diff --git a/2-StudentDB/sdbsc.c b/2-StudentDB/sdbsc.c
new file mode 100644
index 0000000000000000000000000000000000000000..bc650c116bcaba990e660c101f77d5c2fddde490
--- /dev/null
+++ b/2-StudentDB/sdbsc.c
@@ -0,0 +1,587 @@
+#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);
+}