Member function that can return multiple references? (C++)

Question

I have a member function that needs to return multiple references of char member variables.

class Foo {
public:
    Foo() {// ... constructor }
    
    std::string& func();

private:
    char ch1 = 'a', ch2 = 'b', ch3 = 'c';
};

The code below is something would obviously not fulfill my purpose, because the lifetime of the local variable is limited to the scope of the function call:

std::string& func()
{
    std::string total = "";
    total += this-> a;
    total += this-> b;
    total += this-> b;
    
    return total;
}

I would also prefer not to use the method of allocating memory for the local variable using new, then having to delete it after.

I also would not prefer to add a new member variable to the class that is used in the member function and returned.

First of all, is doing this even possible? If so, how can I achieve this?

Many thanks for help.

Answer 1

You can return a std::tuple of references :

std::tuple<char&, char&, char&> foo::func()
{
    return std::tie(ch1, ch2, ch3);
}

You can also use structured binding to unpack the return value :

int main()
{
    foo f;
    auto [a, b, c] = f.func();
    b = 'z';    // Modifies `f.ch2`
}

Live example : https://godbolt.org/z/eM1h6qaxx

---

Edit for C++14 :

Instead of structured binding, you can use std::get to access one of the return values :

int main()
{
    foo f;
    auto result = f.func();
    std::get<1>(result) = 'z';    // Modifies `f.ch2`
}

C++14 live example : https://godbolt.org/z/jrjsr4K7e