diff --git a/src/client/inc/tscSubquery.h b/src/client/inc/tscSubquery.h
index 7876069ccee841485fae9069d1116c13f385ce7b..bc01de110345e4c90cf5c15d3d7f6b010cb7308d 100644
--- a/src/client/inc/tscSubquery.h
+++ b/src/client/inc/tscSubquery.h
@@ -39,7 +39,7 @@ int32_t tscHandleMultivnodeInsert(SSqlObj *pSql);
 int32_t tscHandleInsertRetry(SSqlObj* pSql);
 
 void tscBuildResFromSubqueries(SSqlObj *pSql);
-void **doSetResultRowData(SSqlObj *pSql, bool finalResult);
+TAOS_ROW doSetResultRowData(SSqlObj *pSql, bool finalResult);
 
 #ifdef __cplusplus
 }
diff --git a/src/client/inc/tsclient.h b/src/client/inc/tsclient.h
index 8621f9d28bc90b22bb54bcdb8585c3db7a1bf429..74550c56e8d18ce6a241e5f11b398cdc3650b5ae 100644
--- a/src/client/inc/tsclient.h
+++ b/src/client/inc/tsclient.h
@@ -308,7 +308,7 @@ typedef struct {
   int32_t               numOfGroups;
   SResRec *             pGroupRec;
   char *                data;
-  void **               tsrow;
+  TAOS_ROW              tsrow;
   int32_t*              length;  // length for each field for current row
   char **               buffer;  // Buffer used to put multibytes encoded using unicode (wchar_t)
   SColumnIndex *        pColumnIndex;
@@ -448,9 +448,8 @@ void tscCloseTscObj(STscObj *pObj);
 
 // todo move to taos? or create a new file: taos_internal.h
 TAOS *taos_connect_a(char *ip, char *user, char *pass, char *db, uint16_t port, void (*fp)(void *, TAOS_RES *, int),
-                     void *param, void **taos);
+                     void *param, TAOS **taos);
 TAOS_RES* taos_query_h(TAOS* taos, const char *sqlstr, TAOS_RES** res);
-
 void waitForQueryRsp(void *param, TAOS_RES *tres, int code);
 
 void doAsyncQuery(STscObj *pObj, SSqlObj *pSql, __async_cb_func_t fp, void *param, const char *sqlstr, size_t sqlLen);
@@ -481,11 +480,11 @@ static FORCE_INLINE void tscGetResultColumnChr(SSqlRes* pRes, SFieldInfo* pField
     if (type == TSDB_DATA_TYPE_NCHAR || type == TSDB_DATA_TYPE_BINARY) {
       pData = pInfo->pSqlExpr->param[1].pz;
       pRes->length[columnIndex] = pInfo->pSqlExpr->param[1].nLen;
-      pRes->tsrow[columnIndex] = (pInfo->pSqlExpr->param[1].nType == TSDB_DATA_TYPE_NULL) ? NULL : pData;
+      pRes->tsrow[columnIndex] = (pInfo->pSqlExpr->param[1].nType == TSDB_DATA_TYPE_NULL) ? NULL : (unsigned char*)pData;
     } else {
       assert(bytes == tDataTypeDesc[type].nSize);
 
-      pRes->tsrow[columnIndex] = isNull(pData, type) ? NULL : &pInfo->pSqlExpr->param[1].i64Key;
+      pRes->tsrow[columnIndex] = isNull(pData, type) ? NULL : (unsigned char*)&pInfo->pSqlExpr->param[1].i64Key;
       pRes->length[columnIndex] = bytes;
     }
   } else {
@@ -493,7 +492,7 @@ static FORCE_INLINE void tscGetResultColumnChr(SSqlRes* pRes, SFieldInfo* pField
       int32_t realLen = varDataLen(pData);
       assert(realLen <= bytes - VARSTR_HEADER_SIZE);
 
-      pRes->tsrow[columnIndex] = (isNull(pData, type)) ? NULL : ((tstr *)pData)->data;
+      pRes->tsrow[columnIndex] = (isNull(pData, type)) ? NULL : (unsigned char*)((tstr *)pData)->data;
       if (realLen < pInfo->pSqlExpr->resBytes - VARSTR_HEADER_SIZE) {  // todo refactor
         *(pData + realLen + VARSTR_HEADER_SIZE) = 0;
       }
@@ -502,7 +501,7 @@ static FORCE_INLINE void tscGetResultColumnChr(SSqlRes* pRes, SFieldInfo* pField
     } else {
       assert(bytes == tDataTypeDesc[type].nSize);
 
-      pRes->tsrow[columnIndex] = isNull(pData, type) ? NULL : pData;
+      pRes->tsrow[columnIndex] = isNull(pData, type) ? NULL : (unsigned char*)pData;
       pRes->length[columnIndex] = bytes;
     }
   }
diff --git a/src/client/src/tscLocal.c b/src/client/src/tscLocal.c
index a15673bdb1edf97fda23d879ab69839fd500549e..929b9ffe68333831fcdfef03c545a6b3361d0694 100644
--- a/src/client/src/tscLocal.c
+++ b/src/client/src/tscLocal.c
@@ -296,7 +296,7 @@ static int32_t tscProcessDescribeTable(SSqlObj *pSql) {
   return tscSetValueToResObj(pSql, rowLen);
 }
 static int32_t tscGetNthFieldResult(TAOS_ROW row, TAOS_FIELD* fields, int *lengths, int idx, char *result) {
-  const char *val = row[idx];
+  const char *val = (const char*)row[idx];
   if (val == NULL) {
     sprintf(result, "%s", TSDB_DATA_NULL_STR);
     return -1;
diff --git a/src/client/src/tscProfile.c b/src/client/src/tscProfile.c
index bae0f91dcc40e78c3d2f707ff93ee6ebd5322339..eb6843b0e4fd844c9d13da7f55dca47008f62a79 100644
--- a/src/client/src/tscProfile.c
+++ b/src/client/src/tscProfile.c
@@ -20,8 +20,10 @@
 #include "tutil.h"
 #include "taosmsg.h"
 
+#include "taos.h"
+
 void  tscSaveSlowQueryFp(void *handle, void *tmrId);
-void *tscSlowQueryConn = NULL;
+TAOS *tscSlowQueryConn = NULL;
 bool  tscSlowQueryConnInitialized = false;
 
 void tscInitConnCb(void *param, TAOS_RES *result, int code) {
diff --git a/src/client/src/tscServer.c b/src/client/src/tscServer.c
index 494a8a9c301175352c399317c83324f364a31eb6..40e050e6a47f5f9806e68ef275f1695327a80a08 100644
--- a/src/client/src/tscServer.c
+++ b/src/client/src/tscServer.c
@@ -1366,7 +1366,7 @@ static int tscSetResultPointer(SQueryInfo *pQueryInfo, SSqlRes *pRes) {
 
   for (int i = 0; i < pQueryInfo->fieldsInfo.numOfOutput; ++i) {
     int16_t offset = tscFieldInfoGetOffset(pQueryInfo, i);
-    pRes->tsrow[i] = ((char*) pRes->data + offset * pRes->numOfRows);
+    pRes->tsrow[i] = (unsigned char*)((char*) pRes->data + offset * pRes->numOfRows);
   }
 
   return 0;
diff --git a/src/client/src/tscSql.c b/src/client/src/tscSql.c
index 7594a73c9604b25fb29143e7b88ad7876b2a496d..9799c9129bd4339b675a209aaec915bdf675474d 100644
--- a/src/client/src/tscSql.c
+++ b/src/client/src/tscSql.c
@@ -51,8 +51,8 @@ static bool validPassword(const char* passwd) {
   return validImpl(passwd, TSDB_PASSWORD_LEN - 1);
 }
 
-SSqlObj *taosConnectImpl(const char *ip, const char *user, const char *pass, const char *auth, const char *db,
-                         uint16_t port, void (*fp)(void *, TAOS_RES *, int), void *param, void **taos) {
+static SSqlObj *taosConnectImpl(const char *ip, const char *user, const char *pass, const char *auth, const char *db,
+                         uint16_t port, void (*fp)(void *, TAOS_RES *, int), void *param, TAOS **taos) {
   taos_init();
 
   if (!validUserName(user)) {
@@ -174,7 +174,7 @@ static void syncConnCallback(void *param, TAOS_RES *tres, int code) {
 TAOS *taos_connect_internal(const char *ip, const char *user, const char *pass, const char *auth, const char *db,
                             uint16_t port) {
   STscObj *pObj = NULL;
-  SSqlObj *pSql = taosConnectImpl(ip, user, pass, auth, db, port, syncConnCallback, NULL, (void **)&pObj);
+  SSqlObj *pSql = taosConnectImpl(ip, user, pass, auth, db, port, syncConnCallback, NULL, &pObj);
   if (pSql != NULL) {
     pSql->fp = syncConnCallback;
     pSql->param = pSql;
@@ -243,16 +243,19 @@ static void asyncConnCallback(void *param, TAOS_RES *tres, int code) {
 }
 
 TAOS *taos_connect_a(char *ip, char *user, char *pass, char *db, uint16_t port, void (*fp)(void *, TAOS_RES *, int),
-                     void *param, void **taos) {
-  SSqlObj* pSql = taosConnectImpl(ip, user, pass, NULL, db, port, asyncConnCallback, param, taos);
+                     void *param, TAOS **taos) {
+  STscObj *pObj = NULL;
+  SSqlObj* pSql = taosConnectImpl(ip, user, pass, NULL, db, port, asyncConnCallback, param, &pObj);
   if (pSql == NULL) {
     return NULL;
   }
-  
+ 
+  if (taos) *taos = pObj;
+
   pSql->fetchFp = fp;
   pSql->res.code = tscProcessSql(pSql);
   tscDebug("%p DB async connection is opening", taos);
-  return taos;
+  return pObj;
 }
 
 void taos_close(TAOS *taos) {
@@ -881,7 +884,7 @@ int taos_validate_sql(TAOS *taos, const char *sql) {
   if (pSql->sqlstr == NULL) {
     pRes->code = TSDB_CODE_TSC_OUT_OF_MEMORY;
     tscError("%p failed to malloc sql string buffer", pSql);
-    tscDebug("%p Valid SQL result:%d, %s pObj:%p", pSql, pRes->code, taos_errstr(taos), pObj);
+    tscDebug("%p Valid SQL result:%d, %s pObj:%p", pSql, pRes->code, taos_errstr(pSql), pObj);
     taosTFree(pSql);
     return pRes->code;
   }
@@ -906,7 +909,7 @@ int taos_validate_sql(TAOS *taos, const char *sql) {
   }
 
   if (code != TSDB_CODE_SUCCESS) {
-    tscDebug("%p Valid SQL result:%d, %s pObj:%p", pSql, code, taos_errstr(taos), pObj);
+    tscDebug("%p Valid SQL result:%d, %s pObj:%p", pSql, code, taos_errstr(pSql), pObj);
   }
 
   taos_free_result(pSql);
@@ -1050,7 +1053,7 @@ int taos_load_table_info(TAOS *taos, const char *tableNameList) {
 
   tscDoQuery(pSql);
 
-  tscDebug("%p load multi table meta result:%d %s pObj:%p", pSql, pRes->code, taos_errstr(taos), pObj);
+  tscDebug("%p load multi table meta result:%d %s pObj:%p", pSql, pRes->code, taos_errstr(pSql), pObj);
   if ((code = pRes->code) != TSDB_CODE_SUCCESS) {
     tscFreeSqlObj(pSql);
   }
diff --git a/src/client/src/tscSubquery.c b/src/client/src/tscSubquery.c
index 49759bc4d30fa9a9a89591c33c3dc6666894d1b2..06e1efc9e4fee46d7e8735770b1a0597b2153d66 100644
--- a/src/client/src/tscSubquery.c
+++ b/src/client/src/tscSubquery.c
@@ -2130,7 +2130,7 @@ static void transferNcharData(SSqlObj *pSql, int32_t columnIndex, TAOS_FIELD *pF
     
     int32_t length = taosUcs4ToMbs(pRes->tsrow[columnIndex], pRes->length[columnIndex], pRes->buffer[columnIndex]);
     if ( length >= 0 ) {
-      pRes->tsrow[columnIndex] = pRes->buffer[columnIndex];
+      pRes->tsrow[columnIndex] = (unsigned char*)pRes->buffer[columnIndex];
       pRes->length[columnIndex] = length;
     } else {
       tscError("%p charset:%s to %s. val:%s convert failed.", pSql, DEFAULT_UNICODE_ENCODEC, tsCharset, (char*)pRes->tsrow[columnIndex]);
@@ -2158,7 +2158,7 @@ static char *getArithemicInputSrc(void *param, const char *name, int32_t colId)
   return pSupport->data[index] + pSupport->offset * pExpr->resBytes;
 }
 
-void **doSetResultRowData(SSqlObj *pSql, bool finalResult) {
+TAOS_ROW doSetResultRowData(SSqlObj *pSql, bool finalResult) {
   SSqlCmd *pCmd = &pSql->cmd;
   SSqlRes *pRes = &pSql->res;
 
@@ -2211,7 +2211,7 @@ void **doSetResultRowData(SSqlObj *pSql, bool finalResult) {
 
       tExprTreeCalcTraverse(pRes->pArithSup->pArithExpr->pExpr, 1, pRes->buffer[i], pRes->pArithSup,
           TSDB_ORDER_ASC, getArithemicInputSrc);
-      pRes->tsrow[i] = pRes->buffer[i];
+      pRes->tsrow[i] = (unsigned char*)pRes->buffer[i];
     }
   }
 
diff --git a/src/inc/taos.h b/src/inc/taos.h
index 2d72b1739d1023945f2fff7c4af10d908475c7d1..66b5f930bca4116ae72c1ee60753e4cc22c3b088 100644
--- a/src/inc/taos.h
+++ b/src/inc/taos.h
@@ -22,12 +22,13 @@
 extern "C" {
 #endif
 
-typedef void    TAOS;
-typedef void**  TAOS_ROW;
-typedef void    TAOS_RES;
-typedef void    TAOS_SUB;
-typedef void    TAOS_STREAM;
-typedef void    TAOS_STMT;
+typedef struct STscObj         TAOS;
+typedef struct STscStmt        TAOS_STMT;
+typedef struct SSqlObj         TAOS_RES;
+typedef struct SSqlStream      TAOS_STREAM;
+typedef struct SSub            TAOS_SUB;
+typedef unsigned char**        TAOS_ROW;
+
 
 // Data type definition
 #define TSDB_DATA_TYPE_NULL       0     // 1 bytes
diff --git a/src/kit/shell/inc/shell.h b/src/kit/shell/inc/shell.h
index 765181dbba5c92ca9dc80adb7376e68c70237d6d..f508d186083c84482080f2f8fe251173733f1366 100644
--- a/src/kit/shell/inc/shell.h
+++ b/src/kit/shell/inc/shell.h
@@ -60,7 +60,7 @@ typedef struct SShellArguments {
 extern void shellParseArgument(int argc, char* argv[], SShellArguments* arguments);
 extern TAOS* shellInit(SShellArguments* args);
 extern void* shellLoopQuery(void* arg);
-extern void taos_error(TAOS* con);
+extern void taos_error(TAOS_RES* tres);
 extern int regex_match(const char* s, const char* reg, int cflags);
 void shellReadCommand(TAOS* con, char command[]);
 int32_t shellRunCommand(TAOS* con, char* command);
@@ -72,7 +72,7 @@ void source_dir(TAOS* con, SShellArguments* args);
 void get_history_path(char* history);
 void cleanup_handler(void* arg);
 void exitShell();
-int shellDumpResult(TAOS* con, char* fname, int* error_no, bool printMode);
+int shellDumpResult(TAOS_RES* con, char* fname, int* error_no, bool printMode);
 void shellGetGrantInfo(void *con);
 int isCommentLine(char *line);
 
diff --git a/src/kit/shell/src/shellEngine.c b/src/kit/shell/src/shellEngine.c
index 24388bf50c7a215920a58e79f8d33ab81752c547..748b7e792982352de611227d82a844448d251ee2 100644
--- a/src/kit/shell/src/shellEngine.c
+++ b/src/kit/shell/src/shellEngine.c
@@ -493,7 +493,7 @@ static int dumpResultToFile(const char* fname, TAOS_RES* tres) {
       if (i > 0) {
         fputc(',', fp);
       }
-      dumpFieldToFile(fp, row[i], fields +i, length[i], precision);
+      dumpFieldToFile(fp, (const char*)row[i], fields +i, length[i], precision);
     }
     fputc('\n', fp);
 
@@ -619,7 +619,7 @@ static int verticalPrintResult(TAOS_RES* tres) {
       int padding = (int)(maxColNameLen - strlen(field->name));
       printf("%*.s%s: ", padding, " ", field->name);
 
-      printField(row[i], field, 0, length[i], precision);
+      printField((const char*)row[i], field, 0, length[i], precision);
       putchar('\n');
     }
 
@@ -720,7 +720,7 @@ static int horizontalPrintResult(TAOS_RES* tres) {
     int32_t* length = taos_fetch_lengths(tres);
     for (int i = 0; i < num_fields; i++) {
       putchar(' ');
-      printField(row[i], fields + i, width[i], length[i], precision);
+      printField((const char*)row[i], fields + i, width[i], length[i], precision);
       putchar(' ');
       putchar('|');
     }
diff --git a/src/kit/shell/src/shellImport.c b/src/kit/shell/src/shellImport.c
index ee0a90757bb51a98dd2bf535319afc215dbc04a8..af61995c618bc80389b8abf6d8c6f6c929327925 100644
--- a/src/kit/shell/src/shellImport.c
+++ b/src/kit/shell/src/shellImport.c
@@ -204,7 +204,7 @@ static void shellSourceFile(TAOS *con, char *fptr) {
     int32_t code = taos_errno(pSql);
     
     if (code != 0) {
-      fprintf(stderr, "DB error: %s: %s (%d)\n", taos_errstr(con), fname, lineNo);
+      fprintf(stderr, "DB error: %s: %s (%d)\n", taos_errstr(pSql), fname, lineNo);
     }
     
     /* free local resouce: allocated memory/metric-meta refcnt */
@@ -243,7 +243,7 @@ static void shellRunImportThreads(SShellArguments* args)
     pThread->totalThreads = args->threadNum;
     pThread->taos = taos_connect(args->host, args->user, args->password, args->database, tsDnodeShellPort);
     if (pThread->taos == NULL) {
-      fprintf(stderr, "ERROR: thread:%d failed connect to TDengine, error:%s\n", pThread->threadIndex, taos_errstr(pThread->taos));
+      fprintf(stderr, "ERROR: thread:%d failed connect to TDengine, error:%s\n", pThread->threadIndex, "null taos"/*taos_errstr(pThread->taos)*/);
       exit(0);
     }
 
diff --git a/src/plugins/http/inc/httpInt.h b/src/plugins/http/inc/httpInt.h
index 36a022159f4e8b58ca4179e9ae73d5ad7dd793d2..affc0e838ea97f25dcb2e53947ecbb7b025dffb1 100644
--- a/src/plugins/http/inc/httpInt.h
+++ b/src/plugins/http/inc/httpInt.h
@@ -122,9 +122,9 @@ typedef struct {
 } HttpDecodeMethod;
 
 typedef struct {
-  void (*startJsonFp)(struct HttpContext *pContext, HttpSqlCmd *cmd, void *result);
+  void (*startJsonFp)(struct HttpContext *pContext, HttpSqlCmd *cmd, TAOS_RES *result);
   void (*stopJsonFp)(struct HttpContext *pContext, HttpSqlCmd *cmd);
-  bool (*buildQueryJsonFp)(struct HttpContext *pContext, HttpSqlCmd *cmd, void *result, int numOfRows);
+  bool (*buildQueryJsonFp)(struct HttpContext *pContext, HttpSqlCmd *cmd, TAOS_RES *result, int numOfRows);
   void (*buildAffectRowJsonFp)(struct HttpContext *pContext, HttpSqlCmd *cmd, int affectRows);
   void (*initJsonFp)(struct HttpContext *pContext);
   void (*cleanJsonFp)(struct HttpContext *pContext);
@@ -148,7 +148,7 @@ typedef struct HttpContext {
   char         ipstr[22];
   char         user[TSDB_USER_LEN];  // parsed from auth token or login message
   char         pass[TSDB_PASSWORD_LEN];
-  void *       taos;
+  TAOS *       taos;
   void *       ppContext;
   HttpSession *session;
   z_stream     gzipStream;
diff --git a/src/plugins/http/src/httpGcJson.c b/src/plugins/http/src/httpGcJson.c
index 80e4ae3bc2b51387d5573af00aa1e91d2c1cd663..2c9eca11deb51acc8cc25965b83cc686ac04c6e5 100644
--- a/src/plugins/http/src/httpGcJson.c
+++ b/src/plugins/http/src/httpGcJson.c
@@ -217,7 +217,7 @@ bool gcBuildQueryJson(HttpContext *pContext, HttpSqlCmd *cmd, TAOS_RES *result,
           break;
         case TSDB_DATA_TYPE_BINARY:
         case TSDB_DATA_TYPE_NCHAR:
-          httpJsonStringForTransMean(jsonBuf, row[i], fields[i].bytes);
+          httpJsonStringForTransMean(jsonBuf, (char*)row[i], fields[i].bytes);
           break;
         case TSDB_DATA_TYPE_TIMESTAMP:
           if (precision == TSDB_TIME_PRECISION_MILLI) { //ms
diff --git a/src/plugins/http/src/httpRestJson.c b/src/plugins/http/src/httpRestJson.c
index 954678c24c8fb4597ef3184d2d65060c6d159aa1..a5b156bffc23ea3cdb042f456a327895fc0bdaa6 100644
--- a/src/plugins/http/src/httpRestJson.c
+++ b/src/plugins/http/src/httpRestJson.c
@@ -131,7 +131,7 @@ bool restBuildSqlJson(HttpContext *pContext, HttpSqlCmd *cmd, TAOS_RES *result,
           break;
         case TSDB_DATA_TYPE_BINARY:
         case TSDB_DATA_TYPE_NCHAR:
-          httpJsonStringForTransMean(jsonBuf, row[i], length[i]);
+          httpJsonStringForTransMean(jsonBuf, (char*)row[i], length[i]);
           break;
         case TSDB_DATA_TYPE_TIMESTAMP:
           if (timestampFormat == REST_TIMESTAMP_FMT_LOCAL_STRING) {
@@ -195,4 +195,4 @@ void restStopSqlJson(HttpContext *pContext, HttpSqlCmd *cmd) {
   httpJsonToken(jsonBuf, JsonObjEnd);
 
   httpWriteJsonBufEnd(jsonBuf);
-}
\ No newline at end of file
+}
diff --git a/src/plugins/http/src/httpSql.c b/src/plugins/http/src/httpSql.c
index 883fa574ff19958591051512e717a9b512f3e0ce..70d644146cf5ebe15a42c8f00a2e6e4bd603d081 100644
--- a/src/plugins/http/src/httpSql.c
+++ b/src/plugins/http/src/httpSql.c
@@ -27,8 +27,6 @@
 #include "httpSession.h"
 #include "httpQueue.h"
 
-void *taos_connect_a(char *ip, char *user, char *pass, char *db, uint16_t port, void (*fp)(void *, TAOS_RES *, int),
-                     void *param, void **taos);
 void httpProcessMultiSql(HttpContext *pContext);
 
 void httpProcessMultiSqlRetrieveCallBack(void *param, TAOS_RES *result, int numOfRows);
diff --git a/tests/comparisonTest/tdengine/tdengineTest.c b/tests/comparisonTest/tdengine/tdengineTest.c
index 237403f52565c1b68b21e895d5555a2a673bb5f7..1298aa8323b0f876e3c64ff88323031b8d529648 100644
--- a/tests/comparisonTest/tdengine/tdengineTest.c
+++ b/tests/comparisonTest/tdengine/tdengineTest.c
@@ -108,9 +108,9 @@ void parseArg(int argc, char *argv[]) {
   }
 }
 
-void taos_error(TAOS *con) {
-  printf("TDengine error: %s\n", taos_errstr(con));
-  taos_close(con);
+static void taos_error(TAOS_RES *tres, TAOS *conn) {
+  printf("TDengine error: %s\n", tres?taos_errstr(tres):"null result");
+  taos_close(conn);
   exit(1);
 }
 
@@ -125,13 +125,17 @@ void writeDataImp(void *param) {
   printf("Thread %d, writing sID %d, eID %d\n", pThread->threadId, pThread->sID, pThread->eID);
 
   void *taos = taos_connect("127.0.0.1", "root", "taosdata", NULL, 0);
-  if (taos == NULL)
-    taos_error(taos);
+  if (taos == NULL) {
+    // where to find errstr?
+    // taos_error(NULL, taos);
+    printf("TDengine error: %s\n", "failed to connect");
+    exit(1);
+  }
 
   TAOS_RES* result = taos_query(taos, "use db");
   int32_t code = taos_errno(result);
   if (code != 0) {
-    taos_error(taos);
+    taos_error(result, taos);
   }
   taos_free_result(result);
 
@@ -227,12 +231,17 @@ void writeData() {
   taos_init();
 
   void *taos = taos_connect("127.0.0.1", "root", "taosdata", NULL, 0);
-  if (taos == NULL) taos_error(taos);
+  if (taos == NULL) {
+    // where to find errstr?
+    // taos_error(NULL, taos);
+    printf("TDengine error: %s\n", "failed to connect");
+    exit(1);
+  }
 
   TAOS_RES *result = taos_query(taos, "create database if not exists db");
   int32_t   code = taos_errno(result);
   if (code != 0) {
-    taos_error(taos);
+    taos_error(result, taos);
   }
   taos_free_result(result);
 
@@ -241,7 +250,7 @@ void writeData() {
                       "tags(devid int, devname binary(16), devgroup int)");
   code = taos_errno(result);
   if (code != 0) {
-    taos_error(taos);
+    taos_error(result, taos);
   }
   taos_free_result(result);
 
@@ -293,8 +302,12 @@ void readDataImp(void *param)
   printf("open file %s success\n", arguments.sql);
 
   void *taos = taos_connect("127.0.0.1", "root", "taosdata", NULL, 0);
-  if (taos == NULL)
-    taos_error(taos);
+  if (taos == NULL) {
+    // where to find errstr?
+    // taos_error(NULL, taos);
+    printf("TDengine error: %s\n", "failed to connect");
+    exit(1);
+  }
 
   char *line = NULL;
   size_t len = 0;
@@ -313,7 +326,7 @@ void readDataImp(void *param)
     TAOS_RES *result = taos_query(taos, line);
     int32_t   code = taos_errno(result);
     if (code != 0) {
-      taos_error(taos);
+      taos_error(result, taos);
     }
 
     TAOS_ROW row;
@@ -343,8 +356,12 @@ void readData() {
   printf("---- clients: %d\n", arguments.clients);
 
   void *taos = taos_connect("127.0.0.1", "root", "taosdata", NULL, 0);
-  if (taos == NULL)
-    taos_error(taos);
+  if (taos == NULL) {
+    // where to find errstr?
+    // taos_error(NULL, taos);
+    printf("TDengine error: %s\n", "failed to connect");
+    exit(1);
+  }
 
   ThreadObj *threads = calloc((size_t)arguments.clients, sizeof(ThreadObj));
 
diff --git a/tests/examples/c/demo.c b/tests/examples/c/demo.c
index d64c0de1ce45597e26396979bb693cc0f96873d5..8f8a66a32593bc25d71b554808719ca42f5b32ac 100644
--- a/tests/examples/c/demo.c
+++ b/tests/examples/c/demo.c
@@ -38,7 +38,7 @@ int main(int argc, char *argv[]) {
 
   taos = taos_connect(argv[1], "root", "taosdata", NULL, 0);
   if (taos == NULL) {
-    printf("failed to connect to server, reason:%s\n", taos_errstr(taos));
+    printf("failed to connect to server, reason:%s\n", "null taos"/*taos_errstr(taos)*/);
     exit(1);
   }
   printf("success to connect to server\n");
@@ -48,7 +48,7 @@ int main(int argc, char *argv[]) {
 
   result = taos_query(taos, "create database demo");
   if (result == NULL) {
-    printf("failed to create database, reason:%s\n", taos_errstr(taos));
+    printf("failed to create database, reason:%s\n", "null result"/*taos_errstr(taos)*/);
     exit(1);
   }
   printf("success to create database\n");
@@ -57,7 +57,7 @@ int main(int argc, char *argv[]) {
 
   // create table
   if (taos_query(taos, "create table m1 (ts timestamp, ti tinyint, si smallint, i int, bi bigint, f float, d double, b binary(10))") == 0) {
-    printf("failed to create table, reason:%s\n", taos_errstr(taos));
+    printf("failed to create table, reason:%s\n", taos_errstr(result));
     exit(1);
   }
   printf("success to create table\n");
@@ -70,9 +70,19 @@ int main(int argc, char *argv[]) {
   for (i = 0; i < 10; ++i) {
     sprintf(qstr, "insert into m1 values (%" PRId64 ", %d, %d, %d, %d, %f, %lf, '%s')", 1546300800000 + i * 1000, i, i, i, i*10000000, i*1.0, i*2.0, "hello");
     printf("qstr: %s\n", qstr);
-    if (taos_query(taos, qstr)) {
-      printf("insert row: %i, reason:%s\n", i, taos_errstr(taos));
+    
+    // note: how do you wanna do if taos_query returns non-NULL
+    // if (taos_query(taos, qstr)) {
+    //   printf("insert row: %i, reason:%s\n", i, taos_errstr(taos));
+    // }
+    TAOS_RES *result = taos_query(taos, qstr);
+    if (result) {
+      printf("insert row: %i\n", i);
+    } else {
+      printf("failed to insert row: %i, reason:%s\n", i, "null result"/*taos_errstr(result)*/);
+      exit(1);
     }
+
     //sleep(1);
   }
   printf("success to insert rows, total %d rows\n", i);