Need help - select data from NCLOB column problem

Question

Hi,
Im having problem retrieving data from NCLOB columns via ODBC. After SQLExecdirect on my SELECT statement call to SQLFetch gives me following error:
ORA-24806 LOB form mismatch
I tried following two ways of data retrieval:
SQLExecDirect(hstmt,(SQLTCHAR*)szSQLStatement,SQL_NTS);
SQLBindCol(hstmt,3,SQL_C_TCHAR,chBuffer,sizeof(chBuffer),&iDataLen);
SQLFetch(hstmt);
OR
SQLExecDirect(hstmt,(SQLTCHAR*)szSQLStatement,SQL_NTS);
SQLFetch(hstmt);
SQLGetData(hstmt,3,SQL_C_TCHAR,chBuffer,sizeof(chBuffer),&iDataLen);
Both times call to SQLFetch gives me ORA-24806 LOB form mismatch error.
INSERT and UPDATE for this table works just fine.
If I change NCLOB type to CLOB works just fine, but I will be storing Unicode data, so using CLOB cant be a solution
Any ideas appreciated.
Thanks in advance,
Vlad
Server:
Oracle 9.2 database on Windows 2000 Server
NLS_LANGUAGE = AMERICAN
NLS_TERRITORY = AMERICA
NLS_CHARACTERSET = WE8MSWIN1252
NLS_NCHAR_CHARACTERSET = AL16UTF16
Client:
Unicode C++ application, connects via Oracle 9.2 ODBC driver on Windows XP
NLS_LANG = AMERICAN_AMERICA.WE8MSWIN1252
CREATE TABLE my_nclob_table (
     id number (10,0) NOT NULL ,
     name nvarchar2 (255) NOT NULL ,
     description nvarchar2 (255) NULL ,
     definition nclob NOT NULL ,
     creation date NOT NULL ,
     lastmodified date NOT NULL ,
     CONSTRAINT PK_cat_pricelist PRIMARY KEY
          id
#define     nil NULL
#define     null NULL
#define     SQL_ERR(__sqlerr__)     (((__sqlerr__) != SQL_SUCCESS) && ((__sqlerr__) != SQL_SUCCESS_WITH_INFO))
#define     STOP_IF_SQL_ERR(__sqlerr__)                                                                 \
                                                  do                                                       \
                                                       if (SQL_ERR(__sqlerr__)) goto stop_;     \
                                                  } while (false)                                                  
void eqTestOracleLOBSelect(void)
     SQLHENV henv     = null;
     SQLHDBC hdbc     = null;
     SQLHSTMT hstmt     = null;
     SQLRETURN retcode     = SQL_SUCCESS;
     TCHAR          szSQLStatement[]     = T("select id, name, definition from mynclob_table");
     int               iFetchedRows = 0;
     TCHAR          szMsg[512];
     TCHAR          chBuffer[2049];
     SQLLEN          iDataLen = 0;
     try
          retcode = eqOpenConnectionODBC(_T("myTestDsn"),_T("user"),_T("pwd"),henv,hdbc);
          STOP_IF_SQL_ERR(retcode);
          retcode = SQLAllocHandle(SQL_HANDLE_STMT, hdbc, &hstmt);
          STOP_IF_SQL_ERR(retcode);
          retcode = SQLExecDirect(hstmt,(SQLTCHAR*)szSQLStatement,SQL_NTS);
          STOP_IF_SQL_ERR(retcode);
          retcode = SQLBindCol(hstmt,3,SQL_C_TCHAR,chBuffer,sizeof(chBuffer),&iDataLen);
          STOP_IF_SQL_ERR(retcode);
               while (retcode == SQL_SUCCESS)
                    retcode = SQLFetch(hstmt);
                    if (retcode == SQL_NO_DATA)
                         retcode = SQL_SUCCESS;
                         break;
                    STOP_IF_SQL_ERR(retcode);
               //     retcode = SQLGetData(hstmt,3,SQL_C_TCHAR,chBuffer,sizeof(chBuffer),&iDataLen);
               //     STOP_IF_SQL_ERR(retcode);
                    ++iFetchedRows;
     stop_:
          if (SQL_ERR(retcode))
               MessageBox(null,_T("SQL statement execution error."),_T("Error"),MB_OK);
               eqShowStatementError(SQL_HANDLE_STMT,hstmt,retcode);
          } else     {
                         _stprintf(szMsg,_T("SQL execution success. Fetched rows: %ld"),iFetchedRows);
                         MessageBox(null,szMsg,_T("Success"),MB_OK);
     catch(...)
          MessageBox(null,_T("Unknown exception in eqTestOracleLOBSelect"),_T("Unknown exception"),MB_OK);
     if (hstmt != null)
          SQLFreeHandle(SQL_HANDLE_STMT, hstmt);
          hstmt = null;
     if (hdbc != nil)
          SQLFreeHandle(SQL_HANDLE_DBC, hdbc);
          hdbc = nil;
     if (henv != nil)
          SQLFreeHandle(SQL_HANDLE_ENV, henv);
          henv = nil;
SQLRETURN eqOpenConnectionODBC(TCHAR          *szDSN,
                                   TCHAR          *szUser,
                                   TCHAR          *szPassword,
                                   SQLHENV     &henv,
                                   SQLHDBC &hdbc)
     SQLRETURN retcode;
     henv = nil;
     hdbc = nil;
     //Allocate environment handle
     retcode = SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &henv);
     STOP_IF_SQL_ERR(retcode);
     //Set the ODBC version environment attribute
     retcode = SQLSetEnvAttr(henv, SQL_ATTR_ODBC_VERSION, (void*)SQL_OV_ODBC3, 0);
     STOP_IF_SQL_ERR(retcode);
     // Allocate connection handle
     retcode = SQLAllocHandle(SQL_HANDLE_DBC, henv, &hdbc);
     STOP_IF_SQL_ERR(retcode);
     // Set login timeout to 5 seconds.
     SQLSetConnectAttr(hdbc, SQL_LOGIN_TIMEOUT, (void*)5, 0);
     STOP_IF_SQL_ERR(retcode);
     retcode = SQLConnect(hdbc, (SQLTCHAR*)szDSN, SQL_NTS,
                                        (SQLTCHAR*)szUser, SQL_NTS,
                                        (SQLTCHAR*)szPassword, SQL_NTS);
stop_:
          if (SQL_ERR(retcode))
               MessageBox(null,_T("Connection Error."),_T("Error"),MB_OK);
               if (hdbc != nil)
                    eqShowStatementError(SQL_HANDLE_DBC, hdbc,retcode);
                    SQLFreeHandle(SQL_HANDLE_DBC, hdbc);
                    hdbc = nil;
               if (henv != nil)
                    eqShowStatementError(SQL_HANDLE_ENV, henv,retcode);
                    SQLFreeHandle(SQL_HANDLE_ENV, henv);
                    henv = nil;
          } else MessageBox(null,_T("Connected."),_T("Success"),MB_OK);
     return retcode;
void eqShowStatementError(SQLSMALLINT chHandleType, SQLHANDLE hHandle,long lErrOrig)
     SQLRETURN          nErr          = SQL_SUCCESS;
     int                    nRecNum = 1;
     SQLTCHAR          szSqlState[6];
     SQLTCHAR          szMsg[SQL_MAX_MESSAGE_LENGTH];
     SQLSMALLINT          nMsgLen;
     SQLINTEGER          nNativeError;
     while ((nErr = SQLGetDiagRec(chHandleType,hHandle,nRecNum,
                                        szSqlState, &nNativeError,
                                        szMsg, sizeof(szMsg), &nMsgLen)) != SQL_NO_DATA)
          szSqlState[5] = 0;
          MessageBox(NULL,(const TCHAR *)szMsg,_T("ODBC Error"),MB_OK);
          ++nRecNum;

Answer 1

Yes, the 9.2.0.2 driver can be downloaded from OTN. I don't believe it will solve your particular problem, but it will help in general. If you don't grab the latest version, you'll probably have to chack the "Force SQL_WCHAR Support" option in the DSN configuration.
From the help file
"The C data type, SQL_C_WCHAR, was added to the ODBC interface to allow applications to specify that an input parameter is encoded as Unicode or to request column data returned as Unicode. The macro SQL_C_TCHAR is useful for applications that need to be built as both Unicode and ANSI. The SQL_C_TCHAR macro compiles as SQL_C_WCHAR for Unicode applications and as SQL_C_CHAR for ANSI applications."
My first thought would be that your application is not being compiled as Unicode. If you substitute SQL_C_WCHAR for SQL_C_TCHAR when you're dealing with NCLOB columns, I suspect you'll have better luck.
More help file
"The SQL data types, SQL_WCHAR, SQL_WVARCHAR, and SQL_WLONGVARCHAR, were added to the ODBC interface to represent columns defined in a table as Unicode. These values are potentially returned from calls to SQLDescribeCol, SQLColAttribute, SQLColumns, and SQLProcedureColumns. In Oracle release 8.1.7.0.0 or 9.0.1.0.0, the Oracle database does not support encoding columns as Unicode. These values would not be returned from the ODBC Drivers for Oracle release 8.1.7.0.0 or for Oracle 9.0.1.0.0 databases.
In Oracle release 9.2.0.0.0, Unicode encoding was supported for SQL column types NCHAR, NVARCHAR2, and NCLOB. In addition, Unicode encoding was also supported for SQL column types CHAR and VARCHAR2 if the character semantics were specified in the column definition.
Starting with release 9.2.0.2.0, the ODBC Driver supports these SQL column types and maps NCHAR to the SQL data type SQL_WCHAR, NVARCHAR2 is mapped to SQL_WVARCHAR, and NCLOB is mapped to SQL_WLONGVARCHAR. The SQL CHAR column is mapped to SQL_WCHAR and the VARCHAR2 column is mapped to SQL_WVARCHAR if the character semantics are specified for the column. While the Force SQL_WCHAR Support option is still available in the 9.2.0.2.0 ODBC Driver, it is no longer required for Unicode support."
Justin