Is the string returned by DECRQSS supposed to be usable?

[vefatica]

In CMD, the second line below contains the response from DECRQSS.

It doesn't look much like DECSTBM. Is it supposed to be usable. A sequence modelled after it does nothing.

If I'm not interpreting it correctly, how should I interpret it? Is there anything useful in it besides the 1 and the 42?

DECSTBM does work.

[DHowett]

There is no guarantee that reports are generated in the same format you would use to set the associated property.

Each report has its own format. Parse it.

[vefatica]

Is there some point to the format of the information returned by DECRQSS? If not, it might as well just return top;bottom. OTOH, if it's cryptically telling me to use DECSTBM I'd like to know how to figure that out.

[j4james]

The response format is documented here: https://vt100.net/docs/vt510-rm/DECRPSS.html

Although they've got the Ps parameter backwards: 1 indicates a valid request, and 0 indicates an invalid request.

[DHowett]

I am sure there is a point that was relevant to applications running in DEC terminals.

The little-r in the DECRPSS (response) tells you that--yes--it is a response that indicates the current values of DECSTBM. You should be using DECSTBM if you want to set the current value of the top and bottom margins to be the top and bottom margins.

You also know this because you queried it using little-r.

The table beneath the docs for DECRQSS includes this fragment:

Setting	Mnemonic	Final Character
Set Top and Bottom Margins	DECSTBM	r

telling me to use DECSTBM

However, I don't understand what you're asking.

You are querying the current values of the margin.

The margin is currently set to those values.

Why would it be telling you to set them? They are already set.

You don't ask somebody what time it is and then when they say "it's 2:30" tell them "okay so set your clock to 2:30". They were the source of the information, not the destination.

[DHowett]

In general, you make a request via DECRQSS and provide a control function. That is r for the margin, m for the graphic rendition, *| for the number of lines per each screen, etc. (pretty much any CSI). It then tells you, in the DECRPSS response, the current value of that control function.

When you ask for m (graphic rendition), it tells you the current value of m (graphic rendition).

[vefatica]

Thanks @j4james .

My only recent experience with such queries was using OSC sequences to get the (whole) current palette (thanks for a lot of help there, @DHowett). IIRC, the response there was a usable string. I just assumed ...