All_FAT16

#include <stdio.h>
#include <dos.h>
#include <memory.h>
#include <stdlib.h>
#include <string.h>

struct BOOT {  //for FAT16
    char jmp[3];
    char OEM[8];
    int bytes_per_sector;
    char sectors_per_cluster;
    int reserved;
    char FAT_cnt;
    int ROOT_size;
    int total_sectors;
    char media;
    int FAT_size;
    int sectors_per_track;
    int head_cnt;
    long hidden_sectors;
    long total_sectors_long;
    char unknown[3];
    long serial;
    char volume[11];
    char FAT_type[8];
    char loader[448];
    char mark[2];
};

struct ROOT {
    char name[8];
    char ext[3];
    char attr;
    char reserved[10];
    char time[2];
    char date[2];
    int first_cluster;
    long size;
};

void main()
{

    int drive = 3; //A=0, B=1, C=2, D=3 ...

    //Reading boot sector from disk D
    BOOT boot;

    int res = absread(drive, 1, 0, &boot);
    if(res != 0){
        printf("Cannot read boot sector\n");
        return;
    }
    printf("Reading disk parameters\n");
    printf("-------------------------\n");
    printf("Sector size: %d\n", boot.bytes_per_sector);
    printf("FAT type:");
    int i;
    for(i = 0; i < 8; i++)
        printf("%c", boot.FAT_type[i]);

    //Reading FAT16 table from disk D
    unsigned int *fat = (unsigned int *)malloc (boot.FAT_size * boot.bytes_per_sector);
    if (fat == NULL) {
        printf("Not enough memory\n");
        return;
    }
    printf("\n\n");
    printf("Reading FAT16 parameters\n");
    printf("-------------------------\n");
    printf("FAT size: %d \n", boot.FAT_size);
    printf("Reserved: %d \n", boot.reserved);

    res = absread(drive, boot.FAT_size, boot.reserved, fat);
    if(res != 0){
        printf("Cannot read FAT\n");
        return;
    }
    //printing first 15 FAT cells
    printf("Content of first 15 FAT cells:");
    for (i = 0; i < 15; i++)
        printf("%u ", fat[i]);

    //Counting number of free clusters from first 100 clusters
    int free_count = 0;
    for (i = 2; i < 100; i++){ //first 2 clusters are not used
        if(fat[i] == 0) free_count++;
    }
    printf("\n");
    printf("Number of free clusters from first 100 clusters:");
    printf("%d\n", free_count);

    //Printing clusters of a file from cluster n
    unsigned int n = 5;
    unsigned int cur = n;
    printf("Clusters of a file from %u: ",n);
    while(cur < 0xFFF8){
        printf("->%u", cur);
        cur = fat[cur];
    }

    //Reading ROOT from disk D
    printf("\n\n");
    printf("Reading ROOT information:\n");
    printf("------------------------\n");

    int num_byte = boot.ROOT_size * 32;//sizeof(ROOT)

    ROOT *root = (ROOT *)malloc(num_byte);
    if(root == NULL) return;

    int num_sector = num_byte / boot.bytes_per_sector;
    int root_begin = boot.reserved + boot.FAT_size * boot.FAT_cnt;

    res = absread(drive, num_sector, root_begin, (void *)root);
    if(res != 0){
        printf("\n Cannot read ROOT\n");
        return;
    }


    //Printing first 3 items of root
    printf("3 first items of root:\n");
    for(i = 0; i < 3; i++){
        if(root[i].name[0] == ' ') continue;
        for(int j = 0; j < 8 && root[i].name[j] != ' '; j++)
            printf("%c", root[i].name[j]);
        printf("\t");
        printf("%d \t %ld\n", root[i].first_cluster, root[i].size);
    }

    //Find a file with name given in char filename[]
    printf("\n");
    printf("Clusters belong to file readme:");
    int k;
    char str[9];
    int first_cluster = -1;
    for(i = 0; i < boot.ROOT_size; i++){
        //Copy root[i].name to str to make null-terminated string
        for(k = 0; k < 8 && root[i].name[k] != ' '; k++)
            str[k] = root[i].name[k];
        str[k] = 0;
        //Comparing
        char filename[8];
        printf("\n Enter a file name:");
        scanf("%s",filename);

        if(strcmp(str, filename) == 0){
            first_cluster = root[i].first_cluster;
            break;
        }
    }

    //Printing clusters belonging to the file
    if(first_cluster >= 0){
        cur = first_cluster;
        while(cur < 0xFFF8){
            printf("%u ", cur);
            cur = fat[cur];
        }
    }

    free(root);
    free(fat);

    getchar();
}