Solved

ADO Open Method Options - Bitwise AND

Posted on 2002-03-09
4
197 Views
Last Modified: 2010-05-02
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.adAsyncExecute
  ? 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.
0
Comment
Question by:dancebert
  • 2
4 Comments
 
LVL 69

Expert Comment

by:Éric Moreau
ID: 6853160
Use + instead of AND like this:

CommandTypeEnum.adCmdText + ExecuteOptionEnum.adAsyncExecute
0
 
LVL 17

Expert Comment

by:inthedark
ID: 6853535
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 Or _
            ExecuteOptionEnum.adAsyncExecute)

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...
0
 
LVL 17

Accepted Solution

by:
inthedark earned 100 total points
ID: 6853543
Same post but with some of the typos removed:

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 do the same like:

Private Enum MyOptions
 Option1 = 1
 Option2 = 2
 Option3 = 4
End Type

A long value has 32 bits.  This means you can have 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

Or you can say:
MyOpt = MyOptions.Option1 Or 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 using the + operator.

It should have read:

foo = (CommandTypeEnum.adCmdText Or _
           ExecuteOptionEnum.adAsyncExecute)

(In C/Javascript the "Or" operator is a "|" symbol.


If you go into immediate window you will see that

?1 or 2
is the same as
?1 + 2
Both are 3 i.e. Bits U and 2 have been set.

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 and trying not to speak doubledutch with typos...
0
 
LVL 44

Expert Comment

by:Arthur_Wood
ID: 6853699
the line you posted

 foo = CommandTypeEnum.adCmdText AND _ ExecuteOptionEnum.adAsyncExecute

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
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction While answering a recent question about filtering a custom class collection, I realized that this could be accomplished with very little code by using the ScriptControl (SC) library.  This article will introduce you to the SC library a…
If you need to start windows update installation remotely or as a scheduled task you will find this very helpful.
As developers, we are not limited to the functions provided by the VBA language. In addition, we can call the functions that are part of the Windows operating system. These functions are part of the Windows API (Application Programming Interface). U…
Get people started with the process of using Access VBA to control Excel using automation, Microsoft Access can control other applications. An example is the ability to programmatically talk to Excel. Using automation, an Access application can laun…

943 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

9 Experts available now in Live!

Get 1:1 Help Now