dBase 中有一个复合索引，索引值段可以是一个表达式！那么这种情况如何查询呢？

Here is an example of how to call the generic SearchExpr function:

 {current index key expression is 'DTOS(CRT_DATE)+CRT_CODE'}

 Table1.SetKey;

 Table1.FieldByName('CRT_DATE').AsString := '2/2/94'; {assign search values}

 Table1.FieldByName('CRT_CODE').AsString := 'T002';   {assign search values}

 if SeekExpr(Table1.Handle, [Table1.FieldByName('CRT_DATE'),

                             Table1.FieldByName('CRT_CODE')] ) then

   ShowMessage('Found!')

 else

   ShowMessage('Not found!');

 {note that the record pointer is now on the record it found, if any}

Here is the code for the generic search function:

 function TDBFTest1.SeekExpr(hTable: HDBIcur;

                             aFlds: array of TField): boolean;

   const

     KeyBufSize = 250;        {maximum size of key}

   var

     pRecBuf:   pByte;        {contains a record in memory}

     pKeyBuf:   pByte;        {contains actual key}

     TblProps:  CURProps;     {table properties }

     rslt:      DBIResult;    {result of BDE call}

     i:         integer;      {counter}

     tmpPSZ:    PCHAR;

     tmpDate:   LongInt;

   begin

     {get size of record buffer}

     DbiGetCursorProps(hTable, TblProps);

     {allocate memory for record buffer}

     GetMem(pRecBuf, TblProps.iRecBufSize * sizeof(BYTE));

     GetMem(pKeyBuf, KeyBufSize); {allocate mem for key}

     {initialize record buffer}

     DbiInitRecord(hTable, pRecBuf);

     {set search values in record buffer}

     for i := 0 to High(aFlds) do

     begin

       {TStringField}

       if (aFlds[i] is TStringField) then

         begin

           GetMem(tmpPSZ, Length(aFlds[i].AsString)+1);

           StrPCopy(tmpPSZ, aFlds[i].AsString);

           DbiPutField(hTable,              {TTable}

                       aFlds[i].FieldNo,    {TField}

                       pRecBuf,             {pointer to record buffer}

                       (tmpPSZ));           {pointer to value}

           FreeMem(tmpPSZ, Length(aFlds[i].AsString)+1);

         end

       {TDateField}

       else if (aFlds[i] is TDateField) then

         begin

           tmpDate := Trunc(aFlds[i].AsDateTime);

           DbiPutField(hTable,              {TTable}

                       aFlds[i].FieldNo,    {TField}

                       pRecBuf,             {pointer to record buffer}

                       (@tmpDate));         {pointer to value}

         end

     end;

     {create a key for the above values}

     DbiExtractKey(hTable, pRecBuf, pKeyBuf);

     {search using this key (stored in pKeyBuf)}

     table1.updatecursorpos;

     rslt := DbiGetRecordForKey(hTable, True, 0, 0, pKeyBuf, nil);

     table1.refresh; {update data aware components}

     if rslt <> 0 then

       Result := False

     else

       result := True;

     ShowRecord; {display new record number -- see below}

     {free memory allocated for buffer}

     FreeMem(pRecBuf, TblProps.iRecBufSize * sizeof(BYTE));

     FreeMem(pKeyBuf, KeyBufSize);

   end;

   procedure TDBFTest1.ShowRecord;

   {Show a dBase record number}

   {NOTE: it assumes there is a label component named RecordNo.}

   var

     myrecprop: RECprops;

     recno: integer;

   begin

     table1.updatecursorpos;

     recno := 0;

     dbiGetRecord(table1.handle, dbiNOLOCK, nil, @myrecprop);

     recno := myrecprop.iPhyRecNum;

     RecordNo.Caption := inttostr(recno);

   end;