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Showing content from https://www.tutorialspoint.com/cpp_standard_library/cpp_array_front.htm below:

C++ Array Front Function

The C++ std::array::front() function is used to return the reference to the first element of the array allowing both read and write operations.

When the front() function is invoked on the empty array, it results in undefined behaviour.

Following is the syntax for std::array::front() function.

reference front();
const_reference front() const;

It does not accepts any parameter.

It returns the first element of an array.

Calling this method on empty array container will cause undefined behavior.

Constant i.e. O(1)

In the following example, we are going to consider the basic usage of the front() function.

#include <iostream>
#include <array>
using namespace std;
int main(void) {
   array < int, 5 > arr = {10,20,30,40,50};
   cout << "First element of array = " << arr.front() <<
      endl;
   arr.front() = 1;
   cout << "After modification first element of array = " << arr.front() <<
      endl;
   return 0;
}

Output of the above code is as follows −

First element of array = 10
After modification first element of array = 1

Consider the following example, where we are going to declare a array without size and observing the output.

#include <iostream>
#include <array>
using namespace std;
int main() {
   array < char >
      myarray {'a','b','c','d','e','f','g'};
   cout << myarray.front();
   return 0;
}

Following is the output of the above code −

main.cpp: In function 'int main()':
main.cpp:6:19: error: wrong number of template arguments (1, should be 2)
    6 |         array<char>
      |                   ^
In file included from main.cpp:2:
/usr/include/c++/11/array:95:12: note: provided for 'template<class _Tp, long unsigned int _Nm> struct std::array'
   95 |     struct array
      |            ^~~~~
main.cpp:7:9: error: scalar object 'myarray' requires one element in initializer
    7 |         myarray{ 'a', 'b', 'c', 'd', 'e', 'f', 'g' };
      |         ^~~~~~~

array.htm

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