Re: Diffrence between a sequential binairies file and direct binairies file

Re: Diffrence between a sequential binairies file and direct binairies file

[Nick Roberts]

On Sat, 7 Sep 2002 09:52:13 -0400, "Dominic D'Apice" <dapiced@sympatico.ca>
strongly typed:

>Hello all,
> 
>Can someone can explain what is the main difference between a sequential
>binairies file and direct binairies file ?
> 
>Thank
>Dominic

Technically, the difference is that a sequential binary file is accessed
sequentially, and a direct binary file is accessed directly. Which probably
doesn't answer your question.

In Ada, if you were use Ada.Sequential_IO(T) to write out a file (of data
of type T), and then Ada.Direct_IO(T) to read it back in again, it might
work or it might not. The reason why is that on some systems the data
format used by one package could well be different to that used by the
other (and is entitled to be by the Ada language standard). This is
especially likely, in practice, if type T is indefinite.

As far as a typical modern OS is concerned, it is most likely there is no
distinction between sequential and direct binary files (they are all
randomly accessible, and often memory-mapped anyway).

-- 
Nick Roberts

Re: Diffrence between a sequential binairies file and direct binairies file

[Georg Bauhaus]

Dominic D'Apice <dapiced@sympatico.ca> wrote:
: Can someone can explain what is the main difference between a sequential
: binairies file and direct binairies file ?

If I understand your question correctly, one difference is the
way of access to the elements making up the file. With sequential
files you can read one element after the other, if the file has
been opend with mode In_File. If it has been opened with mode
Out_File, you can write one element after the other.

With direct access files, you can, for example, choose which
element you want to read, directly, without having to read the
sequence of elements before this element.  There is more information
about this the reference manual, see A.8.

-- Georg