How Can We Achieve Python's Zip Functionality for Simultaneous Iteration in C 11?

Zip Function for Sequential Iteration in C 11

With the introduction of range-based for-loops in C 11, looping over sequences has become more concise. However, looping over multiple sequences simultaneously poses a challenge. This article explores solutions for incorporating zip-style functionality into C 11 codes.

Python's zip function offers a convenient way to iterate over multiple lists simultaneously, pairing elements from each list. Can we achieve a similar behavior with new C 11 features?

Boost's Combine and Zip Iterators

In Boost 1.56.0 onwards, the boost::combine function is available to combine multiple ranges into a single range of tuples. Each tuple element corresponds to the value at the current position in the respective ranges.

#include <boost/range/combine.hpp>
#include <vector>
#include <list>

int main() {
    std::vector<int> a {4, 5, 6};
    double b[] = {7, 8, 9};
    std::list<std::string> c {"a", "b", "c"};
    for (auto tup : boost::combine(a, b, c)) {
        int x;
        double y;
        std::string z;
        boost::tie(x, y, z) = tup;
        printf("%d %g %s\n", x, y, z.c_str());
    }
}

Boost also provides boost::zip_iterator for this purpose. In earlier Boost versions, a custom zip function can be defined to create a range of tuples.

#include <boost/iterator/zip_iterator.hpp>
#include <boost/range.hpp>

template <typename... T>
auto zip(T&&... containers) -> boost::iterator_range<boost::zip_iterator<decltype(boost::make_tuple(std::begin(containers)...))>>
{
    auto zip_begin = boost::make_zip_iterator(boost::make_tuple(std::begin(containers)...));
    auto zip_end = boost::make_zip_iterator(boost::make_tuple(std::end(containers)...));
    return boost::make_iterator_range(zip_begin, zip_end);
}

Using these methods, we can effectively iterate over multiple sequences simultaneously, enabling zip-like functionality in C 11 codes.

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