# How to join two Vectors using STL in C++?

Given two vectors, join these two vectors using STL in C++.
Example:

Input:
vec1 = {1, 45, 54, 71, 76, 12},
vec2 = {1, 7, 5, 4, 6, 12}
Output: {1, 4, 5, 6, 7, 12, 45, 54, 71, 76}
Input:
vec1 = {1, 7, 5, 4, 6, 12},
vec2 = {10, 12, 11}
Output: {1, 4, 5, 6, 7, 10, 11, 12}

Approach: Joining can be done with the help of set_union() function provided in STL.
Syntax:

set_union (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result);

## CPP

 // C++ program to join two Vectors// using set_union() in STL #include using namespace std; int main(){    // Get the vector    vector vector1 = { 1, 45, 54, 71, 76, 12 };    vector vector2 = { 1, 7, 5, 4, 6, 12 };     // Sort the vector    sort(vector1.begin(), vector1.end());    sort(vector2.begin(), vector2.end());     // Print the vector    cout << "First Vector: ";    for (int i = 0; i < vector1.size(); i++)        cout << vector1[i] << " ";    cout << endl;     cout << "Second Vector: ";    for (int i = 0; i < vector2.size(); i++)        cout << vector2[i] << " ";    cout << endl;     // Initialise a vector    // to store the common values    // and an iterator    // to traverse this vector    vector v(vector1.size() + vector2.size());    vector::iterator it, st;     it = set_union(vector1.begin(),                   vector1.end(),                   vector2.begin(),                   vector2.end(),                   v.begin());     cout << "\nAfter joining:\n";    for (st = v.begin(); st != it; ++st)        cout << *st << ", ";    cout << '\n';     return 0;}

Output:
First Vector: 1 12 45 54 71 76
Second Vector: 1 4 5 6 7 12

After joining:
1, 4, 5, 6, 7, 12, 45, 54, 71, 76,

Note that the vector should not contain 1 element twice:

In case you enter same elements, the set_union function will only consider 1 instance of the element, and default rest to 0.

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