This shows up in the debugging console in Xcode. What does it mean and should I be concerned?
It generally means that you're debugging ObjC++ and that gdb has gotten confused about what language you're in the middle of. gdb often has trouble in ObjC++, which is one of many reasons to keep your C++ and ObjC separate as much as you can. A related error is along the lines of "No this pointer."
Related
I have a little problem.
I just installed Eclipse CDT and created a C project using MinGW and all my simple warnings (like "unused variable" etc) are shown as errors.
The program build fine and I can run it, but all these errors are annoying.
I already checked the compiler settings and "Warnings as errors (-Werror)" is unchecked.
What do i do?
In my case, the problem was caused because the compiler/builder's message was in a different language than Eclipse.
Thus, Eclipse could not identify them as Warnings and thought they were Errors instead.
I solved by making an environment variable to set the compiler to the right language,
Thanks to this question
As the messages were sent on the right language, Eclipse changed the markers to warnings and compiled without any error messages.
If -Werror would be checked, the build would fail. By the way you should definitely check it so that it enforces you to take care of all the warnings right from the beginning.
You can suppress some warnings (but not all), with special options to GCC (MinGW). You can see which options are needed to suppress this or that warning in the end of the warning itself.
Nevertheless, I strongly recommend against it. It's rather better to resolve all the warnings right from the beginning. Strive to design your projects in the way that they are able to be built with -pedantic -Wall -Wextra -Werror options. There are 3 main benefits of this approach:
Your code would be nearly bulletproof;
Your code would conform to the standard closely;
Your code would be more portable across different compilers
(as some of them tend to treat some warnings as errors by default).
Remember, leaving the annoying warning flood is a bad habit, and you should definitely get rid of it right from the start.
There's an external library I'm working with that frequently pegs my CPU. I'd like to help the author fix it (as I really like the library), but I don't know how to debug the crash properly.
Any tips for debugging Emacs lisp? Bear in mind when it crashes Emacs doesn't work anymore and I have to kill it (so solutions within Emacs itself might not be helpful).
Edit: I should clarify that it is byte-compiled, and this issue doesn't always happen for others, so it may be specific to my architecture/init files. It is definitely related to this library though.
First, always debug the uncompiled version of a Emacs-Lisp program, unless you're convinced the problem is introduced by the byte-compiler.
Second, if the code is hanging Emacs then the code is probably in an infinite loop with inhibit-quit bound non-nil. So the first thing to do is go through the source for the library and change all inhibit-quit references to something else so that C-g will work to stop the looping. After that, load up the library, set debug-on-quit to t and you should get a nice debug trace when you press C-g that shows you where the code is looping. From there, debugging the problem should be as straightforward as debugging any other infinite loop.
From times to times, while debugging an Application, I see this error on Xcode:
Program received signal: “EXC_BAD_ACCESS”.
and the debugger does not stop on the problematic line. In fact the debugger just shows me a page with a bunch assembly language code and that's it.
I have to have paranormal powers to figure out where the exact problem is.
Is there a way to force Xcode to give me more "nutritive" error messages – that can detail the problem – and stop on the offending line when such errors occur?
thanks for any help.
When the crash happens, open the Debugger in Xcode (Run -> Debugger). There should be 3 to 4 panes like this:
http://developer.apple.com/mac/library/documentation/DeveloperTools/Conceptual/XcodeDebugging/art/debugger_disassembly.jpg
On the top-left pane (the "stack trace"), select the topmost row which is not gray.
(Note: Sometimes the stack trace can only find internal functions because of bad memory management triggered in the run loop. Try to Build -> Build and Analyze to eliminate all potential memory management bugs first.)
You can enable NSZombies see here and I've found a good way to see where the actual problem is, is to run and debug the program with the debugger open.
This way when the program stops executing it more often then shows the line that was executing when the program crashed.
I wrote up a blog that tells you how to use some compiler switches that help a lot in finding crashes that are the result of releasing objects before you are done with them.
http://loufranco.com/blog/files/debugging-memory-iphone.html
Build and Analyze is ok, but not as good as scan-build (which it is based on). Instructions for installing that are here:
http://loufranco.com/blog/files/scan-build-better-than-build-analyze.html
My iphone app randomly received this message. I know certain it is memory release problem. However what is the best way to find which object leads this problem. Here are what I have tried
Use Instrument Leak and
ObjectAllocation Trace. Dont saw any
help to know which object have this
problem
Put NSZombieEnabled=YES and project executive ... Dont saw any
help either
Put NSLog everywhere but the EXE_BAD_ACCESS just appear anywhere.
in the debuger, just saw the code
happened in the assembly. like
objc-msg send.
review code many times and read memory management a lot time
and research online a lot time. but
no surprise.
Is there a completed solution to figure out this problem easily. I am a previous Visual C++ programmer, I deal with memory management with years and it is easy to debug and figure out in Visual C++.
If you couldn't see any helpful debug info, I would suggest you find all the places that you are doing a release. It is most likely the case that you have released something that did not need to be released. Code would help us in tracing the issue with you.
As Juan noted, the first stop is the Debugger - what does the debug window give for a stack trace when the app crashes? You should be able to see the line it crashed on... you said in a comment to one response that you saw the crash happen around the lines:
CGPDFDocumnetRef docA=CGPDFDocumentCreatWithURL(myurl);
CGPDFDocumnetRef docB=CGPDFDocumentCreatWithURL(myurl);
Are you really using the same URL object for both calls? Which line is it exactly?
It could be something around the way you make use of the CGPDFDocumentRef, you can find example code how Apple uses them in the QuartzDemo project, file "QuartzImageDrawing.m" (you can find the demo project from the developer portal or embedded in the iPhone documentation with XCode).
XCode is actually pretty powerful, but it does things differently from other IDE's.
In addition to Erich answer, I'd want to add go backward. Start with the most recently added release and work from there.
I ran in to this and it turned out I was releasing an auto-released object that was returned from a convenience method built in to the Cocoa-Touch framework. My problem was as Erich described -- I released this auto-released object. When the system attempted to release it, the program gave the error you are describing.
Regards,Frank
The best way to know what happend is using the xCode Debbuger, give it a try.
You will also receive the message when you don't pass enough parameters to a variable argument method. For example having a NSLog statement like this: NSLog(#"Hello %#");
To check what the error might be
Use NSZombieEnabled.
To activate the NSZombieEnabled facility in your application:
Choose Project > Edit Active Executable to open the executable Info window.
Click Arguments.
Click the add (+) button in the “Variables to be set in the environment” section.
Enter NSZombieEnabled in the Name column and YES in the Value column.
Make sure that the checkmark for the NSZombieEnabled entry is selected.
found this on iPhoneSDK
This is driving me nuts. I just uploaded my first app to the App Store for the first time, and of course, now my app is exploding left and right. When I build with release build configuration, I randomly get an EXC_BAD_ACCESS after banging on the app for some variable amount of time. I turned Zombies back on, but the problem doesn't appear to be over-releasing a variable, as I don't get a message about sending a message to a released variable.
The error does always appear in the same spot in my code. It looks like I'm trying to retain a variable that hasn't been initialized properly. I haven't the slightest idea how I could be doing that.
But here's the weird thing: if I build in debug release configuration, IT NEVER CRASHES. I can bang on the thing all day long, and it's rock solid. I build with Release configuration, and it gets all intermittently crashy.
Looking at the Build settings in the two configurations, there aren't that many differences. In debug, the GCC 4.0 Optimization level is "None", while in Release, it's "Fastest, Smallest." If I switch the optimization level in Release to "None," the app behaves itself. Does anyone have a clue what I should be looking for to fix this? Alternately, how many bad things happen if I Distribute with No optimization?
UPDATE:
Dang! I really need a magic debug tool for memory errors. I've been working this problem for the last day or so. I added an exercise method that would reliably generate a crash and started looking for the area of code that was causing it.
The app would usually crash the 3rd-5th time I performed one particular type of operation. The only thing that was different about that type of operation was the value I returned from an accessory method. The accessory method generally returned NSDecimalNumbers with values of 0-3, but there was one special case when I was returning an NSDecimalNumber with a non-integer value. I would test the result of the accessory method looking for the non-integer value. I changed the special case to return an NSDecimalNumber with a value of -1 instead of the non-integer value, and I can no longer make the app crash.
Basically, the only change I made was switching from
[[NSNumber numberWithDouble:num] decimalValue] --> crash
to
[[NSNumber numberWithInteger:num] decimalValue] --> no crash
It's a little but more complicated than that, but not much.
Now, I'm happy that the app no longer crashes but the change I made does not fill me with confidence, as the old bits of code did not appear to be "broken" in any way. So, while my app doesn't crash anymore, it's not because I "fixed" it, I just changed some random thing and now it works. 8^(
UPDATE:
Debugger does not spit out a stack trace as it usually does when a program crashes. When it crashes, the debug console outputs the following:
Loading program into debugger…
[... copyright stuff...]
This GDB was configured as "i386-apple-darwin".warning: Unable to read symbols for "/System/Library/Frameworks/UIKit.framework/UIKit" (file not found).
warning: Unable to read symbols from "UIKit" (not yet mapped into memory).
warning: Unable to read symbols for "/System/Library/Frameworks/CoreGraphics.framework/CoreGraphics" (file not found).
warning: Unable to read symbols from "CoreGraphics" (not yet mapped into memory).
Program loaded.
sharedlibrary apply-load-rules all
Attaching to program: `/Users/...', process 10066.
Re-enabling shared library breakpoint 1
Cannot access memory at address 0x4
Cannot access memory at address 0x4
(gdb)
If only it were as easy as turning on Zombies and you could always find your over-releases... There are lots of these kinds of errors that Zombies can't detect. There is no magic debug tool for memory errors; only careful programming (and there are patterns that make these errors much more uncommon, and much easier to debug when they do occur).
Optimized code can shake free lots of things that don't show up in unoptimized code. It does suggest slightly that it may be a local variable rather than an ivar, but perhaps not. It may just be timing; being faster may make a race condition go the other way more often.
If you can get it to crash, take a look of in the stack trace as a first step of course.
There's nothing deeply wrong with distributing without optimization, but it's just masking the problem. There's a coding error in there. Optimization isn't breaking your code. Your code is broken.
There's a good discussion of debugging memory problems here. The #1 rule is that you must use accessors. They will save you much heartache, so hopefully you already do this. I provide some other pointers in my short discussion of memory management rules.
I'd suggest cranking up the warning level on your compiler and see if anything pops up. Open up your project settings and enable every 'warning' option you can find. Or, find the project setting named Other C Flags and add the flags -Wall -Wextra.
You're going to get a LOT of white noise for things like signed/unsigned mismatches, possible loss of precision, etc., that you can (usually) safely ignore. However, there may be some key warnings that pop up that you definitely should NOT ignore: things like making a pointer from an integer without a cast (or vice-versa). If you're not 100% sure you can ignore the warning, fix the code so the warning goes away.