Select Git revision
week-1-assignment
-
Charles Barnwell authoredCharles Barnwell authored
sdbsc.c 19.51 KiB
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h> //c library for system call file routines
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdbool.h>
//database include files
#include "db.h"
#include "sdbsc.h"
/*
* open_db
* dbFile: name of the database file
* should_truncate: indicates if opening the file also empties it
*
* returns: File descriptor on success, or ERR_DB_FILE on failure
*
* console: Does not produce any console I/O on success
* M_ERR_DB_OPEN on error
*
*/
int open_db(char *dbFile, bool should_truncate){
// Set permissions: rw-rw----
// see sys/stat.h for constants
mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;
//open the file if it exists for Read and Write,
//create it if it does not exist
int flags = O_RDWR | O_CREAT;
if (should_truncate)
flags += O_TRUNC;
// Now open file
int fd = open(dbFile, flags, mode);
if (fd == -1) {
// Handle the error
printf(M_ERR_DB_OPEN);
return ERR_DB_FILE;
}
return fd;
}
/*
* get_student
* fd: linux file descriptor
* id: the student id we are looking for the name of
* *s: a pointer where the located (if found) student data will be
* copied
*
* returns: NO_ERROR student located and copied into *s
* ERR_DB_FILE database file I/O issue
* SRCH_NOT_FOUND student was not located in the database
*
* console: Does not produce any console I/O used by other functions
*/
int get_student(int fd, int id, student_t *s){
if (fd == -1) return ERR_DB_FILE;
int offset = id * STUDENT_RECORD_SIZE;
lseek(fd, offset, SEEK_SET);
student_t student;
int bytes_read = read(fd, &student, STUDENT_RECORD_SIZE);
if (bytes_read != STUDENT_RECORD_SIZE) { return ERR_DB_FILE;
}
if (student.id == DELETED_STUDENT_ID) {
return SRCH_NOT_FOUND;
}
*s = student;
return NO_ERROR;
}
/*
* add_student
* fd: linux file descriptor
* id: student id (range is defined in db.h )
* fname: student first name
* lname: student last name
* gpa: GPA as an integer (range defined in db.h)
*
* Adds a new student to the database. After calculating the index for the
* student, check if there is another student already at that location. A good
* way is to use something like memcmp() to ensure that the location for this
* student contains all zero byes indicating the space is empty.
*
* returns: NO_ERROR student added to database
* ERR_DB_FILE database file I/O issue
* ERR_DB_OP database operation logically failed (aka student
* already exists)
*
*
* console: M_STD_ADDED on success
* M_ERR_DB_ADD_DUP student already exists
* M_ERR_DB_READ error reading or seeking the database file
* M_ERR_DB_WRITE error writing to db file (adding student)
*
*/
int add_student(int fd, int id, char *fname, char *lname, int gpa){
if (fd == -1) return ERR_DB_FILE;
int offset = id * STUDENT_RECORD_SIZE;
lseek(fd, offset, SEEK_SET);
student_t existing_student;
int bytes_read = read(fd, &existing_student, STUDENT_RECORD_SIZE);
if (bytes_read == STUDENT_RECORD_SIZE && existing_student.id != DELETED_STUDENT_ID) {
printf(M_ERR_DB_ADD_DUP, id);
return ERR_DB_OP;
}
student_t new_student = {id, "", "", gpa};
strncpy(new_student.fname, fname, sizeof(new_student.fname) - 1);
strncpy(new_student.lname, lname, sizeof(new_student.lname) - 1);
lseek(fd, offset, SEEK_SET);
int bytes_written = write(fd, &new_student, STUDENT_RECORD_SIZE);
if (bytes_written != STUDENT_RECORD_SIZE) {
printf(M_ERR_DB_WRITE);
return ERR_DB_FILE;
}
printf(M_STD_ADDED, id);
return NO_ERROR;
}
/*
* del_student
* fd: linux file descriptor
* id: student id to be deleted *
* Removes a student to the database. Use the get_student() function to
* locate the student to be deleted. If there is a student at that location
* write an empty student record - see EMPTY_STUDENT_RECORD from db.h at
* that location.
*
* returns: NO_ERROR student deleted from database
* ERR_DB_FILE database file I/O issue
* ERR_DB_OP database operation logically failed (aka student
* not in database)
*
*
* console: M_STD_DEL_MSG on success
* M_STD_NOT_FND_MSG student not in database, cant be deleted
* M_ERR_DB_READ error reading or seeking the database file
* M_ERR_DB_WRITE error writing to db file (adding student)
*
*/
int del_student(int fd, int id){
if (fd == -1) return ERR_DB_FILE;
int offset = id * STUDENT_RECORD_SIZE;
lseek(fd, offset, SEEK_SET);
student_t student;
int bytes_read = read(fd, &student, STUDENT_RECORD_SIZE);
if (bytes_read != STUDENT_RECORD_SIZE || student.id == DELETED_STUDENT_ID) {
printf(M_STD_NOT_FND_MSG, id);
return ERR_DB_OP;
}
student.id = DELETED_STUDENT_ID;
lseek(fd, offset, SEEK_SET);
write(fd, &student, STUDENT_RECORD_SIZE);
printf(M_STD_DEL_MSG, id);
return NO_ERROR;
}
/*
* count_db_records
* fd: linux file descriptor
*
* Counts the number of records in the database. Start by reading the
* database at the beginning, and continue reading individual records
* until you it EOF. EOF is when the read() syscall returns 0. Check
* if a slot is empty or previously deleted by investigating if all of
* the bytes in the record read are zeros - I would suggest using memory
* compare memcmp() for this. Create a counter variable and initialize it
* to zero, every time a non-zero record is read increment the counter.
*
* returns: <number> returns the number of records in db on success
* ERR_DB_FILE database file I/O issue
* ERR_DB_OP database operation logically failed (aka student
* not in database)
*
*
* console: M_DB_RECORD_CNT on success, to report the number of students in db
* M_DB_EMPTY on success if the record count in db is zero
* M_ERR_DB_READ error reading or seeking the database file
* M_ERR_DB_WRITE error writing to db file (adding student)
*
*/
int count_db_records(int fd){
if (fd == -1) return ERR_DB_FILE;
int count = 0;
student_t student;
lseek(fd, 0, SEEK_SET); while (read(fd, &student, STUDENT_RECORD_SIZE) == STUDENT_RECORD_SIZE) {
if (student.id != DELETED_STUDENT_ID) {
count++;
}
}
printf(M_DB_RECORD_CNT, count);
return count;
}
/*
* print_db
* fd: linux file descriptor
*
* Prints all records in the database. Start by reading the
* database at the beginning, and continue reading individual records
* until you it EOF. EOF is when the read() syscall returns 0. Check
* if a slot is empty or previously deleted by investigating if all of
* the bytes in the record read are zeros - I would suggest using memory
* compare memcmp() for this. Be careful as the database might be empty.
* on the first real row encountered print the header for the required output:
*
* printf(STUDENT_PRINT_HDR_STRING, "ID",
* "FIRST NAME", "LAST_NAME", "GPA");
*
* then for each valid record encountered print the required output:
*
* printf(STUDENT_PRINT_FMT_STRING, student.id, student.fname,
* student.lname, calculated_gpa_from_student);
*
* The code above assumes you are reading student records into a local
* variable named student that is of type student_t. Also dont forget that
* the GPA in the student structure is an int, to convert it into a real
* gpa divide by 100.0 and store in a float variable.
*
* returns: NO_ERROR on success
* ERR_DB_FILE database file I/O issue
*
*
* console: <see above> on success, print table or database empty
* M_ERR_DB_READ error reading or seeking the database file
*
*/
int print_db(int fd){
if (fd == -1) return ERR_DB_FILE;
student_t student;
lseek(fd, 0, SEEK_SET);
printf(STUDENT_PRINT_HDR_STRING, "ID", "FIRST NAME", "LAST NAME", "GPA");
while (read(fd, &student, STUDENT_RECORD_SIZE) == STUDENT_RECORD_SIZE) {
if (student.id != DELETED_STUDENT_ID) {
printf(STUDENT_PRINT_FMT_STRING, student.id, student.fname, student.lname, student.gpa/100.0);
}
}
return NO_ERROR;
}
/*
* print_student
* *s: a pointer to a student_t structure that should
* contain a valid student to be printed
*
* Start by ensuring that provided student pointer is valid. To do this
* make sure it is not NULL and that s->id is not zero. After ensuring
* that the student is valid, print it the exact way that is described
* in the print_db() function by first printing the header then the
* student data:
* * printf(STUDENT_PRINT_HDR_STRING, "ID",
* "FIRST NAME", "LAST_NAME", "GPA");
*
* printf(STUDENT_PRINT_FMT_STRING, s->id, s->fname,
* student.lname, calculated_gpa_from_s);
*
* Dont forget that the GPA in the student structure is an int, to convert
* it into a real gpa divide by 100.0 and store in a float variable.
*
* returns: nothing, this is a void function
*
*
* console: <see above> on success, print table or database empty
* M_ERR_STD_PRINT if the function argument s is NULL or if
* s->id is zero
*
*/
void print_student(student_t *s){
if (s == NULL || s->id == DELETED_STUDENT_ID) {
printf(M_ERR_STD_PRINT);
return;
}
printf(STUDENT_PRINT_FMT_STRING, s->id, s->fname, s->lname, s->gpa / 100.0);
}
/*
* NOTE IMPLEMENTING THIS FUNCTION IS EXTRA CREDIT
*
* compress_db
* fd: linux file descriptor
*
* This assignment takes advantage of the way Linux handles sparse files
* on disk. Thus if there is a large hole between student records, Linux
* will not use any physical storage. However, when a database record is
* deleted storage is used to write a blank - see EMPTY_STUDENT_RECORD from
* db.h - record.
*
* Since Linux provides no way to delete data in the middle of a file, and
* deleted records take up physical storage, this function will compress the
* database by rewriting a new database file that only includes valid student
* records. There are a number of ways to do this, but since this is extra credit
* you need to figure this out on your own.
*
* At a high level create a temporary database file then copy all valid students from
* the active database (passed in via fd) to the temporary file. When this is done
* rename the temporary database file to the name of the real database file. See
* the constants in db.h for required file names:
*
* #define DB_FILE "student.db" //name of database file
* #define TMP_DB_FILE ".tmp_student.db" //for extra credit
*
* Note that you are passed in the fd of the database file to be compressed,
* it is very likely you will need to close it to overwrite it with the
* compressed version of the file. To ensure the caller can work with the
* compressed file after you create it, it is a good design to return the fd
* of the new compressed file from this function
*
* returns: <number> returns the fd of the compressed database file
* ERR_DB_FILE database file I/O issue
*
*
* console: M_DB_COMPRESSED_OK on success, the db was successfully compressed.
* M_ERR_DB_OPEN error when opening/creating temporary database file.
* this error should also be returned after you
* compressed the database file and if you are unable
* to open it to pass the fd back to the caller
* M_ERR_DB_CREATE error creating the db file. For instance the
* inability to copy the temporary file back as
* the primary database file.
* M_ERR_DB_READ error reading or seeking the the db or tempdb file * M_ERR_DB_WRITE error writing to db or tempdb file (adding student)
*
*/
int compress_db(int fd){
printf(NOT_IMPLEMENTED_YET);
return fd;
}
/*
* validate_range
* id: proposed student id
* gpa: proposed gpa
*
* This function validates that the id and gpa are in the allowable ranges
* as per the specifications. It checks if the values are within the
* inclusive range using constents in db.h
*
* returns: NO_ERROR on success, both ID and GPA are in range
* EXIT_FAIL_ARGS if either ID or GPA is out of range
*
* console: This function does not produce any output
*
*/
int validate_range(int id, int gpa){
if ((id < MIN_STD_ID) || (id > MAX_STD_ID))
return EXIT_FAIL_ARGS;
if ((gpa < MIN_STD_GPA) || (gpa > MAX_STD_GPA))
return EXIT_FAIL_ARGS;
return NO_ERROR;
}
/*
* usage
* exename: the name of the executable from argv[0]
*
* Prints this programs expected usage
*
* returns: nothing, this is a void function
*
* console: This function prints the usage information
*
*/
void usage(char *exename){
printf("usage: %s -[h|a|c|d|f|p|z] options. Where:\n", exename);
printf("\t-h: prints help\n");
printf("\t-a id first_name last_name gpa(as 3 digit int): adds a student\n");
printf("\t-c: counts the records in the database\n");
printf("\t-d id: deletes a student\n");
printf("\t-f id: finds and prints a student in the database\n");
printf("\t-p: prints all records in the student database\n");
printf("\t-x: compress the database file [EXTRA CREDIT]\n");
printf("\t-z: zero db file (remove all records)\n");
}
//Welcome to main()
int main(int argc, char *argv[]){
char opt; //user selected option
int fd; //file descriptor of database files
int rc; //return code from various operations
int exit_code; //exit code to shell
int id; //userid from argv[2]
int gpa; //gpa from argv[5]
//space for a student structure which we will get back from
//some of the functions we will be writing such as get_student(), //and print_student().
student_t student = {0};
//This function must have at least one arg, and the arg must start
//with a dash
if ((argc < 2) || (*argv[1] != '-')){
usage(argv[0]);
exit(1);
}
//The option is the first character after the dash for example
//-h -a -c -d -f -p -x -z
opt = (char)*(argv[1]+1); //get the option flag
//handle the help flag and then exit normally
if (opt == 'h'){
usage(argv[0]);
exit(EXIT_OK);
}
//now lets open the file and continue if there is no error
//note we are not truncating the file using the second
//parameter
fd = open_db(DB_FILE, false);
if (fd < 0){
exit(EXIT_FAIL_DB);
}
//set rc to the return code of the operation to ensure the program
//use that to determine the proper exit_code. Look at the header
//sdbsc.h for expected values.
exit_code = EXIT_OK;
switch(opt){
case 'a':
// arv[0] arv[1] arv[2] arv[3] arv[4] arv[5]
//prog_name -a id first_name last_name gpa
//-------------------------------------------------------
//example: prog_name -a 1 John Doe 341
if (argc != 6){
usage(argv[0]);
exit_code = EXIT_FAIL_ARGS;
break;
}
//convert id and gpa to ints from argv. For this assignment assume
//they are valid numbers
id = atoi(argv[2]);
gpa = atoi(argv[5]);
exit_code = validate_range(id,gpa);
if (exit_code == EXIT_FAIL_ARGS){
printf(M_ERR_STD_RNG);
break;
}
rc = add_student(fd, id, argv[3], argv[4], gpa);
if (rc < 0)
exit_code = EXIT_FAIL_DB;
break;
case 'c':
// arv[0] arv[1]
//prog_name -c
//-----------------
//example: prog_name -c
rc = count_db_records(fd);
if (rc < 0)
exit_code = EXIT_FAIL_DB; break;
case 'd':
// arv[0] arv[1] arv[2]
//prog_name -d id
//-------------------------
//example: prog_name -d 100
if (argc != 3){
usage(argv[0]);
exit_code = EXIT_FAIL_ARGS;
break;
}
id = atoi(argv[2]);
rc = del_student(fd, id);
if (rc < 0)
exit_code = EXIT_FAIL_DB;
break;
case 'f':
// arv[0] arv[1] arv[2]
//prog_name -f id
//-------------------------
//example: prog_name -f 100
if (argc != 3){
usage(argv[0]);
exit_code = EXIT_FAIL_ARGS;
break;
}
id = atoi(argv[2]);
rc = get_student(fd, id, &student);
switch (rc){
case NO_ERROR:
print_student(&student);
break;
case SRCH_NOT_FOUND:
printf(M_STD_NOT_FND_MSG, id);
exit_code = EXIT_FAIL_DB;
break;
default:
printf(M_ERR_DB_READ);
exit_code = EXIT_FAIL_DB;
break;
}
break;
case 'p':
// arv[0] arv[1]
//prog_name -p
//-----------------
//example: prog_name -p
rc = print_db(fd);
if (rc < 0)
exit_code = EXIT_FAIL_DB;
break;
case 'x':
// arv[0] arv[1]
//prog_name -x
//-----------------
//example: prog_name -x
//remember compress_db returns a fd of the compressed database.
//we close it after this switch statement
fd = compress_db(fd);
if (fd < 0)
exit_code = EXIT_FAIL_DB;
break;
case 'z':
// arv[0] arv[1]
//prog_name -x
//-----------------
//example: prog_name -x
//HINT: close the db file, we already have fd
// and reopen db indicating truncate=true
close(fd);
fd = open_db(DB_FILE, true);
if (fd < 0){
exit_code = EXIT_FAIL_DB;
break;
}
printf(M_DB_ZERO_OK);
exit_code = EXIT_OK;
break;
default:
usage(argv[0]);
exit_code = EXIT_FAIL_ARGS;
}
//dont forget to close the file before exiting, and setting the
//proper exit code - see the header file for expected values
close(fd);
exit(exit_code);
}