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);}