(Unpacking Characters from Unsigned Integers) Using the right-shift operator, the bitwise AND operator and a mask, write function unpackCharacters that takes the unsigned integer from Exercise 22.11 and unpacks it into two characters. To unpack two characters from an unsigned two- byte integer, combine the unsigned integer with the mask 65280 (11111111 00000000) and right- shift the result 8

Question

bits. Assign the resulting value to a char variable. Then, combine the unsigned in- teger with the mask 255 (00000000 11111111). Assign the result to another char variable. The pro- gram should print the unsigned integer in bits before it’s unpacked, then print the characters in bits to confirm that they were unpacked correctly.

What will be an ideal response?

Answer 1

```
#include
#include
using namespace std;

// prototypes
void unpackCharacters( char * const, char * const, unsigned );
void displayBits( unsigned );

int main()
{
char a;
char b;
unsigned packed = 16706;

cout << "The packed character representation is:\n";
displayBits( packed );

// demonstrate unpacking of characters
unpackCharacters( &a, &b, packed );
cout << "\nThe unpacked characters are \'" << a << "\' and \'" << b
<< "\'\n";
displayBits( a );
displayBits( b );

return 0;
} // end main

// take apart the characters
void unpackCharacters( char * const aPtr, char * const bPtr,
unsigned pack )
{
unsigned mask1 = 65280;
unsigned mask2 = 255;

*aPtr = static_cast< char >( ( pack & mask1 ) >> 8 );
*bPtr = static_cast< char >( pack & mask2 );
} // end function unpackCharacters

// display the bits of value
void displayBits( unsigned value )
{
const int SHIFT = 8 * sizeof( unsigned ) - 1;
const unsigned MASK = 1 << SHIFT;

cout << setw( 7 ) << value << " = ";

for ( unsigned c = 1; c <= SHIFT + 1; c++ )
{
cout << ( value & MASK ? '1' : '0' );
value <<= 1;

if ( c % 8 == 0 )
cout << ' ';
} // end for

cout << endl;
} // end function displayBits
```
The packed character representation is:
16706 = 00000000 00000000 01000001 01000010
The unpacked characters are 'A' and 'B'
65 = 00000000 00000000 00000000 01000001
66 = 00000000 00000000 00000000 01000010