In this article we will discuss different techniques to clone the whole list or copy just a sub list.
Suppose we have a std::list of strings i.e.
// List of strings
std::list<std::string> listOfStrs = { "of", "is", "from", "this", "at", "to" };
Now let’s see how to copy this or a sub list from this list,
Copy a std::list using Copy constructor
std::list provides a copy constructor that clones a given to list to new list i.e.
list (const list& x);
We can use it to copy complete list while creating a new list i.e.
// copy all the contents of one list to another std::list<std::string> listOfStrs_2(listOfStrs);
New list contents will be,
of , is , from , this , at , to ,
Copy a range or sub list to std::list using parameterized constructor
std::list provides a parameterized constructor that accepts a range and copies all the elements in given range to the new list.
list (InputIterator first, InputIterator last, const allocator_type& alloc = allocator_type());
We can use it to copy complete list or any sub list while creating a new list i.e.
// copy all the contents of one list to another std::list<std::string> listOfStrs_3(listOfStrs.begin(), listOfStrs.end());
New list contents will be,
of , is , from , this , at , to ,
 Copy a std::list using assignment operator
std::list provides an assignment operator that that copies all the contents of given list to the existing list i.e.
list& operator= (const list& x);
We can use it to copy complete list while creating a new list i.e.
// copy all the contents of one list to another std::list<std::string> listOfStrsCopy = listOfStrs;
New list contents will be,
of , is , from , this , at , to ,
 Copy a std::list or sub list using list::assign()
std::list provides a member function assign(),
void assign (InputIterator first, InputIterator last);
It accepts a range and copies all the elements in given range to the existing list by replacing it contents.
We can use it to copy complete list to the existing list i.e.
// Create a new list of strings std::list<std::string> listOfStrs_4; /* Copy all list contents using list'a assign member function It accepts a iteratable range and copy all elements in that range to the list. */ listOfStrs_4.assign(listOfStrs.begin(), listOfStrs.end());
New list contents will be,
of , is , from , this , at , to ,
Copying a sub list using list::assign(),
Let’s Copy 2 elements from index 1 and 2 to the new list using std::list::assign()
std::list<std::string> listOfStrs_5; // Copy 2 elements from index 1 and 2 to the new list listOfStrs_5.assign(std::next(listOfStrs.begin(), 1), std::next(listOfStrs.begin() , 3));
New list contents will be,
is , from
 Copy a std::list or sub list using std::copy()
We can use STL algorithm to copy a range from a list i.e. a sub list or complete list to the another list i.e.
Let’s Copy 2 elements from index 1 and 2 to the new list using std::copy
std::list<std::string> listOfStrs_5; // Copy 2 elements from index 1 and 2 to the new list listOfStrs_5.assign(std::next(listOfStrs.begin(), 1), std::next(listOfStrs.begin() , 3));
New list contents will be,
is , from
 Copy a condition based sub list to std::list using std::copy_if() & Lambda Function
We can use STL algorithm to copy a only selective elements from a list to the another list i.e,
Copy string elements with size 2 from existing list to the new list using std::copy(),
std::list<std::string> listOfStrs_7;
// Copy string elements with size 2 to the new list using std::copy
std::copy_if(listOfStrs.begin(), listOfStrs.end(), std::back_inserter(listOfStrs_7), [](const std::string & str) {
if (str.size() == 2)
return true;
else
return false;
});
New list contents will be,
of , is , at , to ,
Complete example is as follows,
#include <iostream>
#include <list>
#include <string>
#include <algorithm>
#include <iterator>
// Print the contents of a list
template <typename T>
void print(T iteratableCont)
{
for (auto elem : iteratableCont)
std::cout << elem << " , ";
std::cout << std::endl;
}
int main()
{
// List of strings
std::list<std::string> listOfStrs = { "of", "is", "from", "this", "at", "to" };
// print the list
print(listOfStrs);
/* Copy a list using list's assignment operator */
// copy all the contents of one list to another
std::list<std::string> listOfStrs_2(listOfStrs);
// print the list
print(listOfStrs_2);
/* Copy a list using list's copy constructor */
// copy all the contents of one list to another
std::list<std::string> listOfStrs_3(listOfStrs.begin(), listOfStrs.end());
// print the list
print(listOfStrs_3);
// Create a new list of strings
std::list<std::string> listOfStrs_4;
/*
Copy all list contents using list'a assign member function
It accepts a iteratable range and copy all elements in that range to the list.
*/
listOfStrs_4.assign(listOfStrs.begin(), listOfStrs.end());
// print the list
print(listOfStrs_4);
std::list<std::string> listOfStrs_5;
/*
Copy a sub list to another list using list's assign member function
*/
// Copy 2 elements from index 1 and 2 to the new list
listOfStrs_5.assign(std::next(listOfStrs.begin(), 1), std::next(listOfStrs.begin() , 3));
// print the list
print(listOfStrs_5);
/*
Copy a sub list to another list using STL Algorithm std::copy
*/
std::list<std::string> listOfStrs_6;
// Copy 2 elements from index 1 and 2 to the new list using std::copy
std::copy(std::next(listOfStrs.begin(), 1), std::next(listOfStrs.begin(), 3), std::back_inserter(listOfStrs_6));
// print the list
print(listOfStrs_6);
/*
Copy a some elements from one list to another list based on some condition using STL Algorithm std::copy
*/
std::list<std::string> listOfStrs_7;
// Copy string elements with size 2 to the new list using std::copy
std::copy_if(listOfStrs.begin(), listOfStrs.end(), std::back_inserter(listOfStrs_7), [](const std::string & str) {
if (str.size() == 2)
return true;
else
return false;
});
print(listOfStrs_7);
return 0;
}
Output:
of , is , from , this , at , to , of , is , from , this , at , to , of , is , from , this , at , to , of , is , from , this , at , to , is , from , is , from , of , is , at , to ,