适配人大金仓数据库，使用DCI获取查询结果时出错

data_tmp = (char *) malloc(STR_LEN_1024);
if (!data_tmp)
{
    printf("data malloc fail\n");
    return NULL;
}
memset(data_tmp, 0, STR_LEN_1024);


status = OCIDefineByPos(ds->stmthp, &defhp, ds->errhp,
                        icolumn,
                        (dvoid *) data_tmp,
                        STR_LEN_1024,
                        SQLT_STR,
                        (dvoid *) 0,
                        (ub2 *) 0,
                        (ub2 *) 0,
                        (ub4) DCI_DEFAULT);
if (status != DCI_SUCCESS)
{
    free_memory(data_tmp);
    return NULL;
}

status = OCIStmtFetch2(ds->stmthp, ds->errhp, 1,
                       DCI_FETCH_ABSOLUTE,
                       recno + 1,
                       DCI_DEFAULT);

if (status == DCI_NO_DATA)
{
    free_memory(data_tmp);
    return NULL;
}

if (strlen(data_tmp) > 0)
{
    data_sz = strlen(data_tmp) + 1;

    if (ds->data)
        ds->data = (char *) realloc(ds->data, data_sz);
    else
        ds->data = (char *) malloc(data_sz);
    memset(ds->data, 0, data_sz);

    strcpy(ds->data, data_tmp);

    if (data_tmp)
        free(data_tmp);
    return ds->data;
}

if (data_tmp)
    free(data_tmp);

return NULL;

查询多次后free(data_tmp); 出错 free(): invalid pointer