Question

In C++ please.

8. Explain why modifying STL algorithms such as remove () and

unique () do not actually eliminate the unsuitable elements from the

container. Describe remove-erase idiom. Assuming that "v" is a vector of

integers. Explain what the below code does.

v.erase(remove_if(v.begin(), v.end(), [](int i){return i > 5;}),

v.end());

Answer 1

1. remove() doesn’t actually delete elements from the container but only moves non-deleted elements on top of deleted elements.
Similarly, unique() does not delete all the duplicate elements, but it only removes duplicate by replacing elements by the next element present in the sequence. All the elements which are replaced are left in an unspecified state.

2. Remove-Erase methods are used to eliminate/delete values from the vector using certain criteria. For eg Suppose we have a vector v { 10, 20, 30, 30, 20, 10, 10, 20 }, v.remove(vec.begin(), vec.end(), 20); will remove 20 from the vector and resultant vector will be { 10, 30, 30, 10, 10 }

3. v.erase(remove_if(v.begin(), v.end(), [](int i){return i > 5;}),v.end());

The mentioned code removes all the elements greated than 5 from a vector v.

e.g If you have an vector { 2, 3, 3, 2, 10, 10, 10,5 } then the resultant vector will be { 10, 10, 10, 5 }