Internal: Creating nested structures in C code linked to IDL with LINKIMAGE

Here is an example on how to create nested structures in C code linked to IDL with LINKIMAGE:

#include <stdio.h>
#include <stdlib.h>
#include "export.h"
 
#ifdef WIN32
 
#include <windows.h>
#include <io.h>
#include <direct.h>
#define IDL_CDECL __declspec(dllexport)
#else
#include <unistd.h>
#endif
 
/* function prototypes */
extern IDL_CDECL IDL_VPTR nested_struct(int, IDL_VPTR *, char *);
 
IDL_CDECL IDL_VPTR nested_struct(int argc, IDL_VPTR argv[], char *argk)
{
 typedef struct mystruct {
 IDL_LONG tag1_data[4];
 float tag2_data;
 IDL_LONG tag3_data;
 IDL_LONG tag4_data;
 } MYSTRUCT;
 
 static IDL_LONG tag1_dims[] = {1,4}; 
 
 void *v;
 static IDL_STRUCT_TAG_DEF m_tags[] = {
 {"TAG1",tag1_dims,(void *) IDL_TYP_LONG},
 {"TAG2",0,(void *) IDL_TYP_FLOAT},
 {"TAG3",0,(void *) IDL_TYP_LONG},
 {"TAG4",0,(void *) IDL_TYP_LONG},
 { 0 }
 }; 
 
 static IDL_LONG one = 1;
 static IDL_STRUCT_TAG_DEF s_tags[5];
 
 typedef struct data_struct {
 IDL_LONG tag1_data[4];
 float tag2_data;
 IDL_LONG tag3_data;
 MYSTRUCT my_data;
 } DATA_STRUCT;
 
 static DATA_STRUCT s_data;
 void *s;
 IDL_VPTR retstruct,retstruct2; 
 char *tstruct, *tstruct2;
 
 /* Before doing anything, store a zero value into the second argument
 this will zero out the memory and make sure that the variable is
 storable (not an expression, str, field, arr subscript). */
 IDL_StoreScalarZero( argv[1], IDL_TYP_INT);
 
 /* Create the structure definition */
 v = IDL_MakeStruct(0, m_tags);
 
 s_tags[0].name = "TAG1";
 s_tags[0].dims = tag1_dims;
 s_tags[0].type = (void *) IDL_TYP_LONG;
 s_tags[0].flags = 0;
 s_tags[1].name = "TAG2";
 s_tags[1].dims = 0;
 s_tags[1].type = (void *) IDL_TYP_FLOAT;
 s_tags[1].flags = 0;
 s_tags[2].name = "TAG3";
 s_tags[2].dims = 0;
 s_tags[2].type = (void *) IDL_TYP_LONG;
 s_tags[2].flags = 0;
 s_tags[3].name = "TAG4";
 s_tags[3].dims = 0;
 s_tags[3].type = (IDL_StructDefPtr *) v;
 s_tags[3].flags = 0;
 
 s_data.tag1_data[0] = 1L;
 s_data.tag1_data[1] = 2L;
 s_data.tag1_data[2] = 3L;
 s_data.tag1_data[3] = 4L;
 s_data.tag2_data = 2.0;
 s_data.tag3_data = 3;
 s_data.my_data.tag1_data[0] = 14L;
 s_data.my_data.tag1_data[1] = 15L;
 s_data.my_data.tag1_data[2] = 16L;
 s_data.my_data.tag1_data[3] = 17L;
 s_data.my_data.tag2_data = 5.0;
 s_data.my_data.tag3_data = 6;
 s_data.my_data.tag4_data = 7;
 
 /* Create the structure definition */
 s = IDL_MakeStruct(0, s_tags);
 
 tstruct = IDL_MakeTempStruct(s, 1, &one,
 &retstruct, IDL_TRUE);
 tstruct2 = IDL_MakeTempStruct(s, 1, &one, 
 &retstruct2, IDL_TRUE);
 
 /* copy the stat structure memory to the return variables
 tstruct represents the data area of the temporary 
 structure that is also the return structure */
 memcpy( (void *) tstruct, (void *) &s_data, sizeof(DATA_STRUCT));
 memcpy( (void *) tstruct2, (void *) &s_data, sizeof(DATA_STRUCT));
 
 /* copy the temporary variable into the second argument */
 IDL_VarCopy(retstruct2, argv[1]); 
 return(retstruct);
 
}
 
 </unistd.h></direct.h></io.h></windows.h></stdlib.h></stdio.h>