UsingCStructInObject

I have an object called Crossword. Inside this object I have typdef’ed a struct like this

typedef struct{ BOOL isSquareInCrossword; General/NSString *letter; BOOL isFirstLetterInWord; }square;

I have declared an array of these squares

square crosswordBoard[50][50];

In regular C, inside the object, I can refer to (and assign values to) elements like this

crosswordBoard[30][15].isSquareInCrossword = 0;

I have a accessor method for crosswordBoard in the object Crossword.

-(square *)crosswordBoard { return crosswordBoard; }

How do I refer to the elements within crosswordBoard when I am in a different object? In a different object, I declare

#include “Crossword.h” … General/IBOutlet Crossword crossword;

I tried

[crossword crosswordBoard][3][7].isSquareInCrossword=1;

This does not work for two reasons. (1) something is wrong with the accessor method. If you could tell me what I am doing wrong, that would be great. (2) the way I refer to the elements in crosswordBoard is not right. Any suggestions on how to do this? –General/AlexanderD

In your accessor, you’re returning a square *, not a square. Either of the following solutions should solve both the problems you specify above.

Either:

Change the return type of the accessor to square (not square *), which means you’d have to either dereference in the accessor or change the type in your class to square also.
OR (don’t do both!) dereference whenever you use -crosswordBoard. (Like this: (*[crossword crosswordBoard])[3][7].isSquareInCrossword = 1;

The first solution is not exactly what I need, because I want to pass an array of squares, not just one square. I like the second idea, but the accessor method still does not work. How do I change the accessor method so that what I return is really a (square *). I am not so good at pointer stuff as you can see. –General/AlexanderD

If you are actually wanting to alter the state of the Crossword object then you really ought to write a method on Crossword that does it, it’s bad karma to do what you seem to want to do! If you are trying to set a flag true / false to say if a square is ‘in the crossword’ then add something like this to the Crossword object.

(void)setSquareAtRow:(int)aRow column:(int)aColumn isIncluded:(BOOL)aFlag { crosswordBoard[aRow][aColumn].isSquareInCrossword = aFlag; }
(BOOL)isIncludedAtRow:(int)aRow column:(int)aColumn { return crosswordBoard[aRow][aColumn].isSquareInCrossword; }

Generally, you should not expose the innards of objects to the outside world as you don’t know who could change it with disastrous consequences and all that. Excuse any typos /etc, I’m tired! I am sure you will understand what I mean.

You need to return a (square[50][50]) from crosswordBoard, not a pointer, since the latter doesn’t work for 2D arrays.

This might seem silly, but why don’t you use this?

typedef struct{ BOOL isSquareInCrossword; char letter; BOOL isFirstLetterInWord; }square;

If letter is never going to be more then one character, why not avoid the extra overhead? –General/DerekCramer

Or use a unichar instead of char…it’s basically the same, but it supports Unicode characters. –General/JediKnil

If you want to initialize a structure in the following way, you have to use General/ObjectiveCPlusPlus (give your source implementation a .mm extension):

struct astruct { int x; int y;

 astruct()
  {
     x=10;
     y=20;
   } };

Or you can do it the C way if you’re in plain Objective C:

typedef struct astruct { int x; int y; } astruct; … astruct blah = { 10, 20 };

I want to use some C code in a standard Cocoa Objective-C app. I want to call the C stuff and get a returned array from it - I’ve tried just sticking the C code into my Obj-C file, but the compiler seems to choke on the “struct data{…}” and on pretty much everything else.

Edit: After some fiddling, I’ve it’s only choking on this:

struct { char x; char y; char z; char pad[57]; }data;

…

struct data inputStructure;

…

structureInputSize = sizeof(struct data);

The struct declaration works fine, whether or not I have a “typedef” before it; the second thing gives an “error: storage size of ‘inputStructure’ isn’t known” and the third gives “error: invalid application of ‘sizeof’ to incomplete type ‘struct blehData’”.

General/ObjectiveC is C code. It’s a superset, so you should be fine.

Where exactly in the code did you add the “data” struct defintion? Hint: You need to add it before your code needs to use it.

It’s before my method declaration, like so:

@implementation Tilter

General/NSString *bookModel; struct { … }data;

(General/NSArray *)getTilt { … struct data inputStructure; … structureInputSize = sizeof(struct data); … }

Edit: Aaand got it. struct data{ … }; worked. Thanks.

Ah, my bad, I didn’t notice you changed the “struct data” declaration. Yeah, that will have stuffed it up.

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