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

Dale Roberts 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 *face; char *suit; }; char *suit; }; struct introduces the definition for structure card struct introduces the definition for structure card card is the structure name and is used to declare variables of the structure type card is the structure name and is used to declare variables of the structure type card contains two members of type char * card contains two members of type char * These members are face and suit

Dale Roberts 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. date : the name of the structure, called structure tag. day, month, …: the elements or variables mentioned in a structure are called members. 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; *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; struct date { }; struct date d1, d2, d3, d4, d5; struct date { } d1, d2, d3; struct date d4, d5; struct { } d1, d2, d3, d4, d5;

Dale Roberts 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 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;

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; struct card myCard; printf( "%s", myCard.suit ); 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 myCardPtr->suit is equivalent to (*myCardPtr).suit

Dale Roberts 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;

Dale Roberts 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 day1int2 bytes monthchar array9 bytes (hole)1 bytes yearint 2 bytes Quad (4 bytes) address alignment – begins (aligns) at quad address, such as VAX 8200 day1int4 bytes monthchar array9 bytes (hole)3 bytes yearint 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.) integer 9 character (hole) integer 9 character (hole)

Dale Roberts 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 = bytes 5 bytes 1 byte (hole) 1 byte 1 byte (hole) bytes 5 bytes 1 byte (hole) 1 byte 1 byte (hole) t2 t1

Dale Roberts 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

Dale Roberts Using Structures With Functions (cont.) Example: day_of_year(struct date *pd) { int i, day, leap; int i, day, leap; day = pd -> day; day = pd -> day; leap = pd->year%4 ==0 && pd->year %100 ==0 || pd->year%400 ==0; leap = pd->year%4 ==0 && pd->year %100 ==0 || pd->year%400 ==0; for (i=1; i month; i++) for (i=1; i month; i++) day += day_tab[leap][i]; return (day); 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 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

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

Dale Roberts 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 o nly creates an alias typedef does not create a new data type while it o nly creates an alias Example: struct card { const char *face; const char *suit; }; typedef struct card Card; void fillDeck( Card * const, const char *[], const char *[] ); int main() { Card deck[ 52 ]; const char *face[] = {"Ace", "Deuce", "Three", "Four", "Five", "Six", Seven", "Eight", “Nine", "Ten", "Jack", "Queen", "King"}; const char *suit[] = { "Hearts", "Diamonds", "Clubs", "Spades"};.... fillDeck( deck, face, suit );.... } void fillDeck(Card * const wDeck, const char * wFace[], const char * wSuit[]) {.. }

Dale Roberts 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; int x; float y; float y;}; union Number value; Valid union operations Assignment to union of same type: = Taking address: & Accessing union members:. Accessing members using pointers: ->

Dale Roberts 1/* Fig. 10.5: fig10_05.c 2 An example of a union */ 3#include 4 5union number { 6 int x; 7 double y; 8}; 9 10int main() 11{ 12 union number value; 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 ); 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} Put a value in the integer member and print both members. int: 100 double: Put a value in the floating member and print both members. int: 0 double: Define union Initialize variables Set variables Print Program Output

Dale Roberts 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}, {“Jane”,180,89,91}, {“John”,190,90,100}, {“John”,190,90,100}, }; /* similar to 2D array */ }; /* 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)  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++; } the inner brace is not necessary “Jane”,180,89,91, “John”,190,90,100,.... 

Dale Roberts 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); }}

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

Dale Roberts 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 face : 4; unsigned suit : 2; unsigned suit : 2; unsigned color : 1; 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; }

Dale Roberts 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)

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

Dale Roberts Storage Management C supports 4 functions, malloc(), calloc(),free(), and cfree() for storage management malloc(n): 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));

Dale Roberts Storage Management (cont.) free(p): free(p): free() will release the memory allocated by malloc(). free() will release the memory allocated by malloc(). p is the pointer containing the address returning from malloc(). p is the pointer containing the address returning from malloc(). Example: int *ip; int *ip; ip = (int*) malloc(sizeof(int)); ip = (int*) malloc(sizeof(int)); free(ip);/* Question: can you free(ip) after ip++ ? */ Example: struct treeNode *tp; struct treeNode *tp; tp=(struct treeNode *)malloc(sizeof(struct treeNode )); 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

Dale Roberts Storage Management (cont.) calloc(n,size): 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. 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. n is the element number of array that you want to allocate. size is the number of byte of each element. 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 2 nd element, the same as ip[1] *(ip+1) refer to the 2 nd element, the same as ip[1] *(ip+i) refer to the i+1 th element, the same as ip[i] *(ip+i) refer to the i+1 th 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(). cfree() releases the memory allocated by calloc(). Example: cfree(ip);