[Info-vax] Example of random access by record number on an RMS fixed record size, relative organization file?

[Arne Vajhøj]

On 9/20/2023 7:39 PM, Arne Vajhøj wrote:
> On 9/20/2023 8:22 AM, Simon Clubley wrote:
>> On 2023-09-20, Arne Vajhøj <arne at vajhoej.dk> wrote:
>>> On 9/19/2023 11:15 PM, gah4 wrote:
>>>> On Tuesday, September 19, 2023 at 5:46:29?PM UTC-7, Arne Vajhøj wrote:
>>>>> open(unit=1,file='rel.dat',status='new',form='formatted',
>>>>> + organization='relative',recl=512,recordtype='variable',
>>>>> + access='direct')
>>>> OP asked about fixed record size, and traditionally that is
>>>> the way it was done.  I haven't followed that detail of later
>>>> Fortran standards. They have to, at least, allocate to the
>>>> maximum size.
>>>
>>> True.
>>>
>>> I added a little more for my example.
>>>
>>> If I understand the docs correctly then the above
>>> allocates 512 bytes (per recl) for each cell, but
>>> handles actual lengths 0-512 within that cell.
>>
>> It allocates 512 bytes for the _data_ within that cell. It then allocates
>> a bit more per record to store the length of each record. Look at the
>> example Hein posted.
>>
>> $ set response/mode=good_natured
>>
>> Even without your statement about never having used relative files,
>> at this point I would be actively suspecting that to be the case. :-)
>>
>> I _have_ used relative files in the past in a number of cases, but I have
>> never, ever, used anything other than fixed length records with them.
>>
>> The idea of variable length records within a relative file is utterly
>> alien to me.
> 
> Maybe.
> 
> I could have used fixed:
...
> But the point was to illustrate usage of relative files.
> 
> The code above is a very poor illustration of relative files.
> 
> Because there is nothing relative specific in it. The exact same code
> works fine with:
>     organization='sequential'
> 
> Direct access for rfm fixed works fine even for org sequential. No need
> for org relative.
> 
> Direct access for rfm variable does not work for org sequential only
> for org relative.

Alternatively I could have used non-existing records
to illustrate relative.

$ type rel3wrt.for
       program rel3wrt
       integer*4 i
       character*20 buf
       open(unit=1,file='rel.dat',status='new',form='formatted',
      +     organization='relative',recl=20,recordtype='fixed',
      +     access='direct')
       do 100 i = 1, 100, 2
         write(buf,'(14HThis is line #,i4.4,2H!!)') i
         write(unit=1,rec=i) buf
100   continue
       close(unit=1)
       end
$ for rel3wrt
$ link rel3wrt
$ run rel3wrt
$ type rel3rdseq.for
       program rel3rdseq
       integer*4 i
       character*20 buf
       open(unit=1,file='rel.dat',status='old',form='formatted',
      +     organization='relative',recl=20,recordtype='fixed',
      +     access='sequential')
100   read(unit=1,fmt='(a)',end=200) buf
       write(*,*) '|'//buf//'|'
       goto 100
200   close(unit=1)
       end
$ for rel3rdseq
$ link rel3rdseq
$ run rel3rdseq
|This is line #0001!!|
|This is line #0003!!|
...
|This is line #0099!!|
$ type rel3rddir.for
       program rel3rddir
       integer*4 i
       character*20 buf
       open(unit=1,file='rel.dat',status='old',form='formatted',
      +     organization='relative',recl=20,recordtype='fixed',
      +     access='direct')
       do 200 i = 1, 100
         read(unit=1,fmt='(a)',rec=i, err=200) buf
         write(*,*) '|'//buf//'|'
200   continue
       close(unit=1)
       end
$ for rel3rddir
$ link rel3rddir
$ run rel3rddir
|This is line #0001!!|
|This is line #0003!!|
...
|This is line #0099!!|

which can be done for org sequential but quite as nice:

$ type seq3wrt.for
       program seq3wrt
       integer*4 i
       character*20 buf
       open(unit=1,file='seq.dat',status='new',form='formatted',
      +     organization='sequential',recl=20,recordtype='fixed',
      +     access='direct')
       do 100 i = 1, 100, 2
         write(buf,'(14HThis is line #,i4.4,2H!!)') i
         write(unit=1,rec=i) buf
100   continue
       close(unit=1)
       end
$ for seq3wrt
$ link seq3wrt
$ run seq3wrt
$ type seq3rdseq.for
       program seq3rdseq
       integer*4 i
       character*20 buf
       open(unit=1,file='seq.dat',status='old',form='formatted',
      +     organization='sequential',recl=20,recordtype='fixed',
      +     access='sequential')
100   read(unit=1,fmt='(a)',end=200) buf
       if(buf(1:1).ne.char(0)) then
         write(*,*) '|'//buf//'|'
       end if
       goto 100
200   close(unit=1)
       end
$ for seq3rdseq
$ link seq3rdseq
$ run seq3rdseq
|This is line #0001!!|
|This is line #0003!!|
...
|This is line #0099!!|
$ type seq3rddir.for
       program seq3rddir
       integer*4 i
       character*20 buf
       open(unit=1,file='seq.dat',status='old',form='formatted',
      +     organization='sequential',recl=20,recordtype='fixed',
      +     access='direct')
       do 200 i = 1, 100
         read(unit=1,fmt='(a)',rec=i,err=200) buf
         if(buf(1:1).ne.char(0)) then
           write(*,*) '|'//buf//'|'
         end if
200   continue
       close(unit=1)
       end
$ for seq3rddir
$ link seq3rddir
$ run seq3rddir
|This is line #0001!!|
|This is line #0003!!|
...
|This is line #0099!!|

Arne