C++ multimap erase() function

The C++ multimap erase() function is used to remove either a single element associated with given key value or a range of elements from the multimap container. Hence, the size will be reduced by the number of elements removed.

Syntax

Parameter

position: Iterator pointing to a single element to be removed from the multimap.

k: Key of the element to be removed from the multimap.

first: Beginning of the range to erase.

last: End of the range to erase.

Return value

It returns an iterator that points to the next element of the deleted element or returns the number of deleted elements.

Complexity

erase(position): Amortized constant.

erase (val): Logarithmic in container size.

erase(first,last): Linear in the distance between first and last.

Iterator validity

Iterators, references and the pointers pointing to elements removed by the function are invalidated.

All other iterators, pointers and references keep their validity.

Data races

The container is modified.

The elements removed are modified. Iterating ranges in the container is not safe although concurrently accessing other elements is safe.

Exception safety

This function does not throw exception.

If an invalid range or position is specified, it causes undefined behavior.

Example 1

Let's see the simple example to erase the element by the iterator.

Output:

Before erasing the element: 
a => 100
b => 200
b => 300
c => 400

After erasing the element: 
a => 100
b => 300
c => 400

In the above example, element is erased by the iterator it.

Example 2

Let's see a simple example to erase the element of the multimap with the given key value:

Output:

Before erasing the element: 
a => 100
b => 200
b => 300
c => 400

After erasing the element: 
a => 100
c => 400

In the above example, erase(key) function erases the all the key 'b' and its value from the multimap.

Example 3

Let's see a simple example to erase the element by the given range:

Output:

Before erasing the element are: 
Size is: 4
a => 100
b => 200
b => 300
c => 400

After erasing the element are: 
Size is: 0

In the above example, erase (first, last) function is used to erase the elements with the given range i.e. begin to end.

Example 4

Let's see a simple example to erase all the odd numbers from the multimap:

Output:

After erasing odd numbers, elements are:
 2, two
 4, four
 6, six

In the above example, all the odd numbers has been erased and displaying even numbers.