| Re: Dynamically creating C++ objects in DLM [message #33452 is a reply to message #33398] |
Thu, 02 January 2003 04:04  |
Nigel Wade
Messages: 286
Registered: March 1998
|
Senior Member |
|
|
Rick Towler wrote:
> It has been a slow day here so maybe this can stir up some passion :)
>
> I have a few .dlm's where I declare a global C++ object and use that
> object
> throughout the dlm. The dlm functions and procedures allow me to
> initialize
> the object, do stuff with it, and destroy it. Easy enough.
>
> The one limitation is that I only have one instance of the object
> available. If I run a second instance of a program that uses that .dlm the
> two IDL programs will overwrite the C++ object causing general mayhem
> (like using a common block in IDL).
>
> A solution to this problem would be dynamically creating the C++ object
> upon
> initialization and returning a pointer to the object back to IDL. When
> calling the dlm routines I could pass the pointer back to my dlm to gain
> access to my object of interest.
A reasonable solution; I do this in several of my DLMs.
>
>
>
> My questions are:
>
> How do I dynamically create a C++ object (I think I use "new" but am a
> little unclear on the correct use)?
>
> myObject *test = new myObject; //?????
Not speaking C++ particularly well, I'd hazzard a guess that that's correct,
it looks ok. My DLM's are all in C.
>
> How do I pass pointers back and forth between my DLM and IDL? Is it as
> simple as passing a long?
>
> return IDL_GetTmpLong(test); //Is it this easy?
I wouldn't recommend this method. There's no guarentee that a long is the
same size as a pointer, or that it will remain so. What I do is to store
the pointer in a byte array which is created the same size as the pointer.
This is an example from one of my DLMs which needs to pass the value of the
pointer PI_handle back to IDL in the 4th positional parameter. Using
IDL_ImportArray allows you to define a callback routine which can free your
allocated memory if the variable stored in IDL is erased, in this case it's
called idl_PI_strategy_cb. Also note that IDL_ImportArray creates a
*temporary* variable, so IDL_VarCopy doesn't allocate new memory; it uses
the memory already allocated by a temp variable :
UCHAR *store;
IDL_VPTR new_array;
IDL_LONG dims[1];
PI_Strategy *PI_handle = NULL;
dims[0] = sizeof(PI_handle);
store = (UCHAR *)malloc( dims[0] );
memcpy( store, &PI_handle, dims[0]);
new_array = IDL_ImportArray( 1, dims, IDL_TYP_BYTE,
store, idl_PI_strategy_cb, NULL );
IDL_VarCopy( new_array, parameters[3] );
I don't know how much of this can be executed directly in C++.
>
>
> If I do pass IDL a long representing my pointer, how do I use it when I
> pass
> it back to my DLM? The compiler sees it as a long, not a pointer to an
> object.
>
> pointer = IDL_LongScalar(argv[0]); //receive the pointer address
> from
> IDL
> *pointer.Test(); //not the way to do it
>
Again, not sure about C++, but in C I use memcpy to copy the data array back
into a pointer:
PI_Strategy *PI_handle;
IDL_ENSURE_ARRAY(argv[0]);
IDL_EXCLUDE_EXPR(argv[0]);
if ( argv[0]->type != IDL_TYP_BYTE ||
argv[0]->value.arr->n_dim != 1 ||
argv[0]->value.arr->dim[0] != sizeof(PI_Strategy *) ||
argv[0]->value.arr->free_cb != idl_PI_strategy_cb )
IDL_Message(IDL_M_NAMED_GENERIC, IDL_MSG_LONGJMP,
"arg 1 is not a valid PI handle.");
/*
* copy the embedded strategy pointer from the IDL byte array into
* the C pointer.
*/
memcpy(&PI_handle, argv[0]->value.arr->data, sizeof(PI_Strategy *));
>
> Thanks for any thoughts.
>
Sorry I don't know C++ well enough to answer the question directly.
Hopefully some of the C code might help though.
--
Nigel Wade, System Administrator, Space Plasma Physics Group,
University of Leicester, Leicester, LE1 7RH, UK
E-mail : nmw@ion.le.ac.uk
Phone : +44 (0)116 2523568, Fax : +44 (0)116 2523555
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
