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Re: volatile in struct member

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David Brown <david.brown@hesbynett.no> writes:

> On 30/09/16 15:29, Ben Bacarisse wrote:
>> Thiago Adams <thiago.adams@gmail.com> writes:
>> 
>>> Can this make sense?
>>>
>>> struct 
>>> {
>>>   volatile int i;
>>> };
>> 
>> People sometimes use volatile to alter the way the optimiser works, so
>> whilst that may not "make sense" in any portable way, I'd not want to
>> rule it out.
>> 
>>> Why this question?  
>>> I was just trying to find some qualifier to hijack and put other
>>> concept on it to use in static analysis if the generated code isn't
>>> affected.
>>>
>>> For curiosity, I tried:
>>>
>>> struct 
>>> {
>>>   register int i1; //error
>>>   auto int i2; //error
>>>   restrict i3; //error
>>>  
>>> }
>> 
>> register and auto are storage class specifiers like static.  volatile is
>> a type qualifier (like const and restrict).  The difference is that type
>> qualifiers go in the declarator and can be mixed in with *s and []s and
>> so on:
>> 
>>    register auto   long long   *const p;
>>    |------------|  |-------|   |------|
>>    storage class     type     declarator
>> 
>
> I would say that the key difference is that storage class specifiers
> affect the placement, lifetime, linkage and scope of the object, while
> the qualifiers affect how the object is accessed.

That's a neat summary though it contains the name/object confusion that
I so dislike!  I'd say

| The key difference is that storage class specifiers affect the
| placement and lifetime of the object as well the linkage and scope of
| the name.  The qualifiers affect how the object is accessed.

> Thus it can make
> sense to access different parts of a struct in different ways (const,
> volatile), but it does not make sense to have different parts of the
> struct have different lifetimes or be in different places.

Yes, that's what I was rather tangentially getting at by pointing out
the syntactic difference.  C embodies this distinction in its syntax by
not permitting storage class specifiers in struct declarations.

-- 
Ben.

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Thread

volatile in struct member Thiago Adams <thiago.adams@gmail.com> - 2016-09-30 04:52 -0700
  Re: volatile in struct member Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-09-30 05:50 -0700
    Re: volatile in struct member Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-30 14:42 +0100
      Re: volatile in struct member Gareth Owen <gwowen@gmail.com> - 2016-09-30 22:09 +0100
        Re: volatile in struct member Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-30 22:24 +0100
  Re: volatile in struct member Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-30 14:29 +0100
    Re: volatile in struct member David Brown <david.brown@hesbynett.no> - 2016-09-30 16:22 +0200
      Re: volatile in struct member Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-30 15:51 +0100
        Re: volatile in struct member David Brown <david.brown@hesbynett.no> - 2016-09-30 17:07 +0200
    Re: volatile in struct member Tim Rentsch <txr@alumni.caltech.edu> - 2016-10-08 15:48 -0700
  Re: volatile in struct member David Brown <david.brown@hesbynett.no> - 2016-09-30 15:36 +0200
    Re: volatile in struct member Thiago Adams <thiago.adams@gmail.com> - 2016-09-30 06:47 -0700
      Re: volatile in struct member James Kuyper <jameskuyper@verizon.net> - 2016-09-30 12:53 -0400
        Re: volatile in struct member supercat@casperkitty.com - 2016-09-30 10:18 -0700
          Re: volatile in struct member raltbos@xs4all.nl (Richard Bos) - 2016-09-30 20:57 +0000
            Re: volatile in struct member supercat@casperkitty.com - 2016-09-30 14:46 -0700
        Re: volatile in struct member Thiago Adams <thiago.adams@gmail.com> - 2016-09-30 10:22 -0700
          Re: volatile in struct member jameskuyper@verizon.net - 2016-09-30 14:08 -0700

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