Function pio_write_dir 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_write_dir(
    net: *const PioNetwork,
    to: *const c_char,
    out_dir: *const c_char,
    out_warnings: *mut *mut c_char,
    errbuf: *mut c_char,
    errlen: usize,
) -> i32

Write net into out_dir as the named directory format to. PyPSA CSV (pypsa-csv/pypsa) is the currently supported directory format; a text format name is an error pointing back at pio_to_format. Returns 0 on success and -1 on error (message into errbuf). Fidelity warnings, if any, are published through out_warnings as one owned C string (free it with pio_string_free), NULL when there are none. Pass NULL to discard them.