a foreign struct: a shameless request

[Catonano]

I'd love to see a template of usage of a complex structure from scheme
That is, I'm asking for someone to write that template for me :-/

This is the foreign struct I have to deal with

https://www.gaia-gis.it/gaia-sins/freexl-1.0.1-doxy-doc/html/structFreeXL__CellValue__str.html

Particulary, I don't know how to treat the "union" thing

A different union field gets populated on the basis of the type of the
content of the spreadsheet cell

If the cell contains an integer number, then cell.int_value field gets
populated

If the cell contains a double float number, then the cell.double_value
field gets populated

And so on

This is an excerpt from the example usage:

switch (cell.type
<https://www.gaia-gis.it/gaia-sins/freexl-1.0.1-doxy-doc/html/structFreeXL__CellValue__str.html#af2b1f157e4dc4508b1c4e303429c01d5>
)
{
   case FREEXL_CELL_INT
<https://www.gaia-gis.it/gaia-sins/freexl-1.0.1-doxy-doc/html/freexl_8h.html#a1a2260897b305108f008c924a7e56778>
:
   printf (", %d", cell.value
<https://www.gaia-gis.it/gaia-sins/freexl-1.0.1-doxy-doc/html/structFreeXL__CellValue__str.html#acaf7ae03285c299b05f0e345eff3c6a1>
.int_value
<https://www.gaia-gis.it/gaia-sins/freexl-1.0.1-doxy-doc/html/structFreeXL__CellValue__str.html#a7dcd352478ee217f4a24e7fcff6170bb>
);
   break;
...

How do I use "make-c-struct" and "parse-c-struct" with a structure like
this ?

Thanks in advance