Re: for S'Image use Func??

[Warren <ve3wwg@gmail.com>]

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Dmitry A. Kazakov expounded in
news:1x8q3p2gvm9fh.aru6nueicagd$.dlg@40tude.net: 

> On Tue, 11 May 2010 20:56:11 +0000 (UTC), Warren wrote:
> 
>> Dmitry A. Kazakov expounded in news:1qfu2ba65pd63$.asc7m201hi6u$.dlg@
>> 40tude.net:
>> 
>>> On Tue, 11 May 2010 17:17:38 +0000 (UTC), Warren wrote:
>>> 
>>>> =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?= =?utf-8?Q?=29?=
>>>> expounded 
>> in
>>>> news:op.vcig7go1ule2fv@garhos: 
>>>> 
>>>>> Le Mon, 10 May 2010 22:56:11 +0200, Maciej Sobczak  
>>>>> <see.my.homepage@gmail.com> a écrit:
>>>>>> Coming back to I/O - what I miss in Ada is the equivalent of
>>>>>> fread 
>> in
>>>>>> C - that is, an operation that reads *up to* the given number of
>>>>>> bytes. Or maybe there is something that I didn't notice?
>>>> 
>>>>> It's there : look at [ARM 2005 13.13.1] which defines the package 
>>>>> Ada.Streams, which in turn contains the following :
>>>>> 
>>>>>     type Root_Stream_Type is abstract tagged limited private;
>>>>>     ...
>>>>>     type Stream_Element is mod implementation-defined;
>>>>>     ...
>>>> ...
>>>>> Well, to be honest, this is not exactly the same as with C, as  
>>>>> Ada.Streams.Stream_Element is implementation defined (which is
>>>>> good,  because this is indeed platform dependent), so you will
>>>>> need .. 
>>>> 
>>>> All this is well and good for applications that can work in 
>>>> "implementation defined" units of type Stream_Element. A pragma
>>>> won't fix the problem should it be different than a byte. Granted,
>>>> it will never likely come up on the platforms I have in mind.
>>> 
>>> If you to read a character stream, just do so:
>>> 
>>>    Item := Character'Read (S);
>>>    Character'Write (S, Item);
>>> 
>>> For octet streams use Unsigned_8.
>> 
>> But this has to include seeking in the stream as well.
> 
> Repeat reading n times.
> 
>> Can you guarantee seeking to an arbitrary "byte boundary"?
> 
> On a machine with 13 bis per character? Can you define "byte
> boundary"? The point is that if Stream_Element is not 8 bits, and the
> environment supports streams of octets, then I see no reason why Ada
> vendor would implement Unsigned_8r'Read incompatible with that.

On those machines, you're not going to have standard C I/O
either. That's an purely academic case.

But the issue I am taking, are machines that define multiples
of a byte.

Warren