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The "insert()" function of the standard list is used to insert new elements to the existing list. While inserting a new element, we need to specify the position and value. We will see an example for each available overload here one by one.
2. Supporting Functions for This Article
Before we move to our example, let us see two helper functions which are going to be used throughout this example. The function Add_ListElements() is written to add default elements to the list. It adds 1,2,3,4,5,6 to the list. Below is the function.
The Print_List() function will iterate through the supplied list and prints the content to the console output window. Below is the function.
3. Inserting Single Element to a List
To insert a single element to the list, we have to use the below specified overload of the insert function:
iterator insert(const_iterator _Where, _Ty&& _Val)
Here, "_Where" parameter is expecting the position in which the new element needs to be inserted. The second parameter _Val is the value that we want to insert. Now have a look at this piece of code.
In the code in 3.1, we created the list and added six default element to it by calling the Add_ListElements() (Listing 1.1) function. Then we printed the content of the list.
In the code in 3.2, we got the iterator for the list by calling the begin() function and moved it twice in steps by performing the increment operation ++. Now, the iterator is pointing at the third element 3. This is shown in the below depiction.
In the code seen in 3.3, we are calling the insert function by supplying the position and the value, which is 7. The call will add a new element in the current position and shifts the remaining elements towards the right of it. In the above picture, the newly inserted element is shown as green and shifted elements are shown in yellow.
4. Inserting Multiple Elements
The standard list's insert function expects three parameters to insert multiple elements in it. The first parameter tells the position in the list from where the insertion starts. The second parameter tells how elements need to be inserted. The third parameter is the actual value that needs to be inserted. The below picture shows inserting three elements of value 11 at the position which is given as first parameter.
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Note that even though we insert multiple values, all the values are same and occupied contiguous location in the list. Now, have a look the sample code below.
Here at line three, we are inserting 3 elements with the value 11. In the next line we are printing the list to the console output window. This insertion is depicted as shown below.
Note that before the insert call, the iterator "Position" is at element 7 (third position in the list). After the call to insert, three elements are added at this position and all the existing elements including 7 are shifted left. The newly added elements are shown in green and shifted elements are shown in yellow.
5. Copy Elements Between List
Using the standard list insert method, one can copy the list elements from some other list as well. The function's parameter list is shown below.
The first parameter "Position" denotes the copy location in the destination list. The second and third parameter tells the start and end position from the source list and this will tell what range of elements should be copied from source to destination. Now, have a look at the below code.
Here the source list is prepared for our example. In line 4,5, a list is created and default elements 1,2,3,4,5,6 is added to it. At line 6 and 7, we grabbed the list iterator which points to start and end of the list. In line 8-11, we re-positioned the start and end iterator so that only two elements copied to the destination list.
Now look at the code below which copies the list elements from "SecondList."
Note that we moved the iterator by one element (Line 2) from its current position. Refer to the previous picture and we can say the position now points to the fourth element in the list. At line 3, we called the insert function which actually performs a copy from source to destination. This is depicted below.
Once the list elements are copied, the content of the destination list is printed in the console output window. The complete example and its output is shown below.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.