How to Efficiently Extract a Subvector from a C std::vector?

Extracting a Subvector from a Vector

In C , std::vector is a container that stores a contiguous sequence of elements. What if you need to extract a subset of elements from a large vector to create a new one?

To construct a new vector consisting of elements X through Y, you can use the following steps:

1. Obtain iterators referencing the first and last elements of the subvector:

vector<T>::const_iterator first = myVec.begin() + X;
vector<T>::const_iterator last = myVec.begin() + Y + 1;

2. Use these iterators to construct a new vector:

vector<T> newVec(first, last);

This approach takes O(N) time to construct the new vector, but it is efficient for large vectors. If you need to create a copy of other elements in the original vector, you can use std::copy :

vector<T> newVec(Y - X + 1);
std::copy(first, last, newVec.begin());

If the original vector is very large and you only need a part of it, you can consider using a std::deque instead of a std::vector. A std::deque supports efficient insertion and deletion at both ends, making it more suitable for dynamic subvector extraction.

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