How to loop through dynamic 2d array with different length in C++

Question

I have a 2d array in which the columns'size length is not the same. So how to loop all elements in that 2d array dynamically?

string** arr = new string*[4];
    arr[0] = new string[5];
    arr[1] = new string[3];
    arr[2] = new string[4];
    arr[3] = new string[2];

Answer 1

Using dynamic arrays like that becomes harder to maintain and doesn't really give you any benefits over using a std::vector. You would need to store the size of each array separately.

Example:

#include <iterator>
#include <memory>
#include <utility>

template<typename T>
struct myarr {
    myarr() = default;
    myarr(size_t size) : arr(std::make_unique<T[]>(size)), m_size(size) {}

    T& operator[](size_t idx) { return arr[idx]; }
    const T& operator[](size_t idx) const { return arr[idx]; }

    auto cbegin() const { return &arr[0]; }
    auto cend() const { return std::next(cbegin(), m_size); }
    auto begin() const { return cbegin(); }
    auto end() const { return cend(); }
    auto begin() { return &arr[0]; }
    auto end() { return std::next(begin(), m_size); }

private:
    std::unique_ptr<T[]> arr;
    size_t m_size;
};

int main() {
    myarr<myarr<std::string>> arr(4);
    arr[0] = myarr<std::string>(5);
    arr[1] = myarr<std::string>(3);
    arr[2] = myarr<std::string>(4);
    arr[3] = myarr<std::string>(2);

    for(auto& inner : arr) {
        for(const std::string& str : inner) {
            // do stuff
        }
    }
}

The std::vector-based code would only require the below and offers far more flexibility:

Example:

std::vector<std::vector<std::string>> arr(4);
arr[0].resize(5);
arr[1].resize(3);
arr[2].resize(4);
arr[3].resize(2);