[SOLVED] Re: converting pointer to value

["Björn Lundin" <b.f.lundin@gmail.com>]

Den 2021-03-04 kl. 18:35, skrev Dmitry A. Kazakov:

Dmitry, this

> 
> You need not to know that:
> 
>     declare
>        P : SQLPOINTER := ...;
>        A : System.Address;
>        pragma Import (Ada, A);
>        for A'Address use P'Address;
>        T : My_Fancy_Object;
>        pragma Import (Ada, My_Fancy_Object);
>        for T'Address use A;
>     begin
>        ... -- Use T at P
> 

combined with

 > This looks wrong because SQLINTEGER is 32-bit. Why do not you use
 > Package System.Storage_Elements.Integer_Address instead, in order to
 > place an integer there?

put me on the right track.
The actual Ada question - rather than ODBC-API question - was how I get 
the value at a certain address.

First - there has to be a pointer to a value - meaning I needed a new 
overload of SqlBindParameter that takes an integer pointer as argument, 
not the integer itself (here called value_pointer)

declare
     L            : SQLULEN := SQLULEN(Length(Tclob));
     Rc           : Sqlreturn := 0;
     Local_Length : Sqllen := Sqllen(Sql_Len_Data_At_Exec(Sqlinteger(L)));
     Length_Pointer   : aliased PTR_SQLLEN     := null;
     Value_Pointer    : aliased PTR_SQLINTEGER := null;
   begin
     Length_Pointer := new Sqllen'(Local_Length);
     Value_Pointer := new SQLINTEGER'(1);

     Rc := Gnu.Db.Sqlcli.Sqlbindparameter
        (Statementhandle  => Statement_Handle,
         Parameternumber  => 1,
         Inputoutputtype  => Sql_Param_Input,
         Valuetype        => Sql_C_Char,
         Parametertype    => Sql_Longvarchar,
         Columnsize       => L,
         Decimaldigits    => 0,
         Value            => Value_Pointer,
         Bufferlength     => 0,
         Strlen_Or_Indptr => Length_Pointer);
     Text_Io.Put_Line("bind clob rc" & Rc'Img);
   end;


then I needed to understand that in call to
Rc := SqlParamdata (Statement_Handle, pvalue'Access);
pvalue itself contains the address of the value_pointer above,
and that I can only tie that address to a variable once the value is known.

   declare
     Rc         :  Sqlreturn := Sqlexecute (Statement_Handle);
     Pvalue     : aliased Sqlpointer;
     Sent       : Integer := 0;
     Datalen    : Integer := 0;
     Buffer_Len : Natural := 0;
     Chunk_Size : Natural := 1024*10; -- 10 k chunks
     S_Ptr      : Ptr_String;
     N          : Positive := 1;
     From,To    : Positive := 1;
   begin
     Text_Io.Put_Line ("Exec: " & Rc'Img);
     -- get address of value_pointer
     Rc := Sqlparamdata (Statement_Handle,Pvalue'Access);
     declare
       Value    : aliased Sqlinteger ;
       Add : System.Address := Gnu.Db.Sqlcli.To_Address(Pvalue);
       for Value'Address use Add;
     begin
       Text_Io.Put_Line ("SQLParamData1: " & Rc'Img );
       --print it and use later on
       Text_Io.Put_Line ("SQLParamData1.2: '" & Value'Img  & "'");
     end;

So now I can putData to clob - I tried 100Mb, and that is all I need.


     -- tclob is an unbounded string containg some Mb of text
     Datalen := Length(Tclob);

     while Sent < Datalen loop
       From := N;
       if Datalen - Sent >= Chunk_Size then
         To := N+ Chunk_Size -1;
       else
         To := N+ Datalen - Sent -1;
       end if;

       Buffer_Len := To - From +1;

       S_Ptr :=  new String'(Slice(Tclob, From, To));
       N := N + Chunk_Size;

       Rc := Sqlputdata(Statementhandle => Statement_Handle,
                        Data            => To_Sqlpointer(S_Ptr),
                        Strlen_Or_Ind   => Sqllen(Buffer_Len));

       Sent := Sent + S_Ptr.all'Length ;

     end loop;
     Rc := Sqlparamdata (Statement_Handle, Pvalue'Access);
     Text_Io.Put_Line ("SQLParamData2.sist: " & Rc'Img);

   end;


I found some API error on my part.
The code above does not use pvalue, but I will need it later on.

Thanks for putting me on the right track




-- 
Björn