Passing a pointer to a function in objective-c

Question

Hi, i've a stupid questiona about passing pointer.

I've this:

@interface MyClass : NSObject
myobj* foo;
-(void)doSomething:(myobj*)aObj;
@end

@implementation MyClass
-(void)doSomething:(myobj*)aObj
{
  cFuncCall(&aObj); //alloc memory and init the object
}

-(id)init
{
  //init stuff...
  [self doSomething:foo]; // foo retun 0x0!!!
}
@end

why foo return nil??? It should be initialized by cFuncCall! [update]

Yes the problem is that foo is not changin outside doSomething. I've tried with myobj** but foo is still nil... This is the real code:

I declare FMOD::DSP *lowpassDSP; in the class interface. No property is set.

This is the function that sould init lowpassDSP. -(void)configFilter:(FMOD::DSP**)dsp { system->createDSPByType(FMOD_DSP_TYPE_LOWPASS, dsp); baseChannel->addDSP(*dsp, 0); } and this is the call: [self configFilter:&lowpassDSP];

in configFilter the dsp variable is correctly initiated but lowpassDSP is nil after calling configFilter.

Answer 1

First of all your -init method isn't defined correctly, perhaps this causes the problem (the superclass of your class isn't properly initialized). Your -init methods should be defined like this in objC:

- (id)init {
  if (self = [super init]) {
     // do custom initialization here, perhaps [self doSomething:foo] if required ...
  }

  return self;
}

-Edit:

Well, in objective-C I've often seen pointers passed to objects like this (notice the pointer-to-pointer notation), I'm not sure if this will work fine in ANSI C as well for passing pointers to methods, but you could check it out:

- (void)callFunction {
   NSError *error = nil;

   [self doSomethingWithError:&error];

   if (error != nil) {
      NSLog(@"error: %@", error];
   }
}

- (void)doSomethingWithError:(NSError **)error {
    // do something ...
}

Answer 2

The problem is that your object variable foo is not changed outside of doSomething:. Try the following:

-(void)doSomething:(myobj**)aObjP
{
    cFuncCall(aObjP);
}

-(id)init
{
    //...
    [self doSomething:&foo];
}