Discussion on: Understanding recursions and memory

[Lalit Yadav]

Thanks for this :) I completely understand it now and how I misused the concepts in the main article however aren't class objects always pass by reference ? in the context of C++.
@pentacular ^

[pentacular]

Consider the following code:

#include <iostream>

class Foo {
 public:
  Foo():v(0) {};
  int v;
};

void bar(Foo x) {
  x.v = 1;
}

int main() {
  Foo a;
  a.v = 0;
  bar(a);
  std::cout << "a.v is " << a.v;
  return 0;
}

What does this output and why? :)

[Lalit Yadav]

This should print 1 but this is printing 0. My thinking is x implicit reference to a so if x changes a should also change.
If I do it like this explicitly void bar(Foo& x) then it is printing 1. I wonder what is happening behind the scenes here.
My source of the learning is from Bjarne c++ 4th edition ( First 2 section done). I also did C++ in 2015-16 during the final year in college I'm familiar with the syntax.
This is extremely helpful to me as I was looking for some guidance already :)

[pentacular]

The explanation is that your thinking is incorrect. :)

In the example x is not a reference, so a is passed by value.
The value of a is assigned to x, which is an independent variable.
So changes to x do not affect a.

There is no 'implicit reference' in C++.

When you change x to be Foo& , a is passed by reference.

This is the difference between pass by value and pass by reference, and class instances are passed by value as usual.

[Lalit Yadav]

Yeah, I was confused initially about why to use references with the object now it makes much more sense to me. C++ is surely deep :). Thanks for your valuable comments, I will be posting my C++ endeavors as I go on learning new stuff but this time I will be precise with my word selection and topic :)