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‎.gitignore

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*.o
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*.out
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*.exe

‎README.md

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# File Allocation Table Simulator

‎dir.c

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#include <stdio.h>
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#include <string.h>
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#include "main.h"
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#define MAX_DIR_SIZE 30
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#define MAX_FILENAME_SIZE 13
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static const char* dir_filename = "dir.dat";
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static char filenames[MAX_DIR_SIZE][MAX_FILENAME_SIZE];
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static int file_start_sectors[MAX_DIR_SIZE];
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FILE* open_dir_file(char * options) {
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static FILE* dir_file;
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if(dir_file == NULL) {
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dir_file = fopen(dir_filename, "w");
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fclose(dir_file);
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dir_file = fopen(dir_filename, options);
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} else {
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dir_file = freopen(dir_filename, options, dir_file);
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}
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return dir_file;
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}
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// Reads the dir.dat file into the directory in memory, one entry per line
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void read_dir() {
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FILE* dir_file = open_dir_file("r");
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char filename[MAX_FILENAME_SIZE];
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int file_start_sector;
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int i = 0;
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while(fscanf(dir_file, "%s %d", filename, &file_start_sector) != EOF) {
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strcpy(filenames[i], filename);
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file_start_sectors[i] = file_start_sector;
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i++;
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}
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fclose(dir_file);
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}
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// Writes the contents of the directory in memory to the dir.dat file, one entry per line
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void save_dir() {
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FILE* dir_file = open_dir_file("w");
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for(int i = 0; i < MAX_DIR_SIZE; i++) {
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if(file_start_sectors[i] != 0) {
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fprintf(dir_file, "%s %d\n", filenames[i], file_start_sectors[i]);
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}
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}
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fclose(dir_file);
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}
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// Prints the contents of the directory in memory, one entry per line
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void print_dir() {
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for(int i = 0; i < MAX_DIR_SIZE; i++) {
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if(file_start_sectors[i] != 0) {
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printf("%s %d\n", filenames[i], file_start_sectors[i]);
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}
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}
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}
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// Returns the number of files that the directory has remaining space for
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int dir_space_left() {
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int space_left = 0;
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for(int i = 0; i < MAX_DIR_SIZE; i++) {
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if(file_start_sectors[i] == 0) {
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space_left++;
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}
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}
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return space_left;
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}
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// Returns the directory index of the file with the given file name if it exists, -1 otherwise
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int does_file_exist_in_dir(char* file) {
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for(int i = 0; i < MAX_DIR_SIZE; i++) {
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if(strcmp(filenames[i], file) == 0) {
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return i;
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}
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}
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return -1;
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}
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// Returns the start sector of the file at directory index position
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int get_start_sector(int position) {
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return file_start_sectors[position];
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}
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// Adds a file to the directory with the given file name and start sector
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void add_file_to_dir(char* file, int start_sector) {
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for(int i = 0; i < MAX_DIR_SIZE; i++) {
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if(file_start_sectors[i] == 0) {
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strcpy(filenames[i], file);
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file_start_sectors[i] = start_sector;
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return;
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}
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}
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}
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// Deletes the file with directory index position from the directory
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void delete_file_from_dir(int position) {
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strcpy(filenames[position], "");
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file_start_sectors[position] = 0;
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}
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‎fat.c

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#include <stdio.h>
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#include "main.h"
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#define FAT_SIZE 32
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static const char* fat_filename = "fat.dat";
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static int fat[FAT_SIZE];
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FILE* open_fat_file(char * options) {
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static FILE* fat_file;
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if(fat_file == NULL) {
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fat_file = fopen(fat_filename, "w");
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fclose(fat_file);
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fat_file = fopen(fat_filename, options);
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} else {
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fat_file = freopen(fat_filename, options, fat_file);
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}
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return fat_file;
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}
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// Reads the fat.dat file into the FAT in memory (int fat[32]), one int per line
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void read_fat() {
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FILE* fat_file = open_fat_file("r");
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int entry;
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int i = 0;
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while(fscanf(fat_file, "%d", &entry) != EOF) {
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fat[i] = entry;
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i++;
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}
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// fclose(fat_file);
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}
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// Writes the FAT in memory (int fat[32]) to the fat.dat file, one int per line
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void save_fat() {
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FILE* fat_file = open_fat_file("w");
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for(int i = 0; i < FAT_SIZE; i++) {
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fprintf(fat_file, "%d\n", fat[i]);
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}
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fclose(fat_file);
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}
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// Clears the FAT in memory (int fat[32])
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void reset_fat() {
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fat[0] = 0;
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fat[1] = 0;
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for(int i = 2; i < FAT_SIZE; i++) {
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fat[i] = 1;
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}
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}
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// Returns the number of free sectors in the FAT
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int free_sectors() {
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int num_free = 0;
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for(int i = 0; i < FAT_SIZE; i++) {
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if(fat[i] == 1) {
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num_free++;
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}
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}
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return num_free;
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}
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// Returns the index of the lowest number sector that is currently free
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int first_free_sector() {
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for(int i = 0; i < FAT_SIZE; i++) {
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if(fat[i] == 1) {
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return i;
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}
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}
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return -1;
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}
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// Allocates a chain of sectors n long, starting at start_sector
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void allocate_sectors(int start_sector, int n) {
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if(n == 1) {
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fat[start_sector] = 0;
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} else {
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int sectors_allocated = 0;
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int previous_sector = start_sector;
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for(int i = 0; i < FAT_SIZE; i++) {
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if(fat[i] == 1 && i != start_sector) {
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fat[previous_sector] = i;
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previous_sector = i;
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sectors_allocated++;
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if(sectors_allocated == n - 1) {
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fat[previous_sector] = 0;
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break;
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}
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}
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}
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}
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}
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// Deallocates the chain of sectors starting at start_sector
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void deallocate_sectors(int start_sector) {
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int current_sector = start_sector;
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int next_sector;
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do {
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next_sector = fat[current_sector];
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fat[current_sector] = 1;
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current_sector = next_sector;
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} while(next_sector != 0);
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}
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// Prints the chain of sectors that starts at start_sector
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void print_sector_chain(int start_sector) {
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int current_sector = start_sector;
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int next_sector;
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do {
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printf("%d", current_sector);
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next_sector = fat[current_sector];
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current_sector = next_sector;
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if(next_sector != 0) {
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printf(" ");
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}
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} while(next_sector != 0);
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printf("\n");
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}
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‎main.c

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#include <stdio.h>
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#include <string.h>
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#include <stdlib.h>
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#include "main.h"
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void command_sectors(char* filename);
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void command_add(char* filename, int num_sectors);
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void command_delete(char* filename);
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int main() {
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reset_fat();
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read_fat();
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read_dir();
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char line[100];
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char command[20];
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char arg1[20];
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char arg2[20];
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while(1) {
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printf(":");
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fgets(line, sizeof(line) / sizeof(line[0]), stdin);
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if(sscanf(line, "%s %s %s", command, arg1, arg2) < 1) {
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break;
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}
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if(strcmp(command, "sectors") == 0) {
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command_sectors(arg1);
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} else if(strcmp(command, "add") == 0) {
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command_add(arg1, strtol(arg2, NULL, 10));
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} else if(strcmp(command, "delete") == 0) {
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command_delete(arg1);
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} else if(strcmp(command, "dir") == 0) {
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print_dir();
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} else if(strcmp(command, "quit") == 0) {
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break;
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}
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}
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return 0;
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}
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// Prints the sectors used by the file with the given filename
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void command_sectors(char* filename) {
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int file_position = does_file_exist_in_dir(filename);
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if(file_position < 0) {
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printf("File does not exist\n");
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return;
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}
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int start_sector = get_start_sector(file_position);
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print_sector_chain(start_sector);
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}
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// Adds a file with the given filename to the directory and allocates it num_sectors in the FAT
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void command_add(char* filename, int num_sectors) {
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if(does_file_exist_in_dir(filename) >= 0) {
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printf("File already exists\n");
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return;
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}
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if(dir_space_left() == 0) {
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printf("Directory is full\n");
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return;
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}
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if(free_sectors() < num_sectors) {
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printf("Not enough free sectors\n");
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return;
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}
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int start_sector = first_free_sector();
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allocate_sectors(start_sector, num_sectors);
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add_file_to_dir(filename, start_sector);
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save_dir();
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save_fat();
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}
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// Deletes the file with the given filename from the directory and deallocates its sectors in the FAT
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void command_delete(char* filename) {
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int file_position = does_file_exist_in_dir(filename);
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if(file_position < 0) {
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printf("File does not exist\n");
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return;
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}
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int start_sector = get_start_sector(file_position);
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deallocate_sectors(start_sector);
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delete_file_from_dir(file_position);
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save_dir();
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save_fat();
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}

‎main.h

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// fat.c
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void read_fat();
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void save_fat();
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void reset_fat();
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int free_sectors();
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int first_free_sector();
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void allocate_sectors(int start_sector, int n);
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void deallocate_sectors(int start_sector);
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void print_sector_chain(int start_sector);
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// dir.c
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void read_dir();
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void save_dir();
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void print_dir();
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int dir_space_left();
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int does_file_exist_in_dir(char* file);
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int get_start_sector(int position);
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void add_file_to_dir(char* file, int start_sector);
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void delete_file_from_dir(int position);

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