How to change NSNumber value in XCode while debugging?

Question

My class has a member variable which is a NSNumber, like so:

@interface C : NSObject {
    NSNumber* _n;
}

During debugging, I am stopped at a breakpoint, and I want to change the value of the NSNumber. How can I do it?

I tried the XCode variables window, but that does not work.

I tried the XCode debug console, for example

expr _n = @1

but that gives the bizarre message error: assigning to 'NSNumber *' from incompatible type 'NSNumber *' -- no kidding! Try it.

I also tried

expr _n = [NSNumber numberWithInt:1]

but that gives the same thing.

Martin R · Accepted Answer · 2013-01-02 23:38:19Z

5

This worked for me:

(lldb) expr -- _n = (NSNumber *)[NSNumber numberWithInt:123]
(NSNumber *) $0 = 0x0000000000007b83 (int)123
(lldb) po _n
(NSNumber *) $1 = 0x0000000000007b83 123

The -- is required to mark the end of command options and beginning of "raw" input.

Strictly speaking, this does not change the value of the existing NSNumber, but assigns a new NSNumber object to _n. But NSNumber objects are immutable, so changing their value is not possible anyway.

edited Jan 2, 2013 at 23:38

answered Jan 2, 2013 at 23:09

Martin R

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8 Comments

JRG-Developer Over a year ago

Can you share any links on good tutorials for learning the debugger in general?

Martin R Over a year ago

@JRG-Developer: I must admit that for me working with the new lldb is often "try and error". But perhaps this thread helps: stackoverflow.com/questions/12974455/….

nielsbot Over a year ago

Looks like boxing syntax works here too. I tried po @(1.5) and got (NSNumber *) $1 = 0x000000010054a520 1.5

Martin R Over a year ago

@nielsbot: I had tried only @123, which does not work in the debugger. So thanks for the feedback, I can add that to the answer if that is OK with you.

nielsbot Over a year ago

Sure, I don't mind. I just assumed the parentheses were required--I've never used any other syntax.

|

Raman · Accepted Answer · 2014-01-13 08:26:30Z

1

Try to use this line:

po _n = @(123)

answered Jan 13, 2014 at 8:26

Raman

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