the maximum memory size allowed in malloc

[Ben Pfaff]

Re: the maximum memory size allowed in malloc

Chris Croughton <chris@keristor .net> writes:
[color=blue]
> On Wed, 26 Jan 2005 02:13:56 GMT, CBFalconer
> <cbfalconer@yah oo.com> wrote:
>[color=green]
>> The C90 standard guarantees that you can get at least one object 32
>> kBytes in size, and this may be static, dynamic, or automatic
>> memory. C99 guarantees at least 64 kBytes. For any higher limit,
>> see your system documentation, and the results are off-topic here.[/color]
>
> Where are those in the standard(s)? I had a long look and couldn't see
> them.[/color]

Here's what C99 says:

5.2.4.1 Translation limits
1 The implementation shall be able to translate and execute at least one program that
contains at least one instance of every one of the following limits:13)
....
- 65535 bytes in an object (in a hosted environment only)
[color=blue]
> Hmm, it seems that there can't be a compliant C99 implementation for
> small processors any more (and that seems like a totally artificial
> requirement, what in the standard requires objects of 64KB?).[/color]

The requirement applies only to hosted implementations .
--
"The way I see it, an intelligent person who disagrees with me is
probably the most important person I'll interact with on any given
day."
--Billy Chambless

[Andrey Tarasevich]

Re: the maximum memory size allowed in malloc

Lawrence Kirby wrote:[color=blue]
> ...[color=green]
>> Also, in a real-life implementation it is quite possible that the actual
>> range of sizes 'malloc' can handle is smaller than the range if 'size_t'
>> type. It is possible that an implementation aliases types 'ptrdiff_t'
>> and 'size_t' to integral types with the same number of bits in value
>> representation.[/color]
>
> Yes, that is typical although not required.
>[color=green]
>> The former type is signed and the latter is unsigned.
>> This automatically means that character array size (or, more generally,
>> object size) in such implementation cannot be greater than SIZE_MAX/2.[/color]
>
> No, there is no requirement that ptrdiff_t be able to represent all
> possible object sizes, it is simply the type of the result you get when
> you take the difference of 2 pointers. The implication of this, which
> is one with real-world consequences, is that taking the difference of two
> pointers to elements of the same array isn't always valid; it can
> result in undefined behaviour.[/color]

That's the case indeed. I missed this important detail. Thanks for
pointing this out. I assumed that 'ptrdiff_t' is required to always be
able to represent the difference between two pointers pointing to
elements of the same array.

--
Best regards,
Andrey Tarasevich

[CBFalconer]

Re: the maximum memory size allowed in malloc

Chris Croughton wrote:[color=blue]
> <cbfalconer@yah oo.com> wrote:
>[color=green]
>> The C90 standard guarantees that you can get at least one object
>> 32 kBytes in size, and this may be static, dynamic, or automatic
>> memory. C99 guarantees at least 64 kBytes. For any higher limit,
>> see your system documentation, and the results are off-topic here.[/color]
>
> Where are those in the standard(s)? I had a long look and couldn't
> see them.[/color]

I don't know exactly, but they are there. Maybe if you grep for
minimum you will find it? Where is Dan Pop when needed? :-[
[color=blue]
>
> Hmm, it seems that there can't be a compliant C99 implementation for
> small processors any more (and that seems like a totally artificial
> requirement, what in the standard requires objects of 64KB?).[/color]

Twas ever so. Embedded and small systems generally know their own
requirements and limitations.

--
"If you want to post a followup via groups.google.c om, don't use
the broken "Reply" link at the bottom of the article. Click on
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"Reply" at the bottom of the article headers." - Keith Thompson

[S.Tobias]

Re: the maximum memory size allowed in malloc

Ben Pfaff <blp@cs.stanfor d.edu> wrote:[color=blue]
> Chris Croughton <chris@keristor .net> writes:[/color]
[color=blue][color=green]
> > On Wed, 26 Jan 2005 02:13:56 GMT, CBFalconer
> > <cbfalconer@yah oo.com> wrote:
> >[color=darkred]
> >> The C90 standard guarantees that you can get at least one object 32
> >> kBytes in size, and this may be static, dynamic, or automatic
> >> memory. C99 guarantees at least 64 kBytes. For any higher limit,
> >> see your system documentation, and the results are off-topic here.[/color]
> >
> > Where are those in the standard(s)? I had a long look and couldn't see
> > them.[/color][/color]

Me too.
[color=blue]
> Here's what C99 says:[/color]
[color=blue]
> 5.2.4.1 Translation limits
> 1 The implementation shall be able to translate and execute at least one program that
> contains at least one instance of every one of the following limits:13)
> ...
> - 65535 bytes in an object (in a hosted environment only)[/color]

But this doesn't say that the object must come from malloc(), which was
in the original question; it could just as well be "char ca[65535]".
Would an malloc() which always returns NULL violate the Standard?

--
Stan Tobias
mailx `echo siXtY@FamOuS.Be dBuG.pAlS.INVALID | sed s/[[:upper:]]//g`

[pete]

Re: the maximum memory size allowed in malloc

S.Tobias wrote:
[color=blue]
> Would an malloc() which always returns NULL violate the Standard?[/color]

No.

--
pete