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POivars when mixing C and Objective-C
 

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  1. POivars when mixing C and Objective-C
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    <p>I'm writing an Objective-C wrapper for a C library and having problems accessing the references of my ivars.</p> <p>The C library requires that I specify a function pointer that handles events, I specify it during the initialization of my Objective-C class.</p> <pre> - (id) init { [super init]; RegisterClient(&handleEvent); return self; } </pre> <p>The C library is able to start searching for something and will then call the handleEvent function in case anything happened during the search. The function (basically) looks like this.</p> <pre> int handleEvent(void *Event) { [delegate didFinishSearching]; return 0; } </pre> <p>At least I'd wish it looked like this. The problem is that the code won't build because <code>'delegate' undeclared (first use in function)</code> (of course I have declared it, I can call <code>[delegate didFinishSearching]</code> from any Objective-C method but not from a C function). Older questions from stackoverflow suggest to define an additional variable (e.g. <code>theDelegate</code>) in the header file:</p> <pre> id theDelegate; @interface Controller : NSObject { id delegate; } @property (assign) id delegate; @end </pre> <p>Then, whenever I change the value of <code>delegate</code> to a new one, I have to assign this value to <code>theDelegate</code>, too.</p> <p>Since my C is somewhat rusty, here are my questions:</p> <p>1) Can I pass the <code>RegisterClient</code> C function a pointer to an Objective-C method instead of a pointer to a function as an argument in order to avoid the C function <code>handleEvent</code> completely?</p> <p>2) If not: When I create multiple instances of this Objective-C class, will <code>theDelegate</code> be the same for all instances? (After all, it's not declared as an instance variable...)</p>
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    1. USJohn Calsbeek
    1. USpruefsumme
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    1. COthe void *Event parameter-- what is it? If it's something you passed in as a context parameter-ish thing, you could just pass the delegate.
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      1. POivars when mixing C and Objective-C
      1. USJared Pochtar
    2. COThe void *Event parameter contains details about the event. But you made a helpful remark: `int handleEvent(void *Event)` is actually `int handleEvent(void *Event, void *Cookie)`. When starting the search I can pass anything I'd like as a "cookie" and in case of an event it will appear in the handleEvent function. Thanks a lot!
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      1. POivars when mixing C and Objective-C
      1. USpruefsumme
 

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