Tracking variable or memory change in Xcode?

Question

Is there any way to track variable changes or memory changes in Xcode? I'm looking for functionality like Visual Studio's data breakpoint.

I want to know where my object's view frame is being changed. I want to set a breakpoint at a member variable and run it. Then I could determine where it's changed.

score 21 · Accepted Answer · edited May 23 '17 at 10:30

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Xcode uses gdb (or lldb, but that's another story) to implement its debugging functionality. gdb has the ability to set hardware watchpoints and hence so does Xcode.

This is a useful page for generic debugging of memory errors. Xcode's debugging console window is really just a gdb shell, you can type in commands as you please. The ever-helpful Quinn Taylor explains how to do so in this related post.

If you'd rather avoid interacting with gdb directly, you can right-click a variable in Xcode's debugging window and select "Watch Variable". Xcode will then alert you whenever your variable's value has been changed.

edited May 23 '17 at 10:30

Community

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answered Jan 27 '11 at 02:33

Aidan Steele

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Appreciate for the detail answer! I'll try! – SeniorLee Feb 08 '11 at 03:44
Never thought to right click on the variables in the watch window! Now to hope it actually hits it ;) Seems ropey enough just displaying variable values — telling me local vars are out of scope is really not helpful – Matt Lacey May 03 '11 at 12:39
@LaceySnr: check my answer. I have the same problem with XCode watch. That's why I am using gdb watchpoint. – Kevin MOLCARD Apr 03 '13 at 09:34
"watchpoints not supported" is what I get when trying this on Xcode 5. – Almo Oct 23 '13 at 15:00
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tl;dr right-click variable and click "Watch Variable" – TheLivingForce May 29 '15 at 05:49
More specifically, Xcode will tell you: "error: Watchpoint creation failed ... watch size of [X] is not supported." – vargonian Mar 23 '18 at 17:41

Kevin MOLCARD · Answer 2 · 2013-04-03T09:39:11.057

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You can use hardware watchpoints.

You have to get the address of the variable you want to track (type p &my_var in gdb prompt).

It will print somehting like 0x12345678.

With gdb: type watch *(int *)0x12345678.
With lldb: watch set expression (int *)0x12345678 (or w s e (int *)0x12345678)

This assumes your variable is an int. It will create an hardware watchpoint on this address.

Hope this helps.

edited Apr 03 '13 at 09:39

answered Apr 03 '13 at 09:30

Kevin MOLCARD

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score 1 · Answer 3 · answered Jan 26 '11 at 03:33

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Yes.

Under the Run menu there is "Debugger" which provides a visual frontend to gdb.

Also, there is a breakpoint button next to the Build and Run button. You can click that and manage your breakpoints under Run > Manage Breakpoints.

answered Jan 26 '11 at 03:33

aqua

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I'm not sure this is what he's looking for. You are talking about standard breakpoints, but he is talking about breaking when data stored at a location in memory changes. More like a watchpoint than a breakpoint. – Marc W Jan 26 '11 at 03:37
Got it. Yeah, I don't know if there are any "triggers" like that. However, through the Debugger and use of standard breakpoints you can see the data changing. Probably not as smooth as Visual Studio. – aqua Jan 26 '11 at 03:46

score 0 · Answer 4 · edited May 23 '17 at 12:34

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I know this post is old but in case you are still wondering I posted a detailed answer here: In XCode 6 how can you set a watchpoint without stopping execution?

edited May 23 '17 at 12:34

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answered Feb 20 '15 at 11:15

DrMad

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Tracking variable or memory change in Xcode?

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