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Map C++ feature to C

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  Map C++ feature to C zgene <nospam@nospam.com> - 2012-06-24 08:23 +0000
    Re: Map C++ feature to C Ian Collins <ian-news@hotmail.com> - 2012-06-24 21:25 +1200
      Re: Map C++ feature to C BGB <cr88192@hotmail.com> - 2012-06-24 13:39 -0500
        Re: Map C++ feature to C Ian Collins <ian-news@hotmail.com> - 2012-06-25 10:15 +1200
          Re: Map C++ feature to C BGB <cr88192@hotmail.com> - 2012-06-25 11:32 -0500
      Re: Map C++ feature to C zgene <nospam@nospam.com> - 2012-06-24 21:33 +0000
        Re: Map C++ feature to C Ian Collins <ian-news@hotmail.com> - 2012-06-25 10:12 +1200
          Re: Map C++ feature to C William Ahern <william@wilbur.25thandClement.com> - 2012-06-24 18:49 -0700
          Re: Map C++ feature to C nroberts <roberts.noah@gmail.com> - 2012-07-23 10:25 -0700
            Re: Map C++ feature to C Andrew Cooper <amc96@cam.ac.uk> - 2012-07-24 01:34 +0100
              Re: Map C++ feature to C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-07-24 15:58 +0000
    Re: Map C++ feature to C "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2012-06-24 11:36 -0700
      Re: Map C++ feature to C Leo Havmøller <rtxleh@nospam.nospam> - 2012-06-25 05:43 +0200
        Re: Map C++ feature to C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-06-25 10:34 +0000
          Re: Map C++ feature to C BGB <cr88192@hotmail.com> - 2012-06-25 11:36 -0500
    Re: Map C++ feature to C Paul N <gw7rib@aol.com> - 2012-06-24 12:19 -0700
      Re: Map C++ feature to C 88888 Dihedral <dihedral88888@googlemail.com> - 2012-06-24 19:49 -0700
    Re: Map C++ feature to C aftnix <aftnix@gmail.com> - 2012-07-26 13:36 -0700

#22602 — Map C++ feature to C

Dear friends

Is there a way to embulate C++'s virtual destructors in pure C. IE just 
using function pointers.

Many Thanks.

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#22605

On 06/24/12 08:23 PM, zgene wrote:
> Dear friends

Why is the question completely different form the subject?

> Is there a way to embulate C++'s virtual destructors in pure C. IE just
> using function pointers.

No, because there isn't a way to fully emulate destructors.

-- 
Ian Collins

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#22616

On 6/24/2012 4:25 AM, Ian Collins wrote:
> On 06/24/12 08:23 PM, zgene wrote:
>> Dear friends
>
> Why is the question completely different form the subject?
>
>> Is there a way to embulate C++'s virtual destructors in pure C. IE just
>> using function pointers.
>
> No, because there isn't a way to fully emulate destructors.
>

strictly speaking, yes.

but if one allows for the case where the destructor is called via the 
object being manually destroyed/"deleted", then it becomes a little 
easier: just have it as a method/function-pointer which is called prior 
to freeing the memory.

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#22630

On 06/25/12 06:39 AM, BGB wrote:
> On 6/24/2012 4:25 AM, Ian Collins wrote:
>> On 06/24/12 08:23 PM, zgene wrote:
>>> Dear friends
>>
>> Why is the question completely different form the subject?
>>
>>> Is there a way to embulate C++'s virtual destructors in pure C. IE just
>>> using function pointers.
>>
>> No, because there isn't a way to fully emulate destructors.
>>
>
> strictly speaking, yes.
>
> but if one allows for the case where the destructor is called via the
> object being manually destroyed/"deleted", then it becomes a little
> easier: just have it as a method/function-pointer which is called prior
> to freeing the memory.

A "little" easier is the appropriate term.  The OP asked for virtual 
destructor functionality, which requires some form of virtual dispatch 
mechanism.  Doable, but ugly.

-- 
Ian Collins

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#22694

On 6/24/2012 5:15 PM, Ian Collins wrote:
> On 06/25/12 06:39 AM, BGB wrote:
>> On 6/24/2012 4:25 AM, Ian Collins wrote:
>>> On 06/24/12 08:23 PM, zgene wrote:
>>>> Dear friends
>>>
>>> Why is the question completely different form the subject?
>>>
>>>> Is there a way to embulate C++'s virtual destructors in pure C. IE just
>>>> using function pointers.
>>>
>>> No, because there isn't a way to fully emulate destructors.
>>>
>>
>> strictly speaking, yes.
>>
>> but if one allows for the case where the destructor is called via the
>> object being manually destroyed/"deleted", then it becomes a little
>> easier: just have it as a method/function-pointer which is called prior
>> to freeing the memory.
>
> A "little" easier is the appropriate term.  The OP asked for virtual
> destructor functionality, which requires some form of virtual dispatch
> mechanism.  Doable, but ugly.
>

IMO, using C function pointers are not that much drastically worse than 
using C++ virtual methods.

yes, one either needs to use a vtable, or assign all of the "methods" on 
object construction, but this isn't really a huge issue IMO.


say, we have something like:
BaseClass *obj;
...
obj=(BaseClass *)FooClass_New();	//FooClass extends BaseClass
...
BaseClass_Delete(obj);	//internally calls FooClass destructor

with, say:
void BaseClass_Delete(BaseClass *obj)
	{ obj->vt->Destroy(obj); myapp_free(obj); }


but, hell, it works...

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#22625

On Sun, 24 Jun 2012 21:25:38 +1200, Ian Collins wrote:

> On 06/24/12 08:23 PM, zgene wrote:
>> Dear friends
> 
> Why is the question completely different form the subject?
> 
>> Is there a way to embulate C++'s virtual destructors in pure C. IE just
>> using function pointers.
> 
> No, because there isn't a way to fully emulate destructors.

I doubt this answer..... do you have any evidence??

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#22628

On 06/25/12 09:33 AM, zgene wrote:
> On Sun, 24 Jun 2012 21:25:38 +1200, Ian Collins wrote:
>
>> On 06/24/12 08:23 PM, zgene wrote:
>>> Dear friends
>>
>> Why is the question completely different form the subject?
>>
>>> Is there a way to embulate C++'s virtual destructors in pure C. IE just
>>> using function pointers.
>>
>> No, because there isn't a way to fully emulate destructors.
>
> I doubt this answer..... do you have any evidence??

Show me a way to automatically call a function on leaving a scope in C 
and we can go from there.

-- 
Ian Collins

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#22636

Ian Collins <ian-news@hotmail.com> wrote:
> On 06/25/12 09:33 AM, zgene wrote:
> > On Sun, 24 Jun 2012 21:25:38 +1200, Ian Collins wrote:
> >
> >> On 06/24/12 08:23 PM, zgene wrote:
> >>> Dear friends
> >>
> >> Why is the question completely different form the subject?
> >>
> >>> Is there a way to embulate C++'s virtual destructors in pure C. IE just
> >>> using function pointers.
> >>
> >> No, because there isn't a way to fully emulate destructors.
> >
> > I doubt this answer..... do you have any evidence??

> Show me a way to automatically call a function on leaving a scope in C 
> and we can go from there.

You could do it the way "portable" alloca implementations work, though
destruction would be lazy, like GC'd langauages.

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#23621

On Sunday, June 24, 2012 3:12:18 PM UTC-7, Ian Collins wrote:
> On 06/25/12 09:33 AM, zgene wrote:
> > On Sun, 24 Jun 2012 21:25:38 +1200, Ian Collins wrote:
> >
> >> On 06/24/12 08:23 PM, zgene wrote:
> >>> Dear friends
> >>
> >> Why is the question completely different form the subject?
> >>
> >>> Is there a way to embulate C++'s virtual destructors in pure C. IE just
> >>> using function pointers.
> >>
> >> No, because there isn't a way to fully emulate destructors.
> >
> > I doubt this answer..... do you have any evidence??
> 
> Show me a way to automatically call a function on leaving a scope in C 
> and we can go from there.

This is probably THE most important feature of C++ missing from standard C but it can be done with GCC extensions:

type var __attribute__(cleanup(destroyType)) = newType();

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#23640

On 23/07/2012 18:25, nroberts wrote:
> On Sunday, June 24, 2012 3:12:18 PM UTC-7, Ian Collins wrote:
>> On 06/25/12 09:33 AM, zgene wrote:
>> > On Sun, 24 Jun 2012 21:25:38 +1200, Ian Collins wrote:
>> >
>> >> On 06/24/12 08:23 PM, zgene wrote:
>> >>> Dear friends
>> >>
>> >> Why is the question completely different form the subject?
>> >>
>> >>> Is there a way to embulate C++'s virtual destructors in pure C. IE just
>> >>> using function pointers.
>> >>
>> >> No, because there isn't a way to fully emulate destructors.
>> >
>> > I doubt this answer..... do you have any evidence??
>>
>> Show me a way to automatically call a function on leaving a scope in C 
>> and we can go from there.
> 
> This is probably THE most important feature of C++ missing from standard C but it can be done with GCC extensions:
> 
> type var __attribute__(cleanup(destroyType)) = newType();
> 

It is not any feature "missing" from the C standard.  C is not C++, nor
should it be.  gcc extensions like this are frankly a bastardisation of
C, and should be discouraged.

C, unlike C++ has only one possible interpretation for any valid
construct.  This makes is substantially more predictable, and reduces
many overheads of the more complex features.

Take the following C++ code:

Foo f = Foo(g);

Care to explain exactly what that statement means?  What would be the
equivalent in meaning for C?

~Andrew

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#23677

On Tue, 2012-07-24, Andrew Cooper wrote:
> On 23/07/2012 18:25, nroberts wrote:
...
>> 
>> This is probably THE most important feature of C++ missing from standard C
>> but it can be done with GCC extensions:
>> 
>> type var __attribute__(cleanup(destroyType)) = newType();
>> 
>
> It is not any feature "missing" from the C standard.  C is not C++, nor
> should it be.  gcc extensions like this are frankly a bastardisation of
> C, and should be discouraged.

I tend to agree.

> C, unlike C++ has only one possible interpretation for any valid
> construct.  This makes is substantially more predictable, and reduces
> many overheads of the more complex features.

Overheads? In compiler complexity, runtime, the reader's head ... ?

> Take the following C++ code:
>
> Foo f = Foo(g);
>
> Care to explain exactly what that statement means?  What would be the
> equivalent in meaning for C?

It means you're left with a Foo object called f, constructed via
Foo(g), doesn't it?  I'm assuming a reasonable implementation of Foo.

/Jorgen

-- 
  // Jorgen Grahn <grahn@  Oo  o.   .     .
\X/     snipabacken.se>   O  o   .

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#22617

On Jun 24, 9:23 am, zgene <nos...@nospam.com> wrote:
> Dear friends
>
> Is there a way to embulate C++'s virtual destructors in pure C. IE just
> using function pointers.
>
> Many Thanks.

Why would you want to do that? If you want to write C++ code, there is
an excellent language for that - it is called C++. Much better than
some half-arsed attempt to simulate it in C.

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#22638

> Why would you want to do that? If you want to write C++ code, there is
> an excellent language for that - it is called C++. Much better than
> some half-arsed attempt to simulate it in C.

Because C++ may not be allowed (e.g. linux kernel mode) or available (e.g. 
linux IAD) for the target platform.

Leo Havmøller. 

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#22666

On Mon, 2012-06-25, Leo Havmøller wrote:
>> Why would you want to do that? If you want to write C++ code, there is
>> an excellent language for that - it is called C++. Much better than
>> some half-arsed attempt to simulate it in C.
>
> Because C++ may not be allowed (e.g. linux kernel mode) or available (e.g. 
> linux IAD) for the target platform.

If C++ is disallowed, half-arsed simulations should be, too.
Especially simulations of tricky features like run-time polymorphism.

(Note: I'm not arguing against all uses of function pointers. Just
against unrestricted use of idioms meant to simulate C++ vtables.)

/Jorgen

-- 
  // Jorgen Grahn <grahn@  Oo  o.   .     .
\X/     snipabacken.se>   O  o   .

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#22695

On 6/25/2012 5:34 AM, Jorgen Grahn wrote:
> On Mon, 2012-06-25, Leo Havmøller wrote:
>>> Why would you want to do that? If you want to write C++ code, there is
>>> an excellent language for that - it is called C++. Much better than
>>> some half-arsed attempt to simulate it in C.
>>
>> Because C++ may not be allowed (e.g. linux kernel mode) or available (e.g.
>> linux IAD) for the target platform.
>
> If C++ is disallowed, half-arsed simulations should be, too.
> Especially simulations of tricky features like run-time polymorphism.
>
> (Note: I'm not arguing against all uses of function pointers. Just
> against unrestricted use of idioms meant to simulate C++ vtables.)
>

it depends on why it is disallowed.

it may not be due entirely to "policy", but maybe something like lack of 
a good C++ compiler, or the relative difficulty to parse C++ code (vs C) 
via custom-written tools, or interface directly between C++ and a 
scripting language (many have an easier time interfacing with C), ...

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#22619

On Jun 24, 9:23 am, zgene <nos...@nospam.com> wrote:
> Dear friends
>
> Is there a way to embulate C++'s virtual destructors in pure C. IE just
> using function pointers.
>
> Many Thanks.

How about something like:

struct Base {
void *destroy(struct Base *this);  // needs to be first member
/// more here
};

struct Derived {
struct Base b;
// even more here
};

When you create a Base or a Derived, you set the function pointer to
the correct destructor. Then just before freeing an object, you do:

(p -> destroy) (p);

which will work whether p actually points to a Base or a Derived.

  ... completely untested, syntax may be wrong as well...

Hope that helps.
Paul.

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#22637

Paul N於 2012年6月25日星期一UTC+8上午3時19分00秒寫道：
> On Jun 24, 9:23 am, zgene <nos...@nospam.com> wrote:
> > Dear friends
> >
> > Is there a way to embulate C++'s virtual destructors in pure C. IE just
> > using function pointers.
> >
> > Many Thanks.
> 
> How about something like:
> 
> struct Base {
> void *destroy(struct Base *this);  // needs to be first member
> /// more here
> };
> 
> struct Derived {
> struct Base b;
> // even more here
> };
> 
> When you create a Base or a Derived, you set the function pointer to
> the correct destructor. Then just before freeing an object, you do:
> 
> (p -> destroy) (p);
> 
> which will work whether p actually points to a Base or a Derived.
> 
>   ... completely untested, syntax may be wrong as well...
> 
> Hope that helps.
> Paul.


Well, that means it might lead to 
the results of  destroying forrests from time 
to time  in my understanding
of the object oriented approach in C++.
 

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#23756

On Sunday, June 24, 2012 2:23:02 PM UTC+6, zgene wrote:
> Dear friends
> 
> Is there a way to embulate C++'s virtual destructors in pure C. IE just 
> using function pointers.
> 
> Many Thanks.

Hi,

Have you looked into this?

http://www.planetpdf.com/codecuts/pdfs/ooc.pdf

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