Re: Can C++ be used for system programming such as OS & DB?

"James Kanze" <>
29 Mar 2007 01:01:57 -0700
On Mar 29, 7:12 am, "Royt" <> wrote:

Maybe it's a stupid question, but I really couldn't figure it out. C++
is expected to be a better C, provides compatibility with C, and is
able to do all that C can do. however, the number of projects in written by C++ is always smaller than that of C, many people
directly turn to Java or C# after they learned C. Now that C++ is a
system programming language, it should have the capability to replace
C in many cases.

I can't imagine starting a new project in C, when C++ exists.

We all know that the most important Operating Systems
are all written by C (the core part),

Well, except maybe for Windows, most of the mainframes, and
significant parts of many Unixes.

Some parts of systems like Solaris are still written in C,
because they were written 15 or 20 years ago. (Other parts of
Solaris are written in C++.)

and in my memory the DB engine
of Oracle is written by C (what about DB2 & sybase?). Why not use C++
to program these projects, since the management of C++ projects is

Until recently, portability was a problem. And of course, a
company like Oracle isn't going to rewrite their entire
application just because it becomes possible to use a new

And another question. What about the runtime efficiency of C++
compared to that of C?

I've not seen any difference. Typically, the two compilers
share a common back end, and when used to do the same thing,
generate exactly the same machine code. In fact, the presence
of inline functions (now supported in C as well) sometimes means
that the C++ code can be faster.

because of the added OO features, C++ may be a
little slower.

Only if you use them.

The big difference between C and C++ is that in C, you define a
struct and a set of functions to manipulate it, and you cross
your fingers that no one manipulates it otherwise. In C++, you
make the data members of the struct private, the set of
functions members, and the compiler ensures that no one
manipulates it otherwise.

Beyond that, of course, C++ supports a number of other idioms,
which may or may not be appropriate in any given application.
But the encapsulation is always appropriate, has no added
run-time cost, and justifies in itself using C++ rather than C,
even if you don't need run-time polymorphism, templates,
exceptions and all the rest.

but if use C to simulate and implement the OO features
as C++ can do, will C be less efficient than C++?

For the programmers, certainly. Probably in terms of execution
run-time as well.

Can we use C++ for
the huge projects mentioned above? or those projects didn't require
any modern features, e.g. Polymorphism? (that sounds terrible)

C++ is definitly usable, and is being used in many places, for
such things. As always, you don't have to use everything the
language offers. Only what's appropriate. (Note however that
every OS uses dynamic polymorphism at some point. A call to
read() results in significantly different code being executed if
the file descriptor designates a keyboard than when it
designates a file on disk.)

James Kanze (GABI Software)
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