dancebert
asked on
ADO Open Method Options - Bitwise AND
The documentation for the ADO Open method Options parameter states: "Can be one or more CommandTypeEnum or ExecuteOptionEnum values, which can be combined with a bitwise AND operator."
Well, if I combine any two of the enum values using AND, the result is zero. For example
dim foo as long
foo = CommandTypeEnum.adCmdText AND _ ExecuteOptionEnum.adAsyncE
? foo
0
This doesn't make sense to me. Can somebody explain it?
I vaguely recall bit level mainuplation from a C class long ago, can't find anything useful in my VB docs.
Well, if I combine any two of the enum values using AND, the result is zero. For example
dim foo as long
foo = CommandTypeEnum.adCmdText AND _ ExecuteOptionEnum.adAsyncE
? foo
0
This doesn't make sense to me. Can somebody explain it?
I vaguely recall bit level mainuplation from a C class long ago, can't find anything useful in my VB docs.
Frequently Microsoft will use Enums as swicthes where each switch is either 1 or a power of 2.
i.e.
U 2 4 6 8 16 32 64 128 256 ...etc
You can si the same like:
Private Enum MyOptions
Option1 = 1
Option2 = 2
Option3 = 4
End Type
A long value as 32 bits that can means you can has 32 different switches than can be detected.
So to use these options you can say either:
Dim MyOpt as Long
MyOpt = MyOptions.Option1 + MyOptions.Option2
This will set the bits U and 2 in MyOpt.
The documentation you read was incorrect, infact options like these have to be or'ed together or as emoreau suggests added.
It should have read:
foo = (CommandTypeEnum.adCmdText
ExecuteOptionEnum.adAsyncE
In C/javascript the or operator is a | symbol.
If you do into imediate window you will see that
?1 or 3
is the same as
?1 + 3
So what Microsoft do in their code is detect that a specifc bit has been set by using the "And" operator
Dim Bit64Set as Boolean
Bit64Set = ((YourOptions And 64) = 64)
Bit64Set will now be either true or false
How this works is:
(YourOptions And 64) will equal 64 or 0
So comparing ot 64 will set tha belean flag.
Hope this helps you understand what's going on....
Forever, inthedark...
i.e.
U 2 4 6 8 16 32 64 128 256 ...etc
You can si the same like:
Private Enum MyOptions
Option1 = 1
Option2 = 2
Option3 = 4
End Type
A long value as 32 bits that can means you can has 32 different switches than can be detected.
So to use these options you can say either:
Dim MyOpt as Long
MyOpt = MyOptions.Option1 + MyOptions.Option2
This will set the bits U and 2 in MyOpt.
The documentation you read was incorrect, infact options like these have to be or'ed together or as emoreau suggests added.
It should have read:
foo = (CommandTypeEnum.adCmdText
ExecuteOptionEnum.adAsyncE
In C/javascript the or operator is a | symbol.
If you do into imediate window you will see that
?1 or 3
is the same as
?1 + 3
So what Microsoft do in their code is detect that a specifc bit has been set by using the "And" operator
Dim Bit64Set as Boolean
Bit64Set = ((YourOptions And 64) = 64)
Bit64Set will now be either true or false
How this works is:
(YourOptions And 64) will equal 64 or 0
So comparing ot 64 will set tha belean flag.
Hope this helps you understand what's going on....
Forever, inthedark...
ASKER CERTIFIED SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
the line you posted
foo = CommandTypeEnum.adCmdText AND _ ExecuteOptionEnum.adAsyncE
SHOULD produce 0, as the two values are NOT the same, and do not have a common POWER of 2:
foo = 1 AND 4 will equate to 0
represented in BINARY
1 = 001
4 = 100
and the bitwise AND of 001 and 100 is 000
Bitwise AND sets the corresponding BIT in the result to 1 if the same bit in BOTH values is 1, and you can clearly see that that is NOT the case with 1 AND 4.
on the other hand, the bitwiose OR operator produces a 1 in the result if the bit is EITHER (or both) numbers is 1:
1 = 001
4 = 100
1 OR 4 = 101 (turning ON the 1 bit and the 4 Bit)
so the OR operator is used to COMBINE binary flags, and the AND operator is used to determine which flags are turned ON.
Arthur Wood
foo = CommandTypeEnum.adCmdText AND _ ExecuteOptionEnum.adAsyncE
SHOULD produce 0, as the two values are NOT the same, and do not have a common POWER of 2:
foo = 1 AND 4 will equate to 0
represented in BINARY
1 = 001
4 = 100
and the bitwise AND of 001 and 100 is 000
Bitwise AND sets the corresponding BIT in the result to 1 if the same bit in BOTH values is 1, and you can clearly see that that is NOT the case with 1 AND 4.
on the other hand, the bitwiose OR operator produces a 1 in the result if the bit is EITHER (or both) numbers is 1:
1 = 001
4 = 100
1 OR 4 = 101 (turning ON the 1 bit and the 4 Bit)
so the OR operator is used to COMBINE binary flags, and the AND operator is used to determine which flags are turned ON.
Arthur Wood
CommandTypeEnum.adCmdText + ExecuteOptionEnum.adAsyncE