file management with C++

This same codes are uploaded to GitHub.

(main.cc)

#include "loader.h"
#include <sstream>
#include <iostream>

using namespace std;

File* gFiles[ 10 ];

void createFile(int num, const char* filename) {
  Loader::instance()->createFile( &gFiles[num], filename);
  cout << num << " th file is created." << endl;
}

void outputFile(int num) {
  Loader::instance()->outputFile(gFiles[num]);
}

void loadFiles() {
  Loader::instance()->loadFiles();
  cout << "files are loaded." << endl;
}

void destroyFile(int num) {
  Loader::instance()->destroyFile( &gFiles[num] );
  cout << num << " th file is destroyed." << endl;
}

int main() {
  if ( !Loader::instance() ) {
    Loader::create();
  }

  createFile(0, "./test.txt");

  loadFiles();

  outputFile(0);

  destroyFile(0);
}

File class manages each files.
(file.h)

#ifndef INCLUDED_FILE_H
#define INCLUDED_FILE_H

#include <string>
using namespace std;

class File {
private:
  File( const char* filename );
  ~File();
  friend class Loader;

  string mFilename;
  char* mData;
  int mSize;

public:
  bool isReady() const;
  int getSize() const;
  const char* getData() const;
};

#endif

(file.cc)

#include "file.h"
#include <fstream>
#include <assert.h>

using namespace std;

File::File( const char* filename ) :
mFilename( filename ),
mData( 0 ),
mSize( 0 ) {
}

File::~File() {
  if ( mData ) {
    delete[]( mData );
  }
  mSize = 0;
}

bool File::isReady() const {
  return ( mData != 0 );
}

int File::getSize() const {
  assert( mData && "loading is not finished." );
  return mSize;
}

const char* File::getData() const {
  assert( mData && "loading is not finished." );
  return mData;
}

Loader class manages a group of files.
(loader.h)

#ifndef INCLUDED_LOADER_H
#define INCLUDED_LOADDR_H

#include <list>
#include <string>
#include "file.h"

using namespace std;

class Loader {
private:
  Loader();
  Loader( const Loader& );
  ~Loader();

  list< File* > mFiles;
  static Loader* mInstance;

public:
  static Loader* instance();
  static void create();
  static void destroy();

  void createFile( File**, const char* filename );
  void loadFiles();
  void outputFile( File *f );
  void destroyFile( File** );
};

#endif

(loader.cc)

#include "loader.h"
#include "assert.h"
#include <fstream>
#include <iostream>

using namespace std;

Loader* Loader::mInstance = 0;

Loader::Loader() {
}

Loader::~Loader() {
  typedef list< File* >::iterator It;
  for ( It i = mFiles.begin(); i != mFiles.end(); ++i ) {
    delete( *i );
  }
}

Loader* Loader::instance() {
  return mInstance;
}

void Loader::create() {
  assert( !mInstance && "already created." );
  mInstance = new Loader();
}

void Loader::destroy() {
  delete( mInstance );
}