Sams Teach Yourself C in 21 Days

Working with Memory 585

20

Operation Example

AND 11110000

& 01010101

----------

01010000

Inclusive OR 11110000

| 01010101

----------

11110101

Exclusive OR 11110000

^ 01010101

----------

10100101

You just read that bitwise ANDand bitwise inclusive ORcan be used to clear or set,

respectively, specified bits in an integer value. Here’s what that means. Suppose you have

a type charvariable, and you want to ensure that the bits in positions 0 and 4 are cleared

(that is, equal to 0 ) and that the other bits stay at their original values. If you ANDthe

variable with a second value that has the binary value 11101110 , you’ll obtain the desired

result. Here’s how this works:

In each position where the second value has a 1 , the result will have the same value, 0 or

1 , as was present in that position in the original variable:

0 & 1 == 0

1 & 1 == 1

In each position where the second value has a 0 , the result will have a 0 regardless of the

value that was present in that position in the original variable:

0 & 0 == 0

1 & 0 == 0

Setting bits with ORworks in a similar way. In each position where the second value has

a 1 , the result will have a 1 , and in each position where the second value has a 0 , the

result will be unchanged:

0 | 1 == 1

1 | 1 == 1

0 | 0 == 0

1 | 0 == 1

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