[GENERAL] User defined Type PostgreSQL in C

I'm developing an extension for postgreSQL in C. I've created two new types, one of var len size (vlen). I do not know how to create the input and output functions for Geo_Polygon type. Anyone have an example? Here's what I've done so far.

typedef struct Geo_Point{  double x;  double y;
}   Geo_Point;

typedef struct Geo_Polygon{ int32 v_len; int32 n_points; Geo_Point point[FLEXIBLE_ARRAY_MEMBER];
} Geo_Polygon;


PG_FUNCTION_INFO_V1(geo_polygon_in);
Datum
geo_polygon_in(PG_FUNCTION_ARGS){

 char *str = PG_GETARG_CSTRING(0); char *new_position = NULL; char aux[1024]; int i, dimension, len; Geo_Polygon *result; Geo_Point *point; double x, y;



point = (Geo_Point *) palloc(sizeof(Geo_Point));
 new_position = strchr(str, '(');
 for (dimension = 0; *new_position != '\0'; dimension++){
   memset(aux, 0, sizeof(aux));   for (i  = 0; *new_position != ')'; i++, ++new_position) {     aux[i] = *new_position;   }   aux[i] = *new_position;   ++new_position;   if (*new_position == ',') {       ++new_position;   }
   point = (Geo_Point *) repalloc(point, (dimension + 1) * sizeof(Geo_Point));   if(sscanf(aux, " ( %lf , %lf )", &x, &y )!= 2)       ereport(ERROR,           (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),            errmsg("entrada errada para o tipo geo_point: \"%s\"",               str)));
   point->x = x;   point->y = y;
 }
 len = sizeof(Geo_Point) * (dimension + 1)+ VARHDRSZ; result = (Geo_Polygon *) palloc0(len); SET_VARSIZE(result, len); // copy the coordinates to the data area destino arqu e quantos bytes memcpy((void *) VARDATA(result),(void *) VARDATA (point),  (dimension) * sizeof(Geo_Point));
 result->n_points = dimension;
 PG_RETURN_POINTER(result);

}


Datum
geo_polygon_out(PG_FUNCTION_ARGS){ Geo_Polygon *geo_polygon = (Geo_Polygon *) PG_GETARG_POINTER(0); StringInfoData buf; int           dim = geo_polygon->n_points;
 int           i; int           ndig = 2;
 initStringInfo(&buf);

 appendStringInfoChar(&buf, '('); for (i = 0; i < dim; i++){
   appendStringInfo(&buf, "%.*g", geo_polygon->point[i].x, "%.*g", geo_polygon->point[i].y);   appendStringInfoChar(&buf, ')');
 } PG_FREE_IF_COPY(geo_polygon, 0); PG_RETURN_CSTRING(buf.data);}