Re: How to extend lanuage C in GCC ?
2008/10/22 Dong Phuong <[EMAIL PROTECTED]>: > > I'm porting for a microcontroller. And now I want to > add some features to the current language C int GCC > (for example some directives such as near, far , > ). SO could you please tell me how I can do that > ? Hi, I am not sure if it is solves all your cases, but things like far, near, that are usually handled as attributes. Please take a look at http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/Function-Attributes.html#Function-Attributes. Cheers, Piotr
Variadic template function full specialization.
Hello all,
Following (bit weird ;-) code shows weird case of variadic template
function specialization, however I am not sure it is legal, (atleast I
haven't found any wording that would prevent such use):
enum SelectFoo {S1, S2, S3};
struct A
{
template
void foo (Args_...);
};
template <> void
A::foo (int) {} // #1 compiles fine
template <> void
A::foo () {} // #2 this won't compile (error: template-id
'foo<(SelectFoo)1u>' for 'void A::foo()' does not match any template
declaration)
template <> void
A::foo (int, int) {} // #3 this won't compile too (error:
template-id 'foo<(SelectFoo)2u>' for 'void A::foo(int, int)' does not
match any template declaration)
I have checked this code with g++-4.3.2 and g++-4.4.0-alpha20081010
(gentoo ebuild)
It seems that variadic type pack Args_... is always treated as one parameter.
When I have tried declaration like:
template
void foo (T_, More_...);
it could match specialization with two parameters only, 'foo(int,
int)' in this example.
If I would provide all three declarations ie.
struct A
{
template
void foo ();
template
void foo (T_);
template
void foo (T1_, T2_);
};
everything compiles fine, with both gcc and Comeau C/C++ online, as
one would expect.
My question is: whether all specializations (#1, #2, #3) should be accept,
or it is just illegal use of variadic templates not reported here, and
#1 is accepted incorrectly,
or this is expected result?
Piotr
Re: Variadic template function full specialization.
2008/11/19 Ben Elliston <[EMAIL PROTECTED]>: >> Following (bit weird ;-) code shows weird case of variadic template >> function specialization, however I am not sure it is legal, (atleast I >> haven't found any wording that would prevent such use): > > This list is not really the place to discuss language issues (unless you > think you've found a bug in g++). The [EMAIL PROTECTED] mailing list > is probably a better place to ask your question. > > Cheers, > Ben > > -- > Ben Elliston <[EMAIL PROTECTED]> > Australia Development Lab, IBM > > Hi, I was suppose to fill bug about, but I am not 100% sure what kind of bug it is: a) gcc should accept this code (I am in favour of this) b) gcc should reject specialization #1 that is why have asked here. I am sorry if it was not clear from my initial message. I am poor language lawyer, but I think that current behaviour is odd, and really couldn't find anything in n2798 paper, that would explain current behaviour. Thanks, Piotr
Re: optimization question: mpl
Hi,
2010/7/28 Hite, Christopher :
>> Generally without knowing the compiler version you are using
>> it is hard to tell.
> I'll use whatever's best. Right now I'm still on 4.4.3. I'll probably
> upgrade soon to 4.5.
>
>> The same is true without a complete compilable testcase.
> I didn't want to make a test case that depends on boost::mpl. How's
> this:
>
> struct DecodeContext;
>
> struct M1{
> static const int id=1;
> static void decode(DecodeContext& ){}
> };
>
> struct M2{
> static const int id=2;
> static void decode(DecodeContext& ){}
> };
>
> struct M3{
> static const int id=3;
> static void decode(DecodeContext& ){}
> };
>
>
> template struct ListMember;
>
> template <> struct ListMember<1>{ typedef M1 type; };
> template <> struct ListMember<2>{ typedef M2 type; };
> template <> struct ListMember<3>{ typedef M3 type; };
>
> template
> void foo(int id, DecodeContext& dc) {
> typedef typename ListMember::type M;
> if(M::id==id)
> M::decode(dc);
> else
> foo(id,dc);
> }
>
> template<>
> void foo<0>(int id, DecodeContext& dc) {}
>
>
>
> int main(){
> DecodeContext& dc= *(DecodeContext*)0;// junk for now
> int id=2; //sometime runtime dependent
> foo<3>(id,dc);
> return 0;
> }
>
>
>> You can use the flatten attribute to tell the compiler to inline all
>> calls in a given function, like
>>
>> void __attribute__((flatten)) foo(void)
>> {
>> ...
>> decode1();
>> ...
>> }
>
> That would cause decode1() to be inlined, which might not be what you
> want.
>
> Hmm maybe I could rewrite things so the switch case returns a function
> pointer. I'm guessing that would make things slower though.
>
Or you could just initialize static array of pointers, like that
(please note, that I never compiled code below):
typedef void (*pfn) (DeclContext&);
tempate
struct InitDispatchHelper
{
static void init(std::tr1::array& a)
{
a[I-1] = ListMemeber::foo;
InitPointersHelper::init(a);
}
};
// End recursion
template<>
struct InitDispatchHelper
{
static void init(std::tr1::array& a)
{/*does nothing */ }
};
// Dispatch table;
template
struct DispatchFoo : std::tr1::array
{
DispatchFoo() : std::tr1::array()
{
InitDispatchHelper::init(*this);
}
};
then your call would look like:
static const int X = /* your maximal I in ListMembers meta-class */
void call_foo(int i, DeclContext& c)
{
static const DispatchFoo foo_dispatch;
foo_dispatch[i] (c);
}
Bonus points for benchmarking both solutions and making it policy
class choosing between those two solutions depending on X.
Good luck,
Piotr
Implementation of string-literal as template parameter
Hi, Recently i have posted an idea of new language feature to comp.lang.c++.moderated. That is "String literal as template parameter?" form 12.04.2008, if anyone is interested to see whole thread. The idea is to allow string-literals as template argument, and make them equivalent to variadic character pack 'char...'. For example: template class Foo; Foo<"abc"> would be equivalent to Foo<'a', 'b', 'c'> I am interested in writing proof of concept implementation. Since i dont have expirience with g++ codebase, I wanted to ask: 1) Is it expected to be hard to implement? (which I rather dont expect to be, but better ask :-) 2) Any hints, how/where should I start? Thanks in advance for any feedback. Piotr Rak
