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Creating a C++ list and iterating through it

Updated on November 14, 2017
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I am a software engineer. I have been come across C++,MFC, .net technologies. I like playing video games & reading books.

1. About C++ List

In CPP, List is the most used data structure. A list is a chunks of similar memories (type) linked in such a way that it can be easily iterated and managed. The c++ list can be iterated in both direction (i.e.) it can be iterated in forward and reverse directions. It is implemented as “Doubly-Linked List”, but we no need to worry much about it. In this hub, we will see creating C++ list and iterating through the elements of it.

2. Declaring and Adding elements to List

The list should be declared as follow:

list<int> theList;

Before placing the declaration, include the header <list>. In the above declaration, we specified that theList will have chain of linked memories that can store integers. Once the list is declared, elements can be added to it using the push_back() function. The below code adds three integers to the List.

Declaring and Adding elements to list

//Sample 1.0 Declare and Add elements to list
list<int> theList;
theList.push_back(2);
theList.push_back(4);
theList.push_back(6);

The push_back() always adds the element at the end of the list. The list at this stage is represented as shown in the below depiction (Pic.1).

Pic.1 - Adding List elements through push_back
Pic.1 - Adding List elements through push_back | Source

3. Traversing the list using List::Iterator

An Iterator is a type and as the name suggest, this is used to iterate the list in both forward and reverse direction. Using the iterator, one can make changes to the list elements. A list iterator can be declared as follows:

list<int>::iterator list_itr;

Here, list_itr is an iterator that will be used to iterate the list of integers. Now have a look at the below code:

Iterating the List

Pic2. Iterating through C++ List
Pic2. Iterating through C++ List | Source

Once the iterator is declared, the “begin()” method of the list is used to get the iterator which has position set to the beginning of the list theList (Marked as 1). Now through this iterator list_itr, the first element can be accessed. The for loop ends when the iterator position reaches the end of the list. To do that, here in our example, the “end()” method of the list is used to get the iterator which pointing to end of the list and this position compared with the other iterator (One we are using to traverse) list_itr (Marked as 2). During each for loop iteration, we are incrementing the list_itr and this will advance the iterator to the next element. Note that to get the value from its current position, we are using pointer dereferencing *list_itr.

4. The push_front function

The push_front() function adds the element towards the beginning of the List. When we keep on adding, the new elements that gets added and stays in the beginning of the list. This is just reverse of what push_back() is doing, right? Now, have a look at the below example:

push-front() code snippet

//Sample 4.0 Push_Front
theList.push_front(1);
theList.push_front(0);
printf("\nThe list elements after push front are:\n");
list_itr = theList.begin();
for (list_itr; list_itr != theList.end(); list_itr++)
	printf("[%d] ", *list_itr);

The output of the above code snipped is shown below. Note that we added the element 1 first and then added the integer element 0. In the list 0 stays first and 1 stays next. This means, the push-front() adds the element at the beginning and all the existing elements shits one index from its current position.

Pic 3. Push-Front() output
Pic 3. Push-Front() output | Source

The complete listing and its output is given below:

Complete Example

#include <stdio.h>
#include <conio.h>
#include <list>

using namespace std;

//Example 01
void main()
{
	//Sample 1.0 Declare and Add elements to list
	list<int> theList;
	theList.push_back(2);
	theList.push_back(4);
	theList.push_back(6);

	//Sample 3.0 Iterate through the list
	list<int>::iterator list_itr;
	printf("The list elements are:\n");
	list_itr = theList.begin();
	for (list_itr; list_itr != theList.end(); list_itr++)
		printf("[%d] ", *list_itr);

	//Sample 4.0 Push_Front
	theList.push_front(1);
	theList.push_front(0);
	printf("\nThe list elements after push front are:\n");
	list_itr = theList.begin();
	for (list_itr; list_itr != theList.end(); list_itr++)
		printf("[%d] ", *list_itr);
	_getch();
	
}

Output

Pic 4. Iterating the List full Example
Pic 4. Iterating the List full Example | Source

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