Creating a File System in C++

File Systems are one of the most essential parts of any operating system; without them, nothing of substance would ever be achieved with computers! A great feature of file systems is their hierarchal structure, which perfectly captures the Composite design pattern. In this example, we'll be modeling our very own file system.

FileSystem Base Class:

#include <string>
#include <vector>
#include <iostream>

// Abstract file system base class:
class FileSystem
{
   public:
       FileSystem()
       : isDir(false), isFile(false), name("")
       {};
       virtual ~FileSystem() {};

       // The virtual ls method to "list" out the contents:
       virtual void ls(int indent = 0) {indent;};

       bool isDir;
       bool isFile;
       std::string name;

   protected:
       // Helper for setting the tab correctly:
       std::string tab(int indent)
       {
           return std::string(indent * 4, ' ');
       }
};

Directory:

class Directory: public FileSystem
{
   public:
       Directory(std::string name)
       : FileSystem()
       {
           this->isDir = true;
           this->name = name;
       };
       virtual ~Directory();

       void ls(int indent = 0) override;

       void Add(FileSystem* listing);

   protected:
       std::vector<FileSystem*> listings;
};

void Directory::ls(int indent)
{
   std::cout  << "\n" << this->tab(indent) << this->name << "/\n";

   // List all items in the directory:
   std::vector<FileSystem*>::iterator itr = this->listings.begin();
   for(itr; itr != this->listings.end(); ++itr)
   {
       (*itr)->ls(indent + 1);
   }
}

void Directory::Add(FileSystem* listing)
{
   this->listings.push_back(listing);
}

Directory::~Directory()
{
   // Iterate all items, delete them:
   std::vector<FileSystem*>::const_iterator it = this->listings.begin();

   for(; it != this->listings.end(); ++it)
   {
       delete *it;
   }
   this->listings.clear();

}

FileType:

// The FileType class for files:
class FileType: public FileSystem
{
   public:
       FileType(std::string name, std::string ext)
       : FileSystem()
       {
           this->name = name;
           this->ext = ext;
           this->isFile = true;
       };
       virtual ~FileType() {};

       void ls(int indent = 0) override;

   protected:
       std::string ext;
};

void FileType::ls(int indent)
{
   std::cout << this->tab(indent) << this->name << "." << this->ext << std::endl;
}

Demo of Composite Pattern:

int main()
{
   Directory* root = new Directory("usr");

   // Create a home directory:
   Directory* homeDir = new Directory("home");
   // Add a few files:
   homeDir->Add(new FileType("howToCode", "pdf"));
   homeDir->Add(new FileType("ThingsToDo", "txt"));
   homeDir->Add(new FileType("grandCanyon", "png"));
     
   // Add home dir to the root:
   root->Add(homeDir);

   // Create a projects bin:
   Directory* projectDir = new Directory("codeProjects");
   // Create a new project:
   Directory* devmakingProj = new Directory("devmaking");
   devmakingProj->Add(new FileType("index", "html"));
   // Create another project:
   Directory* ticTacToeProj = new Directory("AI_tic-tac-toe");
   ticTacToeProj->Add(new FileType("app", "py"));

   // Add the projects to the project directory:
   projectDir->Add(devmakingProj);
   projectDir->Add(ticTacToeProj);

   // Add the project dir to the root:
   root->Add(projectDir); 


   // List everything:
   root->ls();

   
   // Clean up:
   delete root;
}

// Output:
/*
   usr/

       home/
           howToCode.pdf
           ThingsToDo.txt
           grandCanyon.png

       codeProjects/

           devmaking/
               index.html

           AI_tic-tac-toe/
               app.py
*/