How to insert elements in C++ STL List ?
List has been discussed in many articles, but the sole purpose of this article is to cover all types of insertions that are possible to be carried in a list container and to give a detailed insight on the insertion operations.
List and its many functions are defined under the header file “list” . Various list insertions functions are discussed below.
Using assign()
assign() function is used to insert multiple elements in a list in a single operation. “assign()” works in following ways :
- To insert multiple elements at once in a list.
syntax : list.assign(number of times, element).
- To copy elements of 1 list into another.
syntax : list.assign(lis2.begin(),lis2.end())
- To copy array elements into list.
syntax : list.assign(arr,arr+size).
#include <iostream>
#include <list> // for list operations
using namespace std;
int main()
{
list< int > list1;
list< int > list2;
list< int > list3;
int arr[10] = { 1, 2, 3, 4 };
list1.assign(4,2);
cout << "The list after inserting multiple elements is : " ;
for (list< int >::iterator i=list1.begin(); i!=list1.end(); i++)
cout << *i << " " ;
cout << endl;
list2.assign(list1.begin(),list1.end());
cout << "The list after copying list elements is : " ;
for (list< int >::iterator i=list2.begin(); i!=list2.end(); i++)
cout << *i << " " ;
cout << endl;
list3.assign(arr,arr+4);
cout << "The list after copying array elements is : " ;
for (list< int >::iterator i=list3.begin(); i!=list3.end(); i++)
cout << *i << " " ;
cout << endl;
}
|
Output:
The list after inserting multiple elements is : 2 2 2 2
The list after copying list elements is : 2 2 2 2
The list after copying array elements is : 1 2 3 4
Insertion at beginning
- Using push_front() : push_front() is used to insert the element at the beginning of list. Increases list size by 1.
- Using emplace_front() : Works in a similar way as push_front, but the values are constructed in-place in front position of container, where in push_front, an object is created first, and then copied to the container.
#include <iostream>
#include <list> // for list operations
using namespace std;
int main()
{
list< int > list1;
list1.assign(2,2);
list1.push_front(5);
cout << "The list after inserting elements using push_front is : " ;
for (list< int >::iterator i=list1.begin(); i!=list1.end(); i++)
cout << *i << " " ;
cout << endl;
list1.emplace_front(7);
cout << "The list after inserting elements using emplace_front is : " ;
for (list< int >::iterator i=list1.begin(); i!=list1.end(); i++)
cout << *i << " " ;
}
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Output:
The list after inserting elements using push_front is : 5 2 2
The list after inserting elements using emplace_front is : 7 5 2 2
Insertion at end
- Using push_back() : push_back() is used to insert the element at the end of list. Increases list size by 1.
- Using emplace_back() : Works in a similar way as push_back, but the values are constructed in-place at back position of container, where in push_back, an object is created first, and then copied to the container.
#include <iostream>
#include <list> // for list operations
using namespace std;
int main()
{
list< int > list1;
list1.assign(2,2);
list1.push_back(5);
cout << "The list after inserting elements using push_back is : " ;
for (list< int >::iterator i=list1.begin(); i!=list1.end(); i++)
cout << *i << " " ;
cout << endl;
list1.emplace_back(7);
cout << "The list after inserting elements using emplace_back is : " ;
for (list< int >::iterator i=list1.begin(); i!=list1.end(); i++)
cout << *i << " " ;
}
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Output:
The list after inserting elements using push_back is : 2 2 5
The list after inserting elements using emplace_back is : 2 2 5 7
Insertion at any position
- Using insert(pos_iter,ele_num,ele) : insert() is used to insert the elements at any position of list.
. This function takes 3 elements, position, number of elements to insert and value to insert. If not mentioned, number of elements is default set to 1.
- Using emplace(pos_iter,ele) : Works in a similar way as insert(), but the values are constructed in-place in front position of container, where in push_front, an object is created first, and then copied to the container. And only 1 value is allowed to insert at 1 time.
#include <iostream>
#include <list> // for list operations
using namespace std;
int main()
{
list< int > list1;
list1.assign(3,2);
list< int >::iterator it = list1.begin();
advance(it,2);
list1.insert(it,5);
cout << "The list after inserting 1 element using insert() is : " ;
for (list< int >::iterator i=list1.begin(); i!=list1.end(); i++)
cout << *i << " " ;
cout << endl;
list1.insert(it,2,7);
cout << "The list after inserting multiple elements using insert() is : " ;
for (list< int >::iterator i=list1.begin(); i!=list1.end(); i++)
cout << *i << " " ;
cout << endl;
list1.emplace(it,8);
cout << "The list after inserting elements using emplace() is : " ;
for (list< int >::iterator i=list1.begin(); i!=list1.end(); i++)
cout << *i << " " ;
}
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Output:
The list after inserting 1 element using insert() is : 2 2 5 2
The list after inserting multiple elements using insert() is : 2 2 5 7 7 2
The list after inserting elements using emplace() is : 2 2 5 7 7 8 2
Last Updated :
13 Sep, 2023
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