class constructor with const reference

Question

in this class

class Foo {
public:
  Foo(){}
  Foo(Foo const &) {}
};

when would Foo(Foo const &) ever be called? I do not understand this kind of constructor

http://stackoverflow.com/questions/2168201/what-is-a-copy-constructor-in-c — deviantfan, Nov 24 '16 at 07:13
You'll probably find [**this page**](http://en.cppreference.com/w/cpp/language/copy_constructor) informative. — WhozCraig, Nov 24 '16 at 07:13
This page also has a good general explanation of const, with your specific question in the section titled "Where it Gets Messy - in Parameter Passing" : http://duramecho.com/ComputerInformation/WhyHowCppConst.html — Robert M., Nov 24 '16 at 07:18
And while we're here, [What is The Rule of Three?](http://stackoverflow.com/questions/4172722/what-is-the-rule-of-three) Well, it just happens to be one of the, if not the, most important reasons for one of these. — user4581301, Nov 24 '16 at 07:30

score 2 · Accepted Answer · answered Nov 24 '16 at 07:29

This is called copy constructor. When you want to initialize a class instance by copying an existing instance, you'd probably want to use it.

const - you don't want to change the object you are copying.

reference - you don't want to copy the existing instance into the constructor, just to copy it again in the initialization.

1 Answers1