Looking for clarification on | operator

Question

Okay I've seen the pipe (|) used in instances where you want to assign multiple values to a property. A prime example of this is the Anchor property of the System.Windows.Forms.Control class. i.e... // Anchor the button to the bottom right corner of the form button1.Anchor = (AnchorStyles.Bottom | AnchorStyles.Right); This is setting two values for 1 property. I can not find any documentation on this however. Both the MSDN and the C# Spec only refer to the pipe (|) as the bitwise OR operator and does not reference anything about this use of it. Can someone clarify exactly how a property can have two values at the same time? Are there any articles on constructing custom classes using this type of device? thanks -James

spgilmore · Answer

Just to clarify.. When you see this: button1.Anchor = (AnchorStyles.Bottom | AnchorStyles.Right); The ANCHOR property is a variable of type System.Windows.Forms.AnchorStyles. AnchorStyles is defined as an enumeration. An enumeration is a type that only accepts a set of predefined valid values. If this was always true (and it's not) then AnchorStyles could only be ONE of the following but not 2 3 or 4 of the following: Bottom Right Top Left That would mean that you could only assign it one value. The thing that makes it accept 2 or more values and treat each one as an integer whose value is a power of 2 is the [Flags] attribute in its declaration. For more information see the System.Attribute and System.FlagsAttribute classes in the MSDN help. It will tell you all about it. It will show you how to create your own enumerations and sets.

sacresp · Answer

Juliet you're right. As usual :)

juliet_zl · Answer

It uses binary mathematics. For example if: property A's value is 1 its binary value is 1 property B's value is 2 its binary value is 10 property C's value is 4 its binary value is 100 etc. Therefore properties used for bitwise operator usually carries the values 1 2 4 8 16 32.... all are powers of 2. Now if I wish something to have both properties A and C say we would use A|C which calculates as 001 |100 It is like logic table AND - true if both value is true OR - true if one or both value are true therefore 001 OR 100 ----- 101 which calculates as the value 4+1 = 5 Therefore A|C = 1|4 = 5. Do you get what I mean? Correct me if I am wrong.