Single, global, object instance

I've been slowly churning through my first iPhone app, outside of learning within the context of a book. What I would like to have is a single, global variable that tracks whether or not there is a person logged into the application. In the past with C++, what I've done is declared a variable in my "main" function file and then re-declared it in my other files as extern. I've tried this with Objective-C, but I'm running into memory management issues when debugging with Leaks. Here is the code I'm trying to use.

main file

#import "clsPerson.h"

clsPerson *LoggedInPerson = nil;

int main(int argc, char *argv[]) {
//...main code...
}

[App]_Prefix.pch* - Prefix file

...
#import "clsPerson.h"
extern clsPerson *LoggedInPerson;
...

Login code - Login View Controller (Modal popup on top of Root)

I should mention here also, that it currently checks to see if the variable is nil. If it is, then it forces you to login. In order to use nil, I believe I have to alloc and dealloc rather than reusing the same memory address?

...
LoggedInPerson = [[clsPerson alloc] initWithJSON:(NSDictionary*)Network.JsonValues];
[LoggedInPerson retain]; //I don't really know if this is needed?

//Save this person into the default settings for next time
[LoggedInPerson saveUserInfo];
[[self parentViewController] dismissModalViewControllerAnimated:YES];
...

Logout code - Root View Controller

...
- (void)btnLogo开发者_如何学编程utTapped {
    [LoggedInPerson dealloc]; //There is only one object, so I tried to force it to dealloc fully
    LoggedInPerson = nil;
    [clsPerson ClearUserInfo];
    ...
}
...

This seems to work fine and doesn't produce any errors, but watching the app with Leaks shows that my allocation statement is leaking memory somewhere. It typically happens if I logout, force a "low memory warning", and then login again. Are there any glaring problems here? I'm still getting my grips around memory management, but I think I'm pretty close. Thanks for any help in advance!

So, you don't need to retain the object if you've just allocated it. The retain count will already be +1.

But the other issue is you should be releasing it when the user logs out, not deallocating it. You should never call dealloc directly.