Save/SET/Restore of SET Environment Settings (130306)



The information in this article applies to:

  • Microsoft Visual FoxPro for Windows 3.0

This article was previously published under Q130306

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
    						
  2. Create a program with the following code. This code would normally be 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")
    
    						
  3. Run the program created in step 2. The following values should be displayed on the screen:
       Deleted: ON
       Value: deleted, ON
       Deleted: OFF
    						

Modification Type:MajorLast Reviewed:2/10/2000
Keywords:kbcode KB130306