const best practice in function declaration

Question

Ive searched through the archived posts but I couldnt find anything similar.

Just a simple question: whats the best practice in declaring inspecting functions like:

int foo(int a) const { return a+1; }

Im referring to the const keyword, do you usually declare it at the end of an inspecting function? Im just asking because I usually do, even if 99% I wont declare any const class.. I just keep on tellin myself that it could save me some time if I ever should need to, but I was wondering if anybody else really cares about declaring const functions or if Im just paranoid about typesafe code

ah.. just a way to call a method that doesnt change any object member — user815129, Nov 11 '11 at 10:45
That function doesn't access any members, so it should probably be `static` instead. — Sven, Nov 11 '11 at 10:45
static and const methods are not really the same, besides, I said a function that doesnt CHANGE any member, not access — user815129, Nov 11 '11 at 10:46
But you provided an example of a method that doesn't access anything besides its parameter, therefore it should be `static`. I'm not saying all `const` methods should be `static`, I'm just saying the method in your example should be. — Sven, Nov 11 '11 at 10:50
See http://stackoverflow.com/questions/2157458/using-const-in-classs-functions. — Daniel Daranas, Nov 11 '11 at 10:51
I see, you didnt read the last four lines. If you stop at the example, yes you-re right — user815129, Nov 11 '11 at 10:52
@DanielDaranas thanks but this is not a question about whats the meaning/usage of the const keyword, I was just wondering if anybody else cares about declaring const functions — user815129, Nov 11 '11 at 10:54

score 6 · Accepted Answer · answered Nov 11 '11 at 10:48

Assuming that you are talking about member functions (non member functions cannot be const ever), you should write const-correct code always, and that means that each and every function that does not modify the visible state of the object should be const.

Even if you don't ever create a constant object of the type, in many cases you will pass the object to a function through const references and in that case, only const member functions can be called on the object (Incidentally this means that you should pass the object by constant reference to any function that does not need to change the state of the received object)

justin · Answer 2 · 2011-11-11T11:00:31.573

Yes, of course you should if you want your program to support const correctness.

Const correctness has a way of propagating through your program once you begin declaring instances as const. As program complexity and your use of const increases, then you will either:

encounter many compiler errors when using const objects if you do not add them now
or your program will build without (or fewer) errors once you favor using const in the appropriate places.
or you may end up avoiding const for some time - which is (IMO) not a good road to go down if you want to improve your designs.

Over time, many of us have learned to use const in more than 1% of our code.

score 1 · Answer 3 · answered Nov 11 '11 at 10:47

1

The const appended at the end of the function declaration and definition indicates a contract between the caller of the function and the function that the function will not modify any members of that class.

So if your function provides guarantee for such an const-correctness contract you should extend it to users of your function.

answered Nov 11 '11 at 10:47

Alok Save

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thanks but this is not a question about whats the meaning/usage of the const keyword, I was just wondering if anybody else cares about declaring const functions – user815129 Nov 11 '11 at 10:54
@user815129: Every Good C++ Programmer does. – Alok Save Nov 11 '11 at 10:56

const best practice in function declaration

3 Answers3