Can I call Objective-C methods from C function?

Question

I am new to Objective-C so what I'm trying to do might not be possible. I am refactoring a large C function into multiple C functions and Obj-C methods.

Is this possible?

The following will not build and complains

'self' undeclared.

  void serverCB(CFReadStreamRef stream, CFStreamEventType event, void *myPtr)
{
    switch(event) {
        case kCFStreamEventHasBytesAvailable:
            [self readStreamData:stream];
            break;
        case kCFStreamEventErrorOccurred:
            NSLog(@"A Read Stream Error Has Occurred!");
            break;
        case kCFStreamEventEndEncountered:
            NSLog(@"A Read Stream Event End!");
            break;
        default:
            break;
    }
}

-(void) readStreamData: (CFReadStreamRef)stream
{   
        NSData *data = [[NSMutableData alloc] init]; //TODO: I have to flush this at some point..?
        uint8_t buffer[1024];
        unsigned int len = 0;       
        len =  [(NSInputStream *)stream read:buffer maxLength:1024];        
        if(len > 0)
        {
            [data appendBytes:&buffer length:len];
        }
        NSString *serverText = [[NSString alloc]    initWithData: data encoding:NSASCIIStringEncoding];
           [data release]; // I got my string so I think I can delete this
           [self processServerMessages:serverText];

    }
}

In the first function listed, 'serverCB' I am trying to send the 'readStreamData' message to the current object. So can I only call c functions from c functions?

Thanks!

kennytm · Accepted Answer · 2011-03-13 06:58:52Z

2

You can call Objective-C methods from a C function. But as the error told you, the variable self is not defined. You need to pass self as a parameter to serverCB, e.g.

void serverCB(CFReadStreamRef stream, CFStreamEventType event, void* myPtr, id self) {
   ...
   [self readStreamData:stream];
   ...
}

...

serverCB(stream, event, NULL, self);

answered Mar 13, 2011 at 6:58

kennytm

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2 Comments

Caleb Over a year ago

If it makes sense to do that, and particularly if it makes sense to name the parameter 'self', then there's a good chance that the function in question should really be a method of whatever class 'self' belongs to.

Nick Over a year ago

@Caleb.. good point. I should just make this function belong to the class rather than being tied to a particular instance.

Dru Freeman · Accepted Answer · 2011-03-13 07:17:07Z

2

You can also make class functions.

@interface MyClass : NSObject
{}
+ (void) myDoSometing;
@end

void myDo(int foo)
{
  [MyClass DoSomething];
}

answered Mar 13, 2011 at 7:17

Dru Freeman

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1 Comment

Nick Over a year ago

Upvoted. I think that making this a class function is appropriate. Thanks.

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