ECET 264 C Programming Language with Applications. Lecture 13. Structures and Unions

Transcription

1 ECET 264 C Programming Language with Applications Lecture 13 Structures and Unions Professor Paul I-Hai Lin lin@ipfw.edu Prof. Paul I. Lin 1 Lecture 13 Structures and Unions C Structures Structures and Functions Arrays of Structures Unions Bit-Field Structures Type Definitions Enumeration Type Prof. Paul I. Lin 2 1

2 Structures Definitions Structure is a user-defined type that can contains other types An aggregate data type for holding data of different types (int, char, float) under one name It can also also supports more complicate structures such as arrays of arrays, pointers, etc A fundamental building block for data structures Good candidates for structures: Time: year, month, day, hour, minutes, second Complex number: real part, imaginary part Point in a 2-dimensional plane: x axis, y axis Prof. Paul I. Lin 3 Structures (continued) Structure Declaration A structure must be declared before use Defining Structure Variables Simple structure or array of structures can be created from the template structure struct point // Define the point structure int x; // x axis int y; // y axis a, b; struct point c; // Create a point structure c void main() Prof. Paul I. Lin 4 2

3 Structures (continued) Accessing Data Members Member operator: dot. Operator; or pointer operator -> can be used to access the structure For Example void main() a.x = 0; a.y = 0; // Origin, left-top point b.x = 24; b.y = 79; // Last text position on a 25 by 80 points c.x = (a.x + b.x)/2; // calculate middle point c.y = (a.y + b.y)/2;.. Prof. Paul I. Lin 5 Example 13-1: A Point Structure /* ptstruc.c * A point structure example */ #include <stdio.h> #define PRINT(x,y) printf(#x " = %d, ", x);\ printf(#y " = %d\n", y) struct point int x; int y; a, b; struct point c; Output of ptstruc,c a.x = 0, a.y = 0 b.x = 24, b.y = 79 c.x = 12, c.y = 39 void main() a.x = 0; a.y = 0; // Origin, lefttop point b.x = 24; b.y = 79; // Last text position on a 25 by 80 points c.x = (a.x + b.x)/2; // calculate middle point c.y = (a.y + b.y)/2; PRINT(a.x, a.y); PRINT(b.x, b.y); PRINT(c.x, c.y); Prof. Paul I. Lin 6 3

4 Structures (continued) Memory allocation for a structure Member-by-member from left to right, from low to high memory address Accessing data members Member operator: dot. Operator; or pointer operator -> can be used to access the structure ANSI C standard defines structures may be copied, assigned to, passed functions and returned from functions Prof. Paul I. Lin 7 Example 13-2: Account and Address Structures /* account.h */ struct address char street[20]; char city[15]; char state[10]; unsigned zip; ; struct address *addr_ptr; // a structure pointer struct account unsigned acc_no; unsigned acc_type;/* coorporate = 0, individual = 1*/ char name[20]; struct address cust_addr; ; Prof. Paul I. Lin 8 4

5 Example 13-2: Account and Address Structures (cont.) /* struct2.c */ /* Using pointer operator -> to access structure */ #include <stdio.h> #include <stdlib.h> #include "account.h" void main() struct account COMPANY; struct account *aptr; /* define a structure pointer */ aptr = &COMPANY; /* get address for the structure pointer */ printf("enter acc_no: "); scanf("%u", &COMPANY.acc_no); printf("enter acc_type: ");scanf("%u", &COMPANY.acc_type); fflush(stdin); printf("enter customer name: "); gets(company.name); printf("enter Street: "); gets(company.cust_addr.street); Prof. Paul I. Lin 9 Example 13-2: Account and Address Structures (cont.) printf("enter State: "); gets(company.cust_addr.state); printf("enter Zip: "); scanf("%d", COMPANY.cust_addr.zip); printf("account no : %d\n", aptr ->acc_no); printf("account type: %d\n", aptr ->acc_type); printf("customer : %s\n", aptr ->name); printf("address : %s\n", aptr ->cust_addr.street); printf("city : %s\n", aptr ->cust_addr.city); printf("state : %s\n", aptr ->cust_addr.state); printf("zip code : %u\n", aptr ->cust_addr.zip); Prof. Paul I. Lin 10 5

6 Example 13-2: Account and Address Structures (cont.) Output: Enter acc_no: 1010 Enter acc_type: 0 Enter customer name: Lincoln Enter Street: 100 Calhoun St. Enter City: Fort Wayne Enter State: IN Enter Zip: Account no : 1010 Account type: 0 Customer : Lincoln Address : 100 Calhoun St. City : Fort Wayne State : IN ZIP code : Prof. Paul I. Lin 11 Passing Structures to Functions ANSI C Functions can accept structures as arguments and return a structure An example struct RGB int red; int green; int blue; int changecolor(struct RGB color); // Modify computer s monitor screen Prof. Paul I. Lin 12 6

7 Example 13-3: Passing a Structure to a Function The example program strucfun.c, with two functions is modified from the previous program struc2.c. The print() function accepts the argument of structure account type. The getinput() function returns the structure of the structure account type. Prof. Paul I. Lin 13 Example 13-3: Passing a Structure to a Function (cont.) /* strucfun.c */ /* Structure and Functions */ #include <stdio.h> #include <stdlib.h> #include "account.h" struct account getinput(void); /* get input return a account structure */ void print(struct account); /* print the whole structure */ void main() int i; struct account COMPANY; struct account *aptr; /* define a structure pointer */ aptr = &COMPANY; /* get address for a structure pointer */ COMPANY = getinput(); print(*aptr); Prof. Paul I. Lin 14 7

8 Example 13-3: Passing a Structure to a Function (cont.) struct account getinput(void) struct account data; printf("enter acc_no: "); scanf("%u", &data.acc_no); printf("enter acc_type: "); scanf("%u", &data.acc_type); fflush(stdin); printf("enter customer name: "); gets(data.name); printf("enter Street: "); gets(data.cust_addr.street); printf("enter City: "); gets(data.cust_addr.city); printf("enter State: "); gets(data.cust_addr.state); printf("enter Zip: "); scanf("%d", &data.cust_addr.zip); return (data); Prof. Paul I. Lin 15 Example 13-3: Passing a Structure to a Function (cont.) void print(struct account file) struct account *fptr; fptr = &file; printf("account no : %d\n", fptr ->acc_no); printf("account type: %d\n", fptr ->acc_type); printf("customer : %s\n", fptr ->name); printf("address : %s\n", fptr ->cust_addr.street); printf("city : %s\n", fptr ->cust_addr.city); printf("state : %s\n", fptr ->cust_addr.state); printf("zip code : %u\n", fptr ->cust_addr.zip); Prof. Paul I. Lin 16 8

9 Arrays of Structures Each element of the array is a structure Examples: Declaration an array of structure #define N 100 structure account COMPANIES [N]; Accessing members of this array COMPANIES[n].acc_no COMPANIES[n].acct_type COMPANIES[n].name Prof. Paul I. Lin 17 Example 13-4: Arrays of Structures // strucary.c // Array of Structure #include <stdio.h> #include <stdlib.h> #include "account.h" #define N 2 struct account getinput(void); // get input return a // account structure void print(struct account); // print the whole structure void main() int i; struct account COMPANY; struct account *aptr; // define a structure pointer struct account COMPANIES[N]; // an array of structures for // N customers aptr = COMPANIES; // get structure array's address // for the structure pointer for(i = 0; i < N; i++) COMPANIES[i] = getinput(); putchar('\n'); print(*aptr++); #include "account.c" // This file holds the codes of // functions: // getinput() and print() Prof. Paul I. Lin 18 9

10 Unions The same attributes as that of structures for holding data objects of different types Union members are set up and accessed in the same manner as that of the structure member It serves some what different purposes: Passing parameters to functions - All members shared the same memory space, the compiler will reserve enough space so that it can hold the largest variable in the union Memory saving: only one union member can be used at a given time Prof. Paul I. Lin 19 Example 13-5: A Union for CPU Register // union.c #include <stdio.h> #define PRINT(x,y) printf(#x " = %d,\t\t", x); printf(#y " = %d\n",y) union REGISTER // Define a union called REGISTER unsigned int x; // Data member x represents 16-bit register unsigned char h; // Data member h represents 8-bit high byte register unsigned char l; // Data member l represents 8-bit low byte register ax, bx, cpu[6]; // Make ax and bx as two working unions and // cpu[6] as an array of 6 unions of // union REGISTER type Prof. Paul I. Lin 20 10

11 void main() int n, i = 0; bx.x = 1000; ax.x = bx.x; member ax.h = 6; Example 13-5: A Union for CPU Register (cont.) // Assign number to union // Copy union member to another union // Reassign the union ax.h with a new number while(i < 6) // Copy bx.x into all cpu[6] union elements cpu[i++].x = bx.x; n = sizeof(bx); PRINT(bx, n); // Examine all the effects: size and value n = sizeof(ax.h); PRINT(ax.h, n); n = sizeof(cpu); PRINT(cpu, n); n = sizeof(cpu); PRINT(&cpu[2], n); Prof. Paul I. Lin 21 Example 13-5: A Union for CPU Register (cont.) Output of union.c bx = 1000, n = 4 ax.h = 6, n = 1 cpu = , n = 24 &cpu[2] = , n = 24 Prof. Paul I. Lin 22 11

12 Bit-Field Structures Optimize storage space by packing several data objects in a single machine word Define and access several objects in a single machine word May use bit-wise operating on the bit-field structures Applications interface to hardware devices TCP/IP Network protocol frame, accessing Prof. Paul I. Lin 23 Bit-Field Structures struct modem unsigned ready: 1; // reserve 1 bit for ready unsigned offhook: 2; // reserve 2 bits unsigned reserved: 13; // 13-bit reserved com1; Example of Accessing bit-field: com1.ready = 1; // assignment if(com1.offhook == 2) busy(); Prof. Paul I. Lin 24 12

13 Typedef Creating new data types from old or existing ones Hiding the actual data structure from a program and making synonyms The new types can be used in declarations, casts, etc Prof. Paul I. Lin 25 Examples Typedef typedef int INTEGER; typedef char CHAR; typedef float REAL; FILE... defined in <stdio.h> typedef struct char *buffer; // pointer to file buffer int mode; // read, write.. modes int bindex; // index into file buffer int filenum; // file number.... FILE; Prof. Paul I. Lin 26 13

14 Example 13-6: File Type and I/O // mycopy.c // This program works similar to DOS command "copy" and it must // be used under the DOS command line. // For example, after the program is compiled and built, run it // with the following command under the DOS: // c:\mycopy mycopy.c mycopy.bak #include <stdio.h> typedef char CHARACTER ; void main(int argc, char *argv[]) CHARACTER c; FILE *fptr, *fptrw; fptr = fopen(argv[1], "r"); // Open a disk file for reading fptrw = fopen(argv[2], "w"); // Open a disk file for writing Prof. Paul I. Lin 27 Example 13-6: File Type and I/O while((c = getc(fptr))!= EOF) // Copy file to file and // display it on screen until EOF marker is encountered putchar(c); fputc(c, fptrw); fclose(fptr); // Closes opened files fclose(fptrw); Prof. Paul I. Lin 28 14

15 Enumeration Create a subtype.. enumerated type Represented internally by integers Associate constant values with names Assign default values; 0, 1, 2 Access the members of enum.. using the names, and read only Examples: enum boolean NO, YES; // NO == 0, and YES == 1 enum days MON = 1, TUE, WED, THUR, FRI, SAT, SUN saledays; // MON = 1 is initialized and TUE will be 2, WED will be 3, etc. // saledays is an enum variable Prof. Paul I. Lin 29 Example 13-7: Enum Example // enum.c #include <stdio.h> enum days MON = 1, TUE, WED, THU, FRI, SAT, SUN sday; //Note that logic and sday are enum variables void main() float daysale[8], totalsale = 0.0; for(sday = MON; sday <= SUN; sday++) // Total sales for Monday // through Sunday printf("enter daysale[%d] = ",sday); scanf("%f", &daysale[sday]); totalsale += daysale[sday]; printf("total sale = %.2f\n ", totalsale); Prof. Paul I. Lin 30 15

16 Summary Structures Structures and Functions Arrays of Structures Unions Bit-Field Structures Type Definitions Enumeration Type Prof. Paul I. Lin 31 Question? Answers Prof. Paul I. Lin 32 16