how do you resize an array allocated with new?
Jul 19 '05
16  6214 
Christopher Benson-Manica wrote: Rolf Magnus <ra******@t-online.de> spoke thus:
You don't. Yo have to allocate a new block of memory of the target
size and then move the data there and deallocate the original array.
Any reason why you don't use std::vector, which handles resizing for
you?
Just for curiosity's sake, why isn't there something like realloc()
for new? Wouldn't that make situations like this one easier to manage?
For POD types maybe, but if you have "real" classes with constructors,
virtual functions "and stuff", it's not so easy anymore.
Also note that realloc() also uses the "allocate-copy-delete" way.
OTOH, C++ more or less has that functionality, but it's built into
std::vector.
In article <bn**********@c hessie.cirr.com >,
Christopher Benson-Manica <at***@nospam.c yberspace.org> wrote:
Just for curiosity's sake, why isn't there something like realloc() for new?
There's been a *huge* thread recently in comp.lang.c++.m oderated about
this during the past month. I suggest that you look it up in Google
Groups. Use the "Advanced Groups Search", restrict your search to
c.l.c++.m, and search for "realloc".
--
Jon Bell <jt*******@pres by.edu> Presbyterian College
Dept. of Physics and Computer Science Clinton, South Carolina USA
"Andreas Müller" <me@privacy.net > wrote in message
news:bn******** ****@ID-83644.news.uni- When it comes to a point where compatibility to arrays comes into the
game, I usually stick with std::vector, as I can easily pass the content
of a vector into a legacy function (&vector[0]) and converting a
returned array into a vector normally doesn't affect performance in the
stuff that I do. (If it does and it was proven by a profiler, then that
is another story!)
--
I wasn't aware you could do that. Is the memory for the objects stored in
the vector guaranteeed to be contiguous? If so, that would definitely allow
me to use vectors in some places where I've avoided them. But how does the
vector handle the case where re-sizing has moved the data in memory?
Overriding the [] (or &) operator?
-Howard
Howard wrote:
"Andreas Müller" <me@privacy.net > wrote in message
news:bn******** ****@ID-83644.news.uni-
When it comes to a point where compatibility to arrays comes into the
game, I usually stick with std::vector, as I can easily pass the content
of a vector into a legacy function (&vector[0]) and converting a
returned array into a vector normally doesn't affect performance in the
stuff that I do. (If it does and it was proven by a profiler, then that
is another story!)
--
I wasn't aware you could do that. Is the memory for the objects stored in
the vector guaranteeed to be contiguous?
Strictly speaking it is not guaranteed.
But most people feel that it has to be that way and some forced properties
of std::vector force the memory to be practically contiguos. Practically there
is no known implementation which hasn't contigous memory.
That said: There is a defect report on this issue and as far as I know
the next standard will contain the critical sentence.
If so, that would definitely allow
me to use vectors in some places where I've avoided them. But how does the
vector handle the case where re-sizing has moved the data in memory?
Overriding the [] (or &) operator?
Yep. It's a simple exercise.
--
Karl Heinz Buchegger kb******@gascad .at
> > When it comes to a point where compatibility to arrays comes into
the game, I usually stick with std::vector, as I can easily pass the
content of a vector into a legacy function (&vector[0]) and converting a
returned array into a vector normally doesn't affect performance in
the stuff that I do. (If it does and it was proven by a profiler, then
that is another story!)
I wasn't aware you could do that. Is the memory for the objects
stored in the vector guaranteeed to be contiguous?
Officially not (yet). Practically yes.
If so, that would definitely allow
me to use vectors in some places where I've avoided them. But how
does the vector handle the case where re-sizing has moved the data in memory?
Overriding the [] (or &) operator?
In that case the address obtained with &vector[0] before the resize is
no longer valid (to be more precise not guaranteed to be valid), just
like iterators get invalidated when the vector is changed. Because
std::vector overloads the [] operator, moving of the actual objects in
memory is invisible to the user.
--
Peter van Merkerk
peter.van.merke rk(at)dse.nl
"Howard" <al*****@hotmai l.com> wrote in message news:bn******** @dispatch.conce ntric.net...
I wasn't aware you could do that. Is the memory for the objects stored in
the vector guaranteeed to be contiguous? If so, that would definitely allow
me to use vectors in some places where I've avoided them. But how does the
vector handle the case where re-sizing has moved the data in memory?
Overriding the [] (or &) operator?
Technically the standard is mute on the subject, but you can sort of intuit that it
has to be. This will be corrected in the TC1. Nobody knows of any implementations
that don't do it "right."
The value of the address of the internal array is not valid after any capacity changes.
In article <3f************ *********@news. newshosting.com >, Ron Natalie wrote:
"Howard" <al*****@hotmai l.com> wrote in message news:bn******** @dispatch.conce ntric.net...
I wasn't aware you could do that. Is the memory for the objects stored in
the vector guaranteeed to be contiguous? If so, that would definitely allow
me to use vectors in some places where I've avoided them. But how does the
vector handle the case where re-sizing has moved the data in memory?
Overriding the [] (or &) operator?
Technically the standard is mute on the subject, but you can sort of intuit that it
has to be. This will be corrected in the TC1. Nobody knows of any implementations
that don't do it "right."
Hmmm...I was warned away from doing this recently becaus it is non-
standard. However, I found that valarray met most of my needs since it is
guaranteed to be in contiguous memory and it has a resize function (although
data is lost). As I only resize when the data changes completely
(computational electromagnetic s), this is not a problem. I may switch
certain things over to vector, however, if it really is safe. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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