Dale Roberts, Lecturer Computer Science, IUPUI E-mail: droberts@cs.iupui.edu

1. Department of Computer and Information Science,School of Science, IUPUI CSCI 230 Structures Declarations Dale Roberts, Lecturer Computer Science, IUPUI E-mail: droberts@cs.iupui.edu

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. struct date { • .. .. .. • }; • struct date d1, d2, d3, d4, d5; struct date { .. .. .. } d1, d2, d3; struct date d4, d5; struct { .. .. .. } d1, d2, d3, d4, d5; 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: struct card { char *face; char *suit; } oneCard, deck[ 52 ], *cPtr; method 3: Declare only variables. struct { char *face; char *suit; } oneCard, deck[ 52 ], *cPtr;

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" }; 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;

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 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 { • .. .. .. .. • int name; • struct s2 t3; • .. .. .. .. • } d3; • float name;

8. 0 integer 1 2 - 10 9 character 11 (hole) 12 integer 13 0 - 3 integer 4 - 12 9 character 13 - 15 (hole) 16-19 integer 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 month char array 9 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.)

9. 5 bytes 1 byte (hole) 2 bytes 1 byte 1 byte (hole) t1 992 997 998 1000 1001 t2 1002 5 bytes 1 byte (hole) 2 bytes 1 byte 1 byte (hole) sizeof Operator sizeof(struct tag) struct test { 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