Function pio_to_format 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_to_format(
    net: *const PioNetwork,
    to: *const c_char,
    warnbuf: *mut c_char,
    warnlen: usize,
    errbuf: *mut c_char,
    errlen: usize,
) -> *mut c_char

Serialize net to format to.

Returns the converted text as an owned C string (free with pio_string_free), NULL on error. Fidelity warnings, if any, are written \n-joined into warnbuf.