| Re: IDL_MakeStruct() [message #16317] |
Wed, 14 July 1999 00:00 |
Nigel Wade
Messages: 286
Registered: March 1998
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Senior Member |
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Chutter wrote:
>
> I have nested structures in some "c" code which I wish to access in IDL
> via Call_External.
I have only ever done this using LINKIMAGE and DLMs. I can't comment on
whether
it works with CALL_EXTERNAL. I create a temporary variable in and return
the
structures in it.
> Supposedly, the type field of the structure can be:
>
> void *type; /* This may be either a pointer to another
> structure definition, or a simple IDL
> type code (IDL_TYP_*) cast to void
> (e.g. (void *) IDL_TYP_BYTE). If this
> field is NULL, it indicates that IDL
> should search for a structure of the
> given name and fill in the pointer to
> its structure definition. */
>
> from external/export.h
>
This means that there must be a named structure which already exists in
IDL,
then IDL will put in the pointer to its definition. I've only done it
where
the C code creates the named structure, I don't know if it will look up
a named structure created within IDL, I expect it would.
> What is the syntax for using a pointer to another structure definition?
> The following simple example uses NULL for the type, but I want to a
> pointer to another structure definition so that I can choose the value
> for the name field.
From my experience I think this is what happens.
If you leave type as NULL, then when you create the structure IDL will
search for a named structure with the same name as the tag name. If
you set type to be the result of a call to IDL_MakeStruct then it will
use that structure definition and call it by the name in tag name. So
you can use a different name for the tag.
For example, suppose I define the tags for the structures as:
static IDL_STRUCT_TAG_DEF substruct_tags[] = {
{"P", 0, (void *) IDL_TYP_INT},
{"Q", 0, (void *) IDL_TYP_INT},
{0}
};
static IDL_STRUCT_TAG_DEF s_tags[] = {
{ "MATRIX", matrix_dims, (void *) IDL_TYP_FLOAT},
{ "SUBSTRUCT", substruct_dims, NULL}, /* NULL is a placeholder */
{0}
};
The following will work, and will create FOO with tags MATRIX and
SUBSTRUCT, where SUBSTRUCT contains P and Q:
s = IDL_MakeStruct("SUBSTRUCT", substruct_tags);
s = IDL_MakeStruct("FOO", s_tags);
This will fail because when FOO is built there is no structure called
SUBSTRUCT
s = IDL_MakeStruct("BAR", substruct_tags);
s = IDL_MakeStruct("FOO", s_tags);
However, this will work:
s = IDL_MakeStruct("BAR", substruct_tags);
s_tags[1].type = s;
s = IDL_MakeStruct("FOO", s_tags);
FOO still contains tags MATRIX and SUBSTRUCT even though SUBSTRUCT
was built from the structure named BAR.
I've only ever done this inside a LINKIMAGE/DLM routine, so I don't know
what happens when you call IDL_ImportNamedArray from CALL_EXTERNAL.
>
> Thanks for help.
>
No problem.
--
-----------------------------------------------------------
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
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