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Ways to Copy a Vector in C++

Vectors in C++ are the same as arrays, along with additional outstanding features than them, like array lists in Java programming language. In Vectors, the size constraint is eliminated, which we have in Arrays. There are mainly six different ways to copy a vector in C++they are discussed below in detail.

1. Iterative Method

Below is the code to demonstrate the copy of the vector by using the assignment-operator method

Code

// C++ code to demonstrate copy of vector 
// by an iterative method. 
#include<iostream> 
#include<vector> 
using namespace std; 
int main() { 
    // Initializing vector with values 
    vector<int> vect1{221, 1112, 3232223, 22224}; 
    vector<int> vect2; 
    //assignment operator 
    vect2 = vect1; 
    cout << "1st vector elements are : "; 
    for (int i=0; i<vect1.size(); i++) 
        cout << vect1[i] << " "; 
        cout << endl; 
      cout << "present vector elements are : "; 
    for (int i=0; i<vect2.size(); i++) 
        cout << vect2[i] << " "; 
    cout<< endl; 
    // copy has been created. 
    vect1[0] = 2; 
    cout << "this is the first element of old vector:"; 
    cout << vect1[0] << endl; 
    cout << "this is the first element of the new vector is:"; 
    cout << vect2[0] <<endl; 
    return 0; }

Output

1st vector elements are: 221 1112 3232223 22224 
present vector elements are : 221 1112 3232223 22224 
this is the first element of the old vector:2
this is the first element of the new vector:221

2. By Adapting assignment=operator

Below is the code to demonstrate the working of Vectors in C++ programming language and also to copy the vector

Code

//Here, we have written the C++ code to demonstrate a copy of the //vector 
// by adapting assignment=operator
#include<iostream> 
#include<vector> 
using namespace std; 
int main() { 
    //here, we are initializing a vector with values 
    vector<int> vect1{1, 2, 3, 4}; 
    //here we are declaring a new vector 
    vector<int> vect2; 
    for (int i=0; i<vect1.size(); i++) 
        vect2.push_back(vect1[i]); 
    cout << "the old vector elements are : "; 
    for (int i=0; i<vect1.size(); i++) 
        cout << vect1[i] << " "; 
    cout << endl; 
    cout << "the new vector elements are : "; 
    for (int i=0; i<vect2.size(); i++) 
        cout << vect2[i] << " "; 
    cout<< endl; 
    vect1[0] = 2; 
    cout << "first element of old vector is :"; 
    cout << vect1[0] << endl; 
    cout << "first element of new vector is :"; 
    cout << vect2[0] <<endl; 
  
    return 0; 
}

Output

the old vector elements are: 1 2 3 4 
the new vector elements are: 1 2 3 4 
the first element of the old vector is:2
the first element of the new vector is :1

3. By insert() Method

Below is the code to demonstrate the working of C++ vectors and the copy function by the insert() function method

Code

//Here, we have written the C++ code to demonstrate a copy of the //vector 
// by adapting insert() function
#include<iostream>
#include<vector> // for vector
using namespace std;
int main(){
    //here, we are initializing a vector with values
    vector<int> vect1{111111, 3212, 23, 422};
    //here we are declaring a new vector
    vector<int> vect2;
    //here, we are copying vector by inserting function
    vect2.insert(vect2.begin(), vect1.begin(), vect1.end());
    cout << "Old vector elements are : ";
    for (int i=0; i<vect1.size(); i++)
        cout << vect1[i] << " ";
        cout << endl;
    cout << "the new vector elements  : ";
    for (int i=0; i<vect2.size(); i++)
        cout << vect2[i] << " ";
    cout<< endl;
    // copy has been created.
    vect1[0] = 2;
    cout << "first element of old vector :";
    cout << vect1[0] << endl;
    cout << "This is the first element of the new vector is:";
    cout << vect2[0] <<endl;
    return 0;
}

Output

Old vector elements are: 111111 3212 23 422 
the new vector elements  : 111111 3212 23 422 
the first element of old vector:2
This is the first element of the new vector:111111

4. By assign() Operator

Below is the code to demonstrate the working of C++ vectors and the copy function by assign() operator

Code

//Here, we have written the C++ code to demonstrate a copy of the //vector 
// by assign operator()
#include<iostream> 
#include<vector> 
#include<algorithm>  
#include<iterator>  
using namespace std; 
int main() { 
    //here, we are initializing a vector with values 
    vector<int> vect1{11212, 21212, 2223, 2222224}; 
    vector<int> vect2; 
    //assign function 
    vect2.assign(vect1.begin(), vect1.end()); 
    cout << "the old vector elements : "; 
    for (int i=0; i<vect1.size(); i++) 
        cout << vect1[i] << " "; 
    cout << endl; 
  
    cout << "the new vector elements : "; 
    for (int i=0; i<vect2.size(); i++) 
        cout << vect2[i] << " "; 
    cout<< endl; 
    //the copy has been created. 
    vect1[0] = 2; 
  
    cout << "first element of old vector :"; 
    cout << vect1[0] << endl; 
    cout << "first element of new vector :"; 
    cout << vect2[0] <<endl; 
  
    return 0; 
}

Output

the old vector elements: 11212 21212 2223 2222224 
the new vector elements : 11212 21212 2223 2222224 
the first element of old vector:2
the first element of new vector:11212

5. By assign() and copy() Operator

Below is the code to demonstrate the working of C++ vectors and the copy function by assign() and copy() operator

Code

//Here, we have written the C++ code to demonstrate a copy of the //vector 
// by assign operator() and copy() operator
#include<iostream> 
#include<vector> //vector 
#include<algorithm> //copy() and assign() 
#include<iterator>  
using namespace std; 
int main() { 
    vector<int> vect1{1111, 232, 223, 2224}; 
    vector<int> vect2; 
    copy(vect1.begin(), vect1.end(), back_inserter(vect2)); 
    cout << "the old vector elements : "; 
    for (int i=0; i<vect1.size(); i++) 
        cout << vect1[i] << " "; 
    cout << endl; 
   cout << "the new vector elements : "; 
    for (int i=0; i<vect2.size(); i++) 
        cout << vect2[i] << " "; 
    cout<< endl; 
  //copy has been
    vect1[0] = 2; 
    cout << "first element of old vector :"; 
    cout << vect1[0] << endl; 
    cout << "first element of new vector :"; 
    cout << vect2[0] <<endl; 
    return 0; 
}

Output

the old vector elements: 1111 232 223 2224 
the new vector elements : 1111 232 223 2224 
the first element of old vector:2
the first element of new vector:1111

6. By Constructor Method

Below is the code to demonstrate the working of C++ vectors and the copy function by constructor method

Code

//Here, we have written the C++ code to demonstrate a copy of the //vector 
// by constructor method
#include<bits/stdc++.h> 
using namespace std; 
int main() { 
    //here, we are initializing a vector with values 
    vector<int> vect1{1111, 3332, 56783, 13344}; 
    // constructor method, Deep copy 
    vector<int> vect2(vect1); 
    cout << "the old vector elements are : "; 
    for (int i=0; i<vect1.size(); i++) 
        cout << vect1[i] << " "; 
    cout << endl; 
    cout << "the new vector elements are : "; 
    for (int i=0; i<vect2.size(); i++) 
        cout << vect2[i] << " "; 
    cout<< endl; 
    // copy has been created. 
    vect1[0] = 2; 
    cout << "first element of old vector :"; 
    cout << vect1[0] << endl; 
    cout << "first element of new vector :"; 
    cout << vect2[0] <<endl; 
    return 0; 
} 

Output

the old vector elements are: 1111 3332 56783 13344 
the new vector elements are: 1111 3332 56783 13344 
the first element of old vector:2
the first element of new vector:1111

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