g++ says a reinterpret cast from void* is disallowed; however, all I'm
trying to do is de-capsulate a void* argument that holds the pointer
to a class (and static_cast forces cast constructor)
any solutions?
also this pops up: 43: error: expected unqualified-id before 'return'
code:
includes: stdio.h, stdlib.h, time.h, pthread.h
struct:
template <typename Tstruct mergesort_threa d {
T* start;
T* end;
mergesort_threa d(T* _start, T* _end) { start = _start; end = _end; }
static void *invoke(void *_this) {
pthread_t threads[2];
mergesort_threa d<T*child1, *child2;
T *mid, *shift, t;
T* start = (reinterpret_ca st< mergesort_threa d<T(_this))->start;
T* end = (reinterpret_ca st< mergesort_threa d<T(_this))->end;
if (start >= end) return NULL; //recursed deep enough (1 element)
//recursively sort halves of the list
mid = (T*)(start + ((end - start) >1));
child1 = new mergesort_threa d<T>(start, mid);
pthread_create( &threads[0], NULL, mergesort_threa d<T>::invoke, (void
*)child1);
child2 = new mergesort_threa d<T>(mid + 1, end);
pthread_create( &threads[1], NULL, mergesort_threa d<T>::invoke, (void
*)child2);
delete child1;
delete child2;
pthread_join(th reads[0], NULL);
pthread_join(th reads[1], NULL);
for (;(start <= mid) && (mid + 1 <= end); start++) {
if (*start < *(mid + 1)) //sorted (current element belongs in 1st
half)
continue;
else { /* true inplace merge requires insersion-sort-like
* methods because a value from the second half is inserted to
* the current element */
//copy the first element in the second half to t
t = *(mid + 1);
//shift first half to the right
for (shift = mid; shift >= start; shift--)
*(shift + 1) = *shift;
//copy t to start
*start = t;
mid++;
}
}
}
43: return NULL;
};
Oct 31 '07
14  4444 
On Nov 2, 9:34 am, Nick Keighley <nick_keighley_ nos...@hotmail. com>
wrote:
On 1 Nov, 17:23, Erik Wikström <Erik-wikst...@telia. comwrote:
On 2007-11-01 18:06, andreyvul wrote:
>Nick Keighleywrote:
>On 31 Oct, 22:10, andreyvul <andrey....@gma il.comwrote:
g++ says a reinterpret cast from void* is disallowed;
however, all I'm trying to do is de-capsulate a void*
argument that holds the pointer to a class (and
static_cast forces cast constructor)
>what's a "cast constructor"?
This is the first time I've heard that expression.
A copy constructor with an argument of an unrelated object
type.
If the parameter type is unrelated, it isn't a copy constructor.
The official name is converting constructor, if that matters.
aren't those invoked even if there is no cast?
It depends. They're called conversion constructors because they
can be used to convert one type to another---any constructor
which isn't a copy constructor but can be called with exactly
one argument is a conversion constructor. If the constructor
has been declared "explicit", it will only be used for explicit
conversions---some form of a conversion operator. If it hasn't
been declared "explicit", it can be used for implicit
conversions as well.
--
James Kanze (GABI Software) email:ja******* **@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34
On Nov 1, 4:32 pm, terminator <farid.mehr...@ gmail.comwrote:
On Nov 1, 1:10 am, andreyvul <andrey....@gma il.comwrote:
a pointer is an intrinsic type on which modern compilers are
elegant in optimizing. I mean using static_cast must not
impose any overhead .
I'm not sure I understand. A static_cast isn't a no-op, and
compilers do generate executable code for it, when the semantics
require it. About the only cast which is really guaranteed to
be a no-op at execution time (and the standard doesn't actually
make any guarantee here either) is const_cast; on some machines,
even reinterpret_cas t will sometimes require executable code.
--
James Kanze (GABI Software) email:ja******* **@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34
On Nov 2, 12:20 pm, James Kanze <james.ka...@gm ail.comwrote:
On Nov 1, 4:32 pm, terminator <farid.mehr...@ gmail.comwrote:
On Nov 1, 1:10 am, andreyvul <andrey....@gma il.comwrote:
a pointer is an intrinsic type on which modern compilers are
elegant in optimizing. I mean using static_cast must not
impose any overhead .
I'm not sure I understand. A static_cast isn't a no-op, and
compilers do generate executable code for it, when the semantics
require it. About the only cast which is really guaranteed to
be a no-op at execution time (and the standard doesn't actually
make any guarantee here either) is const_cast; on some machines,
even reinterpret_cas t will sometimes require executable code.
static_casting pointers generates a temporary copy of the original
pointer if pointers are of irrelevant types with similar alignment
properties ,but that can be removed by the optimizer .
regards,
FM.
On Nov 5, 3:49 pm, terminator <farid.mehr...@ gmail.comwrote:
On Nov 2, 12:20 pm, James Kanze <james.ka...@gm ail.com>
wrote:On Nov 1, 4:32 pm, terminator
<farid.mehr...@ gmail.comwrote:
On Nov 1, 1:10 am, andreyvul <andrey....@gma il.comwrote:
a pointer is an intrinsic type on which modern compilers are
elegant in optimizing. I mean using static_cast must not
impose any overhead .
I'm not sure I understand. A static_cast isn't a no-op, and
compilers do generate executable code for it, when the semantics
require it. About the only cast which is really guaranteed to
be a no-op at execution time (and the standard doesn't actually
make any guarantee here either) is const_cast; on some machines,
even reinterpret_cas t will sometimes require executable code.
static_casting pointers generates a temporary copy of the original
pointer if pointers are of irrelevant types with similar alignment
properties ,but that can be removed by the optimizer .
I'm having trouble understanding your sentence. The result of a
static_cast (of pointers) is an rvalue; if it is bound to a
reference, or used in any other context which requires an objet,
there will be a copy. Always.
But that doesn't have anything to do with what I was talking
about. A static_cast is not always a no-op; at times, it
requires the compiler to generate code (e.g. most often, adding
a constant to the pointer).
In the case of reinterpret_cas t, on machines where all pointers
have the same representation, the reinterpret_cas t will be a
no-op, almost certainly. For some pointers:
static_cast<T*> ( p ) != reinterpret_cas t<T*>( p )
--
James Kanze (GABI Software) email:ja******* **@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34
On Nov 5, 8:42 pm, James Kanze <james.ka...@gm ail.comwrote:
On Nov 5, 3:49 pm, terminator <farid.mehr...@ gmail.comwrote:
On Nov 2, 12:20 pm, James Kanze <james.ka...@gm ail.com>
wrote:On Nov 1, 4:32 pm, terminator
<farid.mehr...@ gmail.comwrote:
On Nov 1, 1:10 am, andreyvul <andrey....@gma il.comwrote:
a pointer is an intrinsic type on which modern compilers are
elegant in optimizing. I mean using static_cast must not
impose any overhead .
I'm not sure I understand. A static_cast isn't a no-op, and
compilers do generate executable code for it, when the semantics
require it. About the only cast which is really guaranteed to
be a no-op at execution time (and the standard doesn't actually
make any guarantee here either) is const_cast; on some machines,
even reinterpret_cas t will sometimes require executable code.
static_casting pointers generates a temporary copy of the original
pointer if pointers are of irrelevant types with similar alignment
properties ,but that can be removed by the optimizer .
I'm having trouble understanding your sentence. The result of a
static_cast (of pointers) is an rvalue; if it is bound to a
reference, or used in any other context which requires an objet,
there will be a copy. Always.
But that doesn't have anything to do with what I was talking
about. A static_cast is not always a no-op; at times, it
requires the compiler to generate code (e.g. most often, adding
a constant to the pointer).
In the case of reinterpret_cas t, on machines where all pointers
have the same representation, the reinterpret_cas t will be a
no-op, almost certainly. For some pointers:
static_cast<T*> ( p ) != reinterpret_cas t<T*>( p )
its a matter of context ,the OP is not referencing(nor addressing) the
casted pointer ; so there is a chance for removal of the copy as I
wrote before.
BTW while I was looking for a proof that in this context either
operator has the same effect ,I discovered that I had been mislead
here.Look out plz:
On Nov 1, 1:10 am, andreyvul <andrey....@gma il.comwrote:
g++ says a reinterpret cast from void* is disallowed; however, all I'm
trying to do is de-capsulate a void* argument that holds the pointer
to a class (and static_cast forces cast constructor)
any solutions?
also this pops up: 43: error: expected unqualified-id before 'return'
code:
includes: stdio.h, stdlib.h, time.h, pthread.h
struct:
template <typename Tstruct mergesort_threa d {
T* start;
T* end;
mergesort_threa d(T* _start, T* _end) { start = _start; end = _end; }
static void *invoke(void *_this) {
pthread_t threads[2];
mergesort_threa d<T*child1, *child2;
T *mid, *shift, t;
T* start =
(reinterpret_ca st< mergesort_threa d<T(_this))->start;
T* end =(reinterpret_c ast< mergesort_threa d<T(_this))->end;
the template does not inherit from its type-parameter ,hence a pointer
to template('merge sort_thread<T>' ) is not implicitly castable to that
of its type-param('T').So the compiler`s complaign about casting is no
surpris.whateve r the casting operator,the compiler will cry that it
cannot cast.The problem is in initializing from the result of the cast
operator.
regards,
FM. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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