Returning from a function in C++

Question

This question may seem a little bit to broad, because it is a subject that splits into:

1. returning by value

2. returning by reference
3. returning by pointer

And I'm not sure that I'll be able to understand without knowing all of the points (1,2 and 3), so providing some useful links would be awesome. I did search for topics like "returning from functions in C++" but only found some basic examples where things were presented superficially.

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1. It is unclear for me why returning an user_defined object by value from a function does not call the copy constructor
   • I was expecting classic constructor message followed by copy constructor to appear, instead just the first one did.

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class X
{
public:
    int val;

    X(int val)      : val{val}     { cout << "classic constructor\n";}    
    X(const X& ref) : val{ref.val} { cout << "copy constructor\n";   }
};

// function returning an object of type X by VALUE
X f()
{
    X a = X{6};
    return a;
}

int main()
{
    X obj = f();
    return 0;
}

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1. The previous question arises after trying to implement the following operator+ function
   • Each time obj1 + obj2 is going to execute, this operator+ function is going to return a temporary object by value. Here it should call the copy constructor, but instead, the classic constructor is also called.

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X operator+(const X& ref1, const X& ref2)
{
    X var_temp{ref1.val + ref2.val};

    return var_temp;
}

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I feel like I misunderstood how does returning from function works. Maybe you could help me to better understand this.

Thanks in advice.