Question

I have seen code like that in the Application delegate in iPhone project for example.

what is the variable with the underscore means? can I use it as setter and getter for the variable?

also when releasing the variable should I use:

  [variable release]; 

or

 [_variable release]; 

Thanks.

Answer 1

In some coding conventions the underscore before instance variables is used to be able to quickly differentiate them from other variables. It also helps avoid naming conflicts with local variables in methods and subclass methods.

@synthesize variable = _variable 

Creates a setter and getter that set/get the variable you set it to in this case _variable. So outside access uses code like object.variable which is really just returning _variable. however the class usually uses the _variable internally.