Implementation of file allocation methods using vectors

Prerequisite: File Allocation Methods
Different File Allocation methods:

1. Contiguous File Allocation Methods:

This is a type of allocation in which a file occupies contiguous blocks of a given memory. This type of allocation is fastest because we can access any part of the file just by adding it to the starting index of the file. However, this allocation is not useful when you have to insert a file whose size is greater than the greatest empty slot available.

Below is the implementation of Contiguous File Allocation which follows First-Fit Allocation:

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// C++ implementation of the Contiguous
// File Allocation which follow First-Fit
// algorithm
#include <iostream>
#include <vector>
using namespace std;
  
// File Class
class File {
public:
    // Name of File
    string filename;
  
    // Size of file
    size_t size;
  
    // Partition no. is which part of
    // file is present at a particular
    // block of memory
    int partition;
};
class Block {
    // If Block is occupied
    // by a file or not
    bool occupied = false;
  
    // File of the block
    File file;
  
public:
    // This function will set file into
    // current block and set occupied flag
    void set_file(File file)
    {
        this->file = file;
        occupied = true;
    }
  
    // This function will return
    // filename of given block
    string get_file_name()
    {
        return file.filename;
    }
  
    // This function will return
    // partition number of file
    int get_file_partition_no()
    {
        return file.partition;
    }
  
    // This function will return
    // if the block is empty or not
    bool is_empty()
    {
        return !occupied;
    }
  
    // This function will set the occupied
    // flag as false meaning that it will
    // free the given block
    void set_empty()
    {
        occupied = false;
    }
};
  
// Function to return the number of
// empty Blocks from given memory
int get_empty_count(vector<Block> memory)
{
    int sum = 0;
    vector<Block>::iterator slot;
  
    // Count no. of empty blocks in
    // given memory
    for (slot = memory.begin();
         slot != memory.end(); slot++) {
        sum += (*slot).is_empty();
    }
  
    return sum;
}
  
// Function will return if the file
// exists in a given memory
bool file_exists(vector<Block> memory,
                 string name)
{
    vector<Block>::iterator slot;
  
    for (slot = memory.begin();
         slot != memory.end(); slot++) {
        if (!(*slot).is_empty()
            && (*slot).get_file_name() == name) {
            return true;
        }
    }
    return false;
}
  
// Function will set the file in the memory
// this will follow first fit allocation
void set_contiguous_memory(vector<Block>* memory,
                           vector<int>* index,
                           File file)
{
    bool avail = false;
    int i = 0, count = 0, main_index;
    vector<Block>::iterator slot;
  
    // Check if the file already exists
    if (file_exists((*memory),
                    file.filename))
        cout << "File already exists"
             << endl;
  
    else {
  
        // Iterate through full memory
        for (slot = (*memory).begin();
             slot != (*memory).end(); slot++) {
  
            // Check if there are
            // contiguous Blocks available
            if ((*slot).is_empty()) {
                count++;
  
                // This if condition will note
                // the 1st index for each
                // Block empty
                if (count == 1)
                    main_index = i;
  
                // Check if contiguous
                // Blocks are available,
                // it will set our flag
                // avail as true and break
                if (count == file.size) {
                    avail = true;
                    break;
                }
            }
  
            // Else if there is even a
            // single non-empty block
            // in between we will set
            // count as 0
            else {
                count = 0;
            }
            i++;
        }
  
        // If our flag is set,
        // this condition will set
        // our file
        if (avail) {
  
            // Here starting index of
            // our given file will be
            // pushed in index page
            (*index).push_back(main_index);
  
            // Utilize count variable
            // again for setting file
            // partition
            count = 0;
            for (int i = main_index;
                 i < main_index + file.size;
                 i++) {
                file.partition = count;
                (*memory).at(i).set_file(file);
                count++;
            }
            cout << "File " << file.filename
                 << " has been successfully"
                 << " allocated"
                 << endl;
        }
        else {
            cout << "The size of the file is"
                 << " greater than"
                 << endl;
            cout << "the greatest slot available"
                 << " in contiguous memory"
                 << endl;
            cout << "Hence, File "
                 << file.filename
                 << " cannot be allocated"
                 << endl;
        }
    }
}
  
// Function to Delete file from memory
void delete_contiguous_mem(vector<Block>* memory,
                           vector<int>* index_page,
                           string file)
{
    vector<int>::iterator slot;
    int index, i = 0, main_index;
  
    // Check if the file exist or not
    if (!file_exists((*memory), file))
        cout << "File does not exist" << endl;
    else {
  
        // Iterate all the indexes
        for (slot = (*index_page).begin();
             slot != (*index_page).end(); slot++) {
  
            // If specified file is found,
            // this condition will
            // set the value of index no.
            // in index and
            // main_index will have starting
            // location of
            // file in memory
            if ((*memory).at(*slot).get_file_name()
                == file) {
                index = i;
                main_index = (*slot);
                break;
            }
            i++;
        }
  
        // Iterate through the main index until
        // filename is similar to specified
        // filename and status of Block is
        // not empty
        i = main_index;
  
        while (i < (*memory).size()
               && (*memory).at(i).get_file_name()
                      == file
               && !(*memory).at(i).is_empty()) {
            // Set the Block as empty
            (*memory).at(i).set_empty();
            i++;
        }
  
        // Erase entry of file from index page
        (*index_page).erase((*index_page).begin() + index);
        cout << "File " << file
             << " has been successfully deleted"
             << endl;
    }
}
  
// Function to display main index page
void show_contiguous_index(vector<Block> memory,
                           vector<int> index_page)
{
    int max = 9, i, j;
  
    // Iterator
    vector<Block>::iterator slot;
  
    // File Name
    string fname;
  
    // Interate through all index pages
    for (i = 0; i < index_page.size();
         i++) {
  
        if (memory.at(index_page.at(i))
                .get_file_name()
                .length()
            > max) {
            // Get the length of file
            max = memory.at(index_page
                                .at(i))
                      .get_file_name()
                      .length();
  
            cout << "+" << string(max + 2, '-')
                 << "+---------------+----"
                 << "---------+-----------"
                 << "-------+\n|"
                 << string(max / 2
                               + max % 2 - 4,
                           ' ')
                 << "File Name"
                 << string(max / 2 - 3, ' ')
                 << "| Start Address | "
                 << " End Address | Size"
                 << " of the file |\n+"
                 << string(max + 2, '-')
                 << "+---------------+-------"
                 << "------+------------------+"
                 << endl;
        }
    }
  
    // Interate index_pages
    for (i = 0; i < index_page.size();
         i++) {
        cout << "|"
             << string(max / 2 + max % 2
                           - memory
                                     .at(index_page
                                             .at(i))
                                     .get_file_name()
                                     .length()
                                 / 2
                           - memory
                                     .at(index_page
                                             .at(i))
                                     .get_file_name()
                                     .length()
                                 % 2
                           + 1,
                       ' ')
             << memory.at(index_page.at(i))
                    .get_file_name()
             << string(max / 2
                           - memory
                                     .at(index_page
                                             .at(i))
                                     .get_file_name()
                                     .length()
                                 / 2
                           + 1,
                       ' ')
             << "|"
             << string(8
                           - to_string(index_page
                                           .at(i))
                                     .length()
                                 / 2
                           - to_string(index_page
                                           .at(i))
                                     .length()
                                 % 2,
                       ' ')
             << index_page.at(i)
             << string(7
                           - to_string(index_page
                                           .at(i))
                                     .length()
                                 / 2,
                       ' ')
             << "|";
        j = index_page
                .at(i);
        fname = memory
                    .at(j)
                    .get_file_name();
  
        // Till j is less than memory size
        while (j < memory.size()
               && !memory
                       .at(j)
                       .is_empty()
               && memory
                          .at(j)
                          .get_file_name()
                      == fname) {
            j++;
        }
        j -= 1;
  
        // Print the index pages details
        cout << string(7
                           - to_string(j)
                                     .length()
                                 / 2
                           - to_string(j)
                                     .length()
                                 % 2,
                       ' ')
             << j
             << string(6
                           - to_string(j)
                                     .length()
                                 / 2,
                       ' ')
             << "|"
             << string(9
                           - to_string(j
                                       - index_page
                                             .at(i)
                                       + 1)
                                     .length()
                                 / 2
                           - to_string(j
                                       - index_page
                                             .at(i)
                                       + 1)
                                     .length()
                                 % 2,
                       ' ')
             << j - index_page.at(i) + 1
             << string(9
                           - to_string(j
                                       - index_page
                                             .at(i)
                                       + 1)
                                     .length()
                                 / 2,
                       ' ')
             << "|"
             << endl;
    }
    cout << "+" << string(max + 2, '-')
         << "+---------------+------"
         << "-------+------------------+"
         << endl;
}
  
// Function to display index of each
// partition of specified file
void show_contiguous_indexes(vector<Block> memory,
                             vector<int> index_page,
                             string filename)
{
    int index, i;
  
    // Iterator
    vector<int>::iterator slot;
  
    // If file exist then display file
    // index and partition
    if (file_exists(memory, filename)) {
        cout << "File Name = " << filename
             << "\n+------------------+----"
             << "--------------+";
  
        cout << "\n| Current Location |"
             << " Partition Number |";
  
        cout << "\n+------------------+-"
             << " -----------------+\n";
  
        // Iterate through all the index
        for (slot = index_page.begin();
             slot != index_page.end(); slot++) {
            if (memory.at(*slot).get_file_name()
                == filename) {
                index = (*slot);
                break;
            }
        }
  
        // Loop till memory size is greater than
        // index and file is allocated
        // in them
        while (index < memory.size()
               && memory
                          .at(index)
                          .get_file_name()
                      == filename
               && !memory
                       .at(index)
                       .is_empty()) {
            cout << "|"
                 << string(9
                               - to_string(index)
                                         .length()
                                     / 2
                               - to_string(index)
                                         .length()
                                     % 2,
                           ' ')
                 << index
                 << string(9
                               - to_string(index)
                                         .length()
                                     / 2,
                           ' ')
                 << "|"
  
                 << string(9
                               - to_string(memory
                                               .at(index)
                                               .get
                                                   _file
                                                       _partition
                                                           _no())
                                         .length()
                                     / 2
                               - to_string(memory
                                               .at(index)
                                               .get_file
                                                   _partition
                                                       _no())
                                         .length()
                                     % 2,
                           ' ')
  
                 << memory
                        .at(index)
                        .get_file_partition_no()
  
                 << string(9
                               - to_string(memory
                                               .at(index)
                                               .get_file_partition_no())
                                         .length()
                                     / 2,
                           ' ')
                 << "|"
                 << endl;
            index++;
        }
        cout << "+------------------+"
             << "------------------+"
             << endl;
    }
    else
        cout << "File does not exist "
             << "in given memory"
             << endl;
}
  
// Driver Code
int main()
{
    // Declare memory of size 16 Blocks
    vector<Block> memory(16);
  
    // Declare index page
    vector<int> index_page;
    File temp;
  
    cout << "Remaining memory :- "
         << get_empty_count(memory)
         << endl;
  
    // Set the data
    temp.filename = "home.txt";
    temp.size = 5;
    set_contiguous_memory(&memory,
                          &index_page,
                          temp);
  
    temp.filename = "Report.docx";
    temp.size = 6;
    set_contiguous_memory(&memory,
                          &index_page,
                          temp);
  
    temp.filename = "new_img.png";
    temp.size = 3;
    set_contiguous_memory(&memory,
                          &index_page,
                          temp);
  
    temp.filename = "test.cpp";
    temp.size = 2;
    set_contiguous_memory(&memory,
                          &index_page,
                          temp);
  
    cout << "Remaining memory :- "
         << get_empty_count(memory)
         << endl;
  
    // Function call to show all the
    // memory allocation
    show_contiguous_index(memory,
                          index_page);
  
    cout << "Now we will check each partition of";
    cout << " Report.docx and test.cpp before"
         << endl;
  
    cout << "deleting them to see"
         << " which locations ";
  
    cout << "are going to be set free"
         << " as our slots"
         << endl;
  
    // Function call to show all the
    // memory allocation
    show_contiguous_indexes(memory,
                            index_page,
                            "Report.docx");
  
    // Function call to show all the
    // memory allocation
    show_contiguous_indexes(memory,
                            index_page,
                            "test.cpp");
  
    // Now delete Report.docx & test.cpp
  
    delete_contiguous_mem(&memory,
                          &index_page,
                          "Report.docx");
  
    delete_contiguous_mem(&memory,
                          &index_page,
                          "test.cpp");
  
    cout << "Remaining memory :- "
         << get_empty_count(memory)
         << endl;
    // Function call to show all the
    // memory allocation
    show_contiguous_index(memory,
                          index_page);
  
    // Creating hello.jpeg file now
    // and setting it to memory
    temp.filename = "hello.jpeg";
    temp.size = 8;
    set_contiguous_memory(&memory,
                          &index_page,
                          temp);
  
    cout << "Check index page: " << endl;
  
    // Function call to show all the
    // memory allocation
    show_contiguous_index(memory,
                          index_page);
}
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Output:

Remaining memory :- 16
File home.txt has been successfully allocated
File Report.docx has been successfully allocated
File new_img.png has been successfully allocated
File test.cpp has been successfully allocated
Remaining memory :- 0
+-------------+---------------+-------------+------------------+
|  File Name  | Start Address | End Address | Size of the file |
+-------------+---------------+-------------+------------------+
|   home.txt  |       0       |      4      |        5         |
| Report.docx |       5       |      10     |        6         |
| new_img.png |       11      |      13     |        3         |
|   test.cpp  |       14      |      15     |        2         |
+-------------+---------------+-------------+------------------+
Now we will check each partition of Report.docx and test.cpp before
deleting them to see which locations are going to be set free as our slots
File Name = Report.docx
+------------------+------------------+
| Current Location | Partition Number |
+------------------+------------------+
|        5         |        0         |
|        6         |        1         |
|        7         |        2         |
|        8         |        3         |
|        9         |        4         |
|        10        |        5         |
+------------------+------------------+
File Name = test.cpp
+------------------+------------------+
| Current Location | Partition Number |
+------------------+------------------+
|        14        |        0         |
|        15        |        1         |
+------------------+------------------+
File Report.docx has been successfully deleted
File test.cpp has been successfully deleted
Remaining memory:- 8
+-------------+---------------+-------------+------------------+
|  File Name  | Start Address | End Address | Size of the file |
+-------------+---------------+-------------+------------------+
|   home.txt  |       0       |      4      |        5         |
| new_img.png |       11      |      13     |        3         |
+-------------+---------------+-------------+------------------+
The size of the file is greater than
the greatest slot available in contiguous memory
Hence, File hello.jpeg cannot be allocated
Check index page: 
+-------------+---------------+-------------+------------------+
|  File Name  | Start Address | End Address | Size of the file |
+-------------+---------------+-------------+------------------+
|   home.txt  |       0       |      4      |        5         |
| new_img.png |       11      |      13     |        3         |
+-------------+---------------+-------------+------------------+

2. Indexed File Allocation Method:

This is a type of allocation where we have 2 index pages, one is the main index page w.r.t all files and the other is a sub-indexed page which is w.r.t to a particular file. This type of allocation does not require a contiguous slot of memory since we are keeping track of each block individually. In the given program below, the vector of vectors is used for implementing the main index and sub-index.

Below is the implementation for Indexed File Allocation Method:

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// C++ implementation of the Indexed
// File Allocation Method
#include <iostream>
#include <vector>
using namespace std;
  
// File Class
class File {
public:
    // Name of File
    string filename;
  
    // Size of file
    size_t size;
  
    // Partition no. is which part of
    // file is present at a particular
    // block of memory
    int partition;
};
  
// Block class
class Block {
    // If Block is occupied
    // by a file or not
    bool occupied = false;
  
    // File of the block
    File file;
  
public:
    // This function will set file
    // into current block
    // and set occupied flag
    void set_file(File file)
    {
        this->file = file;
        occupied = true;
    }
  
    // This function will return
    // filename of given block
    string get_file_name()
    {
        return file.filename;
    }
  
    // This function will return
    // partition number of file
    int get_file_partition_no()
    {
        return file.partition;
    }
  
    // This function will return
    // if the block is empty or not
    bool is_empty()
    {
        return !occupied;
    }
  
    // This function will set the
    // occupied flag as false
    // meaning that it will free
    // the given block
    void set_empty()
    {
        occupied = false;
    }
};
  
// Function to return the number of
// empty Blocks from given memory
int get_empty_count(vector<Block> memory)
{
    int sum = 0;
    vector<Block>::iterator slot;
  
    // count no. of empty blocks in
    // given memory
    for (slot = memory.begin();
         slot != memory.end(); slot++)
        sum += (*slot).is_empty();
    return sum;
}
  
// This function will generate random indexes
// from empty memory slots to test indexing
int generate_index(vector<Block> memory)
{
    int index = -1;
  
    // Check if memory is full
    if (!get_empty_count(memory) == 0) {
  
        // Here it will generate index until
        // the memory block at generated
        // index is found to be empty
        do {
            index = rand() % memory.size();
            index = abs(index);
  
        } while (!memory.at(index).is_empty());
    }
    return index;
}
  
// This function will return if the file
// exists in a given memory
bool file_exists(vector<Block> memory,
                 string name)
{
    vector<Block>::iterator slot;
  
    for (slot = memory.begin();
         slot != memory.end(); slot++) {
        if (!(*slot).is_empty()
            && (*slot).get_file_name() == name) {
            return true;
        }
    }
  
    return false;
}
  
// This function will set file in
// memory and push index for each partition
// and then push the file index to main
// index vector
void set_indexed_memory(vector<Block>* memory,
                        vector<vector<int> >* index_page,
                        File file)
{
    int index;
  
    // Declaration newpage to set the
    // index page for given file
    vector<int> newpage;
  
    // Check if file exists
    if (file_exists((*memory), file.filename))
        cout << "File already exists" << endl;
    else {
        // Check if available memory is greater than
        // size of given file
        if (get_empty_count(*memory) >= file.size) {
  
            // Iterate till file size
            for (int i = 0; i < file.size; i++) {
  
                // Generate random empty index
                index = generate_index(*memory);
  
                // Set file partition
                file.partition = i;
  
                // Push the file to memory
                (*memory).at(index).set_file(file);
  
                // Push the index to newpage
                newpage.push_back(index);
            }
  
            // Push new index page into main
            // index page
            (*index_page).push_back(newpage);
            cout << "File " << file.filename
                 << " has been successfully allocated"
                 << endl;
        }
        else {
            cout << "Not enough available space"
                 << endl;
        }
    }
}
  
// Function to delete a file from given
// indexed memory
void delete_from_indexed_memory(vector<Block>* memory,
                                vector<vector<int> >* index_page,
                                string file)
{
    vector<int>::iterator slot;
    vector<vector<int> >::iterator it;
    int index, i = 0;
  
    // Check if file exists
    if (file_exists((*memory), file)) {
        // Iterate main index
        for (it = (*index_page).begin();
             it != (*index_page).end(); it++) {
            // Check for sub-index at
            // start location
            slot = (*it).begin();
  
            // Check if it equals filename
            if ((*memory)
                    .at(*slot)
                    .get_file_name()
                == file) {
                // Set for index and break
                index = i;
                break;
            }
            i++;
        }
  
        // Set the memory flag as empty
        for (slot = (*index_page).at(index).begin();
             slot != (*index_page).at(index).end();
             slot++)
            (*memory).at(*slot).set_empty();
  
        // Erase file index from main index page
        (*index_page)
            .erase((*index_page).begin() + index);
        cout << "File " << file
             << " has been successfully deleted"
             << endl;
    }
    else {
        cout << "File does not exist"
             << endl;
    }
}
  
// Function to display the main index
void show_indexed_index(vector<Block> memory,
                        vector<vector<int> > index_page)
{
    int max = 9;
    vector<Block>::iterator slot;
    vector<vector<int> >::iterator it;
  
    // Iterate over index pages
    for (it = index_page.begin();
         it != index_page.end(); it++) {
        if (memory
                .at((*it)
                        .at(0))
                .get_file_name()
                .length()
            > max) {
            max = memory
                      .at((*it)
                              .at(0))
                      .get_file_name()
                      .length();
            cout << "+" << string(max + 2, '-')
                 << "+---------------+----------"
                 << "---+------------------+\n|"
                 << string(max / 2 + max % 2 - 4, ' ')
                 << "File Name"
                 << string(max / 2 - 3, ' ')
                 << "| Start Address | End Address"
                 << " | Size of the file |\n+"
                 << string(max + 2, '-')
                 << "+---------------+------"
                 << "-------+------------------+"
                 << endl;
        }
    }
  
    // Iterate through all the index pages
    for (it = index_page.begin();
         it != index_page.end(); it++) {
        cout << "|"
             << string(max / 2
                           + max % 2
                           - memory
                                     .at((*it)
                                             .at(0))
                                     .get_file_name()
                                     .length()
                                 / 2
                           - memory
                                     .at((*it)
                                             .at(0))
                                     .get_file_name()
                                     .length()
                                 % 2
                           + 1,
                       ' ')
             << memory
                    .at((*it)
                            .at(0))
                    .get_file_name()
             << string(max / 2
                           - memory
                                     .at((*it)
                                             .at(0))
                                     .get_file_name()
                                     .length()
                                 / 2
                           + 1,
                       ' ')
             << "|"
             << string(8
                           - to_string((*it)
                                           .at(0))
                                     .length()
                                 / 2
                           - to_string((*it)
                                           .at(0))
                                     .length()
                                 % 2,
                       ' ')
             << ((*it).at(0))
             << string(7
                           - to_string((*it)
                                           .at(0))
                                     .length()
                                 / 2,
                       ' ')
             << "|"
             << string(7
                           - to_string((*it)
                                           .at((*it)
                                                   .size()
                                               - 1))
                                     .length()
                                 / 2
                           - to_string((*it)
                                           .at((*it)
                                                   .size()
                                               - 1))
                                     .length()
                                 % 2,
                       ' ')
             << (*it)
                    .at((*it).size() - 1)
             << string(6
                           - to_string((*it)
                                           .at((*it)
                                                   .size()
                                               - 1))
                                     .length()
                                 / 2,
                       ' ')
             << "|"
             << string(9
                           - to_string((*it)
                                           .size())
                                     .length()
                                 / 2
                           - to_string((*it)
                                           .size())
                                     .length()
                                 % 2,
                       ' ')
             << (*it).size()
             << string(9
                           - to_string((*it)
                                           .size())
                                     .length()
                                 / 2,
                       ' ')
             << "|" << endl;
        cout << "+" << string(max + 2, '-')
             << "+---------------+----------"
             << "---+------------------+"
             << endl;
    }
}
  
// Function to show each partition details
// w.r.t filename
void show_indexed_indexes(vector<Block> memory,
                          vector<vector<int> > index_page,
                          string filename)
{
    int index, i = 0, main_index;
    vector<vector<int> >::iterator slot;
  
    // Check if file exists
    if (file_exists(memory, filename)) {
        for (slot = index_page.begin();
             slot != index_page.end(); slot++) {
            if (memory.at((*slot).at(0)).get_file_name()
                == filename) {
                main_index = i;
                break;
            }
            i++;
        }
  
        // Display File Details
        cout << "File Name = " << filename << endl;
        cout << "File page index at main index :- "
             << main_index
             << "\n+------------------+------------------+\n";
        cout << "| Current Location | Partition Number |\n";
        cout << "+------------------+------------------+\n";
        for (i = 0;
             i < index_page.at(main_index).size();
             i++) {
            index = index_page
                        .at(main_index)
                        .at(i);
            cout << "|" << string(9
                                      - to_string(index)
                                                .length()
                                            / 2
                                      - to_string(index)
                                                .length()
                                            % 2,
                                  ' ')
                 << index
                 << string(9
                               - to_string(index)
                                         .length()
                                     / 2,
                           ' ')
                 << "|" << string(9
                                      - to_string(memory
                                                      .at(index)
                                                      .get_file_partition_no())
                                                .length()
                                            / 2
                                      - to_string(memory
                                                      .at(index)
                                                      .get_file_partition_no())
                                                .length()
                                            % 2,
                                  ' ')
                 << memory
                        .at(index)
                        .get_file_partition_no()
                 << string(9
                               - to_string(memory
                                               .at(index)
                                               .get_file_partition_no())
                                         .length()
                                     / 2,
                           ' ')
                 << "|" << endl;
        }
  
        cout << "+------------------+----"
             << "--------------+" << endl;
    }
    else {
        cout << "File does not exist"
             << endl;
    }
}
  
// Driver Code
int main()
{
    // Declare memory of size 16 Blocks
    vector<Block> memory(16);
  
    // Declare index page
    vector<vector<int> > index_page;
  
    File temp;
    cout << "Remaining memory :- "
         << get_empty_count(memory)
         << endl;
  
    // Set the data
    temp.filename = "home.txt";
    temp.size = 5;
    set_indexed_memory(&memory,
                       &index_page,
                       temp);
  
    temp.filename = "Report.docx";
    temp.size = 6;
    set_indexed_memory(&memory,
                       &index_page,
                       temp);
  
    temp.filename = "new_img.png";
    temp.size = 3;
    set_indexed_memory(&memory,
                       &index_page,
                       temp);
  
    temp.filename = "test.cpp";
    temp.size = 2;
    set_indexed_memory(&memory,
                       &index_page,
                       temp);
  
    // Print the Remaining memory
    cout << "Remaining memory :- "
         << get_empty_count(memory)
         << endl;
  
    // Print all the index memory
    show_indexed_index(memory, index_page);
    cout << "Now we will check each partition"
         << " for Report.docx and test.cpp"
         << " before deleting them" << endl;
  
    // Print all the index memory
    show_indexed_indexes(memory, index_page,
                         "Report.docx");
  
    // Print all the index memory
    show_indexed_indexes(memory, index_page,
                         "test.cpp");
  
    // Now delete Report.docx and test.cpp
    delete_from_indexed_memory(&memory,
                               &index_page,
                               "Report.docx");
  
    delete_from_indexed_memory(&memory,
                               &index_page,
                               "test.cpp");
  
    cout << "Remaining memory :- "
         << get_empty_count(memory)
         << endl;
  
    // Print all the index memory
    show_indexed_index(memory, index_page);
  
    // Creating hello.jpeg file now
    // and setting it to memory
    temp.filename = "hello.jpeg";
    temp.size = 8;
  
    set_indexed_memory(&memory,
                       &index_page,
                       temp);
    cout << "Check index page :- "
         << endl;
  
    // Print all the index memory
    show_indexed_index(memory, index_page);
  
    // Now we will see index for each partition of
    // hello.jpeg
    cout << "Remaining memory :- "
         << get_empty_count(memory)
         << endl;
    cout << "We will check each partition"
         << " for hello.jpeg to see ";
    cout << "if the locations of deleted files"
         << " are utilized or not" << endl;
  
    // Print all the index memory
    show_indexed_indexes(memory, index_page,
                         "hello.jpeg");
    memory.clear();
    memory.shrink_to_fit();
    index_page.clear();
    index_page.shrink_to_fit();
    return 0;
}
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Output:
Remaining memory :- 16
File home.txt has been successfully allocated
File Report.docx has been successfully allocated
File new_img.png has been successfully allocated
File test.cpp has been successfully allocated
Remaining memory :- 0
+-------------+---------------+-------------+------------------+
|  File Name  | Start Address | End Address | Size of the file |
+-------------+---------------+-------------+------------------+
|   home.txt  |       7       |      1      |        5         |
+-------------+---------------+-------------+------------------+
| Report.docx |       15      |      2      |        6         |
+-------------+---------------+-------------+------------------+
| new_img.png |       4       |      14     |        3         |
+-------------+---------------+-------------+------------------+
|   test.cpp  |       5       |      0      |        2         |
+-------------+---------------+-------------+------------------+
Now we will check each partition for Report.docx and test.cpp before deleting them
File Name = Report.docx
File page index at main index :- 1
+------------------+------------------+
| Current Location | Partition Number |
+------------------+------------------+
|        15        |        0         |
|        10        |        1         |
|        12        |        2         |
|        13        |        3         |
|        11        |        4         |
|        2         |        5         |
+------------------+------------------+
File Name = test.cpp
File page index at main index :- 3
+------------------+------------------+
| Current Location | Partition Number |
+------------------+------------------+
|        5         |        0         |
|        0         |        1         |
+------------------+------------------+
File Report.docx has been successfully deleted
File test.cpp has been successfully deleted
Remaining memory :- 8
+-------------+---------------+-------------+------------------+
|  File Name  | Start Address | End Address | Size of the file |
+-------------+---------------+-------------+------------------+
|   home.txt  |       7       |      1      |        5         |
+-------------+---------------+-------------+------------------+
| new_img.png |       4       |      14     |        3         |
+-------------+---------------+-------------+------------------+
File hello.jpeg has been successfully allocated
Check index page :- 
+-------------+---------------+-------------+------------------+
|  File Name  | Start Address | End Address | Size of the file |
+-------------+---------------+-------------+------------------+
|   home.txt  |       7       |      1      |        5         |
+-------------+---------------+-------------+------------------+
| new_img.png |       4       |      14     |        3         |
+-------------+---------------+-------------+------------------+
|  hello.jpeg |       12      |      13     |        8         |
+-------------+---------------+-------------+------------------+
Remaining memory :- 0
We will check each partition for hello.jpeg to see if the locations of deleted files are utilized or not
File Name = hello.jpeg
File page index at main index :- 2
+------------------+------------------+
| Current Location | Partition Number |
+------------------+------------------+
|        12        |        0         |
|        10        |        1         |
|        11        |        2         |
|        15        |        3         |
|        0         |        4         |
|        2         |        5         |
|        5         |        6         |
|        13        |        7         |
+------------------+------------------+

3. Linked File Allocation Method:

This is a type of allocation where we linked all the partitions of a file to point to the memory location where the next partition of the file is placed. In the given program below, next will be allocated as -1 when the last partition is reached.

Below is the implementation of Linked File Allocation Method:

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// C++ implementation of the Linked
// File Allocation Method
#include <iostream>
#include <vector>
using namespace std;
  
// File Class
class File {
public:
    // Name of File
    string filename;
    // Size of file
    size_t size;
  
    // Partition no is which part of
    // file is present at a particular
    // block of memory
    int partition;
};
  
// Block Class
class Block {
    // If Block is occupied
    // by a file or not
    bool occupied = false;
  
    // File of the block
    File file;
  
    // Location of next partition in given memory
    // By default, it is set to -1
    // which indicates there is no next partition
    int next = -1;
  
public:
    // This will set file into current block
    // and set occupied flag
    void set_file(File file)
    {
        this->file = file;
        occupied = true;
    }
  
    // This will return filename of given block
    string get_file_name()
    {
        return file.filename;
    }
    // Return partition number of file
    int get_file_partition_no()
    {
        return file.partition;
    }
  
    // Return if the block is empty or not
    bool is_empty()
    {
        return !occupied;
    }
  
    // This will set the occupied flag as false
    // meaning that it will free the memory
    void set_empty()
    {
        occupied = false;
    }
  
    // This function will set location of next
    // partition in given memory
    void set_next(int next)
    {
        this->next = next;
    }
  
    // This function will return location
    // of next partition
    int get_next()
    {
        return next;
    }
};
  
// Function to return the number of
// empty Blocks from given memory
int get_empty_count(vector<Block> memory)
{
    int sum = 0;
    vector<Block>::iterator slot;
  
    // Count no. of empty blocks in given memory
    for (slot = memory.begin();
         slot != memory.end(); slot++)
        sum += (*slot).is_empty();
  
    // Return the empty count
    return sum;
}
  
// Function to generate random indexes
// from empty memory slots to test indexing
int generate_index(vector<Block> memory)
{
    int index = -1;
  
    // Check if memory is full
    if (!get_empty_count(memory) == 0) {
        // Here it will generate index until
        // the memory block at generated
        // index is found to be empty
        do {
            index = rand() % memory.size();
            index = abs(index);
        } while (!memory.at(index).is_empty());
    }
    return index;
}
  
// This function will return if the file
// exists in a given memory
bool file_exists(vector<Block> memory,
                 string name)
{
    vector<Block>::iterator slot;
  
    for (slot = memory.begin();
         slot != memory.end(); slot++)
        if (!(*slot).is_empty()
            && (*slot).get_file_name()
                   == name)
            return true;
  
    return false;
}
  
// This function will set the file in memory
void set_linked_memory(vector<Block>* memory,
                       vector<int>* index_page,
                       File file)
{
    int index = -1, prev = -1, i = 0;
  
    // Check if file exists already
    if (!file_exists((*memory), file.filename)) {
  
        // Check if memory is available
        // according to file size
        if (get_empty_count(*memory) >= file.size) {
  
            // Generate empty index
            index = generate_index(*memory);
  
            // Push 1st index to index page
            (*index_page).push_back(index);
            for (i = 0; i < file.size - 1; i++) {
                // Set partition
                file.partition = i;
  
                // Set file into memory
                (*memory).at(index).set_file(file);
  
                // Note down prev index before
                // generating next index
                prev = index;
  
                // Generate empty index
                index = generate_index(*memory);
  
                // Set the next location to generated
                // index in previous index
                (*memory).at(prev).set_next(index);
            }
  
            // Set last partition and file
            file.partition = file.size - 1;
            (*memory).at(index).set_file(file);
  
            cout << "File " << file.filename
                 << " has been successfully allocated"
                 << endl;
        }
        else
            cout << "Not enough available memory"
                 << endl;
    }
    else
        cout << "File already exists in given memory"
             << endl;
}
  
// Function will delete the file from
// memory specified by name
void delete_from_linked_memory(vector<Block>* memory,
                               vector<int>* index_page,
                               string file)
{
    int index, next, previous, main_index, i = 0;
    vector<int>::iterator slot;
  
    // Check if file exists
    if (file_exists((*memory), file)) {
  
        // Iterate through the index page
        // to find 1st partition
        for (slot = (*index_page).begin();
             slot != (*index_page).end();
             slot++) {
  
            // Check if file stored at index has
            // the same name we wish to delete
            if ((*memory)
                    .at(*slot)
                    .get_file_name()
                == file) {
                // Main index is w.r.t memory location
                main_index = (*slot);
  
                // index is w.r.t index page
                // entry location
                index = i;
                break;
            }
            i++;
        }
  
        // 1st partition
        i = main_index;
  
        // Check while next location comes as -1
        while (i != -1
               && (*memory)
                          .at(i)
                          .get_file_name()
                      == file) {
  
            // set the Block free
            (*memory).at(i).set_empty();
  
            // Note the location into previous
            previous = i;
  
            // get the next location
            i = (*memory).at(i).get_next();
  
            // set -1 as next location into
            // previous location
            (*memory).at(previous).set_next(-1);
        }
  
        // Erase the entry of file from index
        // page as well
        (*index_page)
            .erase((*index_page)
                       .begin()
                   + index);
        cout << "File " << file
             << " has been successfully deleted"
             << endl;
    }
    else {
        cout << "File does not exist in given memory"
             << endl;
    }
}
  
// Function to display main index page
void show_linked_index(vector<Block> memory,
                       vector<int> index)
{
    int max = 9, i, count;
  
    // Iterator
    vector<int>::iterator slot;
  
    // File Name
    string fname;
  
    // Iterate through all index pages
    for (slot = index.begin();
         slot != index.end(); slot++) {
  
        if (memory
                .at(*slot)
                .get_file_name()
                .length()
            > max) {
            max = memory
                      .at(*slot)
                      .get_file_name()
                      .length();
            cout << "+" << string(max + 2, '-')
                 << "+---------------+---------"
                 << "----+------------------+";
            cout << "\n|"
                 << string(max / 2 + max % 2 - 4,
                           ' ')
                 << "File Name"
                 << string(max / 2 - 3, ' ');
            cout << "| Start Address | End Address"
                 << " | Size of the file |\n+"
                 << string(max + 2, '-');
            cout << "+---------------+--------"
                 << "-----+------------------+"
                 << endl;
        }
    }
  
    // Iterate through index
    for (slot = index.begin();
         slot != index.end();
         slot++) {
  
        i = (*slot);
        fname = memory
                    .at(i)
                    .get_file_name();
        count = 1;
        while (memory.at(i).get_next() != -1
               && memory
                          .at(i)
                          .get_file_name()
                      == fname) {
            i = memory.at(i).get_next();
            count++;
        }
  
        cout << "|" << string(max / 2 + max % 2
                                  - memory
                                            .at(*slot)
                                            .get_file_name()
                                            .length()
                                        / 2
                                  - memory
                                            .at(*slot)
                                            .get_file_name()
                                            .length()
                                        % 2
                                  + 1,
                              ' ')
             << memory
                    .at(*slot)
                    .get_file_name()
             << string(max / 2 - memory.at(*slot).get_file_name().length() / 2 + 1,
                       ' ')
             << "|"
             << string(8
                           - to_string(*slot)
                                     .length()
                                 / 2
                           - to_string(*slot)
                                     .length()
                                 % 2,
                       ' ')
             << (*slot)
             << string(7
                           - to_string(*slot)
                                     .length()
                                 / 2,
                       ' ')
             << "|"
             << string(7
                           - to_string(i)
                                     .length()
                                 / 2
                           - to_string(i)
                                     .length()
                                 % 2,
                       ' ')
             << i
             << string(6
                           - to_string(i)
                                     .length()
                                 / 2,
                       ' ')
             << "|"
             << string(9
                           - to_string(count)
                                     .length()
                                 / 2
                           - to_string(count)
                                     .length()
                                 % 2,
                       ' ')
             << count
             << string(9
                           - to_string(count)
                                     .length()
                                 / 2,
                       ' ')
             << "|" << endl;
    }
  
    cout << "+" << string(max + 2, '-')
         << "+---------------+----------"
         << "---+------------------+"
         << endl;
}
  
// Function to check all the partitions of file
// w.r.t filename specified
void show_linked_indexes(vector<Block> memory, vector<int> index_page,
                         string filename)
{
    int index;
    vector<int>::iterator slot;
  
    // If file exists
    if (file_exists(memory, filename)) {
        cout << "File Name = " << filename;
        cout << "\n+------------------+----------"
             << "--------+------------------+";
        cout << "\n| Current Location |Next part"
             << " Location| Partition Number |";
        cout << "\n+------------------+----------"
             << "--------+------------------+\n";
  
        // Iterate through all index
        for (slot = index_page.begin();
             slot != index_page.end(); slot++) {
            if (memory
                    .at(*slot)
                    .get_file_name()
                == filename) {
                index = (*slot);
                break;
            }
        }
  
        // Loop till index is not -1
        while (index != -1) {
            cout << "|"
                 << string(9
                               - to_string(index)
                                         .length()
                                     / 2
                               - to_string(index)
                                         .length()
                                     % 2,
                           ' ')
                 << index
                 << string(9
                               - to_string(index)
                                         .length()
                                     / 2,
                           ' ')
                 << "|"
                 << string(9
                               - to_string(memory
                                               .at(index)
                                               .get_next())
                                         .length()
                                     / 2
                               - to_string(memory
                                               .at(index)
                                               .get_next())
                                         .length()
                                     % 2,
                           ' ')
                 << memory
                        .at(index)
                        .get_next()
                 << string(9
                               - to_string(memory
                                               .at(index)
                                               .get_next())
                                         .length()
                                     / 2,
                           ' ')
                 << "|"
                 << string(9
                               - to_string(memory
                                               .at(index)
                                               .get_file_partition_no())
                                         .length()
                                     / 2
                               - to_string(memory
                                               .at(index)
                                               .get_file_partition_no())
                                         .length()
                                     % 2,
                           ' ')
                 << memory
                        .at(index)
                        .get_file_partition_no()
                 << string(9
                               - to_string(memory
                                               .at(index)
                                               .get_file_partition_no())
                                         .length()
                                     / 2,
                           ' ')
                 << "|" << endl;
            index = memory
                        .at(index)
                        .get_next();
        }
  
        cout << "+------------------+---------"
             << "---------+------------------+"
             << endl;
    }
    else {
        cout << "Given file does not exist"
             << " in given memory"
             << endl;
    }
}
  
// Driver Code
int main()
{
  
    // Declare memory of size 16 Blocks
    vector<Block> memory(16);
  
    // Declare index page
    vector<int> index_page;
    File temp;
    cout << "Remaining memory :- "
         << get_empty_count(memory) << endl;
  
    // Set the data
    temp.filename = "home.txt";
    temp.size = 5;
    set_linked_memory(&memory,
                      &index_page,
                      temp);
  
    temp.filename = "Report.docx";
    temp.size = 6;
    set_linked_memory(&memory,
                      &index_page,
                      temp);
  
    temp.filename = "new_img.png";
    temp.size = 3;
    set_linked_memory(&memory,
                      &index_page,
                      temp);
  
    temp.filename = "test.cpp";
    temp.size = 2;
    set_linked_memory(&memory,
                      &index_page
                          temp);
  
    cout << "Files have been successfully set"
         << endl;
    cout << "Remaining memory :- "
         << get_empty_count(memory) << endl;
  
    // Print all the linked index
    show_linked_index(memory, index_page);
    cout << "Now we will check index"
         << " of each partition of ";
    cout << "Report.docx and test.cpp"
         << " before deleting them"
         << endl;
  
    // Print all the linked index
    show_linked_indexes(memory, index_page,
                        "Report.docx");
  
    // Print all the linked index
    show_linked_indexes(memory, index_page,
                        "test.cpp");
  
    // Now delete Report.docx and test.cpp
    delete_from_linked_memory(&memory,
                              &index_page,
                              "Report.docx");
    delete_from_linked_memory(&memory,
                              &index_page,
                              "test.cpp");
    cout << "Remaining memory :- "
         << get_empty_count(memory) << endl;
  
    // Print all the linked index
    show_linked_index(memory, index_page);
  
    // Creating hello.jpeg file now
    // and setting it to memory
    temp.filename = "hello.jpeg";
    temp.size = 8;
  
    // Set Linked memory
    set_linked_memory(&memory,
                      &index_page,
                      temp);
    cout << "Check index page :- "
         << endl;
  
    // Print all the linked index
    show_linked_index(memory, index_page);
  
    // Now we will see index for each partition
    // of hello.jpeg
    cout << "Remaining memory :- "
         << get_empty_count(memory) << endl;
    cout << "We will check each partition for"
         << " hello.jpeg ";
    cout << "to see if deleted locations are"
         << " utilized or not"
         << endl;
  
    // Print all the linked index
    show_linked_indexes(memory,
                        index_page,
                        "hello.jpeg");
    memory.clear();
    memory.shrink_to_fit();
    index_page.clear();
    index_page.shrink_to_fit();
  
    return 0;
}
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Output:
Remaining memory :- 16
File home.txt has been successfully allocated
File Report.docx has been successfully allocated
File new_img.png has been successfully allocated
File test.cpp has been successfully allocated
Files have been successfully set
Remaining memory :- 0
+-------------+---------------+-------------+------------------+
|  File Name  | Start Address | End Address | Size of the file |
+-------------+---------------+-------------+------------------+
|   home.txt  |       7       |      1      |        5         |
| Report.docx |       15      |      2      |        6         |
| new_img.png |       4       |      14     |        3         |
|   test.cpp  |       5       |      0      |        2         |
+-------------+---------------+-------------+------------------+
Now we will check index of each partition of Report.docx and test.cpp before deleting them
File Name = Report.docx
+------------------+------------------+------------------+
| Current Location |Next part Location| Partition Number |
+------------------+------------------+------------------+
|        15        |        10        |        0         |
|        10        |        12        |        1         |
|        12        |        13        |        2         |
|        13        |        11        |        3         |
|        11        |        2         |        4         |
|        2         |        -1        |        5         |
+------------------+------------------+------------------+
File Name = test.cpp
+------------------+------------------+------------------+
| Current Location |Next part Location| Partition Number |
+------------------+------------------+------------------+
|        5         |        0         |        0         |
|        0         |        -1        |        1         |
+------------------+------------------+------------------+
File Report.docx has been successfully deleted
File test.cpp has been successfully deleted
Remaining memory :- 8
+-------------+---------------+-------------+------------------+
|  File Name  | Start Address | End Address | Size of the file |
+-------------+---------------+-------------+------------------+
|   home.txt  |       7       |      1      |        5         |
| new_img.png |       4       |      14     |        3         |
+-------------+---------------+-------------+------------------+
File hello.jpeg has been successfully allocated
Check index page :- 
+-------------+---------------+-------------+------------------+
|  File Name  | Start Address | End Address | Size of the file |
+-------------+---------------+-------------+------------------+
|   home.txt  |       7       |      1      |        5         |
| new_img.png |       4       |      14     |        3         |
|  hello.jpeg |       12      |      13     |        8         |
+-------------+---------------+-------------+------------------+
Remaining memory :- 0
We will check each partition for hello.jpeg to see if deleted locations are utilized or not
File Name = hello.jpeg
+------------------+------------------+------------------+
| Current Location |Next part Location| Partition Number |
+------------------+------------------+------------------+
|        12        |        10        |        0         |
|        10        |        11        |        1         |
|        11        |        15        |        2         |
|        15        |        0         |        3         |
|        0         |        2         |        4         |
|        2         |        5         |        5         |
|        5         |        13        |        6         |
|        13        |        -1        |        7         |
+------------------+------------------+------------------+

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