How to declare a reference to a member in the same class? - c++

Question

I looked at a lot of other questions and answers and no one seems to have the same question I do.
I am trying to make references to variables, both within a class. I took out the part of the larger program I am writing and isolated it in a little file: test.cpp. I thought maybe my problem had something to do with how I was using the variable with the reference, but the same messages appeared as in the larger program.
Here is my code:
#include <iostream>
class Test {
public:
int test;
int& rtest = test;
};
int main() {
std::cout << "Enter an integer: ";
std::cin >> Test.rtest;
std::cout << "\n" << Test.rtest << "\n";
return 0;
}
I received these messages:
warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
int& rtest = test;
In function ‘int main()’: error: expected primary-expression before ‘.’ token
std::cin >> Test.rtest;
error: expected primary-expression before ‘.’ token std::cout << "\n" << Test.rtest << "\n";
Why am I getting these? Is what I am trying to do possible? If so, how can I do it?

Answer 1

warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 int& rtest = test;
You need to pass the flag -std=c++11 to your compiler, otherwise it defaults to an older version of C++ which doesn't allow you to initialize class members in that way.
In function ‘int main()’: error: expected primary-expression before ‘.’ token std::cin >> Test.rtest;
error: expected primary-expression before ‘.’ token std::cout << "\n" << Test.rtest << "\n";
This is because the . operator wants an instance of your class, not the class itself (that's what :: would be for). Declare e.g. Test test; and use test.rtest instead.

Answer 2

You need to have an instance of Test to access non static members of a class:
int main() {
Test t; // <<<<<<<<
std::cout << "Enter an integer: ";
std::cin >> t.rtest;
std::cout << "\n" << t.rtest << "\n";
}
Also you need to initialize the reference with an appropriate constructor, unless you have the -std=c++11 compiler flag enabled as the error message says:
class Test {
public:
int test;
int& rtest; // Nope! = test;
Test() : test(), rtest(test) {} // <<<<<<<<<<<<<<<<<<
};