On 8/12/2015 10:18 PM, Jeffrey Walton wrote:
> On Wed, Aug 12, 2015 at 6:02 PM, David Chapman <dcchap...@acm.org> wrote:
>> On 8/12/2015 1:09 PM, Dan Kegel wrote:
>>> ...
>> So even though I just told you how to guarantee that global variables in C++
>> are initialized before they are used, don't do it. :-) Refactoring sounds
>> expensive but in the long run it is cheaper than debugging interactions
>> between global variables.
> Thanks David.
>
> Just venting here, but...
>
> $ ls *.h *.cpp | wc -l
> 269
> $ grep class *.h *.cpp | wc -l
> 1332
>
> Of 1300+ classes and nearly 270 source files, there are 5 globals that
> are sensitive to their initialization order. 3 are std::strings and 2
> are C++ objects.
>
> Its *really* pathetic the C++ language lacks a mechanism for me to say
> "Object 1 depends upon String 1, 2, 3", and "Object 2 depends upon
> Object 1 and String 1, 2, 3".
>
> It's not like I'm asking the compiler to solve some NP-hard problem.
> It does not have to solve any problem. The language just needs the
> give me the ability to express a relative ordering among a handful of
> objects.
>
You might have only five variables, but the next person will have a few
more, and the next will have still more... I doubt that any standards
committee would provide a solution that would work only for a small set
like that. Also, you can get dependency loops very quickly: "object 1
depends on object 2, object 2 depends on object 3, object 3 depends on
object 1." That's basically what happened to me, and I had to rewrite
an awful lot of code to get rid of it. If the dependency loop goes
through an outside library, or worse yet appears just by linking a set
of outside libraries, you're stuck.
The software package that I mentioned had hundreds of global variables
(I didn't have the nerve to count them all, but the company founder
thought they were a great way to avoid the overhead of passing
parameters to functions). Resolving initialization order dependencies
would have been a nightmare. I don't think initialization order was a
problem in that particular package, but "hey - who changed that
variable???" was a big deal. The code could take hours to run, so
debugging could be very slow and tedious.
--
David Chapman dcchap...@acm.org
Chapman Consulting -- San Jose, CA
Software Development Done Right.
www.chapman-consulting-sj.com
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