Struct containing array of structs in objective C

Question

I have a struct for a tile (all properties are previously-defined enums)

typedef struct {
    ShapeType shape;
    ColorType color;
    PatternType pattern;
    IconType icon;
} TileDefinition;

And I want to create another struct that holds 16 tiles, for a "board". Something like this:

typedef struct {
    TileDefinition[16]

} BoardDefinition;

And then I want to be able to loop through that, like so:

for(int i=0;i<16;i++) {
    TileDefinition tileDef = boardDef[i];
    // Do something with tileDef
}

But obviously the setup for the BoardDefinition struct isn't working. How can I set that up? Where should I and shouldn't I use pointers?

Thanks

struct { TileDefinition[16] } looks really odd to me. What's wrong with struct { TileDefinition tiles[16]; } and then using boardDef.tiles[i]? — cHao
– cHao, Commented May 17, 2013 at 7:53

justin · Accepted Answer · 2013-05-17 08:43:11Z

This is actually a C question.

This bit is fine:

typedef struct {
    ShapeType shape;
    ColorType color;
    PatternType pattern;
    IconType icon;
} TileDefinition;

Here, you need to declare BoardDefinition as:

enum { BoardDefinition_NTiles = 16 }; // << declare a constant for your ease of use
typedef struct {
    TileDefinition tile[BoardDefinition_NTiles];
} BoardDefinition;

Then to loop through them:

// Given:
BoardDefinition boardDef;

for (size_t i = 0; i < BoardDefinition_NTiles; i++) {
    TileDefinition* const tile = &boardDef.tile[i]; // << get a reference to a tile
    // member access of the referenced tile:
    tile->color.red = 1;
}

The version you wrote creates a copy of the tile:

for (size_t i = 0; i < BoardDefinition_NTiles; i++) {
    TileDefinition tile = boardDef.tile[i]; // << creates a copy of the tile, local to the loop body
    // member access of the copied tile:
    tile.color.red = 1;
}

trojanfoe · Accepted Answer · 2013-05-17 07:18:53Z

0

Option 1: Make BoardDefinition an Objective-C object where it can be set-up in the init method.

Option 2: Use (Objective-)C++ and provide a constructor for struct BoardDefinition.

Option 3: Keep with C and provide an initBoardDefinition(BoardDefinition *boardDef); function.

answered May 17, 2013 at 7:18

trojanfoe

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Comments

Nathan Day · Accepted Answer · 2013-05-17 07:49:01Z

0

As trojanfoe suggest, these would be better as Objective-C objects, but if for some reason you don't wont to do that. You probable want to declare an instance variable of type BoardDefinition in some class for example

@interface MyClass : NSObject
{
    BoardDefinition    definition;
}

Also you BoardDefinition is wrong it should be something like

typedef struct {
    TileDefinition      boardDef[16];

} BoardDefinition;

Your loop would then be something like

for(int i=0;i<16;i++) {
    TileDefinition tileDef = definition.boardDef[i];
    // Do something with tileDef
}

You don't need to use pointers put you could for the TileDefinition in the parent struct something like

typedef struct {
    TileDefinition    * tileDefinition;
    NSUInteger        count;
} BoardDefinition;

This way you can have a variable number of TileDefinition. In this case you would have to malloc the tileDefinition soemthing like the following for the class init method.

- (id)init
{
    if( (self = [super init]) != nil )
    {
        definition.count = 16;
        definition.tileDefinition = malloc( definition.count * sizeof(*definition.tileDefinition);
    }
    return self;
}

answered May 17, 2013 at 7:49

Nathan Day

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3 Comments

justin Over a year ago

"these would be better as Objective-C objects" -- Why?

justin Over a year ago

Well, don't take that question seriously -- just my way of pointing out that there's no evident reason/benefit in converting the type to ObjC, given the information/problem in the OP.

jraede Over a year ago

I'm going to send these via Game Center to other players and want to keep them as lightweight as possible

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