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Possible Duplicate:
Prefixing property names with an underscore in Objective C

I am a C/C++ developer and am learning Objective-C. Recently I started on a tutorial that I found on net. The code is as below:

@interface MapDemoAnnotation : NSObject <MKAnnotation> {
    CLLocationCoordinate2D _coordinate;
}

- (id)initWithCoordinate:(CLLocationCoordinate2D)coordinate;

@end

@implementation MapDemoAnnotation

@synthesize coordinate=_coordinate;

- (id)initWithCoordinate:(CLLocationCoordinate2D)coordinate {
    self = [super init];
    if (self != nil) {
        _coordinate = coordinate;
    }
    return self;
}

@end

Can anyone please explain me the meaning of the statement

@synthesize coordinate=_coordinate;

I know the meaning of @synthesize. But could not understand the complete statement. _coordinate is a member variable. But what is coordinate? Where is it declared?

Community
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Nir
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    The `_` is called an underscore, and this question has been asked here many times before. Duplicates: [1](http://stackoverflow.com/questions/5582448/underscore-prefix-on-property-name) [2](http://stackoverflow.com/questions/3521254/prefixing-property-names-with-an-underscore-in-objective-c) [3](http://stackoverflow.com/questions/2371489/why-do-you-use-an-underscore-for-an-instance-variable-but-not-its-corresponding) [4](http://stackoverflow.com/questions/822487/how-does-an-underscore-in-front-of-a-variable-in-a-cocoa-objective-c-class-work) [5](http://goo.gl/8hqNu) – jscs Apr 14 '11 at 06:04

1 Answers1

4

Basically, it doesn't mean anything to the compiler. It's just a coding practice used on private instance variables. Your code isn't going to break if you don't use it.

Aurum Aquila
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