How do I iterate safely under modification with std::deque for large datasets?

Iterating over a `std::deque` in C++ while it is being modified can lead to undefined behavior if not handled properly. When working with large datasets, it's crucial to ensure that iterators remain valid throughout the modification process. Here are some strategies for safely iterating over a `std::deque` while modifying it:

Strategies for Safe Iteration

• Use Index-Based Iteration: Instead of using iterators, use index-based access to iterate through the elements. This minimizes issues related to invalidation.
• Snapshot Approach: Create a copy of the elements you want to iterate over, and then perform modifications on the original `std::deque`.
• Iterate Backwards: If you are removing elements, iterating backwards can prevent invalidation of the still-to-be-visited elements.

Example Code

const int SIZE = 1000000;
std::deque myDeque;

// Fill the deque with large dataset
for (int i = 0; i < SIZE; ++i) {
    myDeque.push_back(i);
}

// Modify deque while iterating safely
for (size_t i = 0; i < myDeque.size(); ++i) {
    if (myDeque[i] % 2 == 0) {
        myDeque.pop_front(); // This would be safe as we're using an index
        --i; // Adjust the index if needed to check next element
    }
}