Transcript Department of Computer and Information Science, School of Science, IUPUI CSCI 230 Structures Declarations Dale Roberts, Lecturer Computer Science, IUPUI E-mail: [email protected] Dale Roberts.

Department of Computer and Information Science,
School of Science, IUPUI
CSCI 230
Structures
Declarations
Dale Roberts, Lecturer
Computer Science, IUPUI
E-mail: [email protected]
Dale Roberts
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
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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
Dale Roberts
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;
struct date {
.. .. ..
};
struct date d1, d2, d3, d4, d5;
method 2: A list of variables can be declared after the right brace and
use comma separated list:
struct card {
char *face;
char *suit;
} oneCard, deck[ 52 ], *cPtr;
method 3: Declare only variables.
struct {
char *face;
char *suit;
} oneCard, deck[ 52 ], *cPtr;
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struct date {
.. .. ..
} d1, d2, d3;
struct date d4, d5;
struct {
.. .. ..
} d1, d2, d3, d4, d5;
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" };
Example:
struct date d1 = {4, 7, 1776, 186, “Jul”};
struct date d2 = {4, 7, 1776, 186, {‘J’,’u’,’l’,’\0’}};
Assignment statements
Example:
struct card threeHearts = oneCard;
Dale Roberts
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
Dale Roberts
Structures
Structure can be nested
• Name Rule
• Members in different structure
can have the same name, since
they are at different position.
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 s1 {
.. .. .. ..
char name[10];
.. .. .. ..
} d1;
struct s2 {
.. .. .. ..
int name;
.. .. .. ..
} d2;
struct s3 {
.. .. .. ..
int name;
struct s2 t3;
.. .. .. ..
} d3;
float name;
struct person emp;
emp.birthday.month = 6;
emp.birthday.year = 1776;
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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
month
char array
(hole)
year
int
2
9
1
2
bytes
bytes
bytes
bytes
Quad (4 bytes) address alignment – begins (aligns)
at quad address, such as VAX 8200
day1
int
month
char array
(hole)
year
int
4
9
3
4
bytes
bytes
bytes
bytes
0
1
2 - 10
11
12
13
0-3
4 - 12
13 - 15
16-19
integer
9 character
(hole)
integer
integer
9 character
(hole)
integer
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.)
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sizeof Operator
sizeof(struct tag)
struct test {
char name[5];
int i;
char s;
} t1, t2;
/* assume int is 2 bytes */
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); t1 992
5 bytes
printf(“address of t1.i = %d\n”, &t1.i);
1 byte (hole)
997
printf(“address of t1.s = %d\n”, &t1.s);
2 bytes
}
998
output:
t2
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
1000
1001
1002
1 byte
1 byte (hole)
5 bytes
1 byte (hole)
2 bytes
1 byte
1 byte (hole)
Dale Roberts