Re: [Q]: arrays into mmap'ed memory

[jsa@alexandria (Jon S Anthony)]

In article <32249A94.4A0A@joy.ericsson.se> Jonas Nygren <jonas@joy.ericsson.se> writes:

> Can anybody help me with how to use mmap'ed memory in Ada. What I want
> to do is mmap a large file and then access parts of the so mapped 
> memory via arrays.

One obvious hack:

    -- Don't create an instance of this or you'll blow out with storage
    -- error or something.  It's just to get a template...
    --
    type my_mmarray_type is array (0..natural'last) of whatever;

    -- Probably should really use Interfaces.C.Pointer stuff, but this
    -- gives the idea...
    --
    type my_mmarray_ref  is access all my_mmarray_type;

    the_file : my_mmarray_ref := address from mmap

You use the len from mmap to get the bounds just like for C.  In your
case, _whatever_ would most likely be Character.  A somewhat nicer
approach would be:

    type my_mmarray_type is array (natural range <>) of character;

    -- Prior to entering the following declarative region call the mmap
    -- function getting the address and len stuff.

    subtype mm_index_type is natural range 0..len;

    -- Create _constrained_ subtype.
    --
    subtype actual_mmarray_type is my_mmarray_type(mm_index_type);
    type actual_mmarray_ref is access all actual_mmarray_type;

    the_file : actual_mmarray_ref := pa;

    ...

begin
    ...
    -- Now you can proceed to write bounds independent stuff:
    --
    for I in mm_index_type'range loop
        text_io.put(the_file(i));
    end loop;

    -- etc.

/Jon
-- 
Jon Anthony
Organon Motives, Inc.
1 Williston Road, Suite 4
Belmont, MA 02178

617.484.3383
jsa@organon.com