Passing a constant is automatically passed by reference?

Question

If I pass a variable to a function but mark that variable as constant will it automatically get passed by reference?

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In C++

void foo(const int a)

After testing: No because it prints different memory locations.

void foo(const int a)
{
    cout << &a << endl;
}

int main()
{
   int a = 5;
   foo(a);
   cout << &a << endl;
   return 0;
}

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C

No right? Because I can only pass a pointer to the memory location, not really by reference. Like here: Passing by reference in C

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Java

Maybe the compiler can figure out that final should point to the same memory location?

void foo(final int a)

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C#

Same as Java?

void foo(const int a)

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I know I included 4 languages in my question but since I use those 4 languages a lot I want to know.

Is there a way to force Java and C# to handle do this? I know in C++ I can add & to the function and it will be exactly what I want.

 void f(const int &a)

Pretty much that is what I am hopping Java and C# compilers are doing behind the scenes.

Answer 1

In Java, all the variables are passed by value.

Primitives are actually copied and object variables are references anyway, meaning that the value of an object variable is actually the reference -> you are passing the reference's value.

Nevertheless, you always pass by value, same as in C++, you will pass by value if you don't use the reference explicitly.

I'm almost certain that it's the same in C#.

Edit: I forgot about C

It's the same in C: pass by value by default. Obviously, you can pass a pointer. In C++, this is extended so you can take a reference as a parameter:

void function(int& intByReference) {
    cout<<&intByReference<<endl; //prints x
}

int main() {
    int n = 0;
    cout<<&n<<endl; //prints x
    function(n);
}

As C++ includes classes, there is a default constructor to copy the object:

class MyClass {

    public:
        MyClass(MyClass& objectToCopy) {
            //copy your object here
            //this will be called when you pass an instance of MyClass to a function
        }
};

Answer 2

You are making a mistake in thinking your intuition can guide you to how the details of the languages are implemented. This is quite simply not true. In the case of C++ and C, the spec states quite clearly how this should be dealt with.

Java as a pass by value language might have some provision for this behaviour in the specs for final/const/not touched values. (I don't know) But it is only the specs that can allow for this behaviour.