| Returning C struct to IDL [message #30692] |
Thu, 09 May 2002 14:54 |
K Banerjee
Messages: 14
Registered: September 2001
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Junior Member |
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Folks,
Here's the platform info:
IDL version 5.3
RedHat Linux
g++ 2.95.2 and g++ 2.96
I have to get IDL to use a C function to read a data
file. This C function returns a structure to IDL. I am using IDL's
linkimage facility.
Four of the fields of the structure are arrays of type IDL_STRING
whose lengths depend on the data file to be read, so these lengths
are not known until run time.
Using g++ 2.95.2, this is how I had things set up:
static IDL_LONG dims_user_header[IDL_MAX_ARRAY_DIM];
dims_user_header[0] = 1;
dims_user_header[1] = userHeaderArrayLength;
(userHeaderArrayLength has been determined previously from the data
file.)
IDL_STRUCT_TAG_DEF headerTags[] =
{
{"VERS", 0, (void *) IDL_TYP_STRING},
{"DATATYPE", 0, (void *) IDL_TYP_INT},
{"T", 0, (void *) IDL_TYP_LONG},
{"X", 0, (void *) IDL_TYP_LONG},
{"Y", 0, (void *) IDL_TYP_LONG},
{"Z", 0, (void *) IDL_TYP_LONG},
{"VOXDIMS", dims_4, (void *) IDL_TYP_LONG},
{"USERHEADER", dims_user_header, (void *) IDL_TYP_STRING},
// The first of the 4 variable length arrays --^
.
.
.
{0}
};
Next I define a C struct to match the headerTags array:
typedef struct
{
IDL_STRING vers;
short dataType;
IDL_LONG t;
IDL_LONG x;
IDL_LONG y;
IDL_LONG z;
IDL_LONG voxDims[4];
IDL_STRING userHeader[userHeaderArrayLength];
.
.
.
} vbHeader;
I populate all the fields of the C struct and then have the lines:
void *psDef = IDL_MakeStruct(NULL, headerTags);
IDL_LONG ilDims[IDL_MAX_ARRAY_DIM];
ilDims[0] = 1;
IDL_VPTR ivReturn = IDL_ImportArray(1, ilDims, IDL_TYP_STRUCT,
(UCHAR *) theHeaderActual, NULL, psDef);
return ivReturn;
(The impelmentation of my C function to read the data file is based on
"Calling C From IDL" by Mr. Ronn Kling.)
Everything works as I expect. The problem arises when I try to
compile this function with g++ 2.96. g++ 2.96 has a problem with
the line:
IDL_STRING userHeader[userHeaderArrayLength];
The specific error message is:
size of member `userHeader' is not constant
So I decided to dynamically allocate memory for the userHeader[]
array and changed the troublesome struct field to:
IDL_STRING *userHeader;
Later on I have:
theHeader->userHeader = new IDL_STRING[userHeaderArrayLength];
where theHeader is a pointer to the C struct. I then go ahead
and populate the struct (I am confident I am populating the
C struct properly), go through the same steps to return the struct
to IDL. However, garbage ends up in the userHeader array of the
IDL structure. It seems to me that I can not properly "marry"
a C struct to an IDL structure when the C struct has pointer
fields. I have not come across any example of where
a C struct with pointer fields are returned to IDL.
I have perused the IDL External Development Guide, but have not
found a solution.
Any ideas as to how I can solve my problem? Is it possible to
return a C struct with pointer fields to IDL?
Thanks.
K. Banerjee
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