| Re: Pass struct with pointer to array to/from dlm [message #39451] |
Tue, 18 May 2004 01:31 |
Nigel Wade
Messages: 286
Registered: March 1998
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Senior Member |
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Ed Wright wrote:
> To: IDL
> From: Ed Wright
>
> I have a requirement to pass a structure between IDL and a DLM. The
> structure has the form:
>
> struct CELL
>
> { SpiceCellDataType dtype; /* An enum */
> SpiceInt length; /* long */
> SpiceInt size; /* long */
> SpiceInt card; /* long */
> SpiceBoolean isSet; /* long */
> SpiceBoolean adjust; /* long */
> SpiceBoolean init;
> void * base;
> void * data; };
>
> My problem concerns the fields 'base' and 'data'. Normally, these
> contain pointers to arrays of either ints, doubles or an array of
> strings. Is it possible to pass from a DLM to IDL (and back) a struct
> where on field points to an array?
>
> As always,
> Ed Wright
>
Yes, it's perfectly possible (but don't do anything with it in IDL). I do
quite a lot of it.
What I do is store it in a byte array (char in C), of length sizeof(pointer)
to take care of 32/64 bit portability. My code is probably overkill
safetywise, but I like to be sure that what is being passed back into C is
really a C pointer.
This code copies the pointer PI_handle to an IDL byte array.
/*
* create an IDL byte array to hold the pointer.
* this is returned in the third positional parameter.
* the callback for destruction of the variable will free the
* allocated memory.
*/
UCHAR *store;
PI_Strategy *pointer;
dims[0] = sizeof(pointer);
store = (UCHAR *)malloc(dims[0]);
memcpy(store, &pointer, dims[0]);
new_array = IDL_ImportArray(1, dims, IDL_TYP_BYTE,
(UCHAR *)store, idl_PI_strategy_cb, NULL);
IDL_VarCopy(new_array, parameters[3]);
To extract it from argv[0]:
PI_Strategy *pointer;
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 pointer from the IDL byte array into
* the C pointer.
*/
memcpy(&pointer, argv[0]->value.arr->data, sizeof(pointer));
void idl_PI_strategy_cb(unsigned char *arg) {
free(arg);
}
--
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 2523548, Fax : +44 (0)116 2523555
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