Flipping the checked state of a menu item

[Gary Beene]

I wrote these two lines of code, which flip the check state of a menu item between %MF_CHECKED (&H8) and %MF_UNCHECKED (&H0).

It works, but only because one of the two values was a zero, making it possible to use the IsFalse the way I did.

Menu Get State hMenuOptions, ByCmd %ID_Backup To iReturn
Menu Set State hMenuOptions, ByCmd %ID_Backup, Abs(IsFalse iReturn)*8

Is there a more common approach used in PowerBASIC land? In my previous world, the two values were 0/1 and accessed directly as a property, making the flip an easy one line of code.

If both values were non-zero, this longer code would also work:

IF iState = 1stvalue Then
   iState = 2ndValue
Else
   iState = 1stValue
End if

But elegant it's not.

Just thought I'd see if there was a common, simpler approach that I've not run across.

[Michael Mattias]

Generally bit masks are managed with the boolean operators AND, OR, NOT, etc.

Untested but should work..

   Menu get State  ....   to iState    
   Menu set State  .....  IIF&(iState AND %MF_CHECKED), %MF_UNCHECKED, %MF_CHECKED)

[Gary Beene]

Thanks, Micheal.

Your approach would work regardless of the values of the two options. Neither has to be zero.

[Scott Slater]

Bit Values can be toggled by using XOR.

Where:

   Local Flags As Dword
   
   Flags = 1  ' Bit 0 ON
   
   Flags = (Flags Xor 2)  ' Toggle Bit 1 (Value of 2) (was off will be on)
   
   ? Format$(Flags)       ' verify that both Bits 0 and 1 are on  (Values 1+2 should = 3)
   
   Flags = (Flags Xor 2)  ' Toggle Bit 1 (Value of 2) (was on will be off)
   
   ? Format$(Flags)       ' verify that Bit 1 remains on, but Bit 2 is back off (should = 1)

Turn them on with OR

Turn them off with AND NOT

[Gary Beene]

Hi Scott,

Bit flipping as you describe works well for a case like %MF_CHECKED (&H8) and %MF_UNCHECKED (&H0), where a flipping a single bit would convert between the desired values. I like that.

In a more general case, flipping between two values could require multiple bit flips, unique to the numbers involved.

My post was to inquire if there are some general algorithms, like these:

Toggle between 1 and 0

A = NOT A           (well, in VB anyway)

Toggle between -1 and 0

x = x XOR 1

Toggle between 1 and 2

x = 3-x

And, as I noted, it's always easy to use

IF iState = 1stvalue Then
   iState = 2ndValue
Else
   iState = 1stValue
End if

For the special cases where a single bit distinguishes two values, the use of XOR as you've noted would work well.

[Scott Slater]

In a more general case, flipping between two values could require multiple bit flips, unique to the numbers involved.

If you mean flipping 2 bits at once, first OR them together then flip them both using XOR.

Bits2Flip = %Property1 OR %Property2

BitField = (BitField XOR Bits2Flip)

I am not sure if this is what you are looking for or not.

[Charles Dietz]

Gary, if I understand your request, maybe you could use

x = IFF(x = u1, u2, u1)

to toggle between x = u1 and x = u2