Unchecked conversion of arrays?

Unchecked conversion of arrays?

[Björn Persson]

Let's say I have a Wide_String that I need to convert to an array of 
bytes. Each byte will of course contain half a Wide_Character, with the 
other half in the next byte. Will I have to copy one character at a time 
or is there a faster way to do this with representation clauses or 
something? I'm thinking Unchecked_Conversion won't be reliable, because 
if for example the byte array is packed and Wide_String is not, then (on 
a 32-bit machine) I'll get two bytes of garbage between every two bytes 
of character data.

-- 
Björn Persson

jor ers @sv ge.
b n_p son eri nu

Re: Unchecked conversion of arrays?

[Wojtek Narczynski]

Bj�rn,

> I'm thinking Unchecked Conversion won't be reliable, because 
> if for example the byte array is packed and Wide String is not, then (on 
> a 32-bit machine) I'll get two bytes of garbage between every two bytes 
> of character data.

Wide_String is packed, says gnatpsta. I don't know if it is part of
the standard.

Unchecked_Conversion will check sizes for you, so I don't think you
need to worry about garbage.

You do need to remember about endian-ness, though.

Regards,
Wojtek

Re: Unchecked conversion of arrays?

[Georg Bauhaus]

Wojtek Narczynski <wojtek@power.com.pl> wrote:
:> I'm thinking Unchecked Conversion won't be reliable, because 
:> if for example the byte array is packed and Wide String is not, then (on 
:> a 32-bit machine) I'll get two bytes of garbage between every two bytes 
:> of character data.
 
 
: Unchecked_Conversion will check sizes for you, so I don't think you
: need to worry about garbage.

Maybe this article is helpful here:
 http://www.adapower.com/lang/accessmem.html
 
: You do need to remember about endian-ness, though.


-- Georg

Re: Unchecked conversion of arrays?

[Jeffrey Carter]

Wojtek Narczynski wrote:

> Wide_String is packed, says gnatpsta. I don't know if it is part of
> the standard.

ARM A.1 has the specification of Standard, which contains the following:

type Wide_String is array(Positive range <>) of Wide_Character;
pragma Pack(Wide_String);

-- 
Jeff Carter
"Sir Robin the-not-quite-so-brave-as-Sir-Lancelot,
who had nearly fought the Dragon of Angnor,
who nearly stood up to the vicious Chicken of Bristol,
and who had personally wet himself at the
Battle of Badon Hill."
Monty Python & the Holy Grail
68

Re: Unchecked conversion of arrays?

[Björn Persson]

Jeffrey Carter wrote:

> ARM A.1 has the specification of Standard, which contains the following:
> 
> type Wide_String is array(Positive range <>) of Wide_Character;
> pragma Pack(Wide_String);

Aha, thanks. I only looked at 3.6.3 (String Types), which didn't say 
anything about packing.

-- 
Björn Persson

jor ers @sv ge.
b n_p son eri nu

Re: Unchecked conversion of arrays?

[Nick Roberts]

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"Bj�rn Persson" <spam-away@nowhere.nil> wrote in message
news:7_Soc.92431$dP1.290953@newsc.telia.net...

Let's say I have a Wide_String that I need to convert to an array of
bytes. Each byte will of course contain half a Wide_Character, with the
other half in the next byte. Will I have to copy one character at a time
or is there a faster way to do this with representation clauses or
something? I'm thinking Unchecked_Conversion won't be reliable, because
if for example the byte array is packed and Wide_String is not, then (on
a 32-bit machine) I'll get two bytes of garbage between every two bytes
of character data.

Have you considered using streams and Wide_String'Write?

-- 
Nick Roberts