Q(uick)BASIC Statement: CHECKPOINT

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CHECKPOINT

Writes all open ISAM database buffers to disk in their current state

Worth knowing

Useful and cross-version information about the programming environments of QBasic and QuickBasic.

Description/Parameter(s)

CHECKPOINT writes all open ISAM database buffers to disk in their current state.

Example

This example uses the CREATETABLE statement to create a new table in an ISAM file and uses the SEEK, RETRIEVE, UPDATE, and INSERT statements to insert records into it. It uses the LOF function to display the number of records in the new table and then destroys the table with DELETETABLE.
Note: To run this program, you must load the ISAM TSR program PROISAMD.EXE. Also, this program assumes a file called BOOKS.MDB exists in the current directory. BOOKS.MDB is a sample ISAM file that SETUP copies to your disk.
If this program is interrupted before the database is closed, the file BOOKS.MDB may be left in an inconsistent state.

DEFINT A-Z
TYPE BookRec
    IDNum AS DOUBLE             'Unique ID number for each book.
    Price AS CURRENCY           'Book's price.
    Edition AS INTEGER          'Book's Edition
    Title AS STRING * 50        'Book's title.
    Publisher AS STRING * 50    'Book's publisher.
    Author AS STRING * 36       'Book's author.
END TYPE
 
CONST Database = "BOOKS.MDB"    'Name of the disk file.
CONST tablename = "BookStock"   'Name of the table.
DIM Library AS BookRec          'Variable for current record.
DIM MinPrice AS CURRENCY        'SEEK criteria.
 
    CLS
    'Open existing table.
    LibraryFile = FREEFILE
    OPEN Database FOR ISAM BookRec tablename AS LibraryFile
    CREATEINDEX LibraryFile, "Library", 0, "Price"
    SETINDEX LibraryFile, "Library"
 
    'Create and open a new table.
    NewFile = FREEFILE
    OPEN Database FOR ISAM BookRec "PricyBooks" AS NewFile
 
    'Fill new table with records for all books with price >= MinPrice.
    DO
  DO
      INPUT "Display books that cost as much or more than "; MinPrice
      IF MinPrice < 0 THEN PRINT "Positive values only, please."
  LOOP UNTIL MinPrice >= 0
 
  SEEKGE LibraryFile, MinPrice
  IF EOF(LibraryFile) THEN
      PRINT "There are no books greater than"; MinPrice
  END IF
    LOOP WHILE EOF(LibraryFile)
 
    DO
  RETRIEVE LibraryFile, Library
  INSERT NewFile, Library
  MOVENEXT LibraryFile
    LOOP UNTIL EOF(LibraryFile)
 
    'Loop through new table twice: first time ask for price increase;
    'second time display new price.
    FOR count = 1 TO 2
  CLS
  PRINT SPC(18); "There are"; LOF(NewFile); "books that cost at least ";
  PRINT USING ("$###.##"); MinPrice
  PRINT " ID Number"; SPC(3); "Title"; SPC(20); "Author";
  PRINT SPC(11); "Publisher"; SPC(10); "Price"
  VIEW PRINT 3 TO 20
  MOVEFIRST NewFile
  DO
      RETRIEVE NewFile, Library
      PRINT Library.IDNum; " "; LEFT$(Library.Title, 20);
      IF LEN(RTRIM$(Library.Title)) > 20 THEN
    PRINT "...  ";
      ELSE
    PRINT "     ";
      END IF
      PRINT LEFT$(Library.Author, 15); "  ";
      PRINT LEFT$(Library.Publisher, 16); "  ";
      PRINT USING ("$###.##"); Library.Price
      MOVENEXT NewFile
  LOOP UNTIL EOF(NewFile)
 
  IF count = 1 THEN
      VIEW PRINT 20 TO 24: LOCATE 20, 1
      DO
    INPUT "Increase cost by how much (0-100%)"; increase
    IF increase < 0 OR increase > 100 THEN PRINT "Illegal value"
      LOOP UNTIL increase >= 0 AND increase <= 100
 
      'Update records in PricyBooks.
      MOVEFIRST NewFile
      DO
    RETRIEVE NewFile, Library
    Library.Price = (Library.Price * (100 + increase)) / 100
    'Overwrite record with increased price.
    UPDATE NewFile, Library
    'Force ISAM to flush the buffer to disk.
    CHECKPOINT
    MOVENEXT NewFile
      LOOP UNTIL EOF(NewFile)
  END IF
  VIEW PRINT 1 TO 19
    NEXT count
 
    'Destroy index and temporary table, close files.
    DELETEINDEX LibraryFile, "Library"
    CLOSE
    DELETETABLE Database, "PricyBooks"
    END