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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: wait does not perform as expected
Date: Thu, 23 Feb 2023 20:29:32 +0200
Organization: Tidorum Ltd
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On 2023-02-23 20:14, Dmitry A. Kazakov wrote:
> On 2023-02-23 18:35, Niklas Holsti wrote:
>> On 2023-02-23 16:26, AdaMagica wrote:
>>> Niklas Holsti schrieb am Mittwoch, 22. Februar 2023 um 18:36:06 UTC+1:
>>>> On my system, Get_Immediate does /not/ use the inputs collected (but 
>>>> not
>>>> "consumed") by Look_Ahead, but instead checks if there are _new_ input
>>>> keystrokes. If there are none, Get_Immediate returns "not Available"
>>>> (Hit is False) and so the loop continues.
>>>
>>> Are you sure?
>>
>> That is what I observe.
> 
> The implementation of Look_Ahead calls getc followed by ungetc. Thus it 
> blocks until an input if there is no buffered. And not just input, but 
> for a line or file end.


That seems in order.

However, the crux of the question is in Get_Immediate. Do you know how 
that is implemented on various systems? It has to disable line buffering 
and line editing on the input stream. One question is whether and how 
such "tty" configuration changes affect whatever buffers getc/ungetc use.

On my system, if Look_Ahead uses getc and ungetc, it seems Get_Immediate 
does not use the same buffers, and has no effect on those buffers. That 
could be desirable behaviour in some cases, undesirable in others.

On AdaMagica's system, it seems that Get_Immediate uses the same buffers 
as Look_Ahead (getc/ungetc).