# 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}

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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);
```

 `// C++ program to join two Vectors ` `// using set_union() in STL ` ` `  `#include ` `using` `namespace` `std; ` ` `  `int` `main() ` `{ ` `    ``// Get the vector ` `    ``vector<``int``> vector1 = { 1, 45, 54, 71, 76, 12 }; ` `    ``vector<``int``> 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<``int``> v(vector1.size() + vector2.size()); ` `    ``vector<``int``>::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,
```

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