James G. Sack (jim) wrote:
> Stewart Stremler wrote:
>
>> ..
>> My problem with const almost always comes down to not using it consistently,
>>
Hehe. Yeah, POSIX and Win32 interfaces were generally defined prior to
widespread use of "const". To a large degree people have gone back and
fixed these declarations, but there is nonetheless a lot of old code.
That said, so long as you really believe that a function will honor a
"const" contract, there is little harm in casting away const when you
call the function.
>> and then starting from the wrong side ("Oh, I think I'll make this a
>> const. Whoops, that function doesn't take const, but now it needs
>> to. Whoops, it passes that value on to a function that doesn't use
>> const either!"). And when one is done inserting "const" in all the places
>> that should have "const" in 'em.... the code has been uglified. Bleah.
>>
Generally, I've found these scenarios tend to be pretty illuminating
experiences actually, as they typically lead to discovering that the
const contract isn't being held somewhere you thought it was. Of course,
failure to use const whenever that contract is implied does create some
problems, but the problem isn't too different from someone using "void*"
when they should be using "char*".
> I think that const is kinda neat in function declarations
> char *strcpy(char *dest, const char *src);
>
I couldn't agree more. It makes it really easy to catch that case where
you got src and dest order mixed up.
> I personally, never felt too much urge to declare my (er..) variables as
> const. Does that happen a lot?
>
I guess it depends. I find it useful to have const member variables. It
also tends to be nicer to define constants using const instead of the
evil #define. For variables within a function, const mostly helps with
readibility, as someone who is reading the code for the first time and
seeing some kind of problem towards the end of a function, they can see
that it is declared const at the beginning and skip over most of the
intervening code.
Note that one other aspect of const is that it makes the optimizer's job
easier/possible, particularly during the compilation phase or if you are
using dynamic linking/shared libraries.
--Chris
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