Q: Is pass-by-value/reference defined strictly by **behavior** or **implementation** wise in C++, and can you provide an authoritative citation? 

I had a conversion with a friend about pass-by-value/reference in C++. We came to a disagreement on the definition of pass-by-value/reference. I understand that passing a pointer to a function is still pass-by-value since the value of the pointer is copied, and this copy is used in the function. Subsequently, dereferencing the pointer in the function and mutating it will modify the original variable. This is where the disagreement appears. 

His stance: Just because a pointer value was copied and passed to the function, performing operations on the dereferenced pointer has the ability to affect the original variable, so it has the behavior of pass-by-reference, passing a pointer to a function. 

My stance: Passing a pointer to a function does copy the value of the pointer, and operations in the function may affect the original variable; however, just because it may affect the original, this behavior does not constitute it to be pass-by-reference since it is the implementation of the language that is what defines these terms, pass-by-value/reference. 

Quoting from the definition given by the highest voted answer here: [Language Agnostic](https://stackoverflow.com/questions/373419/whats-the-difference-between-passing-by-reference-vs-passing-by-value)

**Pass by Reference**

> 
> When a parameter is **passed by reference**, the caller and the callee **use the same variable** for the parameter. If the callee modifies the parameter variable, the effect is visible to the caller's variable.
> 
> 
> 

**Pass by Value**

> 
> When a parameter is **passed by value**, the caller and callee have **two independent variables** with the same value. If the callee modifies the parameter variable, the effect is not visible to the caller.
> 
> 
> 

I still have an ambiguous feeling after reading these. For example, the pass by value/reference quotes can support either of our claims. Can anyone clear up the definitions of whether these definition stem from behavior or implementation and provide a citation? Thanks!

**Edit:** I should be a little more careful of my vocabulary. Let me extend my question with a clarification. What I mean when questioning *pass-by-reference* is **not** talking purely about the C++ implementation of **&** reference, but instead also the theory. In C++, is it that the **&** pass-by-reference is true PBR because not only can it modify the original value, but also the memory address of the value. This leads to this, example with pointers also count as PBR?

```
void foo(int ** bar){
    *bar = *bar+(sizeof(int*));
    cout<<"Inside:"<<*bar<<endl;
}

int main(){
    int a = 42;
    int* ptrA = &a;
    cout<<"Before"<<ptrA<<endl;
    foo(&ptrA);
    cout<<"After:"<<ptrA<<endl;
}

```

The output would be that `After ptrA` is equal to `Inside`, meaning that not only can the function modify `a`, but `ptrA`. Because of this, does this define call-by-reference as a theory: being able to not only modify the value, but the memory address of the value. Sorry for the convoluted example.