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SubjectRe: C++ and the kernel
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>>>>> "Chris" == Chris Friesen <cfriesen@nortelnetworks.com> writes:

>> It is quite unlikely that a C++ compiler will make more
>> efficient code than a C compiler. In fact, the code generator
>> will likely be the same. The C++ compiler will end up
>> generating some preamble code as part of the function-calling
>> mechanism, that is not necessary in C. This means that it will
>> generate a bit more code.

Chris> C++ has tigher constraints on code than C. This can allow
Chris> a compiler to generate better code because it has more
Chris> knowledge about what is going on.

There are also many GNU extensions to C that makes it possible to
generate better code, e.g. marking certain functions as pure
functions.



Chris> Your example is needlessly complex, and I'm sure you know
Chris> this. A more realistic comparison would be:

Chris> cout << "Hello World!\n";

This has demonstrated that you don't know C++ _very_ well. Instead of
the trailing "\n", a C++ programemr ought to write:

cout << "Hello World!" << endl;

You seem to *understand* C++ even worse than Richard. Even Richard
used "endl" in his unnecessarily complex example. And you're not a
better programmer, either, because you failed to distill out the EOL
concept and represent it in an abstract, OS/platform-independent way.


Chris> Now I don't for a moment think that we should go and
Chris> convert everything to = C++.=20 But I do think that certain
Chris> features of the language can be useful, and tha= t there
Chris> are cases when OO style programming makes the code easier
Chris> to read and understand.

I don't find the current Linux fs code is too difficult to understand,
although it is doing OO in a non-OO language. Rather, I think this is
easier to maintain, because you don't have to go through all the
burdens of writing the C++ code. (It's easy to get a working C++ code
work. But making it efficient (e.g. sprinking "const" to wherever
possible so that it becomes a potential for the compiler to do
optimization) and *flawless* (e.g. multithread-safe, reentrant,
SMP-safe, **side-effect-less**, privatizing all dangerous copy
constructors as well as assignment operators, no memory leakage...)
would be very devoting. The time could better be spent on the C
code.)

Unless the FS code gets the complexity comparable to Xt (tall
inheritance trees), I don't think the overhead of doing it in C++
worths. (Xt is still bearable when used as a user. But if you try to
extend it (by writing a few custom widget classes) or maintain code in
it, you'd wish it were in C++.) How deep would the FS code grow to?
If it is shallow, then IMO, don't do it in C++; you'll be spending
more time for the cosmetics than really getting advantage out of it.


--
Sau Dan LEE 李守敦(Big5) ~{@nJX6X~}(HZ)

E-mail: danlee@informatik.uni-freiburg.de
Home page: http://www.informatik.uni-freiburg.de/~danlee

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