Re: xor

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 12-03-25 18:16 , Michael Moeller wrote:
> Thank you for your quick answer.
>
> Can I use Unsigned_Byte_T to read in a byte from a file
> as in C? I haven't looked into this yet.

C has several ways to "read in a byte from a file", depending on the 
type of the file and how you specify which byte you want to read. Can 
you be more specific?

If you mean reading an 8-bit octet from a "binary file" -- that is, not 
a text file -- you can use the Ada library packages Ada.Sequential_IO or 
Ada.Direct_IO, depending on your needs. These are generic packages, so 
you must instantiate them for the type of data, for example Unsigned_Byte_T.

If the file contains a mixture of different kinds of "binary" data, for 
example both 8-bit data and 16-bit data, or more complex structures, you 
should use the Ada "stream" facility from Ada.Streams.Stream_IO. The 
stream facility helps you handle things like different endianness, 
padding, packing, unusual encodings, and so on.

The stream facility does not use generics; instead, it uses a 
combination of tagged types and the special "stream attribute" 
operations T'Read, T'Write, et cetera, which you can define differently 
for each type, T, that is present in your file. For example, your 'Read 
operation for a 16-bit integer will specify whether the integer is 
stored in little-endian or big-endian order in the file (by reading two 
8-bit integers, using 'Read for the 8-bit type, in the corresponding order).

The stream technique takes a bit of study to understand, but it works 
very well, especially if the file has a mixture of different complex 
structures of data, or if the file is created by a different language or 
computer and is not in the "native" form for your Ada compiler.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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