在另一个类中调用ac函数

Question

i am having objective c class, which i have a C function in it. in that C function i want to call to ANOTHER c function in another class.

in the first class C function , i do this :

  HelloWorldLayer *ran;
  ran=[[HelloWorldLayer alloc] init];
  [ran showDigital:BinaryWord];

when HelloWorldLayer is the other class, which have the C function :

void showDigital( int word[4])

and it declared also in the HelloWorldLayer.h .

in the first class, when i am trying to call the other function it says that showDigital function is not found.

is it has to do with the fact that its a C function ?

thanks.

Answer 1

Do you want to call a C function or an Objective-C method? You've got your terminology all muddled. I think you want to define an Objective-C method on HelloWorldLayer and call that, so here is what your header should look like:

HelloWorldLayer.h

@interface HelloWorldLayer : NSObject

- (void)sendDigital:(int[4])word;

@end

Then you can call that method by doing what you have already tried.

You can't declare a C function inside an Objective-C class. You could define it in your @interface block, but it wouldn't be part of that Objective-C class. Only Objective-C methods can be part of the class.

So for instance if you really really really wanted you could do:

HelloWorldLayer.h

@interface HelloWorldLayer : NSObject

void sendDigital(int[4] word);

@end

But when you called sendDigital you'd have to do it like this:

int word[4] = {1,2,3,4};
sendDigital(word);

And you'll notice there's no HelloWorldLayer around at all. Now do you understand the difference here? I really do think you need to define your method as an Objective-C method rather than a C function.

Answer 2

First of all, the C function is not in the other class, it is merely in the same file as the other class. Objective-C classes have methods not functions.

So you can call your C function from anywhere provided you have an extern declaration of it. eg in HelloWorldLayer.h

extern void showDigital(int* word);

If you really want the function to be associated with instances of your class, you need to make it an Objective-C method. You can have that method be a thin wrapper for the original function if you like:

-(void) showDigital: (int*) word
{
    showDigital(word);
}

If you want to pretend that your C function is part of an object, you'll need to add the receiver object as a parameter. You still won't be able to access private instance variables directly though.

void showDigital(id self, int* word)
{
    [self foobar];
}