File handling in c program - I
Filehandling in c program - I
WRITING TO AND READING FROM A FILE
#includemain() { FILE *f1; char c; printf("Data Input\n\n"); /* Open the file INPUT */ f1 = fopen("INPUT", "w"); /* Get a character from keyboard */ while((c=getchar()) != EOF) /* Write a character to INPUT */ putc(c,f1); /* Close the file INPUT */ fclose(f1); printf("\nData Output\n\n"); /* Reopen the file INPUT */ f1 = fopen("INPUT","r"); /* Read a character from INPUT*/ while((c=getc(f1)) != EOF) /* Display a character on screen */ printf("%c",c); /* Close the file INPUT */ fclose(f1); }
Output
Data InputThis is a program to test the file handling
features on this system^Z
Data Output
This is a program to test the file handling
features on this system
HANDLING OF INTEGER DATA FILES
A file named DATA contains a series of integer numbers. Code a program to read these numbers and then write all 'odd' numbers to a file to be called ODD and all `even' numbers to a file to be called EVEN.It uses three files simultaneously and therefore we need to define three-file pointers f1, f2 and f3.
First, the file DATA containing integer values is created. The integer values are read from the terminal and are written to the file DATA with the help of the statement
putw(number, f1);
Notice that when we type -1, the reading is terminated and the file is closed. The next step is to open all the three files, DATA for reading, ODD and EVEN for writing. The contents of DATA file are read, integer by integer, by the function getw(f1) and written to ODD or EVEN file after an appropriate test. Note that the statement
(number = getw(f1)) != EOF
reads a value, assigns the same to number, and then tests for the end-of-file mark.
Finally, the program displays the contents of ODD and EVEN files. It is important to note that the files ODD and EVEN opened for writing are closed before they are reopened for reading.
#includemain() { FILE *f1, *f2, *f3; int number, i; printf("Contents of DATA file\n\n"); f1 = fopen("DATA", "w"); /* Create DATA file */ for(i = 1; i <= 30; i++) { scanf("%d", &number); if(number == -1) break; putw(number,f1); } fclose(f1); f1 = fopen("DATA", "r"); f2 = fopen("ODD", "w"); f3 = fopen("EVEN", "w"); /* Read from DATA file */ while((number = getw(f1)) != EOF) { if(number %2 == 0) putw(number, f3); /* Write to EVEN file */ else putw(number, f2); /* Write to ODD file */ } fclose(f1); fclose(f2); fclose(f3); f2 = fopen("ODD","r"); f3 = fopen("EVEN", "r"); printf("\n\nContents of ODD file\n\n"); while((number = getw(f2)) != EOF) printf("%4d", number); printf("\n\nContents of EVEN file\n\n"); while((number = getw(f3)) != EOF) printf("%4d", number); fclose(f2); fclose(f3); }
Output
Contents of DATA file 111 222 333 444 555 666 777 888 999 000 121 232 343 454 565 -1Contents of ODD file 111 333 555 777 999 121 343 565
Contents of EVEN file 222 444 666 888 0 232 454
ERROR HANDLING IN FILE OPERATIONS
Write a program to illustrate error handling in file operations.The program the use of the NULL pointer test and feof function. When we input filename as TETS, the function call
fopen("TETS", "r");
returns a NULL pointer because the file TETS does not exist and therefore the message "Cannot open the file" is printed out.
Similarly, the call feof(fp2) returns a non-zero integer when the entire data has been read, and hence the program prints the message "Ran out of data" and terminates further reading.
#includemain() { char *filename; FILE *fp1, *fp2; int i, number; fp1 = fopen("TEST", "w"); for(i = 10; i <= 100; i += 10) putw(i, fp1); fclose(fp1); printf("\nInput filename\n"); open_file: scanf("%s", filename); if((fp2 = fopen(filename,"r")) == NULL) { printf("Cannot open the file.\n"); printf("Type filename again.\n\n"); goto open_file; } else for(i = 1; i <= 20; i++) { number = getw(fp2); if(feof(fp2)) { printf("\nRan out of data.\n"); break; } else printf("%d\n", number); } fclose(fp2); }
Output
Input filenameTETS
Cannot open the file.
Type filename again.
TEST
10
20
30
40
APPENDING ITEMS TO AN EXISTING FILE
Write a program to append additional items to the file INVENTORY and print the total contents of the file.It uses a structure definition to describe each item and a function append() to add an item to the file.
On execution, the program requests for the filename to which data is to be appended. After appending the items, the position of the last character in the file is assigned to n and then the file is closed.
The file is reopened for reading and its contents are displayed. Note that reading and displaying are done under the control of a while loop. The loop tests the current file position against n and is terminated when they become equal.
#includestruct invent_record { char name[10]; int number; float price; int quantity; }; main() { struct invent_record item; char filename[10]; int response; FILE *fp; long n; void append (struct invent_record 8x, file *y); printf("Type filename:"); scanf("%s", filename); fp = fopen(filename, "a+"); do { append(&item, fp); printf("\nItem %s appended.\n",item.name); printf("\nDo you want to add another item\ (1 for YES /0 for NO)?"); scanf("%d", &response); } while (response == 1); n = ftell(fp); /* Position of last character */ fclose(fp); fp = fopen(filename, "r"); while(ftell(fp) < n) { fscanf(fp,"%s %d %f %d", item.name, &item.number, &item.price, &item.quantity); fprintf(stdout,"%-8s %7d %8.2f %8d\n", item.name, item.number, item.price, item.quantity); } fclose(fp); } void append(struct invent_record *product, File *ptr) { printf("Item name:"); scanf("%s", product->name); printf("Item number:"); scanf("%d", &product->number); printf("Item price:"); scanf("%f", &product->price); printf("Quantity:"); scanf("%d", &product->quantity); fprintf(ptr, "%s %d %.2f %d", product->name, product->number, product->price, product->quantity); }
Output
Type filename:INVENTORYItem name:XXX
Item number:444
Item price:40.50
Quantity:34
Item XXX appended.
Do you want to add another item(1 for YES /0 for NO)?1
Item name:YYY
Item number:555
Item price:50.50
Quantity:45
Item YYY appended.
Do you want to add another item(1 for YES /0 for NO)?0
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