Thread: Question about classes and structures.

Originally Posted by linkofazeroth

No, you understood it right. I don't know how to make the program search in a file for a certain value and pull it up (I have a function called load()), so I'm stuck with separate files. Like, if I have a file that looks like this...

Code:

1
5
5
4
6
0
0
1

...I can't (or don't know how to) make the program search for a specific number. Maybe if I could tell a function to look at a certain line in the file and pull that line's value out, that'd be helpful, but I don't know how.

Did my previous post help you with your problem at all, though?

I've been doing it like this:

Code:

#include <iostream>
#include <fstream>

class Human
{
private:
  int m_minHealth;
  int m_maxHealth;
  int m_minMana;
  int m_maxMana;
  int m_minStamina;
  int m_maxStamina;
        
public:
  Human ();

  int GetMinHealth () { return m_minHealth; }
  void SetMinHealth (int p_minHealth) { m_minHealth = p_minHealth; }

  bool Save (const char*);
  bool Read (const char*);
};

Human::Human() : m_minHealth(100), m_maxHealth(100), m_minMana(50), m_maxMana(50), m_minStamina(75), m_maxStamina(75) { }

bool Human::Save (const char* p_filename)
{
  int index;

  FILE* saveFile = fopen (p_filename, "wb");
  if (saveFile == 0)
    return false;
  
  fseek (saveFile, 0, SEEK_SET);
  fwrite (&(m_minHealth), sizeof (m_minHealth), 1, saveFile);
  
  fseek (saveFile, sizeof (m_minHealth), SEEK_SET);
  fwrite (&(m_minHealth), sizeof (m_maxHealth), 1, saveFile);
  
  fseek (saveFile, ((sizeof (m_minHealth)) + (sizeof (m_maxHealth))), SEEK_SET);
  fwrite (&(m_minMana), sizeof (m_minMana), 1, saveFile);
  
  fseek (saveFile, ((sizeof (m_minHealth)) + (sizeof (m_maxHealth)) + (sizeof (m_minMana))), SEEK_SET);
  fwrite (&(m_maxMana), sizeof (m_maxMana), 1, saveFile);
  
  fseek (saveFile, ((sizeof (m_minHealth)) + (sizeof (m_maxHealth)) + (sizeof (m_minMana)) + (sizeof (m_maxMana))), SEEK_SET);
  fwrite (&(m_minStamina), sizeof (m_minStamina), 1, saveFile);
  
  fseek (saveFile, ((sizeof (m_minHealth)) + (sizeof (m_maxHealth)) + (sizeof (m_minMana)) + (sizeof (m_maxMana)) + (sizeof (m_minStamina))), SEEK_SET);
  fwrite (&(m_maxStamina), sizeof (m_maxStamina), 1, saveFile);

  fclose (saveFile);
  //if (written != m_size)
  //  return false;

  return true;
}

bool Human::Read (const char* p_filename)
{
  int read = 0;

  FILE* infile = fopen (p_filename, "rb");
  if (infile == 0)
    return false;

  read = fread (this, sizeof(int), 6, infile);

  fclose (infile);
  //if (read != m_size)
  //  return false;

  return true;
}

int main ()
{
  Human Hum1;
  
  std::cout << Hum1.GetMinHealth() << std::endl;
  Hum1.SetMinHealth(200);
  Hum1.Save ("player1.dat"); //save as 200
  std::cout << Hum1.GetMinHealth() << std::endl;
  Hum1.SetMinHealth(300); //set to 300
  Hum1.Read ("player1.dat"); //changes it back to 200
  std::cout << Hum1.GetMinHealth() << std::endl; //output 200
    
 
  std::cin.get();
}

The Save and Read methods use ol' C. The Save method shows how to seek to a certain spot (by how many bytes into the file you want to read, and how many bytes you want to read, ie. bytes 12-16 (m_minMana), or 0-4 (m_minHealth)), and the Read method reads the entire saved class into the class you're in (this).

I'm not sure how to do it the C++ way, or how to seek to a specific variable without searching google and doing some reading. I might actually go do that now, itd be beneficial to know, and cplusplus.com has info on the specific functions.

Dae, do you need <cstdio>?

Oh, never mind . . . .

Originally Posted by Dae

I'm not sure how to do it the C++ way, or how to seek to a specific variable without searching google and doing some reading. I might actually go do that now, itd be beneficial to know, and cplusplus.com has info on the specific functions.

Use ifstream/ofstream objects. The read/write methods for those objects are equivalent to the fread/fwrite functions. The seekp/seekg functions can perform the same task as the fseek function.

I myself might go the path of overwriting the stream insertion/extraction operators for the class (<</>>) and end up with something like:

Code:

// Create our Human object Hum1
Human Hum1;

// Read from input file into Hum1 Human
ifstream input("Player.Txt",ios::in|ios::binary);
input >> Hum1;
input.close();

// Do stuff with the Hum1 Human

// Write out data for Hum1 to the output file
ofstream output("Player.Txt",ios::out|ios::binary);
output << Hum1;
output.close();

Originally Posted by hk_mp5kpdw

Use ifstream/ofstream objects. The read/write methods for those objects are equivalent to the fread/fwrite functions. The seekp/seekg functions can perform the same task as the fseek function.

I myself might go the path of overwriting the stream insertion/extraction operators for the class (<</>>) and end up with something like:

Code:

// Create our Human object Hum1
Human Hum1;

// Read from input file into Hum1 Human
ifstream input("Player.Txt",ios::in|ios::binary);
input >> Hum1;
input.close();

// Do stuff with the Hum1 Human

// Write out data for Hum1 to the output file
ofstream output("Player.Txt",ios::out|ios::binary);
output << Hum1;
output.close();

For the past couple hours I was checking that exact method out, heres the C++ equivalent of what I posted above for the text-adventure saving data style (I used if/else's to make it more versatile, save only health, read only health, read all, etc.):

Code:

bool Human::Save (bool p_minHealth, bool p_maxHealth, bool p_minMana, bool p_maxMana, bool p_minStamina, bool p_maxStamina)
{
  long pos = 0;

  ofstream saveFile ("player2.dat", ofstream::binary);
  if (!saveFile) {
    cerr << "Error: file could not be opened" << endl;
    exit(1);
    return false;
  }

  if (p_minHealth)
    saveFile << m_minHealth << "\n";
  else
    saveFile.seekp (pos + sizeof (m_minHealth));

  pos = saveFile.tellp();
  if (p_maxHealth)
    saveFile << m_maxHealth << "\n";
  else
    saveFile.seekp (pos + sizeof (m_maxHealth));
    
  pos = saveFile.tellp();
  if (p_minMana)
    saveFile << m_minMana << "\n";
  else
    saveFile.seekp (pos + sizeof (m_minMana));

  pos = saveFile.tellp();
  if (p_maxMana)
    saveFile << m_maxMana << "\n";
  else
    saveFile.seekp (pos + sizeof (m_maxMana));
    
  pos = saveFile.tellp();
  if (p_minStamina)
    saveFile << m_minStamina << "\n";
  else
    saveFile.seekp (pos + sizeof (m_minStamina));
    
  pos = saveFile.tellp();
  if (p_maxStamina)
    saveFile << m_maxStamina << "\n";
  else
    saveFile.seekp (pos + sizeof (m_maxStamina));

  saveFile.close();

  return 1;
}

bool Human::Read (bool p_minHealth, bool p_maxHealth, bool p_minMana, bool p_maxMana, bool p_minStamina, bool p_maxStamina)
{
  long pos = 0;

  ifstream readFile ("player2.dat", ofstream::binary);
  if (!readFile) {
    cerr << "Error: file could not be opened" << endl;
    exit(1);
    return false;
  }

  if (p_minHealth)
    readFile >> m_minHealth;
  else
    readFile.seekg (pos + sizeof (m_minHealth));

  pos = readFile.tellg();
  if (p_maxHealth)
    readFile >> m_maxHealth;
  else
    readFile.seekg (pos + sizeof (m_maxHealth));
    
  pos = readFile.tellg();
  if (p_minMana)
    readFile >> m_minMana;
  else
    readFile.seekg (pos + sizeof (m_minMana));

  pos = readFile.tellg();
  if (p_maxMana)
    readFile >> m_maxMana;
  else
    readFile.seekg (pos + sizeof (m_maxMana));
    
  pos = readFile.tellg();
  if (p_minStamina)
    readFile >> m_minStamina;
  else
    readFile.seekg (pos + sizeof (m_minStamina));
    
  pos = readFile.tellg();
  if (p_maxStamina)
    readFile >> m_maxStamina;
  else
    readFile.seekg (pos + sizeof (m_maxStamina));

  readFile.close();

  return 1;
}

int main ()
{
  Human Hum1;

  std::cout << Hum1.GetMinHealth() << std::endl;
  Hum1.SetMinHealth(200);
  Hum1.Save (1, 0, 0, 0, 0, 0);
  std::cout << Hum1.GetMinHealth() << std::endl;
  Hum1.SetMinHealth(300);
  Hum1.Read (1, 0, 0, 0, 0, 0);
  std::cout << Hum1.GetMinHealth() << std::endl;
  
  std::cin.get();
}

I just wonder if all that seeking will make it slower, let alone all that reading/writing (since I think >> and << are formatted also).

I also liked using the C version cause the .dat file was like.. encrypted (maybe it was storing the exe of the struct, and thats what was being imported?), where as in this version its just the value.