How to append a vector to a vector in C++

By Rishabh Agarwal

Hi guys, in this tutorial we are going to learn about several methods that will help us to append a vector to a vector in c++.
For example, we have two vectors v1 and v2 and we have to append v2 to v1.

vector<int>v1 = {4,3,2,1};
vector<int>v2 = {-1,0,7};

The output should be,

v1 = {4,3,2,1,-1,0,7};

Method 1: Using vector::insert function

It will copy the elements of v2 and then inserts them to the end of v1.

Code

#include<iostream>
#include<vector>
using namespace std;

int main()
{
    //Given Vectors
    vector<int>v1 = {4,3,2,1};
    vector<int>v2 = {-1,0,7};

    //insert function used to insert elements in 
    //range of second and third parameter of v2 
    //into v1 from index equal to first parameter
    v1.insert(v1.end(),v2.begin(),v2.end());

    //printing the concatenated vector v1
    for(auto it: v1){
        cout<<it<<" ";
    }
    
    return 0;
}

Method 2: Using std::move and std::copy function

std::move function will just move the whole vector v2 to the end of v1. We will also use an std::back_inserter function which is to allocate space for v2 in v1 and std::copy function will also do the same thing but it will copy the elements of v2 instead of moving them.

Code

#include<iostream>
#include<vector>
using namespace std;

int main()
{
    //Given Vectors
    vector<int>v1 = {4,3,2,1};
    vector<int>v2 = {-1,0,7};

    //move function used to move all elements
    //of v2 to the end of v1 by allocating 
    //space for them using back_inserter function 
    move(v2.begin(),v2.end(),back_inserter(v1));

    //now using copy function
    //copy(v2.begin(),v2.end(),back_inserter(v1));

    //printing the concatenated vector v1
    for(auto it: v1){
        cout<<it<<" ";
    }

    return 0;
}

Method 3: Using while loop and vector::push_back function

This is the most simple way in which we can achieve our goal. We just need to iterate into v2 using a while loop and using push_back function inserts elements of v2 into v1.

Code

#include<iostream>
#include<vector>
using namespace std;

int main()
{
    //Given Vectors
    vector<int>v1 = {4,3,2,1};
    vector<int>v2 = {-1,0,7};

    //here we iterated into v2 and inserted
    //elements of v2 into v1.
    int siz=v2.size();
    while(siz){
        v1.push_back(v2[v2.size()-siz]);
        siz--;
    }

    //printing the concatenated vector v1
    for(auto it: v1){
        cout<<it<<" ";
    }

    return 0;
}

Method 4: Using vector::resize function

Here we will first resize v1 to the sum of sizes of v1 and v2 and then using at() operator assign values of v2 to v1.

Code

#include<iostream>
#include<vector>
using namespace std;

int main()
{
    //Given Vectors
    vector<int>v1 = {4,3,2,1};
    vector<int>v2 = {-1,0,7};

    //resizes size of v1 into size of v1+v2
    v1.resize(v1.size()+v2.size());
    int siz=v2.size();
    while(siz){
        // assigning values of v2 to v1
        v1.at(v1.size()-siz)=v2[v2.size()-siz];
        siz--;
    }

    //printing the concatenated vector v1
    for(auto it: v1){
        cout<<it<<" ";
    }

    return 0;
}

Now take a look at the output for all these codes

Output

4 3 2 1 -1 0 7

These are some of the methods to append a vector to a vector, I hope this will help you.
And you can also read some of my other blogs listed below.

• Strand Sort in C++
• Flatten a 2-Dimensional vector in C++

Thank you.