end ( ) ; Iter2a++ ) cout << *Iter2a << " "; cout << ")." << endl; cout << "Original vector v2b with range sorted by the\n " << "binary predicate greater is v2b = ( " ; for ( Iter2b = v2b.begin ( ) ; Iter2b != v2b.end ( ) ; Iter2b++ ) cout << *Iter2b << " "; cout << ")." << endl; // Constructing vector v3 with ranges sorted by mod_lesser vector <int> v3a ( v1a ), v3b ( v1b ) , v3 ( v1 ); vector <int>::iterator Iter3a, Iter3b, Iter3; sort ( v3a.begin ( ) , v3a.end ( ) , mod_lesser ); sort ( v3b.begin ( ) , v3b.end ( ) , mod_lesser ); cout << "Original vector v3a with range sorted by the\n " << "binary predicate mod_lesser is v3a = ( " ; for ( Iter3a = v3a.begin ( ) ; Iter3a != v3a.end ( ) ; Iter3a++ ) cout << *Iter3a << " "; cout << ")." << endl; cout << "Original vector v3b with range sorted by the\n " << "binary predicate mod_lesser is v3b = ( " ; for ( Iter3b = v3b.begin ( ) ; Iter3b != v3b.end ( ) ; Iter3b++ ) cout << *Iter3b << " "; cout << ")." << endl; // To merge inplace in ascending order with default binary // predicate less <int> ( ) merge ( v1a.begin ( ) , v1a.end ( ) , v1b.begin ( ) , v1b.end ( ) , v1.begin ( ) ); cout << "Merged inplace with default order,\n vector v1mod = ( " ; for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ ) cout << *Iter1 << " "; cout << ")." << endl; // To merge inplace in descending order, specify binary // predicate greater<int>( ) merge ( v2a.begin ( ) , v2a.end ( ) , v2b.begin ( ) , v2b.end ( ) , v2.begin ( ) , greater <int> ( ) ); cout << "Merged inplace with binary predicate greater specified,\n " << "vector v2mod = ( " ; for ( Iter2 = v2.begin( ) ; Iter2 != v2.end( ) ; Iter2++ ) cout << *Iter2 << " "; cout << ")." << endl; // Applying A user-defined (UD) binary predicate mod_lesser merge ( v3a.begin ( ) , v3a.end ( ) , v3b.begin ( ) , v3b.end ( ) , v3.begin ( ) , mod_lesser ); cout << "Merged inplace with binary predicate mod_lesser specified,\n " << "vector v3mod = ( " ; ; for ( Iter3 = v3.begin( ) ; Iter3 != v3.end( ) ; Iter3++ ) cout << *Iter3 << " "; cout << ")." << endl; }

Original vector v1a with range sorted by the binary predicate less than is v1a = ( 0 1 2 3 4 5 ). Original vector v1b with range sorted by the binary predicate less than is v1b = ( -5 -4 -3 -2 -1 0 ). Original vector v2a with range sorted by the binary predicate greater is v2a = ( 5 4 3 2 1 0 ). Original vector v2b with range sorted by the binary predicate greater is v2b = ( 0 -1 -2 -3 -4 -5 ). Original vector v3a with range sorted by the binary predicate mod_lesser is v3a = ( 0 1 2 3 4 5 ). Original vector v3b with range sorted by the binary predicate mod_lesser is v3b = ( 0 -1 -2 -3 -4 -5 ). Merged inplace with default order, vector v1mod = ( -5 -4 -3 -2 -1 0 0 1 2 3 4 5 ). Merged inplace with binary predicate greater specified, vector v2mod = ( 5 4 3 2 1 0 0 -1 -2 -3 -4 -5 ). Merged inplace with binary predicate mod_lesser specified, vector v3mod = ( 0 0 1 -1 2 -2 3 -3 4 -4 5 -5 ).