Is the default constructor not called when declaration and assignment are joined?

Question

I have created a class coor and overloaded a + operator

class coor
{
    coor(){std::cout<<"default constructor called\n";};
    coor operator +(coor param) const;
};

coor coor::operator+(coor param) const
{
    ....    
}


int main() {
    coor obj1;
    coor obj2;
    coor obj3 = obj1 + obj2;
    std::cin.get();
    return 0;
}

Why is the default constructor of obj3 is not called? It is called when declarartion and assignment and seperated.

Here is the case when [the copy constructor](https://stackoverflow.com/questions/2168201/what-is-a-copy-constructor-in-c) gets involved . — user3366592, Dec 01 '18 at 12:51

score 2 · Accepted Answer · answered Dec 01 '18 at 12:51

2

With

coor obj3 = obj1 + obj2

you copy-construct obj3 from the result of obj1 + obj2 (which is a so-called r-value and a temporary object).

Even though = is used here, it's not assignment but initialization.

answered Dec 01 '18 at 12:51

Some programmer dude

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Your answer implies that a copy-constructor will be called. But this not true with C++17 (`operator+` returns a prvalue, so no copy constructor is involved here). – geza Dec 01 '18 at 12:58

score 1 · Answer 2 · answered Dec 01 '18 at 12:51

1

"Why is the default constructor of obj3 is not called?" - Because of the rules of copy initialization - which is what is happening here.

answered Dec 01 '18 at 12:51

Jesper Juhl

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Is the default constructor not called when declaration and assignment are joined?

2 Answers2