C Structures, Unions, Bit Manipulations and Enumerations

1
C Structures, Unions, Bit Manipulations and
Enumerations

• Basics of structures
• Typedef
• Unions
• Bitwise operators
• Bit fields
• Enumeration constants

2
Data Hierarchy

• Byte
• 8 bits (ASCII character A 01000001)
• Field
• Group of characters (character string Fred)
• Record
• Composed of related fields (struct)
• File
• Group of related records (student record file)
• Database
• Group of related files (students, faculty, and
  staff files)

3
Structure Declaration

• Structure
• Collection of related variables
• Structure tag
• student
• Structures members
• first, last, age, gpa, s

• struct studentchar first20char lastint
  agedouble gpa

4
Structure Definition

• Define initialize with list of variables
• Define initialize using the dot operator
  (structure member operator)

• struct student s1 "Ted","Tanaka", 22, 2.22
• struct student s2
• strcpy(s.first, "Sally")
• s.last"Suzuki"
• s.age 33
• s.gpa 3.33

5
Accessing Members

• Structure member operator, or dot operator
• For direct variables (.)
• Structure pointer operator
• For pointers (-gt)

• struct student s2
• struct student sPtr s2
• printf("s d\n",
• s1.last, s1.age)
• /Tanaka 22/
• printf("s d\n",
• (sPtr).last, sPtr-gtage)
• /Suzuki 33/

See complete program at accessingMembers.txt
6
sizeof Operator

• Returns the size in bytes of a data type
• char a, b10
• int c, d10
• double e, f10
• printf("sizeof(a) d\n",sizeof(a))
  printf("sizeof(b) d\n",sizeof(b))
• . . .
• / sizeof(a) 1 sizeof(b) 10 /
• / sizeof(c) 4 sizeof(d) 40 /
• / sizeof(e) 8 sizeof(f) 80 /

7
sizeof Operator

• Examples with pointers
• char b10, p1 b
• int d10, p2 d
• double f10, p3 f
• printf("sizeof(p1) d ",sizeof(p1))
• printf("sizeof(p1) d\n",sizeof(p1))
• . . .
• / sizeof(p1) 4 sizeof(p1) 1 /
• / sizeof(p2) 4 sizeof(p2) 4 /
• / sizeof(p3) 4 sizeof(p3) 8 /

8
sizeof Operator

• Examples with structures
• struct student s1"Ted","Tanaka", 22,2.22
  
• struct student s2
• struct student s3 s2
• struct student s410
• printf("sizeof(s1) d\n", sizeof(s1))
• . . .
• / sizeof(s1) 40
• sizeof(s2) 40
• sizeof(s3) 4
• sizeof(s4) 400 /

9
sizeof Operator

• struct student
• char first20 / 20 bytes /
• char last / 4 bytes /
• int age / 4 bytes /
• double gpa / 8 bytes /
• / total 36 bytes ?? /
• Structures may have extra padding, because
  computers may store specific data types on
  certain memory boundaries
• See complete program at sizeof.txt

10
Structures Functions

• You can pass a structure to a function by value
• struct student s1"Ted","Tanaka", 22, 2.22
  
• incAge1(s1.age)
• printStudent(s1)
• / Name Ted Tanaka
• age 22 gpa 2.22 /
• void incAge1(int a) a
• void printStudent(struct student s)
• printf("Name s s \n age d gpa
  .2f\n",s.first, s.last, s.age, s.gpa)

11
Structures Functions

• Or pass by reference (pointer to a structure)
• struct student s1"Ted","Tanaka", 22, 2.22
• struct student p s1
• incAge2(p)
• printStudent(s1)
• / Name Ted Tanaka
• age 23 gpa 2.22 /
• void incAge2(struct student s)s-gtage
• See complete program at functions.txt

12
Arrays of Structures

• Can also have an array of a structure
• main()
• struct student s100"","", 0, 0.0
  printStudent(s0)
• / Name
• age 0 gpa 0.00 /
• See complete program at array.txt

13

• struct A /See exercise1.txt/
• char b
• int c
• struct A fun(struct A)
• main()
• struct A d 'e', 71 / sizeof(d)8 /
• struct A e20
• printf("sizeof(e)d\n", sizeof(e))
• e0 fun(d)
• printf("bc cd\n", d.b, d.c)
• printf("bc cd\n", e-gtb, (e).c)
• struct A fun(struct A a)
• printf("bc cd\n", a.b, a.c)
• return a

14
typedef

• Creates new data
• type name
• Integer used as a synonym
  for int
• IntegerPtr used as
• synonym for int
• (See program at typedef.txt)

• typedef int Integer
• typedef int IntegerPtr
• main()
• Integer a 10 IntegerPtr b a
  a
• printf("a d\n",a) printf("b
  d\n",b)
• /a 11
• b 11/

15
typedef

• Creates synonyms for previously declared data
  types
• Can be defined after the struct
• Or defined in one statement

• . . .
• typedef struct student Student
• typedef struct student char first20
  char last int age double gpa
• Student

16
typedef

• Does not create a new type
• Instead adds a new name for an exiting type
• Similar to define, except it is interpreted by
  the compiler

• typedef struct student Student
• . . .
• Student s
• s.first "Fred"
• s.last "Tanaka"
• s.age 22
• s.gpa 2.22
• See program at typedef2.txt

17
Example Program

• See fig10_03.c from D D textbook
• Represents a deck of cards as an array of
  structures
• To shuffle the cards, the program randomly swaps
  the cards
• Output displays 52 cards in two columns
• Note the use of the dot operator (.) and the use
  of typedef

18

• typedef int A /See exercise2.txt/
• typedef char B
• struct C
• A a
• B b
• typedef struct C D
• typedef D E
• main()
• D d 40, 'd'
• E e (E) malloc(sizeof(D))
• printf("e d c \n",e-gta, e-gtb)
• e-gta d.a e-gtb 'z'
• d.a
• printf("d d c \n",d.a, d.b) printf("e
  d c \n",e-gta, e-gtb)

19
Unions

• Similar to struct
• Contains multiple data types
• Members share the same data space
• Can manipulate different kinds of data in a
  single unit of storage

• union numberint x/4 bytes/double y/8
  bytes/char z20/20 bytes/

20
Unions

• union number num
• num.x 65
• printf("d\n f\n s\n\n", num.x, num.y, num.z)
  
• num.y 1.000001
• printf("d\n f\n s\n\n", num.x, num.y, num.z)
  
• strcpy(num.z,"1234567890123456789")
• printf("d\n f\n s\n\n", num.x, num.y, num.z)

• 65
• 213568. . .2.000000
• A
• 208632331
• 1.000001
• ?zo??
• 875770417
• 0.000000
• 1234567890123456789

21

• /See exercise3.txt/
• union unionX
• int i
• char c4
• main()
• union unionX x
• x.i 0x41
• printf("x x x x x\n", x.i, x.c0, x.c1,
  x.c2, x.c3)
• x.c0'a' x.c1'b' x.c2'c'
  x.c3'd'
• printf("x x x x x\n", x.i, x.c0, x.c1,
  x.c2, x.c3)

22
Bitwise Operators

• Instructions are applied to each bit
• A B bitwise AND
• Set to 1 if both bits are 1
• A B bitwise OR
• Set to 1 if at least one bit is 1
• A B bitwise exclusive OR
• Set to one if only 1 bit is set to 1
• A ones complement
• All 1s become 0s all 0s become 1s

23
Bitwise Operators

• A ltlt B left shift
• Shift the bits in A to the left B times
• Fill in 0s from the right
• Same as multiplying by a power of 2
• A gtgt B right shift
• Shift the bits in A to the right B times
• Fill in 0s for unsigned, 0s for positive
  signed, and 1s for negative signed
• Same as diving by a power of 2

24
Assignment Operators

• x x 5
• Can also be written as x 5
• a b 5
• Evaluates to a a (b 5)
• And not a a b 5

25
Bitwise Assignment Operators

• A B bitwise AND assignment operator
• Equivalent to A A B
• A B bitwise OR assignment operator
• A B bitwise exclusive OR assignment operator
• A ltlt B left shift assignment operator
• A gtgt B right shift assignment operator

26
Displaying Bits

• See fig10_07.c in D D textbook (slightly
  altered)
• Prints the binary representation of 32-bit
  unsigned integers
• Uses the AND operator and a operand called a mask
• Mask an integer value with specific bits set to
  1
• Used to hide some bits select other bits
• A zero (0) ANDed with anything produces zero (0)
• A one (1) ANDed with anything produces itself

27
Left Right Shifting Example

• See fig10_13.c in D D textbook (slightly
  altered)
• Shifts a signed integer to the left to the
  right
• Note that this is the same as multiplying or
  dividing by 16 (24 16)
• Note that the right shift preserves the sign of
  the number

28
Bit Fields

• Used to save space
• Stores data by byte
• Must use type unsigned int

• struct bitNumunsigned a1/1 bit/unsigned
  b2/2 bits/unsigned c3/3 bits/unsigned
  d4/4 bits/

29

• /Bit-field Example/
• struct bitNum
• unsigned a1
• unsigned b2
• unsigned c3
• unsigned d4
• main()
• struct bitNum x
• x.a x.b x.c x.d 15
• printf("u u u u\n",x.a,x.b,x.c,x.d)
• /1 3 7 15/
• (See program at bitFields.txt)

30
Bit Field Card Example

• See fig10_16.c in D D textbook
• Saves space by using bit fields
• Since color is either black (1) or red (0), only
  need one bit to store it
• Suit has only 4 values, so can be stored in 2
  bits
• Face has values 0 (Ace) to 12 (King), so can be
  stored in 4 bits (15 possible values)

31

• /See exercise4.txt/
• struct bitNum
• unsigned a1
• unsigned b2
• unsigned c3
• unsigned d4
• main()
• struct bitNum x
• x.a x.b x.c x.d 0xA printf("d d
  d d\n",x.a,x.b,x.c,x.d)

32
Enumeration Constants

• Set of integer constants represented by
  identifiers
• Values start with 0 (unless otherwise specified)
  and increment by 1
• See fig10_18.c in D D textbook

• enum months JAN 1, FEB, MAR, APR, MAY, JUN,
  JUL, AUG, SEP, OCT, NOV, DEC

33
Enumeration Constants

• enum months m
• const char name "error", "January",
  "February", "March", "April", "May", "June",
  "July", "August", "September", "October",
  "November", "December"
• for(mJANmltDECm) printf("9s\n",namem)
  

• January
• February
• March
• April
• May
• June
• July
• August
• September
• October
• November
• December