Toggling enum values as bit flags

Question

I have a certain set of available enumed options

typdef enum { 
option1 = 1 << 0,
option2 = 1 << 1,
option3 = 1 << 2,
} availableOptions;

I want to toggle them off and on according to an input from the user before executing them.

For instance:

// iniatially set to all options
myOption = option1 | option2 | option3;

// after some input from the user

void toggleOption1()
{
  // how can I toggle an option that was already set without impacting the other options
}

godel9 · Accepted Answer · 2013-11-17 14:51:17Z

18

Use bit-wise XOR:

void toggleOption1()
{
    myOption ^= option1;
}

The caret symbol ^ is the bit-wise XOR operator. The statement:

a ^= b;

flips only the bits in a where the corresponding bit in b is set. All other bits are left alone.

answered Nov 17, 2013 at 14:51

godel9

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5 Comments

If I have the before and after values of all options - is it possible to know which options were toggled?

Maybe an example would be better:

originalOptions = option1 | option 2; //After toggling laterOptions = option1 | option3; I understand that option2 was "turned off"

@AvnerBarr XOR to the rescue again... oldOptions ^ newOptions will also tell you which ones were flipped.

and then & with each of the option names ?