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vector::front(), vector::back(), vector::at() and vector::data() functions with examples | C++ STL

In this article, we will learn about some of the most useful functions like vector::front(),vector::back(), vector::at() and vector::data() of vector class in C++ STL.
Submitted by IncludeHelp, on August 24, 2018

C++ STL - vector::front(), vector::back(), vector::at() and vector::data() functions

vector::front(), vector::back(), vector::at() and vector::data() functions are the predefined function of vector class, which are used for vector element accessing in C++ STL.

1. vector::front()

Returns reference to the first element of a vector i.e. we can say it returns first element of the vector.

2. vector::back()

Returns reference to the last element of a vector i.e. we can say it returns last element of the vector.

3. vector::at(i)

Returns reference to the i^th element of a vector i.e. we can say it returns i^th element of the vector.

4. vector::data()

As we know, vector is a dynamic array, and it can also be accessed like an array style. vector::data() returns the direct pointer to the first element of array (used by vector in the memory) and we can access all elements.

Sample Input and Output

Input:
vector<int> num{10, 20, 30, 40, 50}

Output:
num.front(): 10
num.back(): 50
num.at(2): 30
All elements using vector::data(): 10 20 30 40 50

Example

In this example, we are demonstrating the examples of vector::front(), vector::back(), vector::at() and vector::data() functions in C++ STL:

#include <iostream>
#include <vector>

using namespace std;

int main() {
  // declare vector
  vector<int> num{10, 20, 30, 40, 50};

  // vector::front ()
  cout << "num.front(): " << num.front() << endl;
  // vector::back ()
  cout << "num.back() : " << num.back() << endl;
  // vector::at ()
  cout << "num.at(2) : " << num.at(2) << endl;

  // vector::data ()
  int *ptr = num.data();
  cout << "All elements using vector::data () : ";
  // note: there is no need to use vector iterator
  for (int i = 0; i < num.size(); i++) cout << *(ptr + i) << " ";

  cout << endl;

  return 0;
}

Output

num.front(): 10
num.back() : 50
num.at(2) : 30
All elements using vector::data () : 10 20 30 40 50