From: Jeffrey Carter <spam@spam.com>
Subject: Re: how to declare a accss type in ada as C's generic pointer
Date: Fri, 10 Dec 2004 01:02:05 GMT
Date: 2004-12-10T01:02:05+00:00 [thread overview]
Message-ID: <hA6ud.6489$yr1.4798@newsread3.news.pas.earthlink.net> (raw)
In-Reply-To: <cp8s17$u2$1@netnews.hinet.net>
bubble wrote:
>
> enum message_type{singer_name=6,music_size=7,playTime=11}
> int querySongStatus(int message_type,char * message ,int
> max_message_length,int * message_length,void * Num);
>
> in Ada.I rewrite it and import it to ada. such as
>
> package work is
> pragma Liner_Options("-lmymusic32");
> type message_type is (singer_name,music_size,play_time);
> subtype myString is string(1..300);
> type mystring_access is access all mystring;
> type integer_access is access all integer;
> function query_Song_Status(
> msg_type:message_type;
> message:mystring;
> max_message_length:integer;
> message_length:integer_access;
> Num:System.address);
> pragma Conversion(C,mystring);
> pragma COnversion(C,integer_access);
> pragma import(Stdcall,query_Song_Status,"querySongStatus");
> private
> for message_Type use (
> singer_name=>6;
> music_size=>7;
> playTime=>11);
> end work;
>
> in C,if I want to query singer name then
> char * name = (char *)malloc (sizeof(char) * 300);
> int length=0;
> //I must pass a char pointer to querySongStatus..
> querySongStatus(singer_name,name,300,&length,null);
> else if I want to query song's disk size then
> int diskByte=0;
> //I must pass a integer pointer to last parameter
> querySongStatus(music_size,null,0,null,&diskByte);
> else if I want to query a song's play time then
> float totalTime;
> //I must pass float pointer to last parameter
> querySongStatus(playTime,null,0,0,&totalTime);
>
> the last parameter is generic pointer,
> the C's function will cast the generic pointer to another type pointer
> according to what the first parameter is?
There are a lot of options, but probably the best is to hide the control
coupling:
procedure Query (Singer_Name : out String; Last : out Natural);
procedure Query (Size : out Natural);
procedure Query (Play_time : out Float);
Each of these would call the same C function, but declared differently
in Ada:
type Dummy_Ptr is access all Integer;
pragma Convention (C, Dummy_Ptr);
procedure Query (Singer_Name : out String; Last : out Natural) is
use Interfaces.C;
Kind_Value : constant := 6;
function C_Query (Kind : Int;
Name : Char_Array;
Name_Length : Int;
Length : access Int;
Dummy : Dummy_Ptr := null)
return Int;
pragma Import (Stdcall, C_Query, "querySongStatus");
...
Result := C_Query (Kind_Value, Buffer, Buffer'Length, Length'access);
For the other versions, you'd use Dummy_Ptr for the Name and Length
parameters, and an appropriate access parameter with an appropriate name
for the last parameter:
function C_Query (Kind : Int;
D1 : Dummy_Ptr;
D2 : Int;
D3 : Dummy_Ptr;
Size : access Int) return Int;
Result := C_Query (Kind_Value, null, 0, null, Local'access);
--
Jeff Carter
"Blessed are they who convert their neighbors'
oxen, for they shall inhibit their girth."
Monty Python's Life of Brian
83
next prev parent reply other threads:[~2004-12-10 1:02 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-12-09 6:29 how to declare a accss type in ada as C's generic pointer bubble
2004-12-10 1:02 ` Jeffrey Carter [this message]
2004-12-15 13:48 ` David Botton
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