list::begin() and list::end() in C++ STL

Lists are containers used in C++ to store data in a non-contiguous fashion, Normally, Arrays and Vectors are contiguous in nature, therefore the insertion and deletion operations are costlier as compared to the insertion and deletion option in Lists.

begin() function is used to return an iterator pointing to the first element of the list container. It is different from the front() function because the front function returns a reference to the first element of the container but begin() function returns a bidirectional iterator to the first element of the container.

Syntax:

listname.begin() 

Parameters : No parameters are passed. Returns : This function returns a bidirectional iterator pointing to the first element.

Examples:  

Input : mylist{1, 2, 3, 4, 5}; mylist.begin(); Output : returns an iterator to the element 1 Input : mylist{8, 7}; mylist.begin(); Output : returns an iterator to the element 8

Errors and Exceptions
1. It has a no exception throw guarantee. 
2. Shows error when a parameter is passed. 

// CPP program to illustrate // Implementation of begin() function #include <iostream> #include <list> using namespace std; int main() {  // declaration of list container  list<int> mylist{ 1, 2, 3, 4, 5 };  // using begin() to print list  for (auto it = mylist.begin(); it !=   mylist.end(); ++it)  cout << ' ' << *it;  return 0; } 

Output: 

1 2 3 4 5

Time Complexity: O(1) 

Auxiliary Space: O(n) where n is size of list container

end() function is used to return an iterator pointing to the last element of the list container. It is different from the back() function because the back() function returns a reference to the last element of the container but end() function returns a bidirectional iterator to the past the last element of the container.

Syntax: 

listname.end()

Parameters: NA

Return Type: This function returns a bidirectional iterator pointing to the past the last element.

Errors and Exceptions

• It has a no exception throw guarantee. 
• Shows error when a parameter is passed.

// CPP program to illustrate // Implementation of end() function #include <iostream> #include <list> using namespace std; int main() {  // declaration of list container  list<int> mylist{ 1, 2, 3, 4, 5 };  // using end() to print list  for (auto it = mylist.begin(); it != mylist.end(); ++it)  cout << ' ' << *it;  return 0; } 

Output: 

1 2 3 4 5

Time Complexity: O(1) 

Auxiliary Space: O(1)

Let us see the differences in a tabular form is shown below as follows: 

iterator begin();

iterator end();