Read booleans from streams

Read booleans from streams

[Erik Sigra]

I tried to read bytes from a stream and interpret each bit as a Boolean. But 
it did not work as expected. It reads 1 byte for each bit. How should I do 
instead?


streamtest.adb
==============
with Ada.Text_IO;           use Ada.Text_IO;
with Ada.Streams;           use Ada.Streams;
with Ada.Streams.Stream_IO; use Ada.Streams.Stream_IO;

procedure Streamtest is
   type Boolean_Aggregate is array (0 .. 7) of Boolean;
   for Boolean_Aggregate'Component_Size use 1;

   Current_Byte : Boolean_Aggregate;

   The_File : Stream_IO.File_Type;

   The_Stream : Stream_Access;

begin

   Open (The_File, In_File, "data");

   The_Stream := Stream (The_File);

   loop
      Boolean_Aggregate'Read (The_Stream, Current_Byte);
      for I in Boolean_Aggregate'Range loop
         Put(Current_Byte (I)'Img & ' ');
      end loop;
      New_Line;
   end loop;
end Streamtest;


data
====
02027203


user > ./streamtest
FALSE FALSE FALSE FALSE TRUE FALSE FALSE TRUE

raised ADA.IO_EXCEPTIONS.END_ERROR : s-stratt.adb:170


I have checked that the size of Boolean_Aggregate is 8 and not 64.

Re: Read booleans from streams

[sk]

Hi,

>raised ADA.IO_EXCEPTIONS.END_ERROR : s-stratt.adb:170

Your loop doesn't do an EOF test.

Your other issue ?

>data
>====
>02027203

Which looks like 

0000_0000,0000_0010,0000_0000,0000_0010,
        ^         ^         ^         ^
        0         0         0         0

0000_0111,0000_0010,0000_0000,0000_0011
        ^         ^         ^         ^
        1         0         0         1


And your results look like 

0 0 0 0 1 0 0 1

Interesting, I havn't checked it but how about 
changing 

"for Boolean_Aggregate'Component_Size use 1;"

to 

"pragma Pack (Boolean_Aggregate);" and if
that doesn't work, try

"for Boolean_Aggregate'Component_Size use 1;"
"for Boolean_Aggregate'Size use 8"; 

if 

"for Boolean_Aggregate'Size use 8"; 

doesn't work by itself.


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Re: Read booleans from streams

[Eric G. Miller]

In <mailman.1017011702.18089.comp.lang.ada@ada.eu.org>, Erik Sigra wrote:

> I tried to read bytes from a stream and interpret each bit as a Boolean. But
> it did not work as expected. It reads 1 byte for each bit. How should I do
> instead?
> 
> 
> streamtest.adb
> ==============
> with Ada.Text_IO;           use Ada.Text_IO;
> with Ada.Streams;           use Ada.Streams;
> with Ada.Streams.Stream_IO; use Ada.Streams.Stream_IO;
> 
> procedure Streamtest is
>    type Boolean_Aggregate is array (0 .. 7) of Boolean;
>    for Boolean_Aggregate'Component_Size use 1;
> 
>    Current_Byte : Boolean_Aggregate;
> 
>    The_File : Stream_IO.File_Type;
> 
>    The_Stream : Stream_Access;
> 
> begin
> 
>    Open (The_File, In_File, "data");
> 
>    The_Stream := Stream (The_File);
> 
>    loop
>       Boolean_Aggregate'Read (The_Stream, Current_Byte);
>       for I in Boolean_Aggregate'Range loop
>          Put(Current_Byte (I)'Img & ' ');
>       end loop;
>       New_Line;
>    end loop;
> end Streamtest;
> 
> 
> data
> ====
> 02027203
> 
> 
> user > ./streamtest
> FALSE FALSE FALSE FALSE TRUE FALSE FALSE TRUE
> 
> raised ADA.IO_EXCEPTIONS.END_ERROR : s-stratt.adb:170
> 
> 
> I have checked that the size of Boolean_Aggregate is 8 and not 64.

I think the problem is in the read procedure.  It sees an array of 8 elements,
so wants to read 8 bytes.  I think you need a 'Read wrapper to read a single
byte (type Byte is mod 2**8), and then do an Unchecked_Conversion:

   function To_Boolean_Aggregate is new
	Ada.Unchecked_Conversion(Byte,Boolean_Aggregate);

   procedure Read_Boolean_Aggregate
        (Stream : Stream_Access; Data : in out Boolean_Aggregate) is
        
        Item : Byte;
   begin
        Byte'Read (Stream, Item);
        Data := To_Boolean_Aggregate (Item);
   end Read_Boolean_Aggregate;

...

   while not End_Of_File (File_Type) loop
        Read_Boolean_Aggregate (Stream, Data);

        ...
   end loop;

Re: Read booleans from streams

[Erik Sigra]

Thanks for your reply!

m�ndagen den 25 mars 2002 03.05 skrev du:
> >raised ADA.IO_EXCEPTIONS.END_ERROR : s-stratt.adb:170
>
> Your loop doesn't do an EOF test.

That was expected. It was the reading I wanted to investigate, so I didn't 
bother with an EOF test.


> >data
> >====
> >02027203
>
> Which looks like
>
> 0000_0000,0000_0010,0000_0000,0000_0010,
>         ^         ^         ^         ^
>         0         0         0         0
>
> 0000_0111,0000_0010,0000_0000,0000_0011
>         ^         ^         ^         ^
>         1         0         0         1
>
>
> And your results look like
>
> 0 0 0 0 1 0 0 1
>
> Interesting, I havn't checked it but how about
> changing

Actually it were the characters '0', '2' and '7' that were stored in the 
file, so it was rather

0001_1000,0001_1010,0001_1000,0001_1010,
        ^         ^         ^         ^
        0         0         0         0
0001_1111,0001_1010,0001_1000,0001_1011
        ^         ^         ^         ^
        1         0         0         1

but that's essentially the same in this matter.


>
> "for Boolean_Aggregate'Component_Size use 1;"
>
> to
>
> "pragma Pack (Boolean_Aggregate);" and if
> that doesn't work, try

I already tried that.


>
> "for Boolean_Aggregate'Component_Size use 1;"
> "for Boolean_Aggregate'Size use 8";

And I tried that too. I even used the test

   Put_Line ("Boolean_Aggregate'Size = " & Boolean_Aggregate'Size'Img);

in the program and it showed "Boolean_Aggregate'Size =  8". I use gnat-3.13p. 
Any other suggestions?

Re: Read booleans from streams

[Erik Sigra]

m�ndagen den 25 mars 2002 04.57 skrev du:
> I think the problem is in the read procedure.  It sees an array of 8
> elements, so wants to read 8 bytes.  I think you need a 'Read wrapper to
> read a single byte (type Byte is mod 2**8), and then do an
> Unchecked_Conversion:
>
>    function To_Boolean_Aggregate is new
> 	Ada.Unchecked_Conversion(Byte,Boolean_Aggregate);
>
>    procedure Read_Boolean_Aggregate
>         (Stream : Stream_Access; Data : in out Boolean_Aggregate) is
>
>         Item : Byte;
>    begin
>         Byte'Read (Stream, Item);
>         Data := To_Boolean_Aggregate (Item);
>    end Read_Boolean_Aggregate;
>
> ...
>
>    while not End_Of_File (File_Type) loop
>         Read_Boolean_Aggregate (Stream, Data);
>
>         ...
>    end loop;

Thanks, it works!

The only problem is that it seems impossible to state
"for Boolean_Aggregate'Read use Boolean_Aggregate_Read;".

Re: Read booleans from streams

[sk]

Hi,

>Actually it were the characters '0', '2' and '7' 
>that were stored in the file, so it was rather
>
>0001_1000,0001_1010,0001_1000,0001_1010,
>        ^         ^         ^         ^
>        0         0         0         0
>0001_1111,0001_1010,0001_1000,0001_1011
>        ^         ^         ^         ^
>        1         0         0         1

Yes, stupid me, CHARACTER not byte, doh ! (Kind
of lucky that there was any correspondence at all :-).


>The only problem is that it seems impossible to state
>"for Boolean_Aggregate'Read use Boolean_Aggregate_Read;".

Have you tried :-

procedure Read_Boolean_Aggregate ( ...);
-- SPEC ONLY

for Boolean_Aggregate'Read use Boolean_Aggregate_Read;".

-- FULL BODY
procedure Read_Boolean_Aggregate (...) is
begin
   ...

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