Vector erase() in C++ STL

In C++, vector erase() is a built-in function that is used to delete elements from the vector. It removes an element of a specific position or range of elements from the vector.

1 2 4 5 

In the above example, erase() method remove the element(3) which is present at index 2.

Syntax

Vector erase method has two implementations:

// Remove single element
v.erase(pos);

// Erase range of elements
v.erase(first, last);

where,

Parameters:

• pos: Iterator to the element to be deleted.
• first: Iterator to the first element in the range.
• last: Iterator to the theoretical element just after the last element in the range.

Return Value:

• Returns an iterator pointing to the next element after deleted elements.
• If we delete the elements up to last element from the vector, then it will return an iterator to the vector end().

Examples of Vector erase()

The following programs illustrates how to use the vector erase() method to remove elements in different cases:

Example: Remove an Element Using Index from a Vector

1 3 4 5 

Explanation: The iterator of the element at index 1 is determined by adding the index to vector begin() iterator. Then vector erase() is used to remove it.

Example: Remove the Last Element from the Vector

1 2 3 4 

In the above program, we use end() iterator to delete the last element of the vector, which is 5.

Example: Remove a Range of Elements from a Vector

1 5 

Explanation: The iterator to the part of the vector to be removed is passed to the vector erase() method. It removed that part from the array.

Vector clear() and erase()

In a vector, both vector clear() and vector erase() are used for element removal, but they serve different purposes. Following are the cases which describe when to use clear() and when to use erase():

• If we have to remove all elements from the vector, then we use vector clear() method.
• If we have to remove some specific elements from the vector, then we use vector erase() method.

Time Complexity:

• erase(pos): O(N) in worst case, because elements after the erased position need to be shifted.
• erase(first, last): O(N) in worst case, as elements after the range are shifted.
• clear(): O(N), as all elements are destroyed.