I am looking for any custom allocator sample code for std::vector.
Thanks.
--
Alex Vinokur
Thanks.
--
Alex Vinokur
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Re: Custom allocator sample code for vector
"Alex Vinokur" <alexvn@big-foot.com> wrote in message
news:2ngusqFp3p gU1@uni-berlin.de...[color=blue]
> I am looking for any custom allocator sample code for std::vector.
>[/color]
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Re: Custom allocator sample code for vector
"Sharad Kala" <no__spam.shara dk_ind@yahoo.co m> wrote in message news:2ngv12Fo88 bU1@uni-berlin.de...[color=blue]
>
> "Alex Vinokur" <alexvn@big-foot.com> wrote in message
> news:2ngusqFp3p gU1@uni-berlin.de...[color=green]
> > I am looking for any custom allocator sample code for std::vector.
> >[/color]
>
> http://www.josuttis.com/libbook/memo...lloc1.cpp.html
>
>[/color]
Thanks.
In that sample we can see that methods 'allocate' and 'deallocate' were invoked.
But methods 'construct' and 'destroy' were not invoked.
When should 'construct' and 'destroy' be invoked?
--
Alex Vinokur
Comment
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Re: Custom allocator sample code for vector
"Alex Vinokur" <alexvn@big-foot.com> wrote in message
news:2nho0uF105 teU1@uni-berlin.de...
[color=blue]
> When should 'construct' and 'destroy' be invoked?[/color]
An allocator has to provide a construct and destruct operation. You may want
to take a look at 20.1.5 (Allocator requirements).
Construct is used to initialize the memory allocated with a value. This is
basically a call to placement new. So basically construct is invoked when an
object is created in the container.
Destroy simply calls the destructor for the object.
-Sharad
Comment
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Re: Custom allocator sample code for vector
"Sharad Kala" <no__spam.shara dk_ind@yahoo.co m> wrote in message news:2njcgfF1iu 4fU1@uni-berlin.de...[color=blue]
>
> "Alex Vinokur" <alexvn@big-foot.com> wrote in message
> news:2nho0uF105 teU1@uni-berlin.de...
>[color=green]
> > When should 'construct' and 'destroy' be invoked?[/color]
>
> An allocator has to provide a construct and destruct operation. You may want
> to take a look at 20.1.5 (Allocator requirements).
>
> Construct is used to initialize the memory allocated with a value. This is
> basically a call to placement new. So basically construct is invoked when an
> object is created in the container.[/color]
For instance, v.push_back (element) for vector?
However, in http://www.josuttis.com/libbook/memo...lloc1.cpp.html construct isn't invoked while push_back invocation.
[color=blue]
> Destroy simply calls the destructor for the object.
>
> -Sharad
>
>
>[/color]
--
Alex Vinokur
Comment
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Re: Custom allocator sample code for vector
"Alex Vinokur" <alexvn@big-foot.com> wrote in message news:2njsjeF1lj vrU1@uni-berlin.de...[color=blue]
>
> "Sharad Kala" <no__spam.shara dk_ind@yahoo.co m> wrote in message news:2njcgfF1iu 4fU1@uni-berlin.de...[color=green]
> >
> > "Alex Vinokur" <alexvn@big-foot.com> wrote in message
> > news:2nho0uF105 teU1@uni-berlin.de...
> >[color=darkred]
> > > When should 'construct' and 'destroy' be invoked?[/color]
> >
> > An allocator has to provide a construct and destruct operation. You may want
> > to take a look at 20.1.5 (Allocator requirements).
> >
> > Construct is used to initialize the memory allocated with a value. This is
> > basically a call to placement new. So basically construct is invoked when an
> > object is created in the container.[/color]
>
> For instance, v.push_back (element) for vector?
>
> However, in http://www.josuttis.com/libbook/memo...lloc1.cpp.html construct isn't invoked while push_back invocation.
>[color=green]
> > Destroy simply calls the destructor for the object.
> >
> > -Sharad
> >[/color][/color]
[snip]
Compiler g++ 3.3.1 (cygming special).
Here is a fragment from file stl_alloc.h.
/**
* @defgroup Allocators Memory Allocators
* @if maint
* stl_alloc.h implements some node allocators. These are NOT the same as
* allocators in the C++ standard, nor in the original H-P STL. They do not
* encapsulate different pointer types; we assume that there is only one
* pointer type. The C++ standard allocators are intended to allocate
* individual objects, not pools or arenas.
*
* In this file allocators are of two different styles: "standard" and
* "SGI" (quotes included). "Standard" allocators conform to 20.4. "SGI"
* allocators differ in AT LEAST the following ways (add to this list as you
* discover them):
*
* - "Standard" allocate() takes two parameters (n_count,hint=0 ) but "SGI"
* allocate() takes one paramter (n_size).
* - Likewise, "standard" deallocate()'s argument is a count, but in "SGI"
* is a byte size.
* - max_size(), construct(), and destroy() are missing in "SGI" allocators.
* - reallocate(p,ol dsz,newsz) is added in "SGI", and behaves as
* if p=realloc(p,new sz).
*
* "SGI" allocators may be wrapped in __allocator to convert the interface
* into a "standard" one.
* @endif
*
* @note The @c reallocate member functions have been deprecated for 3.2
* and will be removed in 3.4. You must define @c _GLIBCPP_DEPREC ATED
* to make this visible in 3.2; see c++config.h.
*
* The canonical description of these classes is in docs/html/ext/howto.html
* or online at http://gcc.gnu.org/onlinedocs/libstd...t/howto.html#3
*/
Perhaps, MyAlloc in the Josuttis' sample works as "SGI" allocator which doesn't contain construct(), and destroy() (?).
--
Alex Vinokur
Comment
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Re: Custom allocator sample code for vector
"Alex Vinokur" <alexvn@big-foot.com> wrote in message
news:2njsjeF1lj vrU1@uni-berlin.de...[color=blue]
>
> For instance, v.push_back (element) for vector?[/color]
Yes
[color=blue]
> However, in http://www.josuttis.com/libbook/memo...lloc1.cpp.html[/color]
construct isn't invoked while push_back invocation.
Try putting a breakpoint in Construct and then see.
-Sharad
Comment
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Re: Custom allocator sample code for vector
"Sharad Kala" <no__spam.shara dk_ind@yahoo.co m> wrote in message news:2nju1qF1ib phU1@uni-berlin.de...[color=blue]
>
> "Alex Vinokur" <alexvn@big-foot.com> wrote in message
> news:2njsjeF1lj vrU1@uni-berlin.de...[color=green]
> >
> > For instance, v.push_back (element) for vector?[/color]
>
> Yes
>[color=green]
> > However, in http://www.josuttis.com/libbook/memo...lloc1.cpp.html[/color]
> construct isn't invoked while push_back invocation.
>
> Try putting a breakpoint in Construct and then see.
>[/color]
I put assert(0) in construct().
No response.
// initialize elements of allocated storage p with value value
void construct (pointer p, const T& value)
{
// initialize memory with placement new
new((void*)p)T( value);
assert (0); // Added by me
}
[snip]
--
Alex Vinokur
Comment
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Re: Custom allocator sample code for vector
[color=blue]
>
> I put assert(0) in construct().
> No response.[/color]
Is NDEBUG macro defined ? I can very much see the assert failure on MS VC 7
if I insert the above line (in debug build). Try putting cout << "In
construct" and then see.
Comment
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Re: Custom allocator sample code for vector
"Sharad Kala" <no__spam.shara dk_ind@yahoo.co m> wrote in message news:2njv3nF1lp auU1@uni-berlin.de...[color=blue]
>[color=green]
> >
> > I put assert(0) in construct().
> > No response.[/color]
>
> Is NDEBUG macro defined ? I can very much see the assert failure on MS VC 7
> if I insert the above line (in debug build). Try putting cout << "In
> construct" and then see.
>
>[/color]
Done: cout << "In construct" has been put.
No response too.
It seems that construct() is not invoked.
--
Alex Vinokur
Comment
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Re: Custom allocator sample code for vector
On Fri, 6 Aug 2004 18:56:06 +0300, "Alex Vinokur"
<alexvn@big-foot.com> wrote:
[color=blue]
>
>"Sharad Kala" <no__spam.shara dk_ind@yahoo.co m> wrote in message news:2ngv12Fo88 bU1@uni-berlin.de...[color=green]
>>
>> "Alex Vinokur" <alexvn@big-foot.com> wrote in message
>> news:2ngusqFp3p gU1@uni-berlin.de...[color=darkred]
>> > I am looking for any custom allocator sample code for std::vector.
>> >[/color]
>>
>> http://www.josuttis.com/libbook/memo...lloc1.cpp.html
>>
>>[/color]
>
>Thanks.
>
>In that sample we can see that methods 'allocate' and 'deallocate' were invoked.
>But methods 'construct' and 'destroy' were not invoked.
>When should 'construct' and 'destroy' be invoked?[/color]
They may never be invoked - containers are not required to call them.
I believe that Dinkumware's lib does call them, since they support
"unusual" pointer types and memory models. I doubt anyone else does.
Tom
Comment
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Re: Custom allocator sample code for vector
[color=blue]
> They may never be invoked - containers are not required to call them.
> I believe that Dinkumware's lib does call them, since they support
> "unusual" pointer types and memory models. I doubt anyone else does.[/color]
Why are they then as part of standard in allocator requirements in 20.1.5 ?
Is it an optional feature or are the compilers not being conformant ?
Comment
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Re: Custom allocator sample code for vector
On Wed, 11 Aug 2004 14:45:24 +0530, "Sharad Kala"
<no__spam.shara dk_ind@yahoo.co m> wrote:
[color=blue]
>[color=green]
>> They may never be invoked - containers are not required to call them.
>> I believe that Dinkumware's lib does call them, since they support
>> "unusual" pointer types and memory models. I doubt anyone else does.[/color]
>
>Why are they then as part of standard in allocator requirements in 20.1.5 ?[/color]
I think the original intention was that they were there to allow
pointer types that aren't T*. However, the standard says for
construct:
Effect: new ((void*)p) T(t)
I think that is a defect, since it requires that
allocator::poin ter_type be castable to void*, which is not a good
requirement to have!
[color=blue]
>Is it an optional feature or are the compilers not being conformant ?[/color]
It's an optional feature whether or not the containers use it or not -
I don't see any mention of whether containers must call it or not,
which I think makes it optional.
Tom
Comment
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Re: Custom allocator sample code for vector
"Alex Vinokur" <alexvn@big-foot.com> wrote in message news:<2nho0uF10 5teU1@uni-berlin.de>...[color=blue]
> "Sharad Kala" <no__spam.shara dk_ind@yahoo.co m> wrote in message news:2ngv12Fo88 bU1@uni-berlin.de...[color=green]
> >
> > "Alex Vinokur" <alexvn@big-foot.com> wrote in message
> > news:2ngusqFp3p gU1@uni-berlin.de...[color=darkred]
> > > I am looking for any custom allocator sample code for std::vector.
> > >[/color]
> >
> > http://www.josuttis.com/libbook/memo...lloc1.cpp.html
> >
> >[/color]
>
> Thanks.
>
> In that sample we can see that methods 'allocate' and 'deallocate' were invoked.
> But methods 'construct' and 'destroy' were not invoked.
> When should 'construct' and 'destroy' be invoked?[/color]
'allocate'only reserves raw memory. Wnen you insert objects in that
allocated memory, for example with vector 'push_back' method,
'construct' method must be invoked. It is invoked from vector
'push_back' method. Can you post vector 'push_back' method code from
the vector library file that you are using ?
Regards,
Jose Luis.
Comment
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Re: Custom allocator sample code for vector
"jose luis fernandez diaz" <jose_luis_fdez _diaz_news@yaho o.es> wrote in message
news:c2f95fd0.0 408110938.1a5ab 7bd@posting.goo gle.com...[color=blue]
> "Alex Vinokur" <alexvn@big-foot.com> wrote in message news:<2nho0uF10 5teU1@uni-berlin.de>...[color=green]
> > "Sharad Kala" <no__spam.shara dk_ind@yahoo.co m> wrote in message news:2ngv12Fo88 bU1@uni-berlin.de...[color=darkred]
> > >
> > > "Alex Vinokur" <alexvn@big-foot.com> wrote in message
> > > news:2ngusqFp3p gU1@uni-berlin.de...
> > > > I am looking for any custom allocator sample code for std::vector.
> > > >
> > >
> > > http://www.josuttis.com/libbook/memo...lloc1.cpp.html
> > >
> > >[/color]
> >
> > Thanks.
> >
> > In that sample we can see that methods 'allocate' and 'deallocate' were invoked.
> > But methods 'construct' and 'destroy' were not invoked.
> > When should 'construct' and 'destroy' be invoked?[/color]
>
> 'allocate'only reserves raw memory. Wnen you insert objects in that
> allocated memory, for example with vector 'push_back' method,
> 'construct' method must be invoked. It is invoked from vector
> 'push_back' method. Can you post vector 'push_back' method code from
> the vector library file that you are using ?
>[/color]
[snip]
--------------------------------------------
GNU g++ version 3.3.1 (cygming special).
GNU Standard C++ Library libstdc++-v3
--------------------------------------------
Here is the push_back() method from file stl_vector.h
--------- push_back() : BEGIN ---------
// [23.2.4.3] modifiers
/**
* @brief Add data to the end of the %vector.
* @param x Data to be added.
*
* This is a typical stack operation. The function creates an element at
* the end of the %vector and assigns the given data to it.
* Due to the nature of a %vector this operation can be done in constant
* time if the %vector has preallocated space available.
*/
void
push_back(const value_type& __x)
{
if (_M_finish != _M_end_of_stora ge)
{
_Construct(_M_f inish, __x);
++_M_finish;
}
else
_M_insert_aux(e nd(), __x);
}
--------- push_back() : END -----------
--
Alex Vinokur
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