lecture on c programming structure and union

8/10/2019 Lecture on C Programming Structure and union

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C Structures, Unions, Bit

Manipulations and Enumerations Basics of structures

Typedef

Unions

Bitwise operators

Bit fields Enumeration constants


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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)


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Structure Declaration

Structure

Collection of related

variables

Structure tag

student

Structures members

first, last, age, gpa, s

struct student{

char first[20];

char *last;int age;

double gpa;

};


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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;


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Accessing Members

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*/

*See complete program at accessingMembers.txt
http://localhost/var/www/apps/conversion/tmp/scratch_1/accessingMembers.txthttp://localhost/var/www/apps/conversion/tmp/scratch_1/accessingMembers.txt


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sizeof Operator

Returns the size in bytes of a data typechar 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 */


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sizeof Operator

Examples with pointerschar 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 */


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sizeof Operator

Examples with structuresstruct 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 */


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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 datatypes on certain memory boundariesSee complete program at sizeof.txt
http://localhost/var/www/apps/conversion/tmp/scratch_1/sizeof.txthttp://localhost/var/www/apps/conversion/tmp/scratch_1/sizeof.txt


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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);}


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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
http://localhost/var/www/apps/conversion/tmp/scratch_1/functions.txthttp://localhost/var/www/apps/conversion/tmp/scratch_1/functions.txt


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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
http://localhost/var/www/apps/conversion/tmp/scratch_1/array.txthttp://localhost/var/www/apps/conversion/tmp/scratch_1/array.txt


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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;}
http://localhost/var/www/apps/conversion/tmp/scratch_1/exercise1.txthttp://localhost/var/www/apps/conversion/tmp/scratch_1/exercise1.txt


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typedef

Creates new data

type name

Integer used asa 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*/
http://localhost/var/www/apps/conversion/tmp/scratch_1/typedef.txthttp://localhost/var/www/apps/conversion/tmp/scratch_1/typedef.txt


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typedef

Creates synonyms

for previously

declared data typesCan be defined after

the struct

Or defined in onestatement

. . .

typedef structstudent Student;

typedef structstudent{char first[20];

char *last;int age;double gpa;

} Student;


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typedef

Does not create anew type

Instead adds a newname for an exitingtype

Similar to #define,except it isinterpreted by thecompiler

typedef struct student

Student;

. . .

Student s;

s.first = "Fred";

s.last = "Tanaka";

s.age = 22;s.gpa = 2.22;

See program at typedef2.txt
http://localhost/var/www/apps/conversion/tmp/scratch_1/typedef.txthttp://localhost/var/www/apps/conversion/tmp/scratch_1/typedef.txt


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Example Program

See fig10_03.cfrom D & D textbook

Represents a deck of cards as an array of

structuresTo shuffle the cards, the program randomly

swaps the cards

Output displays 52 cards in two columnsNote the use of the dot operator (.) and the use

of typedef
http://localhost/var/www/apps/conversion/tmp/scratch_1/fig10_03.c.txthttp://localhost/var/www/apps/conversion/tmp/scratch_1/fig10_03.c.txt


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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);}


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Unions

Similar to struct

Contains multiple

data types Members share the

same data space

Can manipulatedifferent kinds ofdata in a single unitof storage

union number{

int x;

/*4 bytes*/double y;

/*8 bytes*/

char z[20];

/*20 bytes*/};


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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;


strcpy(num.z,"1234567890123456789");


65

213568. . .2.000000

A

208632331

1.000001

zo

8757704170.000000

1234567890123456789


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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


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Bitwise Operators

A > 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


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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;


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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 right shift assignment operator


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Displaying Bits

See fig10_07.cin D & D textbook (slightlyaltered)

Prints the binary representation of 32-bitunsigned integers

Uses the AND operator and a operand called amask

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


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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 ofthe number


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Bit Fields

Used to save space

Stores data by byte

Must use typeunsigned int

struct bitNum{unsigned a:1;/*1 bit*/

unsigned b:2;/*2 bits*/unsigned c:3;/*3 bits*/

unsigned d:4;/*4 bits*/

};


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/*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 atbitFields.txt)
http://localhost/var/www/apps/conversion/tmp/scratch_1/bitFields.txthttp://localhost/var/www/apps/conversion/tmp/scratch_1/bitFields.txt


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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), onlyneed 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 bestored in 4 bits (15 possible values)


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/*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);

}


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Enumeration Constants

Set of integer constants

represented by

identifiers Values start with 0

(unless otherwise

specified) and

increment by 1

See fig10_18.cin D &

D textbook

enum months { JAN

= 1, FEB, MAR,

APR, MAY, JUN,

JUL, AUG, SEP,OCT, NOV, DEC };


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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

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