Copy ctor and copy assignment operator const keyword position

Question

I've recently noticed that the const keyword on some code examples shifted in the middle (from respectable blog sites), something like this:

X(X const& that) { .../... }

X& operator=(X const& other) { .../... }

Is this equivalent to this more familiar syntax?

X(const X& that) { .../... }

X& operator=(const X& other) { .../... }

What is the purpose of switching 'const' that way?

Relevant: [C++: const reference, before vs after type-specifier](http://stackoverflow.com/questions/3694630/c-const-reference-before-vs-after-type-specifier) — cpplearner, Jan 17 '16 at 06:41

score 1 · Accepted Answer · answered Jan 17 '16 at 06:35

1

1) It doesn't matter where to put const: const int & == int const &

2) Why? It is mnemonic rule.

int * const - constant pointer (const after *)

int const * - pointer to the constant value (const after int).

So, its for consistency.

answered Jan 17 '16 at 06:35

SashaMN

708
5
16

code_dredd · Answer 2 · 2016-01-17T06:51:24.970

Is this equivalent to this more familiar syntax?

Yes, both syntaxes here are equivalent.

X(X const& x)
X(const X& x)

This says that x aliases an object of type X, but that the object cannot be changed using x. (It can still be modified if you use some non-const alias, pointer, etc.)

You should read it from right-to-left: x is an alias (or reference) to an object of type X that is const.

I'd also recommend reading C++ FAQ: Const Correctness

Copy ctor and copy assignment operator const keyword position

2 Answers2