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Mirek Fidler
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 Posted: Thu Jul 10, 2003 4:15 pm Post subject: Re: size_type of standard containers |
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| Quote: | According to the standard, std::vector<X>::size_type is required to
be
std::size_t. For all types T (except maybe bool).
Oh, yes. The weasel rules in 20.1.5/4 
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If that is true then it might have negative performance impact on
e.g. AMD64 platform - as all indices will be stored as 64-bit values
(that is what I expect size_t to be), while native int size is 32-bits.
Mirek
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David Abrahams
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| Posted: Sat Jul 12, 2003 7:45 pm Post subject: Re: size_type of standard containers |
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[email]cxl (AT) volny (DOT) cz[/email] ("Mirek Fidler") writes:
| Quote: | According to the standard, std::vector<X>::size_type is required
to be std::size_t. For all types T (except maybe bool).
Oh, yes. The weasel rules in 20.1.5/4 :-)
If that is true then it might have negative performance impact on
e.g. AMD64 platform - as all indices will be stored as 64-bit values
(that is what I expect size_t to be), while native int size is 32-bits.
|
It isn't true. A conforming library implementation is permitted to
assume that size_type is size_t, but it is also allowed to be smarter
and allow for different size_type's.
--
Dave Abrahams
Boost Consulting
www.boost-consulting.com
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Bo Persson
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| Posted: Mon Jul 14, 2003 9:56 pm Post subject: Re: size_type of standard containers |
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""Mirek Fidler"" <cxl (AT) volny (DOT) cz> skrev i meddelandet
news:bej7m0$5edj2$1 (AT) ID-198693 (DOT) news.dfncis.de...
| Quote: | According to the standard, std::vector<X>::size_type is required
to
be
std::size_t. For all types T (except maybe bool).
Oh, yes. The weasel rules in 20.1.5/4 :-)
If that is true then it might have negative performance impact
on
e.g. AMD64 platform - as all indices will be stored as 64-bit values
(that is what I expect size_t to be), while native int size is
32-bits. |
Or not...
| Quote: | From what I have seen, compilers like MSVC and gcc seems to keep int
and long at 32 bits, even though a pointer is 64 bits. How is this |
solved for the standard library?
Bo Persson
[email]bop2 (AT) telia (DOT) com[/email]
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Ben Hutchings
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| Posted: Wed Jul 16, 2003 9:28 pm Post subject: Re: size_type of standard containers |
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In article <RZ_Pa.16087$mU6.15403 (AT) newsb (DOT) telia.net>, "Bo Persson" wrote:
| Quote: |
""Mirek Fidler"" <cxl (AT) volny (DOT) cz> skrev i meddelandet
news:bej7m0$5edj2$1 (AT) ID-198693 (DOT) news.dfncis.de...
According to the standard, std::vector<X>::size_type is required
to be std::size_t. For all types T (except maybe bool).
Oh, yes. The weasel rules in 20.1.5/4 :-)
If that is true then it might have negative performance impact
on e.g. AMD64 platform - as all indices will be stored as 64-bit
values (that is what I expect size_t to be), while native int size
is 32-bits.
Or not...
From what I have seen, compilers like MSVC and gcc seems to keep int
and long at 32 bits, even though a pointer is 64 bits. How is this
solved for the standard library?
|
GCC doesn't do this; for 64-bit architectures it uses 32-bit ints and
64-bit longs. VC++ behaves as you say. It doesn't even support C99's
long long! Instead it has non-standard types called (signed|unsigned)
__int64 and uses these to define size_t and ptrdiff_t for 64-bit
architectures.
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Bo Persson
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| Posted: Thu Jul 17, 2003 4:38 pm Post subject: Re: size_type of standard containers |
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"Ben Hutchings" <do-not-spam-benh (AT) bwsint (DOT) com> skrev i meddelandet
news:slrnbhamo5.1dc.do-not-spam-benh (AT) tin (DOT) bwsint.com...
| Quote: | In article <RZ_Pa.16087$mU6.15403 (AT) newsb (DOT) telia.net>, "Bo Persson"
wrote:
""Mirek Fidler"" <cxl (AT) volny (DOT) cz> skrev i meddelandet
news:bej7m0$5edj2$1 (AT) ID-198693 (DOT) news.dfncis.de...
According to the standard, std::vector<X>::size_type is
required
to be std::size_t. For all types T (except maybe bool).
Oh, yes. The weasel rules in 20.1.5/4 :-)
If that is true then it might have negative performance
impact
on e.g. AMD64 platform - as all indices will be stored as 64-bit
values (that is what I expect size_t to be), while native int
size
is 32-bits.
Or not...
From what I have seen, compilers like MSVC and gcc seems to keep
int
and long at 32 bits, even though a pointer is 64 bits. How is this
solved for the standard library?
GCC doesn't do this; for 64-bit architectures it uses 32-bit ints
and
64-bit longs.
|
ok.
| Quote: | VC++ behaves as you say. It doesn't even support C99's
long long! Instead it has non-standard types called
(signed|unsigned)
__int64 and uses these to define size_t and ptrdiff_t for 64-bit
architectures.
|
Well, in version 7.1 it actually has a long long (as a synonym for its
own __int64). I was more curious on how the C++ standard addresses
compilers were pointers are longer than all of the int types. Using a
C99 type seems like cheating! :-)
Bo Persson
[email]bop2 (AT) telia (DOT) com[/email]
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James Kuyper
Guest
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| Posted: Fri Jul 18, 2003 10:34 pm Post subject: Re: size_type of standard containers |
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[email]do-not-spam-benh (AT) bwsint (DOT) com[/email] (Ben Hutchings) wrote in message news:<slrnbhdt3k.1ik.do-not-spam-benh (AT) tin (DOT) bwsint.com>...
....
| Quote: | I was more curious on how the C++ standard addresses
compilers were pointers are longer than all of the int types. Using a
C99 type seems like cheating! :-)
There's nothing inherently wrong with that. However, for implementations
with a flat memory model it makes sense for ptrdiff_t and size_t to be
the same size as pointers, and I think those types are required to be
typedefs for standard integer types.
|
The C++ standard doesn't specify that directly, apparantly deferring
that issue to the C standard. The current C++ standard
cross-references the C90 standard, and I don't have a copy of that. I
do, however, have a copy of the C99 standard, which specifies that
ptrdiff_t must be a signed integer type, and that size_t must be an
unsigned integer type. In C99, the signed integer types are explicity
defined as including both standard integer types and extended
(implementation-defined) integer types.
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Ross Ridge
Guest
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| Posted: Sat Jul 19, 2003 7:36 pm Post subject: Re: size_type of standard containers |
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James Kuyper <kuyper (AT) wizard (DOT) net> wrote:
| Quote: | The C++ standard doesn't specify that directly, apparantly deferring
that issue to the C standard. The current C++ standard
cross-references the C90 standard, and I don't have a copy of that. I
do, however, have a copy of the C99 standard, which specifies that
ptrdiff_t must be a signed integer type, and that size_t must be an
unsigned integer type. In C99, the signed integer types are explicity
defined as including both standard integer types and extended
(implementation-defined) integer types.
|
I don't have the C90 standard handy either, but I'm pretty sure that's
new for C99. I remember POSIX having a similiar issue because it said
some types were arithmetic types and deferred to the C90 standard for
the definition of what an arithmetic type was.
Ross Ridge
--
l/ // Ross Ridge -- The Great HTMU
[oo][oo] [email]rridge (AT) csclub (DOT) uwaterloo.ca[/email]
-()-/()/ http://www.csclub.uwaterloo.ca/u/rridge/
db //
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