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

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 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 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 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);