Mixing C and objective C in xcode

You don't even have to put your C code in a different file, you can simply just write C code in your .m file. The Objective-C compiler accepts C code.

If, at a later time, you would like to figure out how to separate your code into different files and use header files, you can do that too.

Objective c can call C in-line. For instance:

- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext(); //result of a C method
    [self drawRoundedRectWithContext:context withRect:rect];

}

Try with this way.

void *refToSelf;
int cCallback()
{
    [refToSelf someMethod:someArg]; // here objective-c method is calling in c.
}

@implementation SomeClass
- (id) init
{
     self = [super init];
     refToSelf = self;
}
- (void) someMethod:(int) someArg
{
}