Question

What are the advantages of Vector over an array in C++?

Answer 1

Advantages of Vector over arrays :

Vector is template class and is C++ only construct whereas arrays are built-in language construct and present in both C and C++.

Vector are implemented as dynamic arrays with list interfacewhereas arrays can be implemented as statically or dynamically with primitive data type interface.

#include <bits/stdc++.h>

using namespace std;

  

int main()

{

    int array[100]; // Static Implementation

    int* arr = new int[100]; // Dynamic Implementation

    vector<int> v; // Vector's Implementation

    return 0;

}

Size of arrays are fixed whereas the vectors are resizable i.e they can grow and shrink as vectors are allocated on heap memory.

#include <bits/stdc++.h>

using namespace std;

  

int main()

{

    int array[100]; // Static Implementation

  

    cout << "Size of Array " << sizeof(array) / sizeof(array[0]) << "\n";

  

    vector<int> v; // Vector's Implementation

  

    // Inserting Values in Vector

    v.push_back(1);

    v.push_back(2);

    v.push_back(3);

    v.push_back(4);

    v.push_back(5);

  

    cout << "Size of vector Before Removal=" << v.size() << "\n";

  

    // Output Values of vector

    for (auto it : v)

        cout << it << " ";

  

    v.erase(v.begin() + 2); // Remove 3rd element

  

    cout << "\nSize of vector After removal=" << v.size() << "\n";

  

    // Output Values of vector

    for (auto it : v)

        cout << it << " ";

  

    return 0;

}

Output

Size of Array 100 Size of vector Before Removal=5 1 2 3 4 5 Size of vector After removal=4 1 2 4 5

Arrays have to be deallocated explicitly if defined dynamically whereas vectors are automatically de-allocated from heap memory.

#include <bits/stdc++.h>

using namespace std;

  

int main()

{

    int* arr = new int[100]; // Dynamic Implementation

    delete[] arr; // array Explicitly deallocated

  

    vector<int> v; // Automatic deallocation when variable goes out of scope

    return 0;

}

Size of array cannot be determined if dynamically allocated whereas Size of the vector can be determined in O(1) time.

When arrays are passed to a function, a separate parameter for size is also passed whereas in case of passing a vector to a function, there is no such need as vector maintains variables which keeps track of size of container at all times.

#include <bits/stdc++.h>

using namespace std;

  

int main()

{

    int* arr = new int[100]; // Dynamic Implementation

  

    cout << "Size of array= ";

    cout << sizeof(arr) / sizeof(*arr) << "\n"; // Pointer cannot be used to get size of

    // block pointed by it

    return 0;

}

Output:

Size of array= 2

When array becomes full and new elements are inserted; no reallocation is done implicitlywhereas When vector becomes larger than its capacity, reallocation is done implicitly.

Arrays cannot be returned unless dynamically allocated from a function whereas vectors can be returned from a function.

// Program to demonstrate arrays cannot be returned

#include <bits/stdc++.h>

using namespace std;

  

int* getValues()

{

  

    int arr[10]; // Array defined locally

    for (int i = 0; i < 10; i++) // Putting Values in array

        arr[i] = i + 1;

  

    return arr; // returning pointer to array

}

  

// main function

int main()

{

  

    int* array; // pointer of int type

  

    array = getValues(); // Call function to get arr

  

    for (int i = 0; i < 10; i++) { // Printing Values

        cout << "*(array + " << i << ") : ";

        cout << *(array + i) << endl;

    }

  

    return 0;

}

Output:

warning: address of local variable 'arr' returned [-Wreturn-local-addr] Segmentation Fault (SIGSEGV)

// Program to demonstrate vector can be returned

#include <bits/stdc++.h>

using namespace std;

  

// Function returning vector

vector<int> getValues()

{

  

    vector<int> v; // Vector defined locally

    for (int i = 0; i < 10; i++) // Inserting values in Vector

        v.push_back(i + 1);

  

    return v; // returning pointer to array

}

  

// main function

int main()

{

  

    vector<int> get;

  

    get = getValues(); // Call function to get v

  

    // Output Values of vector

    for (auto it : get)

        cout << it << " ";

  

    return 0;

}