Re: Representing data differently

["Martin Krischik" <Martin.Krischik@T-Online.de>]

On Fri, 07 Feb 2003 06:15:18 +0000, Daniel Allex wrote:

> In C I can represent the same data multiple ways using structs and
> unions.  How and can I do this in Ada?  See example below:
> 
> //
> // Example of C's representation clause
> //
> struct MT_37_header
> {
>     short
> 		:4,
> 		nw:6,
> 		mt:6;
>     short
> 		:16;		// place holder
>     short
> 		:16;		// place holder
>     short
>  		:16;		// place holder
> };

Since it is quite dangerous you have to do a lot of typing:

-- snip
    type
        State
    is record
        uninitialized    : Boolean ;
        on               : Boolean ;
        writeLineNumber  : Boolean ;
        writePrefix      : Boolean ;
    end record;

    for
        State
    use record
        uninitialized   at 0 range 0..0;  
        on              at 0 range 1..1;    
        writeLineNumber at 0 range 2..2;   
        writePrefix     at 0 range 3..3;   
    end record;

-- snap

The first statement defines the record, the second defines the layout.
Nothing stops you from placing two record elements at the same position.

with regards

Martin

PS: If you like you can look at the rest of the (unfinished) source as well:

http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/adacl/adacl/Include/AdaCL-Trace.adb

-- 
Martin Krischik
mailto://Martin@krischik.com
http://www.martin.krischik.com