[Info-vax] The best VMS features, was: Re: openvms renaming file

[Johnny Billquist]

On 2018-05-30 01:47, Arne Vajhøj wrote:
> On 5/29/2018 7:41 PM, Simon Clubley wrote:
>> On 2018-05-29, Johnny Billquist <bqt at softjar.se> wrote:
>>> On 2018-05-29 01:16, Arne Vajhøj wrote:
>>>> On 5/28/2018 4:08 PM, Johnny Billquist wrote:
>>>>> Applications could be clever enough to actually refer to fields based
>>>>> on names, instead of just using fixed, known, chunks of the record.
>>>>> RMS do have names for the fields, which you can set and read.
>>>>
>>>> Both keys and values or only keys?
>>>>
>>>> I suspect key info is in XABKEY, but where do you find value info?
>>>
>>> What do you mean by value info? The values are in the individual records
>>> obviously. And the key info will tell you which bytes in the record that
>>> contains the value. Or are you talking about the type of the value?
>>> Which also also stored with they key info.
>>>
>>> Not entirely sure what you are thinking of....
>>>
>>
>> _If_ I understand Arne correctly, he is asking the following:
>>
>> Consider a C struct which is mapped to a RMS record:
>>
>> struct record_type
>>     {
>>     unsigned char primary_key[10];    /* This is the ISAM primary key */
>>     unsigned char value1[5];    /* Data value 1 */
>>     unsigned char value2[7];    /* Data value 2 */
>>     unsigned char value3[10];    /* Data value 3 and an alternate key */
>>     };
>>
>> You can find "primary_key" and "value3" in the key information.
>>
>> Where is value1 and value2 described in the RMS data structures ?
>> value1 and value2 are data fields only and do not have keys on them.
>>
>> IOW, what happens if value1 is extended from 5 bytes to 8 bytes ?
>>
>> This moves the start position of value2 to the right by 3 bytes.
>>
>> What field(s) in the RMS data structures can the application look
>> at to find the new offset to the start of value2 ?
> 
> Yes.

Got it now. Yes, that information will not be in there. You need to have 
all your fields defined as keys in order to have the information there.

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol