i have a class name X, what is the difference between "const X a" and "X const a"
views:
157answers:
4
+13
A:
Nothing.
A const qualifier applies to whatever is immediately to its left. If there is nothing to its left then it applies to whatever is immediately to its right.
James McNellis
2010-10-21 06:53:13
But there is a difference between `const int *a`, `int *const a` and `const int *const a`.
Benoit
2010-10-21 06:54:38
@Benoit: Yes, there is.
James McNellis
2010-10-21 06:55:06
oh, Thanks lot.
Shadow
2010-10-21 06:58:06
It is better however to write A const x to be in better harmony with the 'Right Left' rule
Chubsdad
2010-10-21 07:58:48
@Chubsdad: Personally I prefer the `A const x` form. But it is hard to argue that one is better than the other (its one of those style things). Now if you have a fantastic reason I would love to hear it (so I can also use it).
Martin York
2010-10-21 10:25:37
@Martin York: Me too!. One thing is that it is in harmony with 'Right Left rule'. The other best reason I have so far encountered is from Chapter 1.4 of 'C++ Templates' by David Vandevoorde. It is definitely worth a read about its superiority in context of templates/typedef declarations
Chubsdad
2010-10-21 10:40:11
While I certainly understand why some people prefer `T const` over `const T` and I see the potential benefit of the style, I have always found it awkward and haven't gotten used to writing it that way. It's just weird.
James McNellis
2010-10-21 13:10:58
+2
A:
No difference at all.
See: http://www.parashift.com/c++-faq-lite/const-correctness.html
ArunSaha
2010-10-21 06:55:13
+5
A:
In this case, there's no difference at all.
When you have a pointer or a reference, a change that might look almost the same is significant though. Given something like:
T * a;
The position of const (or volatile) relative to the asterisk is significant:
T const * a;
T * const a;
The first one says that a is a pointer to a const T (i.e., you can't modify the T object that a refers to). The second one says that a is a const point to a (non-const) T -- i.e., you can modify what a points at, but you can't modify the pointer itself, so you can't point it at a different object. Of course, you can also do both:
T const * const a;
This means you can't change the pointer itself or the T object it refers to.
Jerry Coffin
2010-10-21 07:13:35