How Can I Efficiently Iterate Over Multiple Containers Simultaneously in C ?

Iterating Over Multiple Containers Simultaneously

C 11 offers versatile iteration methods for containers, such as range-based loops and std::for_each. However, a recurring task in data manipulation is to concurrently iterate over two or more containers of identical size.

Range-Based Loops Across Indices

For this specific scenario, iterating over the indices of the containers using range-based loops provides an efficient and expressive solution:

for (unsigned i : indices(containerA)) {
    containerA[i] = containerB[i];
}

The indices function returns a lazily evaluated range of indices for the container. This approach achieves the same efficiency as a manual for loop without sacrificing code readability.

Zip Range

For data structures where this pattern occurs frequently, using a "zip range" can simplify the code further:

for (auto& [a, b] : zip(containerA, containerB)) {
    a = b;
}

The zip function creates a range of tuples, each containing corresponding elements from the input containers. Before C 17, a slightly more verbose syntax was necessary:

for (auto& &items : zip(containerA, containerB))
    get<0>(items) = get<1>(items);

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