Comments on: Objective-C Object as a C Structure

By: Dylan Barrie

Dylan Barrie — Thu, 20 May 2010 11:15:01 +0000

You could simply declare the Obj-C object’s instance vars in a C struct, and then use that C struct as-is.

typedef struct MyObjectStruct
{
float phase;
float frequencies;
} MyObjectStruct;

@interface MyObject : NSObject
{
MyObjectStruct cStruct;
}

@end

By: Helmut Taylor

Helmut Taylor — Sat, 01 May 2010 19:02:22 +0000

Compiling this feature with iPhone 3.1.3 SDK

typedef struct {
@defs(cwPlayer);
//float phase;
//float frequencies;
} *SinewaveDef;

If the target is a 3.1.3 Device and you are using the 3.1.3 SDK you will get a compile error

@defs is no longer supported in new abi

I am certain that some developer fixed this if they used this feature in their code
Any thoughts of what they used to hand stitch to access an
objective C instance of a variables in a C-Style function
float cwWave;
SinewaveDef->phase;
cwWave = 0.5 * sinf(def->phase);

thanks for any comment on this

By: Bob Muller

Bob Muller — Mon, 04 Jan 2010 19:23:28 +0000

Thanks for that. But an object has instance variables -and- methods. How are the addresses of the methods represented in the struct? Is there a field in the struct that contains an address of a virtual dispatch table?

And if TestClass had been a subclass of another class, say Foo, how would the inherited instance variables of Foo be laid out? Are they laid out directly in the struct bound to tmp or is there a pointer to a different struct containing the Foo instance variables?

Thanks for shedding light on this!

Bob Muller

By: p4bl0

p4bl0 — Mon, 02 Mar 2009 20:24:00 +0000

I don’t know if this is useful but it’s so cool 8-)