The program
The C program gives options to insert, retrieve and delete data from a file DB - db.dat. The source code is available here.
There is comment on the important sections of the code and I hope you could understand most of it.
/*
* Coded By: Rahul Krishnan
*
* Description:
* Program implementing basic Database I/O
* using file system instead of DBMS. This
* is to show that files are not designed
* to store structured and related data.
*/
#include
#include
#include
int
main() {
char name[10];
int choice, roll, key, found = 0;
FILE *f_ptr; // File pointer to db.dat
FILE *n_ptr; // File pointer to newdb.dat
while (1) {
printf("\n***** FILE DB Menu ******");
printf("\n1. Enter data\n2. Display All\n3. Search by roll\n4. Delete by roll\n5. Exit");
printf("\nEnter your choice : ");
scanf("%d", &choice);
switch (choice) {
case 1:
// Adds an entry into the file DB.
f_ptr = fopen("db.dat", "a");
printf("Enter the: ");
// Read from stdin and write to file.
fscanf(stdin, "%d %s", &roll, &name);
fprintf(f_ptr, "%d %s\n", roll, name);
fclose(f_ptr);
break;
case 2:
// Displays all the contents of the file DB.
printf("\nShowing DB\n----------\n");
f_ptr = fopen("db.dat", "r");
// Read from "db.dat" and write to stdout.
while ((fscanf(f_ptr, "%d %s", &roll, &name)) != EOF) {
printf("%d %s\n", roll, name);
}
fclose(f_ptr);
break;
case 3:
// Search the file DB with roll as the key.
printf("Enter the roll to be searched : ");
scanf("%d", &key);
f_ptr = fopen("db.dat", "r");
found = 0; // Set to 1 if record found.
// Search through all the entries comparing the key.
while ((fscanf(f_ptr, "%d %s", &roll, name)) != EOF) {
if (roll == key) {
printf("\nRecord Found\n-------------\n%d %s\n-------------", roll, name);
found = 1;
}
}
if (found != 1) {
printf("\nRecord NOT found !!");
}
fclose(f_ptr);
break;
case 4:
// Deletes a file DB entry based on the roll as key.
printf("Enter the ROLL of the entry to be deleted : ");
scanf("%d", &key);
f_ptr = fopen("db.dat", "r");
n_ptr = fopen("newdb.dat", "w");
found = 0; // Set to 1 if record found.
// Copy all the entries except the one with the key
// to a new file "newdb.dat", which is rename later to
// "db.dat".
while ((fscanf(f_ptr, "%d %s", &roll, name)) != EOF) {
if (roll != key) {
fprintf(n_ptr,"%d %s\n", roll, name);
}
if (roll == key)
found = 1;
}
// To rename the newdb.dat to db.dat.
fclose(f_ptr);
fclose(n_ptr);
remove("db.dat");
rename("newdb.dat", "db.dat");
// If the key is not found, then output NOT found.
// But the file is already duplicated and the file names
// changed, even if the key is not found.
if (found != 1) {
printf("\nRecord NOT found !!");
}
break;
case 5:
exit(0);
default:
printf("\nInvalid Choice");
}
}
return 0;
}
