Using struct with Objective-C methods

Question

I'm writing a simple game, and thought it would be much easier to use structures. However, I can't declare methods that need the structs.

How could I use a struct as an argument to an Objective-C method and get an object of the struct returned?

//my structure in the .h file
struct Entity
{
  int entityX;
  int entityY;
  int entityLength;
  int entityWidth;
  int entityType;
  bool isDead;
};

//And the methods i'm trying to use
-(BOOL)detectCollisionBetweenEntity:Entity ent1 andEntity:Entity ent2;

-(struct Entity)createEntityWithX:int newEntityX andY:int newEntityY, withType:int newEntityType withWidth:int newEntityWidth andLength:int newEntityLength;

If you're going to use C data structures I suggest you familiarise yourself with how you manage memory in C, and how pointers work. This topic is far too big to cover in a SO question & answer. Your other option is to stick with Objective-C, this might be less confusing to start off with. — pmdj
– pmdj, Commented May 5, 2012 at 15:59

cobbal · Accepted Answer · 2012-05-05 16:04:49Z

3

You can use structs exactly like you would expect, your problem seems to be with the syntax of methods:

struct Entity
{
  int entityX;
  int entityY;
  int entityLength;
  int entityWidth;
  int entityType;
  bool isDead;
};

//And the methods i'm trying to use
-(BOOL)detectCollisionBetweenEntity:(struct Entity) ent1 andEntity:(struct Entity) ent2;

-(struct Entity)createEntityWithX:(int) newEntityX andY:(int) newEntityY withType:(int) newEntityType withWidth:(int) newEntityWidth andLength:(int) newEntityLength;

Types in methods need to be in parens, and you have to refer to struct Entity instead of Entity unless you typedef (in plain Objective-C, Objective-C++ might let you do it)

answered May 5, 2012 at 16:04

cobbal

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Comments

Pang · Accepted Answer · 2017-08-01 06:53:54Z

2

Structs are used as parameters in Objective-C all the time. For example the CGRect from Apple's CGGeometry Reference

struct CGRect {
  CGPoint origin;
  CGSize size; 
}; 
typedef struct CGRect CGRect;

You just have to create a type for your struct, which can be done in the same way as Apple, or could have been done as

typedef struct CGRect {
  CGPoint origin;
  CGSize size; 
} CGRect;

So in your case:

typedef struct
{
  int entityX;
  int entityY;
  int entityLength;
  int entityWidth;
  int entityType;
  bool isDead;
} Entity;

Should allow you to define

-(BOOL)detectCollisionBetweenEntity:(Entity) ent1 andEntity:(Entity) ent2;
-(Entity)createEntityWithX:int newEntityX andY:int newEntityY, withType:int newEntityType withWidth:int newEntityWidth andLength:int newEntityLength;

edited Aug 1, 2017 at 6:53

Pang

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answered May 5, 2012 at 16:07

Peter M

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