C Structures, Unions, Bit Manipulations and Enumerations

C Structures, Unions, Bit Manipulations and Enumerations • Basics of structures • Typedef • Unions • Bitwise operators • Bit fields • Enumeration constants

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)

Structure Collection of related variables Structure tag “student” Structure’s members first, last, age, gpa, s struct student{char first[20];char *last;int age;double gpa; }; Structure Declaration

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; Structure Definition

Structure member operator, or dot operator For direct variables (.) Structure pointer operator For pointers (->) struct student s2; struct student*sPtr = s2; printf("%s %d\n", s1.last, s1.age); /*Tanaka 22*/ printf("%s %d\n", (*sPtr).last, sPtr->age); /*Suzuki 33*/ Accessing Members *See complete program at accessingMembers.txt

sizeof Operator • Returns the size in bytes of a data type char a, b[10]; int c, d[10]; double e, f[10]; 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 */

sizeof Operator • Examples with pointers char b[10], *p1 = b; int d[10], *p2 = d; double f[10], *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 */

sizeof Operator • Examples with structures struct student s1={"Ted","Tanaka", 22,2.22}; struct student s2; struct student *s3 = &s2; struct student s4[10]; printf("sizeof(s1) = %d\n", sizeof(s1)); . . . /* sizeof(s1) = 40 sizeof(s2) = 40 sizeof(s3) = 4 sizeof(s4) = 400 */

sizeof Operator struct student{ char first[20]; /* 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

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);}

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->age++;} • See complete program at functions.txt

Arrays of Structures • Can also have an array of a structure main(){ struct student s[100]={"","", 0, 0.0}; printStudent(s[0]); } /* Name = age = 0 gpa = 0.00 */ • See complete program at array.txt

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 e[20]; printf("sizeof(e)=%d\n", sizeof(e)); e[0] = fun(d); printf("b=%c c=%d\n", d.b, d.c); printf("b=%c c=%d\n", e->b, (*e).c); } struct A fun(struct A a){ printf("b=%c c=%d\n", a.b++, ++a.c); return a;}

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*/ 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 first[20]; char *last; int age; double gpa; } Student; 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 typedef

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 Example Program

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->a, e->b); e->a = d.a; e->b = 'z'; d.a++; printf("d = %d %c \n",d.a, d.b); printf("e = %d %c \n",e->a, e->b);}

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 number{int x;/*4 bytes*/double y;/*8 bytes*/char z[20];/*20 bytes*/ }; 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 Unions

/*See exercise3.txt*/ union unionX{ int i; char c[4]; }; main(){ union unionX x; x.i = 0x41; printf("%x %x %x %x %x\n", x.i, x.c[0], x.c[1], x.c[2], x.c[3]); x.c[0]='a'; x.c[1]='b'; x.c[2]='c'; x.c[3]='d'; printf("%x %x %x %x %x\n", x.i, x.c[0], x.c[1], x.c[2], x.c[3]); }

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 one’s complement • All 1’s become 0’s & all 0’s become 1’s

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

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;

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 <<= B left shift assignment operator • A >>= B right shift assignment operator

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

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

Used to save space Stores data by byte Must use type unsigned int struct bitNum{unsigned a:1;/*1 bit*/unsigned b:2;/*2 bits*/unsigned c:3;/*3 bits*/unsigned d:4;/*4 bits*/ }; Bit Fields

/*Bit-field Example*/ struct bitNum{ unsigned a:1; unsigned b:2; unsigned c:3; unsigned d:4; }; 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)

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)

/*See exercise4.txt*/ struct bitNum{ unsigned a:1; unsigned b:2; unsigned c:3; unsigned d:4; }; 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); }

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 }; Enumeration Constants

enum months m; const char *name[] = {"error", "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"}; for(m=JAN;m<=DEC;m++) printf("%9s\n",name[m]); January February March April May June July August September October November December Enumeration Constants

C Structures, Unions, Bit Manipulations and Enumerations