Re: xor

["Randy Brukardt" <randy@rrsoftware.com>]

"Niklas Holsti" <niklas.holsti@tidorum.invalid> wrote in message 
news:9ti9k2FjcvU1@mid.individual.net...
> On 12-03-29 02:25 , Randy Brukardt wrote:
>> "Niklas Holsti"<niklas.holsti@tidorum.invalid>  wrote in message
>> news:9tgqomFflrU1@mid.individual.net...
>>> On 12-03-28 18:23 , Michael Moeller wrote:
>> ...
>>>> I don't want to push your helpfulness to far, but I still don't
>>>> know whether there is any means to determine the size of a file
>>>> from within Ada other than using a C subroutine calling fstat.
>>>
>>> Two ways:
>>>
>>> - Ada.Directories.Size, given the file name.
>>> - Ada.Direct_IO.Size, given an open (Direct_IO) file.
>>
>> Actually, three ways:
>
> Ok, I showed two ways, but did not mean that there aren't other ways.
>
>> Ada.Stream_IO.Size, given an open (Stream_IO) file.
>
> If "positioning is not supported" for the stream file, the result of 
> Ada.Stream_IO.Size is implementation defined. Positioning is probably 
> supported for the kinds of files the OP uses now, but it is a bit of trap 
> for possible future uses of the program, for example if the program is 
> later used in a shell pipeline. A pipe probably does not support 
> positioning.

I'm pretty sure that if "positioning is not supported" for a particular 
stream file, none of the other mechanisms will provide any useful answers, 
either. That's especially true as most Ada compilers use a common I/O system 
to implement all of these packages, so the effects will be similar on all of 
them.

File for which "positioning is not supported" are likely to be things like 
sockets, pipes, and devices. Those won't have a meaningful size no matter 
how they're accessed. I suppose an implementer could make all stream files 
not support positioning and do something different for Text_IO, but as is 
commonly mentioned, "implementers don't intentionally cripple their 
implementations".

In any case, your point is really just another argument for not depending 
upon the size at all; depending on the sort of file, it may not even be a 
meaningful concept. So depending on the size decreases the utility and 
reusability of your code. That said, the OP knows that and it surely is 
their decision how to write their code.

                                             Randy.