Equivalent of python list multiplying with a scale in c++

Question

How would you code list multiplying with a scale in c++?

In python I would do:

lst = [1,2,3]
lst*3 # we will get [1,2,3,1,2,3,1,2,3]

What is the c++ equivalent of that?

Answer 1

If you really need the operation of multiplication, for example, you are developing some math library, you can consider the operator overloading. Otherwise, I suggest you throwing the python style away while working with C++, just use std::copy or vector::insert with a loop to insert repeated elements into a vector.

std::vector<int>& operator*(std::vector<int>& vec, std::size_t n) {
    auto initSize = vec.size();
    for (std::size_t i = 0; i < n - 1; ++i) {
        vec.insert(vec.end(), vec.begin() + initSize * i, vec.end());
    }
    return vec;
}

// commutative principle for multiplication
std::vector<int>& operator*(std::size_t n, std::vector<int>& vec) {
    return operator*(vec, n);
}

int main()
{
    std::vector<int> vec {1, 2, 3};
    vec = vec * 3; // 3 * vec is OK too

    for (auto val : vec) {
        std::cout << val << ' ';
    }

    return 0;
}