The rule is simple : it is how you declare it.
int i = 5;
auto a1 = i; // value
auto & a2 = i; // reference
Next example proves it :
#include <typeinfo>
#include <iostream>
template< typename T >
struct A
{
static void foo(){ std::cout<< "value" << std::endl; }
};
template< typename T >
struct A< T&>
{
static void foo(){ std::cout<< "reference" << std::endl; }
};
float& bar()
{
static float t=5.5;
return t;
}
int main()
{
int i = 5;
int &r = i;
auto a1 = i;
auto a2 = r;
auto a3 = bar();
A<decltype(i)>::foo(); // value
A<decltype(r)>::foo(); // reference
A<decltype(a1)>::foo(); // value
A<decltype(a2)>::foo(); // value
A<decltype(bar())>::foo(); // reference
A<decltype(a3)>::foo(); // value
}
The output:
value
reference
value
value
reference
value