Question

If I want to delete all the elements with a value from vector,I call remove algorithm and then call vector’s erase member function to physically delete it.
But in the case of list , simple call remove member function and it will delete all elements with that value.
I am not sure why vector does’t provide the remove MF while list does it.

For Exp: I want to delete value ‘4’ from vector v.

vector<int> v;
vector<int> ::iterator Itr;
for (int i=0; i< 6; i++)
   v.push_back(i*2);
v.push_back(4);
v.push_back(8);
v.push_back(4);
v.erase(remove(v.begin(),v.end(),4), v.end()); 

and for list:

list.remove(4); // will delete all the element which has value 4

Answer 1

The question is not why std::vector does not offer the operation, but rather why does std::list offer it. The design of the STL is focused on the separation of the containers and the algorithms by means of iterators, and in all cases where an algorithm can be implemented efficiently in terms of iterators, that is the option.

There are, however, cases where there are specific operations that can be implemented much more efficiently with knowledge of the container. That is the case of removing elements from a container. The cost of using the remove-erase idiom is linear in the size of the container (which cannot be reduced much), but that hides the fact that in the worst case all but one of those operations are copies of the objects (the only element that matches is the first), and those copies can represent quite a big hidden cost.

By implementing the operation as a method in std::list the complexity of the operation will still be linear, but the associated cost for each one of the elements removed is very low, a couple of pointer copies and releasing of a node in memory. At the same time, the implementation as part of the list can offer stronger guarantees: pointers, references and iterators to elements that are not erased do not become invalidated in the operation.

Another example of an algorithm that is implemented in the specific container is std::list::sort, that uses mergesort that is less efficient than std::sort but does not require random-access iterators.

So basically, algorithms are implemented as free functions with iterators unless there is a strong reason to provide a particular implementation in a concrete container.