LLDB COMMAND : 'fr v var' vs 'p var'

Question

I'm new to LLDB and try to familiar those commands in the official website.
I'm confusing about the function of fr v bar and p bar.
As you can see from the website, they are described to 'Show the contents of local variable "bar"' and put in the same place. But When I put them into real use in Xcode 4.6.4, there is some differences?

(lldb) fr v self
(FGPLoginViewController *const) self = 0x07566350
(lldb) p self
(FGPLoginViewController *) $0 = 0x07566350
(lldb) fr v self.initCount
error: "self" is a pointer and . was used to attempt to access "initCount". Did you mean    "self->initCount"?
(lldb) p self.initCount
(NSInteger) $1 = 0

initCount is a NSInteger property of FGPLoginViewController.
And my questions is what's the real differences between fr v bar and p bar?

Answer 1

The difference (as I understand it) is that frame variable is only for printing the contents of variables, whereas print is a shortcut for expression -- and can evaluate arbitrary C and Objective-C expressions.

In your example, self.initCount is the property syntax for [self initCount]. To evaluate that expression, the debugger compiles it and executes the code in the context of the application.

Another example: p 2+3 computes the sum and prints the result, but fr v 2+3 gives an error message.

On the other hand, frame variable has much more options to display variables. For example, fr v -r "app.*" shows all variables starting with "app". You cannot do that with the print command.

To summarize: frame variable is for variables and print (or expr) is for expressions. In the case of one variable they both work equally well.