Testing how C++11 initializes native arrays and std vectors

vec-init.cpp

// here it is shown how implicit std vector initialization uses copy 
// constructor to replicate a single object when populating the vector
// also cheking the use of 'std::span', 'std::vector' and 'std::array' 
// as function parameters
//
// Compile with: -std=c++20

#include <iostream>
#include <vector>
#include <array>
#include <string>
#include <span>

using namespace std ;

class A
{
   public:
      A()
      {
         x = 0 ;
         cout << "constructor (), x == " << x << endl ;
      }
      A( int ix )
      {
         x = ix ;
         cout << "constructor (int), x == " << x << endl ;
      }
      A( const A & a )
      {
         x = a.get_x() ;
         cout << "copy constructor, x == " << x << endl ;
      }
      int get_x() const { return x ; }
   private:
      int x ;
} ;



void print_array( const std::vector<A> & v  )
{
   cout << "As vector: { " ;
   for( int i = 0 ; i < v.size() ; i++ )
   {
      cout << v[i].get_x() ;
      if (i < v.size()-1 ) cout << ", " ;
   }
   cout << " }" << endl << endl ;
}

void print_array( const std::span<const A>  v )
{
    cout << "As span: { " ;
    for( int i = 0 ; i < v.size() ; i++ )
    {
      cout << v[i].get_x() ;
      if (i < v.size()-1 ) cout << ", " ;
    }
    cout << " }" << endl << endl ;
}

template<class T, int N>
void print_array( const std::array<T,N> & v )
{
   cout << "As array<T " << N << ">: { " ;
   for( int i = 0 ; i < v.size() ; i++ )
   {
      cout << v[i].get_x() ;
      if (i < v.size()-1 ) cout << ", " ;
   }
   cout << " }" << endl << endl ;
}

int main()
{
   const int N = 4 ;

   cout << "using native array initialization" << endl ;
   const A a1[N] = {1,2,3,4} ;
   print_array(a1);

   cout << "using 'std::vector' initialization" << endl ;
   const std::vector<A> a2 = {1,2,3,4}  ;
   print_array(a2);

   cout << "using 'std::vector' (initialized with a single replicated value)" << endl ;
   const std::vector<A> a3(N,123)  ;
   print_array(a3);

   cout << "using 'std::array'" << endl ;
   const std::array<A,N> a4 = {1,2,3,4} ;
   print_array(a4);


   // using an initializer list, it is converted to a vector 
   cout << "using an initializer lists" << endl ;
   print_array( {1,2,3,4} );

}