Re: 64 bit
Re: 64 bit
- Subject: Re: 64 bit
- From: Alastair Houghton <email@hidden>
- Date: Tue, 25 Dec 2007 00:42:32 +0000
On 24 Dec 2007, at 22:49, David Fang wrote:
Yes, I know, this reply comes awfully late, but 'twas the night
before Christmas, and I'm bored in the house, catching up on mailing
lists without using a mouse...
Of course this all assumes that portability is indeed a goal :-)
Sure, and it all stems from the fact that there isn't a portable 64-
bit integer type in C++.
(FWIW, I wasn't paying a great deal of attention and hadn't
actually noticed that he was using C++ rather than C. Also, on the
<inttypes.h> point, I seem to recall reading somewhere that
<inttypes.h> is supposed to be more widely deployed in practice
than <stdint.h>, so maybe using the former is better for
portability.)
One option is to use -m64, which results in 64b long.
In general that's an extremely bad idea. It fundamentally changes the
ABI, so calling system routines (even fundamental things like the C
runtime library) might not work.
This gets around having to use the pedantically rejected "long
long". (ints are still 32b, pointers are 64b.)
...(and any "long" parameters to APIs you were using are going to get
passed as 64-bit values when the API expects them to be 32-bit)...
If you need *exactly* 64b, look for types like "int64_t" in the
system's type headers.
<inttypes.h> is probably the best place if you want portability, since
it's defined by C99 but was already present on some systems prior to
that. I tend to include <stdint.h> myself, but then I only care about
systems with C99.
BSD also defines some similar types (in <sys/types.h>), though the
unsigned variants have an additional underscore (i.e. u_int16_t versus
the C99 uint16_t).
And there are some Apple types that come from Carbon (e.g. SInt32,
UInt32).
Anyway, there are plenty of types to choose from. The C99 ones have
the advantage of being able to specify that e.g. you want something
with at least 64 bits that will be fast, or you'd like something that
can hold integers and pointers.
Kind regards,
Alastair.
--
http://alastairs-place.net
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| References: | |
| | >64 bit (From: email@hidden) |
| | >Re: 64 bit (From: Nick Zitzmann <email@hidden>) |
| | >Re: 64 bit (From: Perry Winkel <email@hidden>) |
| | >Re: 64 bit (From: Alastair Houghton <email@hidden>) |
| | >Re: 64 bit (From: "Sean McBride" <email@hidden>) |
| | >Re: 64 bit (From: Peter O'Gorman <email@hidden>) |
| | >Re: 64 bit (From: Alastair Houghton <email@hidden>) |
| | >Re: 64 bit (From: David Fang <email@hidden>) |