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EXAM10.PAS
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Pascal/Delphi Source File
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1989-07-12
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10KB
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229 lines
(* EXAM10.PAS *)
program driver;
{$R+}
uses
Exam0,
Btree,
Compare,
FileBuff,
FileDecs,
Files,
Logical,
LRecList,
Numbers,
Page,
SetOps,
Sort;
var
dataFile,
indexFile1,
indexFile2 : FnString; (* holds file name strings *)
testRec : TestRecord; (* variable to hold a data record *)
lrLst1,
lrLst2,
lrLst3 : LrList; (* variable which user declares and passes in to
LRLIST unit. LRLIST will build a list of
logical records which fulfill a query criteria.
(Actually the list will be built by a call
to the BTREE unit which in turn uses the LRLIST
unit. *)
lrNum : LrNumber; (* a couple of variable used in this demo program
to keep track of logical record number
currently being processed. *)
tempByte : Byte; (* this variable is used to pass in the selection
criteria for retrievals. A variable or typed
constants must be used. Constants do not work
since the call is by reference and not by
value *)
sPtr : SortFieldList;
exitSave : Pointer; (* used as pointer to my terminiation procedure *)
(* This procedure will be called prior to termination of the program whether
there is an error or not. This is a demonstration of a good technique to
use in conjunction with TBTREE. Calls to write the buffer to disk and
close the files should be included. This is also a place top handle runtime
error since I do not attempt to deal with errors or maintain global error
variables in TBTREE. *)
{$F+} procedure MyExit; {$F-}
begin
ExitProc := ExitSave; (* reinstall the saved value of ExitProc *)
Writeln('Writing Records To Disk ...'); (* just a note so you can
follow along *)
WriteEntireBufferToDisk; (* very important step!! Before leaving
the program the buffer must be written
to disk or some changes will be lost.
This will cause major problems and lost
data!!! This is not really required in
in this program since nothing is
modified. A logical record list is
created, but it happens to be small
enough that a temporary file is not
needed. If a file was needed, it would
have been destroyed on the call to
DestroyLrList anyway. *)
Writeln('Closing Files ...'); (* just a note so you can
follow along *)
CloseAllFiles; (* Close the files to clean up. It is
important to realize that CloseAllFiles
DOES NOT write the buffer to disk, it only
deals with the files open list. *)
end;
(* This routine should be called before anything else happens. It calls
the various routines to set up parameters according to values applicable
to your particular application. *)
procedure SetUp;
begin
SetMaxBufferPages(100); (* a call to the PAGE unit to set up the number
of pages in the buffer. If this is not done a
default of one page is used. This will cause
poor performance but will not cause any
runtime errors *)
SetMaxOpenFiles(10); (* a call to the FILEBUFF unit to set the number
of files the FILEBUFF unit can have open at
once. See FILEBUFF unit for details. *)
SetImmediateDiskWrite(FALSE); (* changed and newly created pages will be
buffered in the page buffer and will only
written to disk when they are swapped out
or explicitly written out by a user
request *)
end;
(* This procedure initializes the file names as required. Also, if will
create the files if they do not exist. Therefore, you can use one
initialization routine whether the file exists or must be created. *)
procedure InitFiles;
begin
dataFile := 'myFile1.dat';
if not FileExists(dataFile) then
begin
CreateDataFile(dataFile,SizeOf(TestRecord));
end;
indexFile1 := 'testByte.idx';
if not FileExists(indexFile1) then
begin
CreateIndexFile(indexfile1,SizeOf(BYTE),BYTEVALUE);
end;
indexFile2 := 'testStrg.idx';
if not FileExists(indexFile2) then
begin
CreateIndexFile(indexfile2,SizeOf(TestString),STRINGVALUE);
end;
end;
(*****************************************************************************)
(* *)
(* M A I N P R O G R A M *)
(* *)
(*****************************************************************************)
begin
Writeln('Setting up termination routine ...'); (* just a note so you can
follow along *)
exitSave := ExitProc; (* see page 376 - 377 of Turbo Pascal 4.0 manual *)
ExitProc := @MyExit;
Writeln('Initializing Parameters ...'); (* just a note so you can
follow along *)
SetUp; (* set file open buffer size and page buffer size limits *)
(* set immediate disk write parameter as well *)
InitFiles;
Writeln('Looking for logical records which match selection criterion and',
' building logical record list ... this may take a minute ...' );
(* just a note so you can
follow along *)
tempByte := 240;
GetValuesFromBTree(indexFile1,tempByte,LE,lrLst1); (* build list of logical
record numbers with
values <= 240 *)
tempByte := 50;
GetValuesFromBTree(indexFile1,tempByte,GE,lrLst2); (* build list of logical
record numbers with
values >= 50 *)
Intersection(lrLst1,lrLst2,lrLst3); (* create new list (lrLst3) which
is the intersection of lrLst1
and lrLst2 *)
(* The following loop will fetch the data records associated with the
record numbers found in the newly created logical record list. Each
of the records will be printed. Since the list was built using
indexFile1 which is the index corresponding to the randByte field in
testRec, the records will be printed in ascending order by
testRec.randByte. If the opposite order was desired the list should
be traversed in reverse by using GetLastLr and GetPrevLr. *)
lrNum := GetFirstLr(lrLst3); (* get the first record number and set the cursor
the front of the list. *)
while lrNum <> 0 do
begin
GetALogicalRecord(dataFile, (* variable holding name of data file *)
lrNum, (* logical record number from list *)
testRec); (* place to put the data *)
Writeln(lrNum,' ',testRec.randByte,' ',testrec.randString);
lrNum := GetNextLr(lrLst3); (* advance the cursor to next in list *)
end;
(* The following three calls are for demo purposes to show a couple of
utilities available. *)
Writeln('Total records found matching criteria = ',GetCountLr(lrLst3));
Writeln('Number of files presently open = ',GetNumberOpenFiles);
DestroyLrList(lrLst1);
DestroyLrList(lrLst2);
DestroyLrList(lrLst3); (* we're done with list so let's get rid of them. This
is important so that there aren't a bunch of
temporary files upon termination. Also, lists
take up data space and also space in the page
buffer *)
end.