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,
    warnbuf: *mut c_char,
    warnlen: usize,
    errbuf: *mut c_char,
    errlen: usize,
) -> i32

Write net into the directory out_dir as the named directory-shaped format to: the directory sibling of pio_to_format. PyPSA CSV (pypsa-csv/pypsa) is the one such format today; 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 written \n-joined into warnbuf.