[Info-vax] CRTL and RMS vs SSIO

[Simon Clubley]

On 2021-10-07, Dave Froble <davef at tsoft-inc.com> wrote:
> On 10/7/2021 8:59 AM, Simon Clubley wrote:
>> On 2021-10-07, Greg Tinkler <tinklerg at gmail.com> wrote:
>>> On Thursday, 7 October 2021 at 11:26:38 pm UTC+11, Simon Clubley wrote:
>>>
>>>> How do you find byte 12,335,456 in a variable length RMS sequential file
>>>> without reading from the start of the file ?
>>>>
>>>> That's why there are restrictions on RMS supported file formats in an
>>>> application in some cases.
>>>
>>> The same way it is done on Unix, calculate the block offset, go get it, and extract the byte.  no difference and nothing to do with the underlying format.
>>>
>>
>> You don't know the block offset without scanning the file when it comes
>> to some RMS file formats.
>>
>> IOW, data byte 12,335,456 will not be the same thing as file byte 12,335,456
>> unless you restrict yourself to record formats that do not have embedded
>> record metadata.
>>
>
> I'm guessing Unix files don't have metadata and such.  So the comparison 
> is not valid.
>

No, Unix doesn't. At Unix filesystem level, files are just a stream of bytes.

The next layer up on Unix is the C RTL. There's nothing like RMS
between the filesystem and the C RTL on Unix.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Walking destinations on a map are further away than they appear.