Re: Usage of Ada.Streams

["David C. Hoos, Sr." <david.c.hoos.sr@ada95.com>]

Joerg Ruedenauer <ruedenjg@trick.informatik.uni-stuttgart.de> wrote in
message news:862lc7$s8a$1@inf2.informatik.uni-stuttgart.de...
> Hello there,
>
> I don't quite know how to use Ada.Streams to read Objects using
> dispatching.
> To be specific, I have a private tagged type, say Data, and want to
> read/write Objects derived from that type. Writing works fine like this:
> Data_Pointer: PData; -- an access all Data'class
> Str: Stream_Access;
> ...
> Data'Class'Write(Str, Data.all);
> But I can't find a solution to read the objects equally nice. From the
> Ada95 Rationale I gather I should use 'Input and 'Output somehow, but I'm
> just missing an example. Could anyone help me?
>
If you want to have the tags in the stream (so that the specific
types can be distinguished when reading back), you need to use:
Data'Class'Output(Str, Data_Pointer.all);

Then, to read them back, you would say:
Data_Pointer := new Data'Class'(Data'Class'Input (str));

That statement allocates memory for the object, and initializes it
with the value read from the stream.