Re: Compiled C vs C++
Hello
Ulrich Hobelmann wrote:
mlimber wrote:
What do *you* mean by "pay as you go"?
That - as IIRC mentioned in Bruce Eckel's Book - I can use a class as
a struct; that a (non-virtual) function in the struct will be called
as efficiently as a C function, because it is fully, statically known
at
compile-time. If everything is there, and I don't use more advanced
features, I don't see why the code should be different from C.
At what price on the C side? See below.
Interestingly so far it seems as if I could get *more* efficient code
by writing my own C++ to C compiler (remember the very first C++
compiler?) than by using something as high-tech as GCC 4.
Try some real world sized examples. Try to support all features C++
offers, e.g. templates, exceptions, inheritance, overloading. Anything
else is comparing apples and oranges.
Taking the higher abstraction C++ offers out of consideration, it is
sure that C++ will have a few overheads at places a C programmer could
easily have done better. In the past the trend was more towards
improving speed than code size.
They were both in the assembler output (c++ -O2 -S) and in the final
executable, as I said. The source only has one constructor (see
below),
but the translation has two. I can't even *guess* how any compiler
would get the idea of doing something like this...
If you want to program against binary code you need an ABI (application
binary interface), defining what can be expected from binary code. If
some implementation detail requires two variants of a constructor to be
available, which in general are different, then both variants will be
produced so they are available at link time. Probably they will be
produced consistently for all classes, because it is an ABI.
As already requested, please post your code for both the comparable C
program and the C++ program. That will help us get to the bottom of
this.
I.e. there are two constructors, and if I use one, AFAIK only one (the
one with the '1' in the name) is used. In this case it's just a few
bytes, but I'm wondering about the general case.
Then try the general case, find an example, where the other variant is
called. AFAIK gcc needs the second to implement inheritance, and other
C++ compilers are similar. After 20+ years there should be agreement on
the best way to implement something that basic.
Just in the case it helps, I think on some platforms there are
possibilities to remove unused code from the final binary at link time.
Bernd Strieder