void ddlSetFetchDataCb(
      CONTROL *ctl,
      char *pszTableName,
      FetchDataRtn UserFetch,
      WtCastPtr UserWord)
 
   Prototype of the fetch callback function:
 
   typedef int (STDCALL *FetchDataRtn)(
      /* value: 0 - OK; > 0 - terminate; < 0 - deleted record */
      WtCastPtr UserWord,
      char *DestImage,           /* [IN/OUT] virtual TB rec */
      TBAPI_FETCHCB_HEADER *sFetchInfoArray,   /* [IN] */
      char *pszTableAliasName,   /* [IN] */
      long RecNo);
 
   Structures used by the fetch callback:
 
   typedef struct TBAPI_FETCHCB_HEADER{
      int iStructureLength;     /* total length of this structure in bytes */
      int iItemCount;           /* number of TBAPI_FETCHCB_INFO{} members */
      int iOffsetToInfo;        /* offset to first TBAPI_FETCHCB_INFO{} */
    
      /* added in TBAPI 8.0.115 ... */
      int iFetchCbFlags;        /* Ref TBAPI_FETCHCB_FLAG_xxx */
      int iItemBuffSize;        /* size of DestImage (virtual TB record) */
      int iReserved[4];         /* reserved for future use */
    
      char szInternalTableName[TBAPI_INTERNAL_TABLENAME_LENGTH+8];
   }TBAPI_FETCHCB_HEADER;
    
   typedef struct TBAPI_FETCHCB_INFO{
      int iDataType;            /* Ref DdDataType enum{} */
      int iStartOffset;         /* 0-rel offset to start of data */
      int iDataLength;
      int iDataPoint;           /* for N() data type only */
      char szInternalColumnName[TBAPI_INTERNAL_COLUMNNAME_LENGTH+8];
      char cVirtualDataFlag;    /* !=0 - virtual; 0 - non-virtual */
      char cNullFlag;           /* !=0 - null; 0 - non-null; [non-virtual data only */
      char cDataRequestFlag;    /* !=0 - data is requested [virtual data only] */
   }TBAPI_FETCHCB_INFO;
 
   Symbolic constants for TBAPI_FETCHCB_HEADER iFetchCbFlags
 
   enum{
      TBAPI_FETCHCB_FLAG_NONE     = 0x0000,
      TBAPI_FETCHCB_FLAG_FIRST    = 0x0001,
      TBAPI_FETCHCB_FLAG_NOBATCH  = 0x0002,
      TBAPI_FETCHCB_FLAG_RANDOM   = 0x0004,
   };

Description:

The ddlSetFetchDataCb() API function defines a user callback that is triggered whenever a TBAPI function requests virtual data. The fetch callback is defined for a specific table whenever the ddlSetFetchDataCb() parameter UserFetch is non-null. The fetch callback is undefined for a specific table whenever the UserFetch parameter is null; the fetch callback is also undefined by default. In particular, the fetch callback is triggered whenever a TB API read data function:        1) requests data from a virtual table; AND        2) the request includes one or more virtual columns; With one specific exception, the fetch callback cannot call another TBAPI function. The exception is DdGetFetchInfo(). The description of collection processing modes gives more insight into the various contexts where the fetch callback is invoked. A simple graphical outline of the connection between a TB API function, TB API internal and the UserFetch CB: ddlGetRec() etal ... TB API call from user App | + db_rdata() TB API internal call | + db_rdataVirt() TB API internal call | + UserFetch() TB API call to user fetch callback A simple logical outline of the connection between a TB API function, TB API internal and the UserFetch CB: 1) Read non-virtual record to buffer; 2) Move non-virtual data to new buffer using virtual csp; 3) Call DefaultFetchRtn(); 4) If defined, call UserFetch CB; 5) If UserFetch CB returned non-zero value, exit 6) Else, move virtual buffer to user's buffer using user's csp;

   TBAPI_FETCHCB_HEADER
   TBAPI_FETCHCB_ITEM #1
   TBAPI_FETCHCB_ITEM #2
   ...
   TBAPI_FETCHCB_ITEM #N
 
   TBAPI_FETCHCB_HEADER *header = 0;
   TBAPI_FETCHCB_ITEM *item = 0;
 
   header->iItemCount is the number of items being returned;
   header->iOffsetToInfo is Buffer-0 relative offset to the first item;
   header->iFetchCbFlags is one or more of the constants TBAPI_FETCHCB_FLAG_xxx;
   header->iItemBuffSize is the size of DestImage;