Xcode debugger doesn't print objects and shows nil, when they aren't

Question

Xcode shows an error when trying to print an object with po <objectName>, but only for one project.

error: Couldn't materialize struct: size of variable <varName> disagrees with the ValueObject's size Errored out in Execute, couldn't PrepareToExecuteJITExpression

The Xcode debugger also shows ALL objects as nil (self excluded), when they aren't (NSLog shows correct output, as seen in the image). I don't know what's wrong with the project. Every other project works fine.

Any idea what it could be? (Cleaning the project had no effect.)

To me it sound like some kind of pointer issue, but i'm sure entirely sure to be honest. What are you trying to do/accomplish? — user2967030, Nov 08 '13 at 23:23
The error occurs on **every** object of that project. Even `NSString`s created one line above the breakpoint! — Binarian, Nov 08 '13 at 23:42
Maybe it's a system level error. Have you tried cleaning it? — user2967030, Nov 09 '13 at 01:04
As said in the question, cleaning does not change anything ;(, but thanks for trying. Added the error message. — Binarian, Nov 09 '13 at 11:54
Are you sure that you are building without optimizations? (-O0) — iccir, Nov 09 '13 at 12:34
Optimizations can be set not only in project settings but in targets also. There was m stuck :( — basil, Aug 15 '19 at 16:39

score 285 · Accepted Answer · edited Nov 30 '13 at 02:38

285

Are you sure you are not in "Release mode"?

If you want to see variable values you have to be in "Debug mode" (click on your project name on the top left corner near start/stop buttons, then "Edit scheme...", then "Run" settings, then "Info" tab, then "Build Configuration". Here set "Debug". If it was on "Release" that's the matter you saw all nils).

edited Nov 30 '13 at 02:38

Ry-

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answered Nov 11 '13 at 10:33

Mick

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I only have one configuration, how to change the configuration so that it is like a `debug configuration`? – Binarian Nov 11 '13 at 10:53
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Ah ok, I created an empty project and can now see all the differences in the `Build Settings`, the deployment property `Strip debug symbols during copy` was set to YES. – Binarian Nov 11 '13 at 11:32
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@Alex1987 I set `Strip debug symbols during copy` to `NO` and the `Optimization Level` to `None -O0` in the project `Build Settings` – Binarian Dec 15 '13 at 17:16
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Unfortunately, in certain situations lldb has been doing this when in debug mode, with optimizations off, and debugging symbols present. Time to visit bug report.apple.com – ctpenrose Feb 05 '14 at 20:08
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@ctpenrose ditto. going into Debug mode / changing debug symbol stripping did nothing for me. – Dan Loewenherz Feb 19 '14 at 02:09
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I have a custom configuration 'Debug_Staging' that is basically a copy of the original Debug and I'm also getting this error... – kraftydevil Apr 30 '14 at 07:53
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Had the same issue - Optimization level was "None". Problem was that Link-Time Optimization (LTO) was set to "Yes" also for debug mode. – pi3 May 23 '14 at 18:35
It would just start doing it some times for no apparent reason, only restarting XCode helped me. – Boris Gafurov May 01 '15 at 18:06
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Just curious, do any of you have `Enable Address Sanitizer` on? – hhanesand Nov 06 '15 at 01:14

score 42 · Answer 2 · edited Dec 18 '20 at 08:02

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I've set "Optimization Level" for Debug configuration to "None" and it solved problem.

Go to project Build settings
Search Debug
Under Apple Clang - Code Generation check Optimization Level
Set Debug to None [-OO]

After that, you will be able to see variable values in the debug area or console.

edited Dec 18 '20 at 08:02

Glorfindel

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answered Nov 13 '14 at 15:54

Leszek Zarna

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Funny, that didn't work. I did the opposite. I switched to `Fastest, Smallest[-Os]` and it worked. – Nate Hat Dec 16 '14 at 21:26
Lots of different suggestions, but this one (setting Debug optimization to None) fixed it for me. – Dejal Jan 21 '15 at 05:02

score 32 · Answer 3 · edited Jun 20 '20 at 09:12

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Make sure that Address Sanitizer is turned off in your Scheme settings. The Address Sanitizer does not work well with the debugger.

Go to Edit Scheme (Product >> Scheme >> Edit Scheme), choose Run, and go to the Diagnostics tab.
Make sure "Enable Address Sanitizer" is off.

edited Jun 20 '20 at 09:12

Community

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answered Sep 25 '15 at 11:24

Igor Kovryzhkin

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This was the solution for me. Apparently there are lots of reasons this can happen though. – manroe Sep 25 '15 at 20:17

score 16 · Answer 4 · answered Jan 19 '15 at 06:58

It seems everyone has their own solution.

For me, I use Objective-C and Swift at the same time.

First of all, go to TARGETS -> Build Settings and search the code generation

You’ll find Apple LLVM 6.0 and Swift Compiler

Change their Optimization Level all to None, then Debug, you may find the value not nil

Amazingly once you can see the value, you solve this problem permanently, then you can change the Optimization Level to it used to be.

ThomasW · Answer 5 · 2014-09-12T08:15:49.880

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There are other ways this can occur. For me it was because the "Other C Flags" value was set to "-O2", even for the debug build. Turning this off for the debug build resolved the issue.

edited Sep 12 '14 at 08:15

answered Jun 17 '14 at 10:37

ThomasW

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score 9 · Answer 6 · answered Dec 03 '16 at 00:19

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For me, Xcode was filtering out the debugger output. Make sure your output setting is Debugger Output or All Output

answered Dec 03 '16 at 00:19

Curmudgeonlybumbly

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score 7 · Answer 7 · answered Oct 15 '14 at 11:21

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I just encountered this issue and found that it was because Deployment Postprocessing = YES in the Build Settings.

Changing this to NO fixed it, as seen in the screenshot below:

enter image description here

Xcode version: 6.0.1 (6A317) on OSX 10.9.5

answered Oct 15 '14 at 11:21

Luke

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score 5 · Answer 8 · answered Dec 11 '14 at 10:06

I just run into a similar problem: At one point suddenly the Xcode debugger printed out some object types especially NSStrings as (null) although they were initialized with a value. Printed out via

NSLog(@"String value: %@", myString);

the correct value for the object was shown.

Confusing! Solving the problem was rather easy: I just shut down Xcode and restarted my computer. After I restarted Xcode everything works fine again :).

score 5 · Answer 9 · answered Oct 02 '16 at 01:40

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Make sure Link-Time Optimization = No for debug mode in Build Settings.

answered Oct 02 '16 at 01:40

llama591

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I just meet this issue in Xcode 8 only on my dynamic framework build settings ! Thx – vmeyer Oct 03 '16 at 08:18

score 3 · Answer 10 · answered Sep 07 '17 at 17:21

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Delete Derived Data
Quite Xcode / Restart
Clean Project

That's all it took for me.

answered Sep 07 '17 at 17:21

TMin

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score 2 · Answer 11 · answered Jan 31 '15 at 01:04

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The solutions here will also fix the bug where you see error: <EXPR>:1:1: error: use of unresolved identifier every time you try to po a variable.

For me the solution was to go to Build Settings and search for Optimization Level and make sure each Debug setting was set to None.

answered Jan 31 '15 at 01:04

Kevin Xu

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This actually fixed it for me. Any idea what the downside is for disabling the setting? – Jasper Sep 23 '15 at 12:24

score 1 · Answer 12 · answered Jun 21 '16 at 07:51

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Go to "Other C Flags" in build setting and set debug value from -o2 to -O0

answered Jun 21 '16 at 07:51

Muhammad Shauket

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score 1 · Answer 13 · answered Aug 11 '17 at 16:31

I have run into this as well and when I found I was in release mode I switch to debug ... no fix. Turns out that I had to do a clean first (cmd+shift+k).

So I think what happens is that after built in release mode not everything is recompiled in develop and so lldb can't properly read the symbols. After cleaning and recompiling in develop it worked for me.

score 1 · Answer 14 · answered Nov 23 '20 at 23:33

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I ran on this problem when some dependency was added in a very specific way - it works but when you try to print something from this framework you get error

Solution was to add this dependency in a general way

answered Nov 23 '20 at 23:33

yoAlex5

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score -4 · Answer 15 · answered Nov 25 '16 at 13:55

The reality is that the system should work out of the box and doesn't due to links to a multiple quantity of different settings, to a point that things may work for you, or not.

Why doesn't the system allows always to debug when in debug mode is a mystery that only Apple can answer (if they cared, which latelly i doubt they do).

After all, the difference between debug / non-debug would be extra tables with metadata which only fill in memory / disk space.

If you are compiling against the simulator or a device directly, you will not care of those extra megabytes.

So we need to run extra loops to just do a very basic and plain thing that all ides that i know since last century do just fine.

And to add, for me what worked was changing on "Debug" the Link-Time Optimization from "Monolithic" to "No" (xcode 8).

Xcode = No package manager out of the box, autocomplete and other features work on will, compile times are huge, etc. — zirinisp, Dec 07 '16 at 14:43

Xcode debugger doesn't print objects and shows nil, when they aren't

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