How to save game state in C in Allegro?

Question

I'm developing my 1st board-game (go-game) in C with Allegro 5, for a course project. Part of my goal is to make a gamesave of the current gamestate. Let's say for 2 players if we exit the game, and log in the game, we want to reload the previous gamestate such that the position of the stones by 2 players to be preserved in their positions. How can I achieve this? I will appreciate any related reference, tutorial, or a git reference I can learn more about saving the states of the game.

P.S. I checked the old questions about saving game state, but there are guides only for other languages/libraries not in C/Allegro.

Answer 1

First, decide what information of your game describes a "game state". In other words, what is the difference between a "new game" and what state the user currently is?

Examples of that are:

• Character's stats (Name, level, experience, strength, intelligence, money, etc)
• Quests (What quests have the user completed? What progress do they have on active ones?)
• Maps (Has the player visited a place before? Do they have fog of war that is explored next time they visit it? After the user has killed enemies on one stage, do they respawn or remain permanently dead?)

Once you have all this information down, it's time to write a file that includes all that information, which is going to be saved on the disc, so it remains there until someone removes it manually. You can pick a simple format like var=value and save all data like this:

character_name=john
character_level=4

quest_kill_dragon=0 # assuming -1 is not started, 0+ started and current state
quest_find_jewel=-1

map_mountain_explored=0 # maybe if you go to a map for the first time a cinematic plays
map_mountain_enemy_2=-1 # -1 on enemy is that they are dead and won't respawn

Please note I used # to display comments, but normally you wouldn't need comments as this file is not meant to be readable by humans. What data you want to save is up to you and what game you are making.

Alternatively you can use JSON to save data on a file, there are plenty of libraries online that help you do that. Unfortunately I haven't used any in the past, so I can't recommend any.

In case its needed, the manual of how to open/close files in C: GNU - Opening and Closing Files

Answer 2

The name of the method you're looking for is called 'serialization'. Whether it is output to a text file or a binary file doesn't matter. What matters is that you store the data necessary to recreate a game state and that you read it back the same way you save it.

In Allegro 5, you can use the https://liballeg.org/a5docs/trunk/file.html (FILE I/O) routines to save your text or to save binary data.

As for your specific situation, you have a board (a 2D array) of stone types (an enum).

The value of a position on the board can be in one of 3 different states ; 1) empty 2)black 3)white.

So first, make an enum for your data :

enum PIECE {
   NONE = 0,
   WHITE = 1,
   BLACK = 2
};

const char[3] piecetypes = {'-' , 'O' , 'X'};

In GO, there are usually 19x19 pieces.

In serializing data like an array, we need to record its size somewhere.

First job is to open a file. Typical usage is of http://www.cplusplus.com/reference/cstdio/fopen/ fopen, or in Allegro 5, https://liballeg.org/a5docs/trunk/file.html#al_fopen al_fopen.

Once the file is open for writing (make sure to specify whether you're writing in text or binary mode!!!), write the board to the file.

Since we're using an enum with less than 8 values, and there aren't that many values (19x19 = 361), we'll represent our data in the file with a char (a single byte).

ALLEGRO_FILE* f = al_fopen("go.sav" , "w");/// Opening in text mode for writing
if (!f) {Bail();}
for (unsigned int y = 0 ; y < 19 ; ++y) {
   for (unsigned int x = 0 ; x < 19 ; ++x) {
      al_fputc(piecetypes[board[y][x]]);
   }
   al_fputc('\n');
}
al_fputc('\n');
al_fclose(f);
/// All done

Now our data should be saved something like this (open the text file in your favorite editor and verify the contents) :

-------------------
-------------------
-------------------
-------------------
-------------------
-----XX------------
------O------------
---------O---------
---------XX--------
----------OO-------
---------O---------
-------------------
-------------------
-------------------
-------------------
-------------------
-------------------
-------------------
-------------------

Now you need to be able to 'unserialize' the data, that is to say, to read it back from the file.

Open the file for reading and copy the data back into your board :

ALLEGRO_FILE* f = al_fopen("go.sav" , "r");
if (!f) {Bail();}
for (unsigned int y = 0 ; y < 19 ; ++y) {
   for (unsigned int x = 0 ; x < 19 ; ++x) {
      char c = al_fgetc(f);
      if (c == '-') {board[y][x] = NONE;continue;}
      board[y][x] = (c == 'O')?WHITE:BLACK;
   }
   al_fgetc(f);/// consume the newline
}
al_fclose(f);