Re: [slang-users] Some Collaboration Requested ....

["John E. Davis" <davis@xxxxxxxxxxxxx>]

Ben Duncan <ben@xxxxxxxxxxxxxxxxxx> wrote:
>Sooo... what I am trying to do is use a "generic" File Module that can be passed
>the values, and return the record into a structure defined in S-Lang. But I
>  think
>for the time, such a Module is above my ability to write it.

Returning data as a slang structure from C code is rather simple.  How
to do this is described in slang/doc/text/cslang.txt in the section
dealing with "Interpreter Structures".

Here is an example of this technique from another project:

   slsh> print (maplib_new ("linear"));
   {name="linear", x0=0, y0=0, x1=0, y1=0, A=Double_Type[2,2]}

The function "maplib_new" is defined in a module and returns a
structure that varies with its argument ("linear" in this case).  As
you can see, the structure conists of 6 fields (name, x0, x1,...).
Here is the C code responsible for this.  Note how it is mapped onto a
C structure.  See cslang.txt for more details.  Good luck, --John

typedef struct
{
   char *name;			       /* required field */
   double x_0, y_0;
   double x_1, y_1;
   SLang_Array_Type *at;
   double a[4];
   double a_inv[4];
}
Linear_Projection_Type;

static SLang_CStruct_Field_Type Linear_Projection_Struct[] =
{
   MAKE_CSTRUCT_FIELD(Linear_Projection_Type, name, "name", SLANG_STRING_TYPE, 0),
   MAKE_CSTRUCT_FIELD(Linear_Projection_Type, x_0, "x0", SLANG_DOUBLE_TYPE, 0),
   MAKE_CSTRUCT_FIELD(Linear_Projection_Type, y_0, "y0", SLANG_DOUBLE_TYPE, 0),
   MAKE_CSTRUCT_FIELD(Linear_Projection_Type, x_1, "x1", SLANG_DOUBLE_TYPE, 0),
   MAKE_CSTRUCT_FIELD(Linear_Projection_Type, y_1, "y1", SLANG_DOUBLE_TYPE, 0),
   MAKE_CSTRUCT_FIELD(Linear_Projection_Type, at, "A", SLANG_ARRAY_TYPE, 0),
   SLANG_END_CSTRUCT_TABLE
};

static int linear_new (char *name)
{
   Linear_Projection_Type g;
   SLang_Array_Type *at;
   int dims[2];
   int ret;

   dims[0] = 2;
   dims[1] = 2;

   if (NULL == (at = SLang_create_array (SLANG_DOUBLE_TYPE, 0, NULL, dims, 2)))
     return -1;
   ((double *)at->data)[0] = 1.0;
   ((double *)at->data)[1] = 0.0;
   ((double *)at->data)[2] = 0.0;
   ((double *)at->data)[3] = 1.0;
   g.at = at;

   g.name = name;
   g.x_0 = g.y_0 = 0.0;
   g.x_1 = g.y_1 = 0.0;
   
   ret = SLang_push_cstruct (&g, Linear_Projection_Struct);
   SLang_free_array (at);
   return ret;
}

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