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

1. Department of Computer and Information Science,School of Science, IUPUI CSCI 230 Structures 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 continent 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: 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 s3 t3; /* name */ • .. .. .. .. • } d2; • 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

10. Using Structures With Functions • Passing structures to functions • Pass entire structure or pass individual members • Both pass call by value • It is not a good idea to pass a structure to or return from function.The better way is passing a pointer to the structure to the functions and returning a pointer from function. • To pass structures call-by-reference • Pass its address • Pass reference to it • To pass arrays call-by-value • Create a structure with the array as a member • Pass the structure

11. Using Structures With Functions (cont.) Example: day_of_year(struct date *pd) { int i, day, leap; day = pd -> day; leap = pd->year%4 ==0 && pd->year %100 ==0 || pd->year%400 ==0; for (i=1; i<pd -> month; i++) day += day_tab[leap][i]; return (day); } • The declaration struct date *pd; says that pd is a pointer to a structure of the type date • If p is a pointer to a structure, then p-> member_of_structure refers to the particular members, like pd -> year • p-> member_of_structure is equivalent to (*p).member_of_structure • Notice:‘.’has higher precedence than‘*’; *pd.year is wrong, since pd.year is not a pointer. • Both->and . associate from left to right. So p -> q -> member are (p->q)->member. Example: emp.birthday.month are (emp.birthday).month

12. Using Structures With Functions (cont.) • -> and . both are at the highest precedence (together with ()for function and [] for array subscripts) Example: struct { int *x; int *y; } *p; ++p->x; is equivalent to ++(p->x) /* increment x, not p */ (++p)->x; /* increment p before access x */ *p->y; /* fetch whatever y points to */ *p->y++; /* increments y after accessing whatever y point to */ (*p->y)++; /* increments whatever y point to, just like *p->y++ */ *p++->y; /* increments p after accessing whatever y point to */

13. struct card { constchar *face; constchar *suit; }; typedefstruct card Card; void fillDeck( Card * const, constchar *[], constchar *[] ); int main() { Card deck[ 52 ]; constchar *face[] = {"Ace", "Deuce", "Three", "Four", "Five", "Six", Seven", "Eight", “Nine", "Ten", "Jack", "Queen", "King"}; constchar *suit[] = { "Hearts", "Diamonds", "Clubs", "Spades"}; .. .. fillDeck( deck, face, suit ); .. .. } void fillDeck(Card * const wDeck, constchar * wFace[], constchar * wSuit[]) { .. .. } typedef • typedef • Creates synonyms (aliases) for previously defined data types • Use typedef to create shorter type names • Example: typedef struct card *CardPtr; • Defines a new type name CardPtr as a synonym for type struct card * • typedef does not create a new data type while it only creates an alias Example:

14. Unions • union • Memory that contains a variety of objects over time • Only contains one data member at a time • Members of a union share space • Conserves storage • Only the last data member defined can be accessed • union declarations • Same as struct union Number { int x; float y; }; union Number value; • Valid union operations • Assignment to union of same type: = • Taking address: & • Accessing union members: . • Accessing members using pointers: ->

15. 1 /* Fig. 10.5: fig10_05.c 2 An example of a union */ 3 #include <stdio.h> 4 5 union number { 6 int x; 7 double y; 8 }; 9 10 int main() 11 { 12 union number value; 13 14 value.x = 100; 15 printf( "%s\n%s\n%s%d\n%s%f\n\n", 16 "Put a value in the integer member", 17 "and print both members.", 18 "int: ", value.x, 19 "double:\n", value.y ); 20 21 value.y = 100.0; 22 printf( "%s\n%s\n%s%d\n%s%f\n", 23 "Put a value in the floating member", 24 "and print both members.", 25 "int: ", value.x, 26 "double:\n", value.y ); 27 return 0; 28 } Define union Initialize variables Set variables Print Program Output Put a value in the integer member and print both members. int: 100 double: -92559592117433136000000000000000000000000000000000000000000000.00000 Put a value in the floating member and print both members. int: 0 double: 100.000000

16. Array of Structures Example: (before) char name[PERSON][NAMESIZE]; int tscore[PERSON] int math[PERSON] int english[PERSON] • Initialization of structure array struct person_data{ .. .. .. .. } person[]={ {“Jane”,180,89,91}, {“John”,190,90,100}, .. .. .. .. }; /* similar to 2D array */ Example: using separated arrays average (int tscore, int math, int eng, int n) { int i, total=0,mathtotal = 0, engtotal=0; for (i=0; i<n, i++) { total += *tscore++; mathtotal += *math++; engtotal += *eng++; } • struct person_data{ • char name[NAMESIZE]; • int tscore; • int math; • int english; • } person[PERSON]; (now)  the inner brace is not necessary “Jane”,180,89,91, “John”,190,90,100, .. .. .. ..  • Example: using pointer to structure • average (struct person_data *person, int n) • { • int i, total=0,mathtotal = 0, engtotal=0; • for (i=0; i<n, i++) { • total += person->tscore; • mathtotal += person->math; • engtotal += person->eng; • person++; • }

17. Self-Reference Structure • Dynamic Data Structure • Data Structure: link list, tree, graph, … Example: Binary Tree Struct treeNode { char word[SIZE]; int count; struct treeNode *left; struct treeNode *right; /* or struct treeNode *left, *right; */ }; /* Inorder traversal */ tree_print(struct treeNode *p) { if (p!=NULL){ tree_print(p->left); printf(“.. ..”, p->word, .. ..); tree_print(p-> right); } }

18. Link list Example: Struct listNode { char word[SIZE]; int count; struct listNode *next; }; /* Inorder traversal */ list_print(struct listNode *p) { while (p!=NULL) { printf(“.. ..”, p->word, .. ..); p = p->next; } }

19. Bit Fields • Bit field • Member of a structure whose size (in bits) has been specified • Enable better memory utilization • Must be declared as int or unsigned • Cannot access individual bits • Declaring bit fields • Follow unsigned or int member with a colon (:) and an integer constant representing the width of the field Example: struct BitCard { unsigned face : 4; unsigned suit : 2; unsigned color : 1; }; • Unnamed bit field • Field used as padding in the structure • Nothing may be stored in the bits • Unnamed bit field with zero width aligns next bit field to a new storage unit boundary struct Example { unsigned a : 13; unsigned : 3; unsigned b : 4; }

20. Enumeration Constants • Enumeration • Set of integer constants represented by identifiers • Enumeration constants are like symbolic constants whose values are automatically set • Values start at 0 and are incremented by 1 • Values can be set explicitly with = • Need unique constant names Example: enum Months { JAN = 1, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC}; • Creates a new type enum Months in which the identifiers are set to the integers 1 to 12 • Enumeration variables can only assume their enumeration constant values (not the integer representations)

21. 1 /* Fig. 10.18: fig10_18.c 2 Using an enumeration type */ 3 #include <stdio.h> 4 5 enum months { JAN = 1, FEB, MAR, APR, MAY, JUN, 6 JUL, AUG, SEP, OCT, NOV, DEC }; 7 8 int main() 9 { 10 enum months month; 11 constchar *monthName[] = { "", "January", "February", 12 "March", "April", "May", 13 "June", "July", "August", 14 "September", "October", 15 "November", "December" }; 16 17 for ( month = JAN; month <= DEC; month++ ) 18 printf( "%2d%11s\n", month, monthName[ month ] ); 19 20 return 0; 21 } 1 January 2 February 3 March 4 April 5 May 6 June 7 July 8 August 9 September 10 October 11 November 12 December

22. Storage Management • C supports 4 functions, malloc(), calloc(),free(), and cfree() for storage management • malloc(n): • allocate a node while its content is still ‘garbage’ • n is an integer, indicating the size of memory in byte which you would like to allocate • malloc() return a character pointer to that memory • So, you have to use cast operator (type), to change the type of the pointer. Example: int *ip; ip = (int*) malloc(sizeof(int)); struct treeNode *tp; tp = (struct tnode *) malloc(sizeof(struct tnode));

23. Storage Management (cont.) • free(p): • free() will release the memory allocated by malloc(). • p is the pointer containing the address returning from malloc(). Example: int *ip; ip = (int*) malloc(sizeof(int)); ... .. .. free(ip); /* Question: can you free(ip) after ip++ ? */ Example: struct treeNode *tp; tp=(struct treeNode *)malloc(sizeof(struct treeNode )); ... .. .. free(tp); • When there is no further memory, malloc() will return NULL pointer. It is a good idea to check the returning value of malloc(). if ((ip=(int *)malloc(sizeof(int))) == NULL){ printf(“\nMemory is FULL\n”); exit(1); } • When you free the memory, you must be sure that you pass the original address returning from malloc() to function free(). Otherwise, system exception may be happened

24. Storage Management (cont.) • calloc(n,size): • calloc() allow you to allocate an n elements array of same data type. Because n can be an integer variable, you can use calloc() to allocate a dynamic size array. • n is the element number of array that you want to allocate. • size is the number of byte of each element. • Unlike malloc(), calloc() guarantees that memory contents are all zero Example: allocate an array of 10 elements int *ip; ip = (int*) calloc(10, sizeof(int)); *(ip+1) refer to the 2nd element, the same as ip[1] *(ip+i) refer to the i+1th element, the same as ip[i] • Like malloc(), calloc() will return NULL, if no further memory is available. • cfree(p): • cfree() releases the memory allocated by calloc(). Example: cfree(ip);