copy_backward

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Contents
  1. Definition
  2. Interface
  3. Description
  4. Return Value
  5. Complexity
  6. References
  7. See Also

Copies a range starting with the last element

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Computing Stl Algorithms Modifying

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Definition

The copy_backward() algorithm is defined in the standard header <algorithm> and in the nonstandard backward-compatibility header <algo.h>.

Interface

#include <algorithm>
template < class BidirectionalIterator1, class BidirectionalIterator2 >
   BidirectionalIterator2 copy_backward(
      BidirectionalIterator1 first, 
      BidirectionalIterator1 last,
      BidirectionalIterator2 result
   );

Parameters:

ParameterDescription
firstA bidirectional iterator addressing the position of the first element in the source range
lastA bidirectional iterator addressing the position that is one past the final element in the source range
resultA bidirectional iterator addressing the position of the one past the final element in the destination range

Description

Copy_backwards is the same as http://www.codecogs.com/reference/computing/stl/algorithms/modifying/copy.php"copy", but the copy is made from the end of the source sequence to its beginning.

Return Value

Returns an iterator on the element following the last copied element, result - (last - first).

Complexity

The complexity is linear, there are last - first assignments.

References

Example 1
Problem

The following example demonstrates the difference between copy() and copy_backward().

Workings
#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
  // initialize source collection with ".......... abcdef.........."
  vector<char> source(10,'.');
  for (int c='a'; c<='f'; C++) 
    source.push_back(c);
    
  source.insert(source.end(),10,'.');
  PRINT_ELEMENTS(source,"source: ");

  //copy all letters three elements in front of the 'a'
  vector<char> c1(source.begin(),source.end());
  copy (c1.begin()+10, c1.begin()+16,   //source range
                       c1.begin()+7);   //destination range
  PRINT_ELEMENTS(c1,"c1: ");

  //copy all letters three elements behind the 'f'
  vector<char> c2(source.begin(),source.end());
  copy_backward (c2.begin()+10, c2.begin()+16,   //source range
                                c2.begin()+19);  //destination range
  PRINT_ELEMENTS(c2,"c2: ");

  return 0;
}
Solution

Output:

source: . . . . . . . . . . a b c d e f . . . . . . . . . .
c1: . . . . . . . a b c d e f d e f . . . . . . . . . .
c2: . . . . . . . . . . a b c a b c d e f . . . . . . .

References
  • Nicolai M. Josuttis: "The C++ Standard Library"

See Also