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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: wait does not perform as expected
Date: Thu, 23 Feb 2023 19:14:38 +0100
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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.

As for ungetc POSIX layer under Windows, ungetc probably does not work 
correctly, I am too lazy to verify. One possibility is that file 
positioning (fseek etc) kill unget buffer.

In any case, subprograms like Look_Ahead, End_Of_File etc exit strictly 
for decoration, not for any practical reason. As a rule of thumb no 
program should ever use them.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de