Hi,
If I do another delete on an object which has been deleted earlier, then
how is
the system expected to behave ?
Is it an unpredictable behavior ??
Thanks
Sandeep
19  2694 
Sandeep Grover wrote: Hi,
If I do another delete on an object which has been deleted earlier, then
how is
the system expected to behave ?
Is it an unpredictable behavior ??
Yes, unpredictable.
Some will choke, some destructors SEGV, it goes on and on.
Sandeep Grover wrote: If I do another delete on an object which has been deleted earlier, then
how is the system expected to behave?
Is it an unpredictable behavior ??
It's undefined, so in theory, yes; anything could happen.
S Sandeep Grover wrote:
If I do another delete on an object which has been deleted earlier, then
how is the system expected to behave?
Is it an unpredictable behavior ??
It's undefined, so in theory, yes; anything could happen.
S
Thanks !
So, if I have an array of pointers; more than one of the entries could point
to
the same chunk of memory (allocated using new). How do I ensure that I
end up deleting that entry only once. I dont want to use reference-counting
kind of thing in constructor.
On Fri, 11 Jul 2003 16:53:31 -0700, Sandeep Grover <sa*****@magm a-da.com> wrote: [i]f I have an array of pointers; more than one of the entries could
point to the same chunk of memory (allocated using new). How do I ensure
that I end up deleting that entry only once. I dont want to use
reference-counting kind of thing in constructor.
The sane thing to do would be to use reference-counting.
Reference-counting is automated by many smart-pointers; the most general
and compatible with upcoming standard is boost::shared_p tr (go to
<url:hhtp://www.boost.org> to download the Boost library, it's free).
Without reference-counting you can just sort the array first, on the
pointer values; even though pointers that do not point into the same
variable are not formally comparable, they are comparable in practice.
But you need to know that the array contains pointers to all objects
that you need to delete. And in that case, why not store the unique
pointers in a separate array of the same size or less?
"Sandeep Grover" <sa*****@magm a-da.com> wrote in message
news:3F******** *******@magma-da.com...
Sandeep Grover wrote:
If I do another delete on an object which has been deleted earlier,
then how is the system expected to behave?
Is it an unpredictable behavior ??
It's undefined, so in theory, yes; anything could happen.
S
Thanks !
So, if I have an array of pointers; more than one of the entries could
point to
the same chunk of memory (allocated using new). How do I ensure that I
end up deleting that entry only once. I dont want to use
reference-counting kind of thing in constructor.
Use a vector of the objects you want, or a list if it suits better the
problem, and not a built in array of pointers.
--
Ioannis
* Programming pages: http://www.noicys.freeurl.com
* Alternative URL 1: http://run.to/noicys
* Alternative URL 2: http://www.noicys.cjb.net
"Alf P. Steinbach" wrote:
Without reference-counting you can just sort the array first, on the
pointer values; even though pointers that do not point into the same
variable are not formally comparable, they are comparable in practice.
If you use std::greater, std::less, std::greater_eq ual, or
std::less_equal they are comparable. It's just the builtin operators
that are allowed to be fast. <g>
--
"To delight in war is a merit in the soldier,
a dangerous quality in the captain, and a
positive crime in the statesman."
George Santayana
"Bring them on."
George W. Bush
Sandeep Grover wrote: Sandeep Grover wrote:
If I do another delete on an object which has been deleted earlier, then
how is the system expected to behave?
Is it an unpredictable behavior ??
It's undefined, so in theory, yes; anything could happen.
S
Thanks !
So, if I have an array of pointers; more than one of the entries could point
to the same chunk of memory (allocated using new). How do I ensure that I
end up deleting that entry only once. I dont want to use reference-counting
kind of thing in constructor.
A flippant answer would be not to alias pointers.
On the other hand, techniques such as reference-counting
are for when you need multiple pointers to the same object
which you wish to dispose of independently, but don't need
an invasive implementation, i.e. an implementation inside
the pointed-to object.
But this is really a design issue, not a language issue.
S
"Ioannis Vranos" <iv*@nothis.ema ils.ru> wrote in message
news:3f******** *************@r ead.news.gr.uu. net...
| "Sandeep Grover" <sa*****@magm a-da.com> wrote in message
| news:3F******** *******@magma-da.com...
| > Hi,
| >
| > If I do another delete on an object which has been deleted earlier, then
| > how is
| > the system expected to behave ?
|
|
| It will get angry.
Depends.
| > Is it an unpredictable behavior ??
| Yes it is undefined behaviour. It may die, it may continue living and die
| later, it may truncate data, everything.
Again it depends.
If you set the pointer to zero straight after you have deleted
it, then the behaviour is very defined, and safe.
For example:
# include <iostream>
# include <ostream>
struct Base
{
int N;
};
int main()
{
Base* B = new Base;
delete B;
B = 0; // Introduce a safety net.
for( int Idx( 0 ); Idx < 5; ++Idx )
delete B; // Safe - no opp.
return 0;
}
Cheers.
Chris Val
"Chris ( Val )" <ch******@bigpo nd.com.au> wrote in message
news:be******** ****@ID-110726.news.uni-berlin.de...
| Yes it is undefined behaviour. It may die, it may continue living and
die | later, it may truncate data, everything.
Again it depends.
If you set the pointer to zero straight after you have deleted
it, then the behaviour is very defined, and safe.
He/she said:
"If I do another delete on an object which has been deleted earlier, then
how is the system expected to behave ?".
That means that the pointer will not point to 0.
--
Ioannis
* Programming pages: http://www.noicys.freeurl.com
* Alternative URL 1: http://run.to/noicys
* Alternative URL 2: http://www.noicys.cjb.net This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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//////////////////////////////////
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/////////////////////
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