Function pio_read_gridfm 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_read_gridfm(
    dir: *const c_char,
    scenario: i64,
    warnbuf: *mut c_char,
    warnlen: usize,
    errbuf: *mut c_char,
    errlen: usize,
) -> *mut PioNetwork

Read one scenario of a gridfm-datakit Parquet dataset into a network handle — the inverse of the gridfm writer. dir resolves leniently: the raw/ leaf holding the parquet files, a <case>/ directory with a raw/ child, or a parent holding exactly one such case. Returns NULL on error and writes the message into errbuf; the lossy read’s fidelity warnings (what the gridfm schema couldn’t round-trip) are written \n-joined into warnbuf. Free the handle with pio_network_free. Built --features gridfm.