|=

[Compound Operators]

Description

The compound bitwise OR operator |= is often used with a variable and a constant to "set" (set to 1) particular bits in a variable.

A review of the Bitwise OR | operator:

0  0  1  1    operand1
0  1  0  1    operand2
----------
0  1  1  1    (operand1 | operand2) - returned result

Syntax

x |= y;   // equivalent to x = x | y;

Parameters

x: variable. Allowed data types: char, int, long
y: variable or constant. Allowed data types: char, int, long

Example Code

Bits that are "bitwise ORed" with 0 are unchanged, so if myByte is a byte variable,

myByte | B00000000 = myByte;

Bits that are "bitwise ORed" with 1 are set to 1 so:

myByte | B11111111 = B11111111;

Notes and Warnings

Because we are dealing with bits in a bitwise operator - it is convenient to use the binary formatter with constants. The numbers are still the same value in other representations, they are just not as easy to understand. Also, B00000000 is shown for clarity, but zero in any number format is zero.

Consequently - to set bits 0 & 1 of a variable, while leaving the rest of the variable unchanged, use the compound bitwise OR operator (|=) with the constant B00000011

1  0  1  0  1  0  1  0    variable
0  0  0  0  0  0  1  1    mask
----------------------
1  0  1  0  1  0  1  1
bits unchanged
                 bits set

Here is the same representation with the variables bits replaced with the symbol x

x  x  x  x  x  x  x  x    variable
0  0  0  0  0  0  1  1    mask
----------------------
x  x  x  x  x  x  1  1
bits unchanged
                 bits set

So if:

myByte =  B10101010;
myByte |= B00000011 == B10101011;

See also