Using Structs in C

Question

Hi im building a simple game in c (im new to the language). Im using the following structs:

typedef struct
{
    int adjacent_mines;
    bool revealed;
    bool is_mine;
} Tile;

struct GameState
{
    Tile tiles[NUM_TILES_X][NUM_TILES_Y];
};
typedef struct GameState GameState;

Im wondering how to properly call and set the structs? I have the following code where i would like to set state of each Tile.

void intialize_mines(){
    for (int i =0; i < NUM_TILES_X; i++){
        for (int j =0; j < NUM_TILES_Y; j++){
            tiles[i,j].revealed = false;
        }
    }
}

But according to my console output i have done this incorrectly. How would i go about setting this correctly?

Possible duplicate of [What is an 'undeclared identifier' error and how do I fix it?](https://stackoverflow.com/questions/22197030/what-is-an-undeclared-identifier-error-and-how-do-i-fix-it) — dandan78, Sep 25 '18 at 07:49
please do not edit the code part of your question to fix errors when they are referenced in the answers. That invalidates (parts of) the answers of people that try to help you. — Kami Kaze, Sep 25 '18 at 07:57

Kami Kaze · Answer 1 · 2018-09-25T07:55:03.950

struct GameState just declares a type (just as int is just a type). You have to create a real struct in memory with GameState foo; similar to a normal variable (int foo;). And you can not access the contents of a struct without referencing the struct like foo.tiles. tiles on it's own is not known in this scope.

Afterwards you can access the struct with foo.tiles[i][j].revealed.

But to have access to this struct in your function you either have to pass it to the function as a pointer or declare the struct in filescope ( also called global). I would prefer the first version it is clearer an more function like.

Your function would look like this:

void intialize_mines( GameState *foo){
    for (int i =0; i < NUM_TILES_X; i++){
        for (int j =0; j < NUM_TILES_Y; j++){
            foo->tiles[i][j].revealed = false; // -> is a special operator for pointers to structs. It's the same as (*foo).
        }
    }
}

the corresponding function call would be:

GameSate bar;
intialize_mines( GameState &bar);

You should also check how to use multidimensional arrays. You declared it correctly with two seperate [] but in your function you use [x,y] which is not correct in C. It would be the same as in the declaration tiles[i][j]

P.W · Answer 2 · 2018-09-25T10:10:11.540

For a multi-dimensional array like tiles, you have to specify array subscript of each dimension within [] like this:

tiles[i][j].revealed = false;

This means that revealed belonging to jth column of ith row of tiles is set to false.

And you will have to define a structure variable of the type GameState before performing any operations on it.

GameState initGS;

void intialize_mines(){
    for (int i =0; i < NUM_TILES_X; i++){
        for (int j =0; j < NUM_TILES_Y; j++){
            initGS.tiles[i][j].revealed = false;
        }
    }
}

score 0 · Answer 3 · answered Sep 25 '18 at 07:38

0

You just missed to instantiate a GameState structure.

GameState gs;

void initialize_mines() {
    for (int i =0; i < NUM_TILES_X; i++) {
        for (int j =0; j < NUM_TILES_Y; j++) {
            gs.tiles[i][j].revealed = false;
        }
    }
}

answered Sep 25 '18 at 07:38

Jorg B Jorge

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Using Structs in C

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