How do I create a save file for a C++ game?

Question

I am coding my final for a Video game Programming course, and I want to know how to create a save file for my game, so that a user can play, and then come back later. Any idea how this is done, every thing I have done before has been single run programs.

Answer 1

You need use serialization to save your variables in memory to your hard drive. There are many types of serialization, in .NET XML is a common format, though there are binary and JSON serializers available. There is an entry in the C++ FAQ on general serialization techniques:

• https://isocpp.org/wiki/faq/serialization

There are libraries that can aid in implementing serialization. Some are mentioned in other answers. Also refer to this StackOveflow Question for more information.

The variables needing to be serialized are probably going to be related to game state. For example, you will probably want to know this type of information

1. The player was playing level 3
2. The player was at X, Y world coordinates
3. The player has three items in his backpack
4. Weapon
5. Armor
6. Food

You wont really care what textures are being used (unless your player can change their appearance, that's a special case), because they are usually the same. You need to focus on saving important gamestate data.

When you start your game, you start as normal for a "new" game (this loads your textures, models, etc) but at appropriate time you load the values from your save file back into the game state object replacing the "default" new game state. Then you allow the player to resume playing.

I've greatly simplified it here, but you should get the general idea. If you have a more specific question ask a new question here and we can try to help you with it.

Answer 2

Typically this is specific to your game. I'm sure you've learned about writing to and reading from files in your classes so far. The basic idea is:

1. When exiting the game, write the values you want to save to a file.
2. When loading the game, check to see if a save file exists, if it does, load the read the values in to your program. If the file does not exist, continue like you do now and set the values to their starting/default values.

What you write is up to you, it depends on your game. One way of writing is to write out the variables you want in a specific order as a byte stream. Then when loading, read them in to your program in the same order.

For example (in quick pseudo code):

SaveGame(FileInput file) {
    file.writeInt(playerLevel);
    file.writeInt(playerHealth);
    file.writeInt(gameProgress);
}

LoadGame(FileInput file) {
    if(file.exists()) {
        playerLevel= file.readInt();
        playerHealth = file.readInt();
        gameProgress = file.readInt();
    } else {
        playerLevel = 1;
        playerHealth = 100;
        gameProgress = 0;
    }
}

Answer 3

There are probably a large number of ways to do this, but the simplest that I always found and have used both personally and professionally is to make a structure that contains all of the values I want saved.

struct SaveGameData
{
    int              characterLevel; // Any straight up values from the player
    int              inventoryCount; // Number of items the player has on them or stored or what not
    int[STAT_COUNT]  statistics;     // This is usually a constant size (I am tracking X number of stats)
    // etc
}

struct Item
{
    int itemTypeId;
    int Durability; // also used as a 'uses' count for potions and the like
    int strength;   // damage of a weapon, protection of armor, effectiveness of a potion
    // etc
}

I then just fwrite/fread the data to and from a file using the basic File IO values. The inventoryCount is the number of Item structures that are saved after the main SaveGameData structure in the file so I know how many of those to read after fetching that data. The key here is that when I want to save something new, unless its a list of items or the like, all I have ever have to do is add a value to the structure some where. If its a list of items then I will have to add a read pass like I have already implied for the Item objects, a counter in the main header and then the entries.

This does have the downside of making different versions of a save file incompatible with each other with out special handling (even if it is just default values for each entry in the main structure). But overall this makes the system easy to extend just by adding in a new data value and putting a value into it when needed.

Again, quite a few ways to do this and this might lead more towards C than C++, but it has gotten the job done!

Answer 4

First you need to decide what data needs to be saved. For instance, this could be the location of the character, his score, and the number of coins. Of course, your game will likely be much more complex, and so you will need to save additional data such as the level number and enemy list.

Next, write code to save this to a file (use ofstream). A relatively simple format you can use is as follows:

x y score coins

And so the file would look like:

14 96 4200 100

Which would mean he was at position (14, 96) with a score of 4200 and 100 coins.

You also need to write code to load this file (use ifstream).

---

Saving enemies can be done by including their position in the file. We can use this format:

number_of_enemies x1 y1 x2 y2 ...

First the number_of_enemies is read and then each position is read with a simple loop.

Answer 5

One addition/suggestion would to add a level of encryption to your serialization so users cannot text edit their values to "9999999999999999999". One good reason to do this would be to prevent integer overflows (for example).

Answer 6

I think your best bet is boost::serialization because is easy to propagate down in your hierarchy. You only need to call the top object's save/load function and all your classes are easily created.

See: http://www.boost.org/doc/libs/1_49_0/libs/serialization/doc/index.html

Answer 7

For completeness sake I want to mention a c++ serialization library, that I personally use and was not mentioned yet: cereal.
It's easy to use and has a nice, clean syntax for serializing. It also offers multiple types of formats you can save to (XML, Json, Binary (including a portable version with respects endianess)). It supports inheritance and is header-only,

Answer 8

Your game will compromise data structures (hopefully?) that you need to transform into bytes (serialize) so you can store them. In a future, you may load those bytes back and transform them back into your original structure (deserialization). In C++ it is not so tricky since reflection is very limited. But still, some libraries can help you here. I wrote an article about it: https://rubentorresbonet.wordpress.com/2014/08/25/an-overview-of-data-serialization-techniques-in-c/ Basically, I would suggest you to have a look at cereal library if you may target C++ 11 compilers. No need to create intermediate files like with protobuf, so you will save some time there if you want quick results. You may also choose between binary and JSON, so it can quite help debugging here.

On top of that, if security is a concern, you may want to encrypt/decrypt the data you are storing, especially if you are using human-readable formats like JSON. Algorithms like AES are helpful here.

Answer 9

You need to use fstream for input / output files. The syntax is simple EX:

#include <fstream>
// ...
std::ofstream flux ; // to open a file in ouput mode
flux.open("myfile.whatever") ; 

Or

#include <fstream>
// ...
std::ifstream flux ; // open a file in input mode
flux.open("myfile.whatever") ;

Other actions are possible on your file: append, binary, trunc, etc. You would use the same syntax as above instead we put std::ios::(flags), for instance:

• ios::out for output operation
• ios::in for input operation
• ios::binary for binary (raw byte) IO operation, instead of character-based
• ios::app for to start to write at the end of the file
• ios::trunc for if the file already exist replace delete the old content and replace by new
• ios::ate - position the file pointer "at the end" for input/output

Ex:

#include <fstream>
// ...
std::ifstream flux ;
flux.open("myfile.whatever" , ios::binary) ;

Here is a more complete but simple example.

#include <iostream>
#include <fstream>

using namespace std ;

int input ;
int New_Apple ;
int Apple_Instock ;
int Eat_Apple ;
int Apple ;

int  main()
{
  bool shouldQuit = false;
  New_Apple = 0 ;
  Apple_Instock = 0 ;
  Eat_Apple = 0 ;

  while( !shouldQuit )
  {
    cout << "------------------------------------- /n";
    cout << "1) add some apple " << endl ;
    cout << "2) check apple in stock " << endl ;
    cout << "3) eat some apple " << endl ;
    cout << "4) quit " << endl ;
    cout << "------------------------------------- /n";
    cin >> input ;

    switch (input)
    {
      case 1 :
      {
        system("cls") ;

        cout << "------------------------------------ /n";
        cout << " how much apple do you want to add /n";
        cout << "------------------------------------ /n";      
        cin >> New_Apple ;

        ifstream apple_checker ;
        apple_checker.open("apple.apl") ;
        apple_checker >> Apple_Instock ;
        apple_checker.close() ; 

        Apple = New_Apple + Apple_Instock ;

        ofstream apple_adder ;
        apple_adder.open("apple.apl") ;
        apple_adder << Apple ;
        apple_adder.close() ;

        cout << "------------------------------------ /n";
        cout << New_Apple << " Apple has been added ! /n";
        cout << "------------------------------------ /n";
        break;
      }

      case 2 :  
      {
        system("cls") ;

        ifstream apple_checker ;
        apple_checker.open("apple.apl") ;
        apple_checker >> Apple_Instock ;
        apple_checker.close() ;

        cout << "------------------------------------ /n";
        cout << " there is " << Apple_Instock ;
        cout << "apple in stock /n" ;
        cout << "------------------------------------ /n";
        break;
      }

      case 3 :
      {
        system("cls") ;

        cout << "------------------------------------ /n";
        cout << "How many apple do you want to eat /n" ;
        cout << "------------------------------------ /n";
        cin >> Eat_Apple ;

        ifstream apple_checker ;
        apple_checker.open("apple.apl") ;
        apple_checker >> Apple_Instock ;
        apple_checker.close() ;

        Apple = Apple_Instock - Eat_Apple ; 

        ofstream apple_eater ;
        apple_eater.open("apple.apl") ;
        apple_eater << Apple ;
        apple_eater.close() ;

        cout << "----------------------------------- /n";
        cout << Eat_Apple ;
        cout << " Apple has been eated! /n";
        cout << "----------------------------------- /n";
        cout << Apple << " Apple left in stock /n";
        cout << "----------------------------------- /n";
        break;
      }

      case 4 :
      {
        shouldQuit = true;
        break;
      }

      default :
      {
        system("cls") ;

        cout << "------------------------------------ /n";
        cout << " invalide choice ! /n";
        cout << "------------------------------------ /n"; 
        break;
      }
    }
  }
  return 0;
}