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From: Chris <enderx12@my-deja.com>
Newsgroups: comp.lang.ada
Subject: Interface to C; Storage_Error
Date: Tue, 19 Dec 2000 22:28:11 GMT
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Date: 2000-12-19T22:28:11+00:00
List-Id: <comp.lang.ada>

Hi, all... after a long hiatus in the C++ world, I'm finally getting a
chance to do some more Ada work, at my own suggestion. The ability to
write production-quality multithread code an order of magnitude faster
in Ada might have something to do with it.

Anyway, I'm having an irritating problem interfacing with a vendor C
library. The relevant stuff:

  typedef void* SRV_HANDLE;
  typedef void* CTX_HANDLE;
  typedef void* RSLT_HANDLE;
  typedef void* FLT_HANDLE;

   int GetNextVal(SRV_HANDLE srv, RSLT_HANDLE rslt, CTX_HANDLE *ctx,
                  char* name, double* dbl, FLT_HANDLE flt);

My take on it in Ada (GNAT 3.13p) is:

   type Srv_Handle is new System.Address;
   -- same for the other handles

   procedure GetNextVal(Ret  : out int;
                        Srv  : Srv_Handle;
                        Rslt : Rslt_Handle;
                        Ctx  : access Ctx_Handle;
                        Name : out chars_ptr;
                        Dbl  : access double;
                        Flt : Flt_Handle);
   pragma Import(C, GetNextVal);
   pragma Import_Valued_Procedure(GetNextVal);

Both Name and Dbl are supposedly set/alloc'd by the library. When I
call this, it raises Storage_Error on the library call. I am totally
stumped as to what to fix, or even where to look. Is my Ada declaration
even remotely correct?
Other suggestions?


Many thanks.

--chris


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