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Coding Convention for using Binary FlagWords?
Hi all ---
I'm thinking of putting the .Tag property to use by using a binary ("bitwise") encoded flag word. Over time I've come across different possible uses for .Tag but have never standardized how I use it. Has someone developed a convention for "parsing" binary flag words? A simple IF works if I only need to test for one flag, but if I need to check for the presence of multiple bits the only construct that comes to mind is a series of IF statements .... something along the lines of: Enum FlagWord FlagA = 1 FlagB = 2 FlagC = 4 .... End Enum Dim vFlags as FlagWord 'validation and error handling omitted for simplicity vFlags = Me.ctlx.Tag IF vFlags AND FlagA then 'do something EndIF If vFlags AND FlabB then 'do something else EndIf If vFlags AND FlabC then 'do a different thing EndIf -- Clif |
#2
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Coding Convention for using Binary FlagWords?
"Clif McIrvin" wrote in message
... Hi all --- I'm thinking of putting the .Tag property to use by using a binary ("bitwise") encoded flag word. Over time I've come across different possible uses for .Tag but have never standardized how I use it. Has someone developed a convention for "parsing" binary flag words? A simple IF works if I only need to test for one flag, but if I need to check for the presence of multiple bits the only construct that comes to mind is a series of IF statements .... something along the lines of: Enum FlagWord FlagA = 1 FlagB = 2 FlagC = 4 ... End Enum Dim vFlags as FlagWord 'validation and error handling omitted for simplicity vFlags = Me.ctlx.Tag IF vFlags AND FlagA then 'do something EndIF If vFlags AND FlabB then 'do something else EndIf If vFlags AND FlabC then 'do a different thing EndIf I haven't done what you're attempting, but I don't think you can do this: Dim vFlags as FlagWord vFlags = Me.ctlx.Tag You will probably need to store the current flag settings in the Tag property as the string representation of a number that is the sum or bitwise-Or of the desired combination of flags. For example, to set the Tag to the combination of FlagA (1) and FlagC (4), you would do this: Me.ctlx.Tag = CStr(FlagA + FlagC) ' the Tag is now "5" If you set up your individual flag values so that each is a different power of 2, then you can just add them, as above. To test the flags, you would get the Tag value, convert it to an integer, and then use the bitwise And operator to see what flags are set. To test for an individual bit value, you would do it like this: Dim intFlags As Integer intFlags = CInt(Me.ctlx.Tag) ' Is FlagA set? If (intFlags And FlagA) Then ' FlagA was set End If To test for a combination of flags, you would do this: ' Are both FlagA and FlagC set? If (intFlags And (FlagA + FlagC)) = (FlagA + FlagC) Then ' Both flags are set. End If I believe that works, but I haven't tested it. -- Dirk Goldgar, MS Access MVP Access tips: www.datagnostics.com/tips.html (please reply to the newsgroup) |
#3
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Coding Convention for using Binary FlagWords?
"Dirk Goldgar" wrote in message
... "Clif McIrvin" wrote in message ... Hi all --- I'm thinking of putting the .Tag property to use by using a binary ("bitwise") encoded flag word. Over time I've come across different possible uses for .Tag but have never standardized how I use it. Has someone developed a convention for "parsing" binary flag words? A simple IF works if I only need to test for one flag, but if I need to check for the presence of multiple bits the only construct that comes to mind is a series of IF statements .... something along the lines of: Enum FlagWord FlagA = 1 FlagB = 2 FlagC = 4 ... End Enum Dim vFlags as FlagWord 'validation and error handling omitted for simplicity vFlags = Me.ctlx.Tag IF vFlags AND FlagA then 'do something EndIF If vFlags AND FlabB then 'do something else EndIf If vFlags AND FlabC then 'do a different thing EndIf I haven't done what you're attempting, but I don't think you can do this: Dim vFlags as FlagWord vFlags = Me.ctlx.Tag You will probably need to store the current flag settings in the Tag property as the string representation of a number that is the sum or bitwise-Or of the desired combination of flags. For example, to set the Tag to the combination of FlagA (1) and FlagC (4), you would do this: Me.ctlx.Tag = CStr(FlagA + FlagC) ' the Tag is now "5" If you set up your individual flag values so that each is a different power of 2, then you can just add them, as above. To test the flags, you would get the Tag value, convert it to an integer, and then use the bitwise And operator to see what flags are set. To test for an individual bit value, you would do it like this: Dim intFlags As Integer intFlags = CInt(Me.ctlx.Tag) ' Is FlagA set? If (intFlags And FlagA) Then ' FlagA was set End If To test for a combination of flags, you would do this: ' Are both FlagA and FlagC set? If (intFlags And (FlagA + FlagC)) = (FlagA + FlagC) Then ' Both flags are set. End If I believe that works, but I haven't tested it. -- Dirk Goldgar, MS Access MVP Access tips: www.datagnostics.com/tips.html (please reply to the newsgroup) Thanks, Dirk. As always, your reply is detailed and helpful! I haven't done what you're attempting, but I don't think you can do this: Dim vFlags as FlagWord vFlags = Me.ctlx.Tag I was actually intending to use something like: if Len(Me.ctlx.Tag)=0 then --- no flags if val(Me.ctlx.Tag)=0 then --- no flags vFlags = cLng(split(Me.ctlx.Tag)(0)) (if that syntax works) but abbreviated a lot of the detail on purpose to simplify the question grin. Thanks again for the reply. Clif |
#4
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Coding Convention for using Binary FlagWords?
"Clif McIrvin" wrote:
I'm thinking of putting the .Tag property to use by using a binary ("bitwise") encoded flag word. Over time I've come across different possible uses for .Tag but have never standardized how I use it. I just use multiple string values in there and do an Instr to see what's appropriate. As a developer I want to see at a glance what that tag is being used for at a glance. That's far more important that any storage saving. Tony -- Tony Toews, Microsoft Access MVP Tony's Main MS Access pages - http://www.granite.ab.ca/accsmstr.htm Tony's Microsoft Access Blog - http://msmvps.com/blogs/access/ For a convenient utility to keep your users FEs and other files updated see http://www.autofeupdater.com/ Granite Fleet Manager http://www.granitefleet.com/ |
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