Implement the copy_backward() in C++

[Agustíne]

Hello, I am the student of the MscIT. I have learned the C++ language in the BscIT. But I can not know about the Header file functions. So, I would like to know about the copy_backward() function. I aslo would like to know about how can I able to implement the copy_backward() function in the C++ program and what can be the use of the copy_backward() function in the C++ language. Can anyone help me???

[absolute55]

The copy_backward() function can be used to Copy an elements in the given range [first,last) into a range whose element which is last can be the result. the following can be the syntax of the copy_backward() function as :

template <class BidirectionalItrtr1, class BidirectionalItrtr2>
  BidirectionalItrtr2 copy_backward ( BidirectionalItrtr1 first,
                                         BidirectionalItrtr1 last,
                                         BidirectionalItrtr2 result );

[Reegan]

The following code of lines demonstrates you that how can you implement the copy_backward() function in the C++ language :

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main ()
 {
  vector<int> mvcto;
  vector<int>::iterator t;
  for (int j=1; j<=5; j++)
    mvctr.pushback(j*10);    
  mvctr.resize(mvctr.size()+3); 
  copybackward ( mvctr.begin(), mvctr.begin()+5, mvctr.end() );
  cout << "mvctr contains:";
  for (t=mvctr.begin(); t!=mvctr.end(); ++t)
    cout << " " << *t;
  cout << endl;
  return 0;
}

Output:

mvctr contains: 10 20 30 10 20 30 40 50

[opaper]

Program :

    #include <algorithm>   
      #include <iostream>    
      #include <vector>      
      int main ()
      {
          typedef std::vector<short, std::allocator<short> > vector;
          const vector::valuetype e1[] = { 1, 2, 3, 4 };
          const vector::valuetype e2[] = { 5, 6, 7, 8 };
          vector w1(e1 + 0, e1 + 4), 
                 w2(e2 + 0, e2 + 4), 
                 w3(e2 + 0, e2 + 4);
          vector w4;
          std::copy(w1.begin(), w1.end(), w2.begin());
          std::copybackward(w1.begin(), w1.end(), w3.end());
          std::copy(w1.begin(), w1.end(), std::backinserter(w4));
          std::ostreamiterator<vector::valuetype, char,
          std::chartraits<char> > out(std::cout, " ");
          std::copy(w1.begin(), w1.end(), out);
          std::cout << std::endl;
          std::copy(w2.begin(), w2.end(), out);
          std::cout << std::endl;
          std::copy(w3.begin(), w3.end(), out);
          std::cout << std::endl;
          std::copy(w4.begin(), w4.end(), out);
          std::cout << std::endl;
          return 0;
      }

Output :

      1 2 3 4 
      1 2 3 4 
      1 2 3 4 
      1 2 3 4

[MindSpace]

There can be one more example on the copy_backward() function in C++ language :

#include <iostream>
#include <cassert>
#include <algorithm>
#include <vector>
#include <string>
#include <iostream>
using namespace std;
int main()
{
  string t("abcdefghihklmnopqrstuvwxyz");
  vector<char> vctr1(t.begin(), t.end());
  copy_backward(vctr1.begin(), vctr1.end() - 2, vctr1.end());
  vector<char>::iterator ps;
  for (ps=vctr1.begin(); ps!=vctr1.end(); ++ps)
 {
        cout << *ps << ' ';
  }
  return 0;
}

OUTPUT :

a b a b c d e f g h i h k l m n o p q r s t u v w x

[Modifier]

The copy_backward() function can begins by copying *(lst-1) into *(rslt-1), and after that the copy_backward() function can follows the backwards by an elements that can be preceding these, until first can be reached.
The behavior of the copy_backward() function template can be similar to the following :

template<class BdrctnlItrtr1, class BdrctnlItrtr2>
  BdrctnlItrtr2 copy_backward ( BdrctnlItrtr1 fst,
                                         BdrctnlItrtr1 lst,
                                         BdrctnlItrtr2 rslt )
{
  while (lst!=fst) *(--rslt) = *(--lst);
  return rslt;
}