Question

I am very lost in Xcode 4. Watching a simple variable is a nightmare. I do not figure out how to just “watch a variable value”. It was easier in Xcode 3…

I have the following piece of code:

if (labelEast.center.x > (east_oldPosition.x + 50) )
        NSLog(@"Time to switch to previous exercise !");
    else if (labelEast.center.x < (east_oldPosition.x - 50) )
        NSLog(@"Time to switch to next exercise !");

After setting a breakpoint, I am just trying to watch labelEast.center.x (labelEast is a UILabel object). Since I could not find a watch item in a Xcode 4 menu, I am trying to use gdb. I am used to print variable/object values with po (print object). But now, I cannot display labelEast center property because it is inherited from a mother class.

(gdb) po labelEast.center
There is no member named center.

I do not understand why gdb says this whereas the code works fine and sees the property.

Thus I have 2 questions:

1. How to watch such a property without gdb in a graphical way (as simply as in Visual Studio) ?
2. How to do the same with gdb ?

Many thanks,
Franz

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Unfortunately, I tried it but got this:

po [labelSouth center]

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x1a000356 0x343c7d06 in
objc_msgSend_stret () The program being debugged was signaled while in
a function called from GDB. GDB remains in the frame where the signal
was received. To change this behavior use “set unwindonsignal on”
Evaluation of the expression containing the function (objc_msgSend)
will be abandoned.

And when I try:

(gdb) print labelSouth.center
There is no member named center.

I really suspect there is no access to center property in UILabel. But how can me code run ???

Answer 1

I’ve hit this thing a few times myself just to remember “oh, that’s right, gdb doesn’t support dot notation so I have to use getter”. Then just do:

(gdb) po [myObject someProperty]

and all is well with the world again. Also rereading your question I see that you’re requesting a non object to be printed, hence you have to give gdb a hint of what type of property you want to print:

(gdb) p (CGRect)[myView frame]
(gdb) p (CGPoint)[myView center]

and so on.