CODEWITHSUNDEEP
c++dequec++03capacity
WilliamKF
WilliamKF

Reputation: 43089

How to efficiently insert a series of values into a std::deque?

I have some C++03 code to insert a series of values into a std::deque:

void example(std::deque<int> &_recentSent,
             const int beginOffset,
             const int lastOffset) {
  for (int offset = beginOffset; offset <= lastOffset; ++offset) {
    _recentSent.push_back(offset);
  }
}

If this were a std::vector, I would use reserve() to ensure the container was large enough for all the entries to be inserted before entering the loop:

std::vector<int> _recentSent;

_recentSent.reserve(_recentSent.size() + (lastOffset + 1 - beginOffset));

But since there is not one, what might I do to efficiently insert the series of items into the std::deque so that it is only resized once if necessary?

Upvotes: 1

Views: 100

Answers (2)

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272467

Unlike in a vector, the storage for a deque is never reallocated upon appending new elements. That means that existing elements never have to be moved. Thus there is no benefit to reserving ahead of time.

Upvotes: 4

wilx
wilx

Reputation: 18228

Since there is no std::deque::reserve(), what about preallocating all the storage by _recentSent.resize (_recentSent.size () + lastOffset + 1 - beginOffset) and then inserting using iterator std::deque<int>::iterator it = _recentSent.end () - (lastOffset + 1 - beginOffset);.

Upvotes: 0

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