Various reasons for usage of 'const' in Copy constructor

Question

I know much things about copy constructor. How is it called and why '&' and 'const' is needed. When it is created by default and what kind of copies it generate etc.

Recently, I was having a discussion with one of my juniors about it and he asked: "Why do we use const in copy constructor parameters". I told him two-fold answer:

One, We should use const wherever possible. Two, We should use it so that compiler deals with temporary objects and do not let them die.

But his smile seems to suggest me that there is more about "Why do we use const". More about this is here.

I browsed through the internet and I was getting only above two reasons. Interested to know what are the other reasons for using 'const'.

Because if you don't, it's not a copy constructor. How would that even work? — melpomene, May 16 '17 at 06:48
The only other reason I've heard of is to prevent you from accidentally modifying the object your are trying to copy as a safeguard. — Bill F, May 16 '17 at 07:14
@melpomene, Even if you do not write 'const', copy constructor still gets called. Having said that 'const' is recommended to write. — Hemant Bhargava, May 16 '17 at 07:40
@BillF, Isn't that implicit? Preventing from accidentally modifying the object by passing const. — Hemant Bhargava, May 16 '17 at 07:41
Possible duplicate of [Why C++ copy constructor must use const object?](http://stackoverflow.com/questions/16956693/why-c-copy-constructor-must-use-const-object) — el.pescado - нет войне, May 16 '17 at 08:13
If the copy-constructor takes a non-const argument, you cannot copy a const object. So `A const a; A cpy(a);` would fail to compile. — pschill, May 16 '17 at 08:14

Various reasons for usage of 'const' in Copy constructor

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