Is a std::vector *guaranteed* to be contiguous in memory? Bjarne
Stroustrup says it takes constant time to access a vector element and
that implies contiguous storage but I just wanted to double-check. I
heard that ISO 14882 standard did not guarantee this. Has this changed?
Any pointers will be appreciated.
Thanks,
Ravi.
8  2377 
Ravi wrote: Is a std::vector *guaranteed* to be contiguous in memory? Bjarne
Stroustrup says it takes constant time to access a vector element and
that implies contiguous storage
Not necessarily; it could mean that there is an array of pointers to
elements, and that the array is contiguous.
--
Mike Smith
Ravi wrote: Is a std::vector *guaranteed* to be contiguous in memory? Bjarne
Stroustrup says it takes constant time to access a vector element and
that implies contiguous storage but I just wanted to double-check. I
heard that ISO 14882 standard did not guarantee this. Has this changed?
Any pointers will be appreciated.
Karl Heinz Buchegger summarized the situation nicely in this post: http://tinyurl.com/36adz
Quoting Karl:
The concensus is this:
* There is no guarantee
* This has probably been an oversight while comming up with the
standard
* The next version of the standard will guarantee this
* It is hard or impossible to fullfill the requirements of
std::vector if the data is not stored contigous
* There is no known version which does not store the data
contigous.
--
Russell Hanneken rg********@pobo x.com
Remove the 'g' from my address to send me mail.
> * It is hard or impossible to fullfill the requirements of std::vector if the data is not stored contigous
Why would it be impossible to fullfill the requirements by using a
trasparent array of pointers? (the external program doesn't see pointers...
The Vector class hide them)
I could conceive an implementation that stores POD directly in the vector
and class/structures in pointers.
--- bye
"Ravi" <rg**@cse.buffa lo.edu> wrote in message
news:c2******** **@prometheus.a csu.buffalo.edu ... Is a std::vector *guaranteed* to be contiguous in memory? Bjarne
Stroustrup says it takes constant time to access a vector element
and that implies contiguous storage but I just wanted to double-check. I
heard that ISO 14882 standard did not guarantee this. Has this
changed? Any pointers will be appreciated.
A vector's storage is guaranteed to be contiguous. From ISO 14882, 2nd
ed., 23.2.4 [lib.vector]:
"The elements of a vector are stored contiguously, meaning that if v
is a vector<T, Allocator> where T is some type
other than bool, then it obeys the identity &v[n] == &v[0] + n for all
0 <= n < v.size()."
Jonathan
On Fri, 5 Mar 2004 15:57:14 -0700, "Jonathan Turkanis"
<te******@kanga roologic.com> wrote:
"Ravi" <rg**@cse.buffa lo.edu> wrote in message
news:c2******* ***@prometheus. acsu.buffalo.ed u... Is a std::vector *guaranteed* to be contiguous in memory? Bjarne
Stroustrup says it takes constant time to access a vector element
and that implies contiguous storage but I just wanted to double-check. I
heard that ISO 14882 standard did not guarantee this. Has this
changed? Any pointers will be appreciated.
A vector's storage is guaranteed to be contiguous. From ISO 14882, 2nd
ed., 23.2.4 [lib.vector]:
"The elements of a vector are stored contiguously, meaning that if v
is a vector<T, Allocator> where T is some type
other than bool, then it obeys the identity &v[n] == &v[0] + n for all
0 <= n < v.size()."
Jonathan
Right, I believe it is whether or not it uses a "dynamic array" that isn't
(yet) nailed down in the standard. See Josuttis, the start of section 6.2.
-leor
Leor Zolman
BD Software le**@bdsoft.com www.bdsoft.com -- On-Site Training in C/C++, Java, Perl & Unix
C++ users: Download BD Software's free STL Error Message
Decryptor at www.bdsoft.com/tools/stlfilt.html
Jonathan Turkanis wrote: A vector's storage is guaranteed to be contiguous. From ISO 14882, 2nd
ed., 23.2.4 [lib.vector]:
I guess my copy of the standard is out of date. So this was fixed in
Technical Corrigendum 1?
--
Russell Hanneken rg********@pobo x.com
Remove the 'g' from my address to send me mail.
Russell Hanneken <rg********@pob ox.com> wrote in message news:<4K******* ************@ne wsread1.news.pa s.earthlink.net >... Ravi wrote: Is a std::vector *guaranteed* to be contiguous in memory? Bjarne
Stroustrup says it takes constant time to access a vector element and
that implies contiguous storage but I just wanted to double-check. I
heard that ISO 14882 standard did not guarantee this. Has this changed?
Any pointers will be appreciated.
Yes. The 2003 "technical corrigendum" corects that. 23.2.4[1] says
"The elements of a vector are stored contiguously".
As Russell pointed out, this was always the intent and all
implementations always did it that way
-- Bjarne Stroustrup; http://www.research.att.com/~bs
"Ravi" <rg**@cse.buffa lo.edu> wrote in message
news:c2******** **@prometheus.a csu.buffalo.edu ... Is a std::vector *guaranteed* to be contiguous in memory? Bjarne
Stroustrup says it takes constant time to access a vector element and
that implies contiguous storage but I just wanted to double-check. I
heard that ISO 14882 standard did not guarantee this. Has this changed?
I think this is mandated in TC1
-Mike This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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