Save/SET/Restore of SET Environment Settings

ID: Q130306

3.00 WINDOWS

The information in this article applies to:

• Microsoft Visual FoxPro for Windows, version 3.0

SUMMARY

In version 2.x, environment settings such as "DELETED" were often stored into memory variables at the beginning of a section of code. At the end, the settings were manually reassigned to the original value. This article demonstrates an object-oriented approach to saving and restoring environment settings.

MORE INFORMATION

The class "cSET" demonstrates this technique. In this class, a number of the current SET environment settings for DELETED, ALTERNATE, and DECIMALS are stored in objects. One object is created for each environment setting that should be stored. This class could easily be expanded to include additional environment settings.

When the class, cSET, is instantiated in your form or other application component, an object is created for each desired environment setting. The CONSTRUCTOR method is invoked whenever you want to change an environment setting. It creates a command string that sets the desired temporary environment setting. When the instantiated class object is released, the DESTRUCTOR method is called. This method restores each environment setting to its state at the time cSET was instantiated.

1. To use this approach in an application, begin by creating a program

   that contains the class definition.

   * Begin code example
   * Save This as CSET.PRG
   * This class provides SET environment save/SET/restore capabilities
   * When the class is instantiated, the current SET environment is
   * saved & SET to the desired value. When the instantiated object goes
   * out of scope, the environment is restored.

   * Usage:
   *  CreateObject( "CSET", <cExpr1>, <cExpr2> | <nExpr2> [, <cExpr3>] )
   *
   *   cExpr1 = One of the SET commands
   *   cExpr2 = Appropriate character value for the SET command
   *   nExpr2 = Appropriate numeric value for the SET command
   *   cExpr3 = Optional character value for SET commands that are both
   *            ON | OFF
   *            and have another value (like ALTERNATE, FIELDS, etc.)
   *
   * Examples:
   *   loDeletedSave   = createobject( "CSET", "deleted", "on" )
   *   loDecimalsSave  = createobject( "CSET", "decimals", 5 )
   *   loAlternateSave = createobject( "CSET", "alternate", "on", ;
   *                     "alter.txt")

   DEFINE CLASS CSET AS CUSTOM

   * PROTECTED Data Members
   * =====================================================
   PROTECTED mcSET               && SET command
   PROTECTED muOrgValue          && Original value of the SET
   PROTECTED muOrgValue1         && Original secondary value of the SET

   * Public Data Members
   * ========================================================
   * NONE

   * PROTECTED Function Members
   * =================================================

   * Constructor Method
   * ----------------------------------------------------------

   PROTECTED FUNCTION Init
   PARAMETER pcSET, puNewValue, pcNewValue1

   LOCAL lnParmCount          && number of PARAMETERs sent to init
   LOCAL lcSETCommand            && constructed SET command

   lnParmCount = PARAMETERS()

   * Default the data members
   This.mcSET = ""
   This.muOrgValue = ""
   This.muOrgValue1 = ""

   IF ( lnParmCount < 2 )
   *   This.error( "some error" )
      RETURN
   ENDIF

   * Save current environment

   This.mcSET       = pcSET
   This.muOrgValue  = SET( pcSET )
   This.muOrgValue1 = SET( pcSET, 1 )
   IF ( This.muOrgValue == This.muOrgValue1 )
      * throw This away because we don't need it
      This.muOrgValue1 = ""
   ENDIF

   IF ( lnParmCount = 3 )
      * optional argument handling
      lcSETCommand = pcSET + " to " + pcNewValue1
      SET &lcSETCommand
   ENDIF

   IF ( TYPE( "This.muOrgValue" ) == 'C' )
      * character type of SET
      lcSETCommand = puNewValue
      IF ( ! INLIST( This.muOrgValue, "ON", "OFF" ) )
         * not a simple ON|OFF so add a TO keyword
         lcSETCommand = "TO " + puNewValue
      ENDIF
   ELSE
      * numeric type of SET
      lcSETCommand = "TO " + STR( puNewValue )
   ENDIF

   lcSETCommand = pcSET + " " + lcSETCommand
   SET &lcSETCommand                          && change the SET

   * Destructor Method
   * ---------------------------------------------------- ------
   PROTECTED function Destroy

   *LOCAL lcSETCommand            && constructed SET command

   IF ( EMPTY( This.mcSET ) )
      RETURN
   ENDIF

   IF ( TYPE( "This.muOrgValue" ) == 'C' )
      * character type of SET
      lcSETCommand = This.muOrgValue
      IF ( ! INLIST( This.muOrgValue, "ON", "OFF" ) )
         * not a simple ON|OFF so add a TO keyword
         lcSETCommand = "TO " + This.muOrgValue
      ENDIF
   ELSE
      * numeric type of SET
      lcSETCommand = "TO " + STR( This.muOrgValue )
   ENDIF

   lcSETCommand = This.mcSET + " " + lcSETCommand
   SET &lcSETCommand                              && restore the SET

   IF ( ! EMPTY( This.muOrgValue1 ) )
      * restore secondary SET information
      lcSETCommand = This.mcSET + " TO " + This.muOrgValue1
      SET &lcSETCommand
   ENDIF

   * Public Function Members
   * ====================================================

   * Value Method
   * ---------------------------------------------------------------

   * RETURN the current values of the PROTECTED data members in a comma
   * delimited string.

   FUNCTION Value
   LOCAL lcRETURNValue

   IF ( TYPE( "This.muOrgValue" ) == 'C' )
      lcRETURNValue = This.mcSET + "," + This.muOrgValue
   ELSE
      lcRETURNValue = This.mcSET + "," + ;
         ALLTRIM( STR( This.muOrgValue ) )
   ENDIF

   IF ( ! EMPTY( This.muOrgValue1 ) )
      lcRETURNValue = lcRETURNValue + "," + This.muOrgValue1
   ENDIF

   RETURN lcRETURNValue

   ENDDEFINE

   *** END CODE EXAMPLE FOR cSET.PRG

   placed in the load event of a form, or at the top of a .PRG file. For
   the purposes of demonstration, it is being placed in a separate
   program file:

   ******************************************************************
   *Begin code example
   ******************************************************************

   * Driver program to test CSET class

   SET PROCEDURE TO cset ADDITIVE

   CLEAR
   SET DELETED ON       && start it out on for testing

   _Screen.Show
   ? "Deleted:", SET("deleted")
   loDeletedSave = CreateObject( "CSET", "deleted", "off" )
   ? "Value:", loDeletedSave.Value()
   ? "Deleted:", SET("deleted")

   displayed on the screen:

   Deleted: ON
   Value: deleted, ON
   Deleted: OFF

Keywords          : kbcode FxprgClassoop 
Version           : 3.00
Platform          : WINDOWS