Thread: COnfused about the |= symbol?

| is bitwise OR
|= means you're setting a bit..i think

It's very much like +=

Only it's bitwise-or rather than addition.

Look up assignment operators.

Originally Posted by shrink_tubing

Hi read this in a book. What does this symbol mean the vertical line and the equals sign?

|=

It's a shorthand version of : x = x | y;

It does a bitwise OR...

The logic "truth table" is like this...

0 OR 0 = 0
1 OR 0 = 1
0 OR 1 = 1
1 OR 1 = 1

and it's done on every bit of the variable...

That is to say that the two numbers are compared at the binary level and all the 1 bits are merged, like this...

Code:

char a = 3;             // in binary  00000011
char b = 24;            // in binary  00011000
a |= b;                 // in binary  00011011

Printf("%d",a);       // should display 27;

char a = 27;           // in binary  00011011
char b = 24;           // in binary  00011000
a |= b;                // in binary  00011011

Printf("%d",a);        // should still display 27;

It gets into binary logic which isn't really used in programming for general purpose things, but when working with I/O ports (etc) at the bit level it can be helpful.