How to pass array reference from function? [duplicate] - c++

Question

This question already has answers here:
pass reference to array in C++
(3 answers)
Closed 8 years ago.
I want to pass value of array in function by reference
My first try with variable (it works well):
#include <iostream>
using namespace std;
int input(int &);
int main()
{
int a;
input(a);
cout << "the value : " << a << endl;
system("pause");
return 0;
}
int input(int &a)
{
cin >> a;
}
But when i change a to a[] like in the following code, it
doesn't work
#include <iostream.h>
using namespace std;
int input(int &[]);
int main()
{
int a[2], i;
input(a);
for(i=0;i<=2;i++)
{
cout << a << endl;
}
system("pause");
return 0;
}
int input(int &a[])
{
int i;
for(i=0;i<=2;i++)
{
cin >> a[i];
}
}

Answer 1

It should be:
void input(int (&a)[2]);
or simply
void input(int (&)[2]);
But in function definition, you need also to give the array name:
void input(int (&a)[2]) {...}
You need to use (&array) to clarify to the compiler that you want a reference to an array, rather than the (invalid) array of references int &array[2];.
And call it like this:
input(a);

Answer 2

This record
int &[]
denotes an array of references that is forbided in C++.
Declare the function the following way
void input( int ( & )[2] );
Also you are using invalid range of indeces. The valid range is [0, 1]. So the function will look as
void input( int ( &a )[2] );
{
for ( size_t i = 0; i < 2; i++ ) std::cin >> a[i];
}
Also you could define the function the following way
void input( int a[], size_t n );
{
for ( size_t i = 0; i < n; i++ ) std::cin >> a[i];
}
and call it as
input( a, 2 );

Answer 3

The syntax for returning and taking array references is:
template<typename T, size_t N>
T(&do_nothing(T(&arg)[N]))[N]
{
return arg;
}
Or, more simply with a templated type alias:
template<typename T, size_t N> using arrayref = T(&)[N];
template<typename T, size_t N>
arrayref<T, N> do_nothing(arrayref<T, N> arg)
{
return arg;
}
When you have defined the previous type alias template, it becomes very simple to work with array references, e.g. This is how you would declare a function that takes a reference to an array of two integers:
void give_me_two_ints(arrayref<int, 2> two_ints);
To be used like:
int a[] = {1,2,3};
for(auto const& i : do_nothing(a)) std::cout << i << "\n";