1. Structures Declarations CSCI 230
Department of Computer and Information Science, School of Science, IUPUI
CSCI 230
Structures
Declarations
Dale Roberts, Lecturer
Computer Science, IUPUI

2. Introduction Structures
A collection of one or more variables, possibly of different types, grouped together under a single name for convenient handling.
Commonly used to define records to be stored in files
Combined with pointers, can create linked lists, stacks, queues, and trees
Example:
struct card {
char *face;
char *suit; };
struct introduces the definition for structure card
card is the structure name and is used to declare variables of the structure type
card contains two members of type char *
These members are face and suit

3. Structure Definitions
Example:
A date consists of several parts, such as the day, month, and year, and the day of the year, and the month name
struct date {
int day;
int month;
int year;
int year_date;
char month_name[4]; };
date: the name of the structure, called structure tag.
day, month, …: the elements or variables mentioned in a structure are called members.
struct information
A struct cannot contain an instance of itself
Can contain a member that is a pointer to the same structure type
A structure definition does not reserve space in memory
Instead creates a new data type used to declare structure variables

4. Declaration of Variables of Structure
Declarations
method 1: declared like other variables: declare tag first, and then declare variable.
struct card {
char *face;
char *suit; };
struct card oneCard, deck[ 52 ],
*cPtr;
method 2: A list of variables can be declared after the right brace and use comma separated list:
} oneCard, deck[ 52 ], *cPtr;
method 3: Declare only variables.
struct {
struct date { };
struct date d1, d2, d3, d4, d5;
struct date {
} d1, d2, d3;
struct date d4, d5;
struct {
} d1, d2, d3, d4, d5;

5. Structure Definitions
Valid Operations
Assigning a structure to a structure of the same type
Taking the address (&) of a structure
Accessing the members of a structure
Using the sizeof operator to determine the size of a structure
Initialization of Structures
Initializer lists
Example:
struct card oneCard = { "Three", "Hearts" };
struct date d1 = {4, 7, 1776, 186, “Jul”};
struct date d2 = {4, 7, 1776, 186, {‘J’,’u’,’l’,’\0’}};
Assignment statements
struct card threeHearts = oneCard;

6. Accessing Members of Structures
Accessing structure members
Dot (.) is a member operator used with structure variables
Syntax: structure_name.member
struct card myCard;
printf( "%s", myCard.suit );
One could also declare and initialize threeHearts as follows:
struct card threeHearts;
threeHearts.face = “Three”;
threeHearts.suit = “Hearts”;
Arrow operator (->) used with pointers to structure variables
struct card *myCardPtr = &myCard;
printf( "%s", myCardPtr->suit );
myCardPtr->suit is equivalent to (*myCardPtr).suit

7. Structures Structure can be nested Name Rule
struct date {
int day;
int month;
int year;
int year_date;
char month_name[4]; };
struct person {
char name [NAME_LEN];
char address[ADDR_LEN};
long zipcode;
long ss__number;
double salary;
struct date birthday;
struct person emp;
emp.birthday.month = 6;
emp.birthday.year = 1776;
Name Rule
Members in different structure can have the same name, since they are at different position.
struct s1 {
char name[10];
} d1;
struct s2 {
int name;
} d2;
struct s3 {
struct s2 t3;
} d3;
float name;

8. Memory Layout Example: struct data1 {
int day1;
char month[9];
int year; };
Word (2 bytes) alignment machine – begins (aligns)
at even address, such as PC, SUN workstation
day1 int 2 bytes
month char array 9 bytes
(hole) 1 bytes
year int 2 bytes
Quad (4 bytes) address alignment – begins (aligns)
at quad address, such as VAX 8200
day1 int 4 bytes
(hole) 3 bytes
year int 4 bytes
You must take care of hole, if you want to access data from very low level (i.e. low-level I/O, byte operations, etc.) 1
2 - 10 11 12 13
integer
9 character
(hole)
0 - 3
4 - 12
16-19
integer
9 character
(hole)

9. sizeof Operator sizeof(struct tag) output: sizeof(struct test) = 10 t1
char name[5];
int i; /* assume int is 2 bytes */
char s;
} t1, t2;
main() {
printf(“sizeof(struct test) = %d\n”, sizeof (struct test));
printf(“address of t1 = %d\n”, &t1);
printf(“address of t2 = %d\n”, &t2);
printf(“address of t1.name = %d\n”, t1.name);
printf(“address of t1.i = %d\n”, &t1.i);
printf(“address of t1.s = %d\n”, &t1.s); }
output:
sizeof(struct test) = 10
address of t1 = 992
address of t2 = 1002
address of t1.name = 992
address of t1.i = 998
address of t1.s = 1000
2 bytes
5 bytes
1 byte (hole)
1 byte
992
998
1000
1002
1001
997 t2 t1