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Practical C++ Programming, 2nd Edition by Steve Oualline

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Chapter 11. Bit Operations

To be or not to be, that is the question.

Shakespeare on Boolean algebra

This chapter discusses bit-oriented operations. A bit is the smallest unit of information; normally represented by the values 1 and 0. (Other representations include on/off, true/false, and yes/no.) Bit manipulations are used to control the machine at the lowest level. They allow the programmer to get "under the hood" of the machine. Many higher-level programs will never need bit operations. Low-level coding such as writing device drivers or pixel-level graphic programming requires bit operations.

Eight bits together form a byte, represented by the C++ data type char. A byte might contain the following bits: 01100100.

The binary number 01100100 can also be written as the hexadecimal number 0x64. (C++ uses the prefix "0x" to indicate a hexadecimal—base 16—number.) Hexadecimal is convenient for representing binary data because each hexadecimal digit represents 4 binary bits. Table 11-1 gives the hexadecimal (hex) to binary conversion.

Thus, the hexadecimal number 0xAF represents the binary number 10101111.

Table 11-1. Hex and binary

Hex

Binary

Hex

Binary

0

0000

8

1000

1

0001

9

1001

2

0010

A

1010

3

0011

B

1011

4

0100

C

1100

5

0101

D

1101

6

0110

E

1110

7

0111

F

1111

Bit Operators

Bit, or bitwise, operators allow the programmer to work on individual bits. For example, a short integer holds 16 bits (on most machines). The bit operators treat each of these as an independent bit. By contrast, an add operator treats the 16 bits ...

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