htsFile *fp_in = hts_open(bam_file,"rb");
hts_idx_t *idx_in = bam_index_load(bam_file);
hts_itr_t *iter = sam_itr_queryi(idx_in, tid_t, beg_t, end_t);
bam_itr_next(fp_in, iter, b);

#define bam_itr_next(htsfp, itr, r) hts_itr_next((htsfp)->fp.bgzf, (itr), (r), 0)

int hts_itr_next(BGZF *fp, hts_itr_t *iter, void *r, void *data)
{
    int ret, tid;
    hts_pos_t beg, end;
    if (iter == NULL || iter->finished) return -1;
    if (iter->read_rest) {
        if (iter->curr_off) { // seek to the start
            if (bgzf_seek(fp, iter->curr_off, SEEK_SET) < 0) {
                hts_log_error("Failed to seek to offset %"PRIu64"%s%s",
                              iter->curr_off,
                              errno ? ": " : "", strerror(errno));
                return -2;
            }
            iter->curr_off = 0; // only seek once
        }
        ret = iter->readrec(fp, data, r, &tid, &beg, &end);

hts_itr_t *sam_itr_queryi(const hts_idx_t *idx, int tid, hts_pos_t beg, hts_pos_t end)
{
    const hts_cram_idx_t *cidx = (const hts_cram_idx_t *) idx;
    if (idx == NULL)
        return hts_itr_query(NULL, tid, beg, end, sam_readrec_rest);
    else if (cidx->fmt == HTS_FMT_CRAI)
        return cram_itr_query(idx, tid, beg, end, sam_readrec);
    else
        return hts_itr_query(idx, tid, beg, end, sam_readrec);

static int sam_readrec(BGZF *ignored, void *fpv, void *bv, int *tid, hts_pos_t *beg, hts_pos_t *end)
{
    htsFile *fp = (htsFile *)fpv;
    bam1_t *b = bv;
    fp->line.l = 0;