How to Efficiently Iterate Over Multiple C Containers Simultaneously?

Iterating Simultaneously Over Multiple Containers in C

C 11 offers various mechanisms for iterating over containers, including range-based loops and the 'std::for_each' function. However, the question arises: what is the recommended approach for iterating over two or more containers of equal size to perform an action similar to the following:

for (unsigned i = 0; i < containerA.size(); ++i) {
  containerA[i] = containerB[i];
}

Using Indices with a Range-Based Loop

An efficient solution involves iterating over the container's indices using a range-based loop. This approach provides the same level of efficiency as a classical for loop. The code snippet below exemplifies this method:

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

The 'indices' function returns a lazily evaluated range of indices for the container. Its implementation is available on GitHub.

Zipping Containers

If this pattern occurs frequently in your data, an alternative approach is to zip the containers, creating a range of tuples whose elements correspond to the paired elements:

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

The 'zip' function can be easily implemented based on the 'indices' function.

This approach also provides efficient iteration, and it is a more concise and readable solution in certain cases.

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