vector : : resize() in C++ STL

Vectors are known as dynamic arrays which can change its size automatically when an element is inserted or deleted. This storage is maintained by container.

vector::resize()

The function alters the container’s content in actual by inserting or deleting the elements from it. It happens so,

• If the given value of n is less than the size at present then extra elements are demolished.
• If n is more than current size of container then upcoming elements are appended at the end of the vector.

Syntax:

vectorname.resize(int n, int val)

Parameters:

n – it is new container size, expressed in number of elements.

val – if this parameter is specified then new elements are initialized with this value.

Return value:





This function do not returns anything.

Exception:

The only exception if it so happens is Bad_alloc thrown, if reallocation fails.

Below programs illustrate the working of the function

1. Size of the vector container is lowered.

   // resizing of the vector
   #include <iostream>
   #include <vector>
   
   using namespace std;
   
   int main()
   {
       vector<int> vec;
   
       // 5 elements are inserted
       // in the vector
       vec.push_back(1);
       vec.push_back(2);
       vec.push_back(3);
       vec.push_back(4);
       vec.push_back(5);
   
       cout << "Contents of vector before resizing:"
            << endl;
   
       // displaying the contents of the
       // vector before resizing
       for (int i = 0; i < vec.size(); i++)
           cout << vec[i] << " ";
   
       cout << endl;
   
       // vector is resized
       vec.resize(4);
   
       cout << "Contents of vector after resizing:"
            << endl;
   
       // displaying the contents of the
       // vector after resizing
       for (int i = 0; i < vec.size(); i++)
           cout << vec[i] << " ";
   
       return 0;
   }

   Output:

   Contents of the vector before resizing:
   1 2 3 4 5 
   Contents of the vector after resizing:
   1 2 3 4 
   

2. Size of the vector container is increased.

   // resizing of the vector
   #include <iostream>
   #include <vector>
   
   using namespace std;
   
   int main()
   {
       vector<int> vec;
   
       // 5 elements are inserted
       // in the vector
       vec.push_back(1);
       vec.push_back(2);
       vec.push_back(3);
       vec.push_back(4);
       vec.push_back(5);
   
       cout << "Contents of vector before resizing:"
            << endl;
   
       // displaying the contents of the
       // vector before resizing
       for (int i = 0; i < vec.size(); i++)
           cout << vec[i] << " ";
   
       cout << endl;
   
       // vector is resized
       vec.resize(8);
   
       cout << "Contents of vector after resizing:"
            << endl;
   
       // displaying the contents of
       // the vector after resizing
       for (int i = 0; i < vec.size(); i++)
           cout << vec[i] << " ";
   
       return 0;
   }

   Output:

   Contents of the vector before resizing:
   1 2 3 4 5 
   Contents of the vector after resizing:
   1 2 3 4 5 0 0 0 
   

3. Size of the vector container is increased and new elements are initialized with specified value.

   // resizing of the vector
   #include <iostream>
   #include <vector>
   
   using namespace std;
   
   int main()
   {
       vector<int> vec;
   
       // 5 elements are inserted
       // in the vector
       vec.push_back(1);
       vec.push_back(2);
       vec.push_back(3);
       vec.push_back(4);
       vec.push_back(5);
   
       cout << "Contents of vector before resizing:"
            << endl;
   
       // displaying the contents of
       // the vector before resizing
       for (int i = 0; i < vec.size(); i++)
           cout << vec[i] << " ";
   
       cout << endl;
   
       // vector is resized
       vec.resize(12, 9);
   
       cout << "Contents of vector after resizing:"
            << endl;
   
       // displaying the contents
       // of the vector after resizing
       for (int i = 0; i < vec.size(); i++)
           cout << vec[i] << " ";
   
       return 0;
   }

   Output:

   Contents of the vector before resizing:
   1 2 3 4 5 
   Contents of the vector after resizing:
   1 2 3 4 5 9 9 9 9 9 9 9 
   

Attention reader! Don’t stop learning now. Get hold of all the important C++ Foundation and STL concepts with the C++ Foundation and STL courses at a student-friendly price and become industry ready.