C++ STL: arrays (Complete Guide)

Arrays in STL are sequential containers that are very similar to static arrays. They are continuous blocks of memory and have static sizes. Although there are very similar to static arrays in C++, their member functions make them more efficient. They are implemented as static arrays in memory. The array is present in #include<array> header file.

Array Declaration

Syntax:

array<data_type,size> name;

data_type: The data types of the elements to be stored in the array

size: The size of the array

Example:

array < int, 5 > arr; //initializes a array of size 5 which stores integer values 

Array Initialization

Syntax:

array<data_type,size> name{initial_values};

initial_values: optional parameter which initializes the array with the given values.

Example:

array < int, 5 > arr { 1, 2, 3, 4, 5 }; //initializes a array of size 5 having intial values 1,2,3,4,5

Functions on arrays

• [i]: It is used to access the element stored at index i. 
  Time Complexity: O(1) 
  Parameters: index of the element
  Return type: element at index i
   
• at(i): It is also used to access the element stored at index i. 
  Time Complexity: O(1) 
  Parameters: index of the element
  Return type: element at index i if i in range of array otherwise out_of_bound error is thrown
   
• front(): It returns the first element of the array.  
  Parameters: None 
  Return type: the first element of the array
   
• back(): It returns the last element of the array. 
  Parameters: None 
  Return type: last element of the array.
   
• size(): It tells us the number of elements in the array. 
  Parameters: None 
  Return type: integer - elements in the vector
   
• fill(element): It inserts the given value at every array index. 
  Parameters: value to be inserted. 
  Return type: void
   
• front(): It returns an iterator pointing to the first element of the array. 
  Parameters: None 
  Return type: iterator
   
• back(): It returns an iterator pointing to the last element of the array. 
  Parameters: None 
  Return type: iterator
   
• empty(): It tells us whether the array is empty or not. 
  Parameters: None 
  Return type: Boolean, true if the array is empty else false
   
• data(): It returns a pointer pointing to the first element of the array. 
  Parameters: None 
  Return type: iterator, pointing to the first element of the array
   
• swap(array_name): It swaps the content of the two arrays.
  Parameters: array_name to be swapped with 
  Return type: void

#include<iostream>
#include<array>
using namespace std;

int main() {
  array < int, 5 > arr { 1, 2, 3, 4, 5 };
  for (int i = 0; i < 5; i++) {
    cout << arr[i] << " ";
  }
  cout << '\n';
  cout << "Size of array is " << arr.size() << '\n';
  cout << "First element of array is " << arr.front() << '\n';
  cout << "Last element of array is " << arr.back() << '\n';
  cout << "Second element of array is " << arr.at(1) << '\n';
  cout << "First element of array using data method is " << * (arr.data()) << '\n';
  arr.fill(10);
  cout << "The new array is ";
  for (int i = 0; i < 5; i++) {
    cout << arr[i] << " ";
  }
  cout << '\n';
  if (arr.empty() == false) {
    cout << "array is not empty!";
  }
  return 0;
}

Output

1 2 3 4 5 
Size of array is 5
First element of array is 1
Last element of array is 5
Second element of array is 2
First element of array using data method is 1
The new array is 10 10 10 10 10 
array is not empty!