[Libreoffice] [PATCH] improve style according to cppcheck

[Norbert Thiebaud]

On Sat, Nov 27, 2010 at 3:02 PM, Caolán McNamara <caolanm at redhat.com> wrote:
> On Sat, 2010-11-27 at 13:39 -0600, Norbert Thiebaud wrote:
>> On Sat, Nov 27, 2010 at 12:09 PM, Christian Lohmaier
>> <lohmaier+libreoffice at googlemail.com> wrote:
>> > Hi *,
>> >
>> > On Sat, Nov 27, 2010 at 5:40 PM, Takeshi Abe <tabe at fixedpoint.jp> wrote:
>> >> [cppcheck patches]
>> >
>> > I'm curious: Why does cppcheck "complain" about "for.... i++" and
>> > suggests/demands pre-increment instead (for ... ++i)?
>> >
>> > Is there any noticable difference?
>>
>> In my opinion:
>> If there is a noticeable difference -- in a place where the 2 forms
>> are indeed interchangeable -- then this is a bug to be filed with the
>> compiler.
>> And if they are not interchangeable in the context, then cppcheck
>> should be silent....
>
> Just in case anyone was wondering, this is about stl iterators not plain
> ints or floats. Compilers do typically have no problem with plain old
> types. I'm a fan of saying what you mean nevertheless even in those
> cases :-)
>
> As Takeshi pointed out in another mail, the postfix form returns a copy
> of the iterator as it was before the increment, while the prefix form
> returns a reference to the current value after its increment. So postfix
> requires an extra copy which makes it inherently slower.
>
> I'm not so sure that compilers can optimize STL postfix operators with
> the ease they do for basic types. Their implementation differs quite a
> bit from one impl to another.

Yes, I'm victim of my deep entrenchment in the C-world...
operator-overloading is not something that comes naturally to me...

> I expect that the full impl would need to
> be visible to the compiler for it to have a chance to do the right
> thing. Typically that's probably the case and the full template is
> available to the compiler in each compilation unit in order to elide out
> the code patchs that generate the old copy which the postfix form
> returns, so they *may* be able to do it. But you're at the mercy of what
> the compiler can do at that stage, the compiler may be forced to e.g.
> stop inlining and optimize for size, and so make function calls, and at
> that stage they nay merge all the postfix++ calls together, with the
> corresponding performance loss in the cases where the temporary isn't
> needed.
>
> Anyway, I reckon its worth tackling the cppcheck warnings about the
> postfix operator being used where a prefix would suffice.

I'm always all for making warnings disappears. :-)

Norbert

>
> C.
>
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