Messages in this thread | | | Date | Wed, 9 Nov 2005 08:22:15 -0800 (PST) | From | Vadim Lobanov <> | Subject | Re: typedefs and structs |
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On Wed, 9 Nov 2005, J.A. Magallon wrote:
> On Tue, 8 Nov 2005 20:51:25 -0500, Kyle Moffett <mrmacman_g4@mac.com> wrote: > > > > > Pass by value in C: > > do_some_stuff(arg1, arg2); > > > > Pass by reference in C: > > do_some_stuff(&arg1, &arg2); > > > > This is very obvious what it does. The compiler does type-checks to > > make sure you don't get it wrong. There are tools to check stack > > usage of functions too. This is inherently obvious what the code > > does without looking at a completely different file where the > > function is defined. > > > > > > Pass by value in C++: > > do_some_stuff(arg1, arg2); > > > > Pass by reference in C++: > > do_some_stuff(arg1, arg2); > > > > This is C++ being clever and hiding stuff from the programmer, which > > is Not Good(TM) for a kernel. C++ may be an excellent language for > > userspace programmers (I say "may" here because some disagree, > > including myself), however, many of the features are extremely > > problematic for a kernel. > > > > Why is it not good for kernel ? > You want to pass an struct to a function in the best way you can. > Reference just pases a pointer instead of copying, but you don't > realize. > If you want the funcion to be able to modify the struct, code it as > > void do_some_stuff(T& arg1,T& arg2) > > If you DO NOT want the funcion to be able to modify the struct, code it as > > void do_some_stuff(const T& arg1,const T& arg2)
A diligent C programmer would write this as follows: void do_some_stuff (struct T * a, struct T * b); versus void do_more_stuff (const struct T * a, const struct T * b); So I don't see C++ winning at all here.
> This is far better than in C,. because you get the benefits from > reference pass without the problems of accidental modification of > pointer contents. And get rid of arrows -> ;). > > If the function modifies the struct it should be obvious from its name, > not depending if you put an & in the call or not. > And you stop worrying about argument pass methods.
I think I'll call this my rule #1: The moment you stop worrying about something is the moment it bites you in the butt. :-) Much firsthand experience.
> The person who programs the function decides and can even change it without > you user even noticing.
And if the caller is passing in something that's not meant to be modified, then the modification causes much badness. Happens with both languages, too.
> And gcc does nice optimizations when you mix const& and inlining...
As far as I know, nothing stops GCC from doing the exact same optimizations in the function prototypes given above.
> > -- > J.A. Magallon <jamagallon()able!es> \ Software is like sex: > werewolf!able!es \ It's better when it's free > Mandriva Linux release 2006.1 (Cooker) for i586 > Linux 2.6.14-jam1 (gcc 4.0.2 (4.0.2-1mdk for Mandriva Linux release 2006.1)) >
-Vadim Lobanov - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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