std::vector::insert() is a built-in function in C++ STL which inserts new elements before the element at the specified position, effectively increasing the container size by the number of elements inserted.

1. Syntax:

   vector_name.insert (position, val)
   

   Parameter:The function accepts two parameters specified as below:

   • position – It specifies the iterator which points to the position where the insertion is to be done.
   • val – It specifies the value to be inserted.

   Return value: The function returns an iterator which points to the newly inserted element.

   Example 1: Below program illustrates the above mentioned function where new elements are inserted at the front.

   
   

   
   
   

   // Program below illustrates the // vector::insert() function    #include <bits/stdc++.h> using namespace std;    int main() {     // initialising the vector     vector<int> vec = { 10, 20, 30, 40 };        // inserts 3 at front     auto it = vec.insert(vec.begin(), 3);     // inserts 2 at front     vec.insert(it, 2);        int i = 2;     // inserts 7 at i-th index     it = vec.insert(vec.begin() + i, 7);        cout << "The vector elements are: ";     for (auto it = vec.begin(); it != vec.end(); ++it)         cout << *it << " ";        return 0; }

   Output:

   
   

   
   

   The vector elements are: 2 3 7 10 20 30 40
   

   Example 2: Below program illustrates the above mentioned function where new elements are inserted at a specific position.

   
   

   
   
   

   // Program below illustrates the // vector::insert() function    #include <bits/stdc++.h> using namespace std;    int main() {     // initialising the vector     vector<int> vec = { 10, 20, 70, 80 };     int x = 50;        // inserting multiple elements     // at specific positions     vec.insert(vec.begin() + 2, { 30, 40, x, 60 });        cout << "The vector elements are: ";     for (auto it : vec)         cout << it << " ";        return 0; }

   Output:

   The vector elements are: 10 20 30 40 50 60 70 80
   

2. Syntax:

   vector_name.insert(position, size, val)
   

   Parameter:The function accepts three parameters specified as below:

   • position – It specifies the iterator which points to the position where the insertion is to be done.
   • size – It specifies the number of times a val is to be inserted at the specified position.
   • val – It specifies the value to be inserted.

   Return value: The function returns an iterator which points to the newly inserted element.

   Below program illustrates the above mentioned function:

   
   

   
   
   

   // program below illustrates the // vector::insert() function    #include <bits/stdc++.h> using namespace std;    int main() {     // initialising the vector     vector<int> vec = { 10, 20, 30, 40 };        // inserts 3 one time at front     auto it = vec.insert(vec.begin(), 1, 3);        // inserts 4 two times at front     vec.insert(it, 2, 4);        cout << "The vector elements are: ";     for (auto it = vec.begin(); it != vec.end(); ++it)         cout << *it << " ";        return 0; }

   Output:

   The vector elements are: 4 4 3 10 20 30 40
   

3. Syntax:

   vector_name.insert(position, iterator1, iterator2)
   

   Parameter:The function accepts three parameters specified as below:

   • position – It specifies the position at which insertion is to be done in vector.
   • iterator1 – It specifies the starting position from which the elements are to be inserted
   • iterator2 – It specifies the ending position till which elements are to be inserted

   Return value: The function returns an iterator which points to the newly inserted element.

   Below is the illustration of above function:

   
   

   
   
   

   // program below illustrates the // vector::insert() function    #include <bits/stdc++.h> using namespace std;    int main() {     // initialising the vector     vector<int> vec1 = { 10, 20, 30, 40 };     vector<int> vec2;        // inserts at the beginning of vec2     vec2.insert(vec2.begin(), vec1.begin(), vec1.end());        cout << "The vector2 elements are: ";     for (auto it = vec2.begin(); it != vec2.end(); ++it)         cout << *it << " ";        return 0; }

   Output:

   The vector2 elements are: 10 20 30 40
   

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