Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c > #106311

Re: Parsing struct memory?

Show all headers | View raw

On 03/17/17 03:09 PM, James Kuyper wrote:
> On 03/16/2017 06:16 PM, Ian Collins wrote:
>> On 03/17/17 09:21 AM, Thiago Adams wrote:
> ...
>>> And how about aligned_alloc? Why do we need it?
>>
>> To allocate a block on some externally specified boundary, greater than
>> alignof(max_align_t).  Unix (and no doubt windows) systems already have
>> system specific functions for doing this, such as getting a block of
>> memory aligned to a page boundary.
>
> "The value of alignment shall be a valid alignment supported by the
> implementation and the value of size shall be an integral multiple of
> alignment." (7.22.3.1p2)
>
> "Valid alignments include only those values returned by an _Alignof
> expression for fundamental types, plus an additional
> implementation-defined set of values, which may be empty." (6.2.8p4)
>
> By definition, for every type, _Alignof(type) <= _Alignof(max_align_t).
> Thus, all valid alignments greater than _Alignof(max_align_t) are
> implementation-defined, and there need not be any. If there are
> implementation-defined valid alignments greater _Alignof(max_align_t),
> aligned_alloc() certainly could be used for the purpose you describe.
> However, since there need not be any such alignments, I think it's more
> reasonable to assume that the primary purpose of aligned_alloc() is to
> allow the allocation of memory that is LESS strictly aligned than the
> memory allocated by malloc().

I have never used the existing Posix/Solaris memalign functions in that 
way, but I concede they can be.  On systems that support them, the are 
only 1 (on 64bit) and 2 (on 32bit) smaller alignments than 
alignof(max_align_t) where there are many more greater!  I have 
typically used page size alignment.

-- 
Ian

Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Parsing struct memory? Thiago Adams <thiago.adams@gmail.com> - 2017-03-16 12:58 -0700
  Re: Parsing struct memory? Thiago Adams <thiago.adams@gmail.com> - 2017-03-16 13:21 -0700
    Re: Parsing struct memory? Ian Collins <ian-news@hotmail.com> - 2017-03-17 11:16 +1300
      Re: Parsing struct memory? James Kuyper <jameskuyper@verizon.net> - 2017-03-16 22:09 -0400
        Re: Parsing struct memory? Ian Collins <ian-news@hotmail.com> - 2017-03-17 15:23 +1300
        Re: Parsing struct memory? David Brown <david.brown@hesbynett.no> - 2017-03-17 10:11 +0100
          Re: Parsing struct memory? "James R. Kuyper" <jameskuyper@verizon.net> - 2017-03-17 11:35 -0400
    Re: Parsing struct memory? gordonb.7zilv@burditt.org (Gordon Burditt) - 2017-03-16 20:17 -0500
      Re: Parsing struct memory? James Kuyper <jameskuyper@verizon.net> - 2017-03-16 21:56 -0400
  Re: Parsing struct memory? supercat@casperkitty.com - 2017-03-16 13:51 -0700
    Re: Parsing struct memory? Lowell Gilbert <lgusenet@be-well.ilk.org> - 2017-03-16 19:39 -0400
      Re: Parsing struct memory? BartC <bc@freeuk.com> - 2017-03-17 12:16 +0000
      Re: Parsing struct memory? "Peter \"Shaggy\" Haywood" <phaywood@alphalink.com.au> - 2017-03-24 18:06 +1100
        Re: Parsing struct memory? supercat@casperkitty.com - 2017-03-24 14:35 -0700
  Re: Parsing struct memory? Keith Thompson <kst-u@mib.org> - 2017-03-16 19:14 -0700
    Re: Parsing struct memory? scott@slp53.sl.home (Scott Lurndal) - 2017-03-17 12:45 +0000
  Re: Parsing struct memory? scott@slp53.sl.home (Scott Lurndal) - 2017-03-17 12:41 +0000
  Re: Parsing struct memory? Thiago Adams <thiago.adams@gmail.com> - 2017-03-17 08:17 -0700
  Re: Parsing struct memory? Thiago Adams <thiago.adams@gmail.com> - 2017-03-20 05:07 -0700

csiph-web