10.3. Copying vectors

There is one more constructor for vectors, which is called a copy constructor because it takes one vector as an argument and creates a new vector that is the same size, with the same elements.

vector<int> copy (count);

Although this syntax is legal, it is almost never used for vectors because there is a better alternative:

vector<int> copy = count;

The = operator works on vectors in pretty much the way you would expect.

Take a look at the active code below, which uses the copy constructor.

#include <iostream> #include <vector> using namespace std; void print_vec(vector<int> vec); int main() { vector<int> count = {1,2,3,4}; cout << "count = "; print_vec(count); vector<int> copy_1 (count); vector<int> copy_2 = count; cout << "copy_1 = "; print_vec(copy_1); cout << "copy_2 = "; print_vec(copy_2); cout << "We just made two copies of count. As you can see, both methods work the same!" << endl; } ==== void print_vec(vector<int> vec) { size_t i = 0; cout << "["; while (i < vec.size()-1) { cout << vec[i] << ","; i++; } cout << vec[vec.size()-1]; cout << "]" << endl; }

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Q-2: Multiple Response How would you make a copy of vector<double> decimals called nums?

• vector<double> nums = decimals;

• This is one way to make a copy.

• vector<double> decimals = nums;

• This makes a copy of nums called decimals.

• vector<double> nums (decimals);

• This is one way to make a copy.

• vector<double> decimals (nums);

• This makes a copy of nums called decimals.

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