Re: C++ pushback

[Roman Kononov <kononov195-far@yahoo.com>]

Linus Torvalds wrote:
> On Wed, 26 Apr 2006, Jan-Benedict Glaw wrote:
> > There's one _practical_ thing you need to keep in mind: you'll either
> > need 'C++'-clean kernel headers (to interface low-level kernel
> > functions) or a separate set of headers.
>
> I suspect it would be easier to just do
>
> 	extern "C" {
> 	#include <linux/xyz.h>
> 	...
> 	}
>
> instead of having anything really C++'aware in the headers.
>
> If by "clean" you meant that the above works, then yeah, there might be 
> _some_ cases where we use C++ keywords etc in the headers, but they should 
> be pretty unusual and easy to fix.
>
> The real problem with C++ for kernel modules is:
>
>  - the language just sucks. Sorry, but it does.
Sorry, you do not know the language, and your statement is not 
credible. I think that C sucks.

>  - some of the C features we use may or may not be usable from C++ 
>    (statement expressions?)
Statement expressions are working fine in g++. The main difficulties are:
   - GCC's structure member initialization extensions are syntax
     errors in G++: struct foo_t foo={.member=0};
   - empty structures are not zero-sized in g++, unless they are like
     this one: struct really_empty_t { char dummy[0]; };

>  - the compilers are slower, and less reliable. This is _less_ of an issue 
>    these days than it used to be (at least the reliability part), but it's 
>    still true.
G++ compiling heavy C++ is a bit slower than gcc. The g++ front end is 
reliable enough. Do you have a particular bug in mind?

>  - a lot of the C++ features just won't be supported sanely (ie the kernel 
>    infrastructure just doesn't do exceptions for C++, nor will it run any 
>    static constructors etc).
A lot of C++ features are already supported sanely. You simply need to 
understand them. Especially templates and type checking. C++ 
exceptions are not very useful tool in kernels. Static constructor 
issue is trivial. I use all C++ features (except exceptions) in all 
projects: Linux kernel modules, embedded real-time applications, 
everywhere. They _really_ help a lot.

> Anyway, it should all be doable. Not necessarily even very hard. But I 
> doubt it's worth it.
>
> 		Linus

I think that allowing C++ code to co-exist with the kernel would be a 
step forward.

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