cc: [email protected]
Subject: Re: Re: [ast-developers] ksh: problem with arrays
--------
> >
> > This bug was already reported and is fixed for the first bug fix release of
> > ksh93u which will be distributed this quarter.
> >
> > The problem is that the declaration
> >
> > typeset xx[7];
> >
> > is incorrectly treating xx as a fixed size array of size 7 and currently
> > fixed sized arrays only for for fixed sized objects. The declaration for
> > fixed size arrays should be
> > typeset -a xx[7];
> > and the declaration
> > typeset xx[7];
> > is not even necessary, but should not have been treated as a fixed array.
>
> I'll have to answer some questions, so I'd like to confirm a few things.
>
> 1) It is expected that typeset xx[7]; creates array with one empty element
> [7] s
> o
> ${#xx[@]} is really expected to be 1 despite all other shells I've tested
> don't
> create that
> element, so they report zero. Old ksh reported 0 too, this changed between
> 2008-10-01 and 2008-10-10, but I did not find anything about this in RELEASE
> fil
> e.
> This was original complain I've got so I'd like to be sure this is expected
> befo
> re I tell
> it to our users :)
No, this was caused by the fixed array bug.
typeset xx[7]
just creates an indexed array with at least 7 elements and none are set
${#xx[@]} should be 0. This is a bug and will be fixed.
There is no need to declare index arrays since any variable becomes
an array when a subscript > 0 is assigned. For large arrays
typeset xx[100000]
will improve performance slightly since the array doesn't have to grow
dynamically.
>
> 2) I was looking for fixed arrays at ksh man page (just searched for 'fixed'
> key
> word),
> but did not find anything. So I've looked at RELEASE file and I've found
> fixed a
> rrays
> mentioned only once (10-09-28):
>
> > ... It allows fixed sized indexed arrays be to defined
> > using "typeset array[dim1][dim2]...[dimn]". ...
>
> so should it be typeset -a xx[7] or typeset xx[7] ?
The purpose of fixed arrays was to provide a faster and more memory
efficient array mechanism for applications that did not require
the generality of the current array mechanism which allowed each
element to be different.
Fixed arrays were added as a compile option which is on by default but
not document in the man page. The reason is that it is not complete. It
only works for fixed size objects like integer, float, and typeset -LRZ.
It might be completed in ksh93u. The declaration will be
typeset -a array[dim1][dim2]...[dimn]
For variable objects, there is a debate as to whether unspecifed objects
will be initialized or not. For example, will
typeset -a xx[7]
have xx[i] unset or the empty string. Similarly for arrays of types,
will unset elements of type Foo_t be equivalent to Foo_t xx[i] or will
they be unset? I would interested in your opinions.
>
>
> 3) Is there any document/web page/something about fixed arrays I could
> forward t
> o users
> who ask me about this?
No, but this e-mail exchange is in the mailing list archives and can
be used for further comments and exchange of ideas.
>
>
> And last thing. Cosmetic issue when ksh reports problem "subscript out of
> range"
> . I
> don't care about this, it just looks odd so if there isn't any more serious
> bug
> hidden:
> $ typeset -a -i xx[7]
> $ xx[8]=1
> ksh: xx: subscript out of range
> $ xx[6]=1
> $ xx[8]=1
> ksh: xx[6]: subscript out of range
>
> in first error there is "xx" in second error there is "xx[6]", always the
> last u
> sed (valid)
> index is reported in error message
>
>
> >
> > Therefore the workaround is to delete this declaration
> > or use the declaration
> > typeset -a xx
> > instead. This is also the cause of the core dump you reported with
> > typeset -p.
> >
> > Here is a patch that should fix this problem.
>
> Thanks, now it works the same way as prev. version and typeset -p crash is
> gone
> too
>
David Korn
[email protected]
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