STD::array in C++

Difficulty Level : Easy
Last Updated : 24 Jul, 2021

The array is a collection of homogeneous objects and this array container is defined for constant size arrays or (static size). This container wraps around fixed-size arrays and the information of its size are not lost when declared to a pointer.
In order to utilize arrays, we need to include the array header:

 #include <array>

Let’s see an example.

CPP

// CPP program to demonstrate working of array
#include <algorithm>
#include <array>
#include <iostream>
#include <iterator>
#include <string>
using namespace std;
 
int main() {
 
  // construction uses aggregate initialization
  // double-braces required
  array<int, 5> ar1{{3, 4, 5, 1, 2}};
  array<int, 5> ar2 = {1, 2, 3, 4, 5};
  array<string, 2> ar3 = {{string("a"), "b"}};
 
  cout << "Sizes of arrays are" << endl;
  cout << ar1.size() << endl;
  cout << ar2.size() << endl;
  cout << ar3.size() << endl;
   
  cout << "\nInitial ar1 : ";
  for (auto i : ar1)
    cout << i << ' ';
 
  // container operations are supported
  sort(ar1.begin(), ar1.end());
 
  cout << "\nsorted ar1 : ";
  for (auto i : ar1)
    cout << i << ' ';
 
  // Filling ar2 with 10
  ar2.fill(10);
 
  cout << "\nFilled ar2 : ";
  for (auto i : ar2)
    cout << i << ' ';
 
 
  // ranged for loop is supported
  cout << "\nar3 : ";
  for (auto &s : ar3)
    cout << s << ' ';
 
  return 0;
}

Output:

Sizes of arrays are
5
5
2

Initial ar1 : 3 4 5 1 2 
sorted ar1 : 1 2 3 4 5 
Filled ar2 : 10 10 10 10 10 
ar3 : a b

This C++ STL array is a kind of sequential container and is not used extremely in regular programming or in competitive programming but sometimes its member function provides an upper edge to it over the regular normal array that we use in our daily life. So, we are discussing some of the important member function that is used with such kind of array:

Member Functions for Array Template are as follows:

Syntax: array<object_type, arr_size> arr_name;

a) [ ] Operator : This is similar to the normal array, we use it to access the element store at index ‘i’ .

Ex:

C++

#include <iostream>
#include <array>
using namespace std;
 
int main() {
    array <char , 3> arr={'G','f','G'};
    cout<<arr[0] <<" "<<arr[2];
    return 0;
}

Output

G G

b) front( ) and back( ) function: These methods are used to access the first and the last element of the array directly.

C++

#include <iostream>
#include <array>
using namespace std;
 
int main() {
    array <int , 3> arr={'G','f','G'};  // ASCII val of 'G' =71
    cout<<arr.front() <<" "<<arr.back();
    return 0;
}

Output

71 71

c) swap( ) function: This swap function is used to swap the content of the two arrays.

Ex:

C++

#include <iostream>
#include <array>
using namespace std;
 
int main() {
    array <int , 3> arr={'G','f','G'};  // ASCII val of 'G' =71
    array <int , 3> arr1={'M','M','P'}; // ASCII val of 'M' = 77 and 'P' = 80
    arr.swap(arr1);  // now arr = {M,M,P}
    cout<<arr.front() <<" "<<arr.back();
    return 0;
}

Output

77 80

d) empty( ) function: This function is used to check whether the declared STL array is empty or not , if it is empty then it returns false else true.

Ex:

C++

#include <iostream>
#include <array>
using namespace std;
 
int main() {
    array <int , 3> arr={'G','f','G'};  // ASCII val of 'G' =71
    array <int , 3> arr1={'M','M','P'}; // ASCII val of 'M' = 77 and 'P' = 80
    bool x = arr.empty(); // false ( not empty)
    cout<<boolalpha<<(x);
    return 0;
}

Output

false

e) at( ) function: This function is used to access the element stored at a specific location, if we try to access the element which is out of bounds of the array size then it throws an exception.

Ex:

C++

#include <iostream>
#include <array>
using namespace std;
 
int main() {
    array <int , 3> arr={'G','f','G'};  // ASCII val of 'G' =71
    array <int , 3> arr1={'M','M','P'}; // ASCII val of 'M' = 77 and 'P' = 80
    cout<< arr.at(2) <<" " << arr1.at(2);
    //cout<< arr.at(3); // xception{Abort signal from abort(3) (SIGABRT)}
    return 0;
}

Output

71 80

f) fill( ) function: This is specially used to initialize or fill all the indexes of the array with a similar value.

Ex:

C++

#include <iostream>
#include <array>
using namespace std;
 
int main() {
    array <int , 5> arr;
    arr.fill(1);
    for(int i: arr)
       cout<<arr[i]<<" ";
    return 0;
}

Output

1 1 1 1 1

g) size( ) or max_size( ) and sizeof( ) function: Both size( ) or max_size( ) are used to get the maximum number of indexes in the array while sizeof( ) is used to get the total size of array in bytes.

C++

#include <iostream>
#include <array>
using namespace std;
 
int main() {
    array <int , 10> arr;   
    cout<<arr.size()<<'\n'; // toatal num of indexes
    cout<<arr.max_size()<<'\n'; // toatal num of indexes
    cout<<sizeof(arr); // toatal size of array
    return 0;
}

Output

10
10
40

h) data( ): This function returns the pointer to the first element of the array object. Because elements in the array are stored in contiguous memory locations. This data( ) function return us the base address of the string/char type object.

Ex:

C++

#include <iostream>
#include <cstring>
#include <array>
 
using namespace std;
 
int main ()
{
  const char* str = "GeeksforGeeks";
  array<char,12> arr;
  memcpy (arr.data(),str,13);
  cout << arr.data() << '\n';
  return 0;
}

Output

GeeksforGeeks

I) cbegin( ) and cend( ): go to this gfg link : Click_me

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