If I'm using something like this:
xr.Settings.ValidationFlags |= XmlSchemaValidationFlags.ReportValidationWarnings; What precisely is the |= accomplishing?
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6 Answers
|= is a shortcut for OR'ing two values together and assigning the result to the first variable.
xr.Settings.ValidationFlags |= XmlSchemaValidationFlags.ReportValidationWarnings; Is equivalent to:
xr.Settings.ValidationFlags = xr.Settings.ValidationFlags | XmlSchemaValidationFlags.ReportValidationWarnings; | is the OR operator in C#, so the code above effectively sets the ReportValidationWarnings flag on the value xr.Settings.ValidationFlags.
4 Comments
elucid8
How does the comparison after the assignment operator actually occur? I know it's comparing the bits, but I'm having a little difficulty getting my head around it.
Matthew
It's not comparing bits at all. If you have two bytes
1001 1101 and you OR it with 1100 1011 you would get 1101 1111. If a bit it set in either operand, then it is set in the result. The shorthand of |= just states that the left operand of the OR is the operand to the left of the |=.elucid8
Doesn't the link below indicate that the bitwise comparison is taking place? msdn.microsoft.com/en-us/library/h5f1zzaw%28v=vs.71%29.aspx. I suppose my confusion lies in something like this:
bool b = true; b |= false; and yet b still returns true. I feel stupid, but I'm not seeing how that translates into what's happening above.In this case you are setting XmlSchemaValidationFlags.ReportValidationWarnings flag in your ValidationFlags.
|= is generally bitwise or operator, in case of Flags it's used to set flag.
Comments
This is boolean OR-Equals.
Equivilent to:
xr.Settings.ValidationFlags = xr.Settings.ValidationFlags | XmlSchemaValidationFlags.ReportValidationWarnings; Which is ensuring that the bits in XmlSchemaValidationFlags.ReportValidationWarnings are set.
Comments
That is a compound assignment. Essentially you are doing:
xr.Settings.ValidationFlags = xr.Settings.ValidationFlags | XmlSchemaValidationFlags.ReportValidationWarnings; Which will essentially add XmlSchemaValidationFlags.ReportValidationWarnings to the set of flags contained in xr.Settings.ValidationFlags.
1 Comment
elucid8
So, why does it do that? I'm having trouble getting my head around the operation.
As others have mentioned, a |= b is shorthand for a = a | b, in much the same way as a += b is short for a = a + b. Now what does the | operator do? It can be overloaded, but the general use of it is bit-wise OR. It's similar to the || operator, but it works on a bit by bit basis (think of each bit as a boolean):
false || true is true
0100 | 0110 is 0111
Then the last thing is that one of the classic ways to pass a bunch of boolean flags is to encode them in an integer. A single 32 bit integer can hold 32 individual flags, one per bit. to set a flag, you set the corresponding bit to 1.
So 0000 has no flags set, while 1001 has flags at position 1 and 4 set.
Then |= is a convenient way to set a specific flag.
int my_flags = 0;
my_flag |= validate_flag;
Comments
driis' answer is correct.
|= is the same as using the | operator in a conditional test, as in the following examples:
xr.Settings.ValidationFlags |= XmlSchemaValidationFlags.ReportValidationWarnings is semantically identical to
xr.Settings.ValidationFlags = xr.Settings.ValidationFlags | XmlSchemaValidationFlags.ReportValidationWarnings Additional note about | vs ||
One additional tidbit I found to be useful was the difference between the logical OR (|) and the conditional OR (||):
The logical OR will always evaluate both operands, even if the first is true. The conditional OR will only evaluate the second if the first is false, effectively short-circuiting if the execution of the second operand is unnecessary to determine the final result.
