I get an EXC_BAD_ACCESS error at a place that doesn't have anything to do with the root cause. I fortunately found the reason to be an array that was too small for the following statement [data getBytes:&tcpBuffer length:i];.
Now my question: I tried all these theree methods - but without success:
Using NSZombiesEnabled did not change anything in the debug window printout
When I set the scheme to debug and to use Leaks instrument it starts the leaks instruments but I don't see the debugger.
When I just run the app in iPhone Simulator and the start Instruments separately, selecting the running app as a target (in the pop-up-menu in Instruments) it stops with an error saying something like "couldn't find the target ".
How does one find the root cause in cases like that? Keep in mind, at the end, it wasn't even a Zombie error! This error message is REALLY more confusing than helpful!
(luckily I just thought of my array, but surely, the next time this will haunt me somewhere else)
It's quite likely that the place you get the EXC_BAD_ACCESS will not be related to the root cause. It could be related and could therefore offer a clue. But that's not certain.
To answer your points:
NSZombiesEnabled will only have an effect if you invoke a method on an object that has been deallocated. That might not be the cause of your EXC_BAD_ACCESS.
Using Instruments is separate to the debugger. If you profile in Instruments, the debugger is not active. Basically, it's a different tool.
This should be ok. Check that your Build Configuration is set to "Debug" and not "Release".
Here's a great link on what causes EXC_BAD_ACCESS and how to track down the root problem:
Lou Franco's Understanding EXC_BAD_ACCESS
Related
It's an aspx web site. It's Huuuge. Oftentimes, we won't see errors until building the entire site. But it's always told us where the error is.
This time, I'm getting an Object reference not set to instance of an object. error with file, no line, no location. Double clicking on the error just does... nothing.
Error 3 Object reference not set to an instance of an object.
I've tried a few things that I've found here and elsewhere but nothing seems to be helping out or giving me more information. I've tried change the verbosity of compiler/build messages but those goggles don't seem to help.
Edit: Very specifically, the first time I try to build the site after opening the project, it says it builds just fine. Trying to build it again causes the error. Closing VS (2013) and reopening the project allows a first time build success and subsequent builds are failures. It should also be noted that it's not actually building anything because it completes far far too quickly - almost instantly.
Can anyone give me some ideas on how to track this down?
It turns out that the VS installation is completely broken. Banging on the keyboard like a monkey and then trying to build succeeds when it should not.
I'm working on an embedded Linux application in Qt and am running into SIGSEGV problems that I'm unable to trace. I'd love to be able to post code but Qt Creator only shows me some assembly code and doesn't provide much of a stack to trace back through.
I can see that the crash happens in QApplicationPrivate::notify_helper(QObject*, QEvent*) after an attempt to branch to an invalid address. I can see that this was called by QApplication::notify() but that's all the stack information Qt Creator gives me. The only thing I can think of at this point is that previous segmentation faults looked like they had something to do with killing a QTimer (many of the timers I'm using are single shot) but I was dumped into the disassembly and could never determine which QTimer was causing the issue. That crash was sporadic while this one seems to be pretty consistent.
Can anyone suggest what I might be able to do to get some more information to allow me to track down the source of this fault? I can provide additional details as needed, though I might need to know where I should even be looking.
EDIT:
It turns out the cause of the previous error was an array index that wasn't properly bounds checked. I still occasionally see a crash that appears to be related to a QTimer as the disassembly points to QObject::startTimer(int) but I can't see any obvious cause in this case. Again, the stack provides no insight into which timer may be causing the problem; I can only see a call to QTimer::start() followed by QObject:startTimer(int).
A Qt project gives a number of errors - that I do not actually consider errors I think:
Some examples:
Fontconfig error: "/etc/fonts/conf.d/65-khmer.conf", line 32: out of memory
// ?
QGraphicsItem::ungrabMouse: not a mouse grabber
// i think happens when the mouse grab didn't quite happen, user moved too fast...
A few others
the first one seems it has an answer here https://askubuntu.com/questions/421891/fontconfig-error-out-of-memory
So I cannot fix it through software, the user must fix it... since it is system dependent...
Even built in release, these errors will still show up on command line... Since they do not cause the application to behave abnormally, I don't think the user should see them.
How can I build/deploy the application without these errors showing ?
ideally of course there would be no errors in a deployed application, but I don't know what I can do about those types of errors...
It is possible to redirect a stream (in this case stderr) after the fact using
freopen("/dev/null", "w", stderr);
Just place this in your main before any other code runs and you should be good. Keep in mind that this might need more work on Windows.
If the error message is posted through the Qt Message infrastructure (qDebug etc.) you can set a new message handler through the function qInstallMsgHandler.
I have this very strange problem on a big flex app where it would run fine with the debug swf if the user has debug flash installed but will have some disparities for people with standard version of flash.
These disparities include:
No pop ups
loose all event catching
Weird positioning of a button
I read somewhere that updatedisplaylist was handled differently ?
For now i will try the export release way instead of the bin-debug swf, and to go back in the commits to see what was the turning point.
Any similar experiences ?
I've been using Flex for a long time and have never heard of any problems like these being related to using the debug vs standard versions of the Flash player, but I have experienced problems similar to what you're experiencing.
When an exception occurs in your application, like attempting to access something in a null class or trying to access element 10 in an array that only has 9, the debug player will pop up a window stating that an exception has occurred and give you a stack trace, even if you're not actively debugging the app. The standard player does not, so the user will have no way of knowing that something went wrong.
In my experience after an uncaught exception occurs it can make all running code from that point on very unstable, causing all of the problems you list and more.
I doubt your problem has anything to do with the two different players beyond the standard one not giving you any feedback about the state of your app.
How many can relate do this?
Server Error in / Application
Object reference not set to an object
Description: Object reference not set to an object.
Exception Details: System.NullReferenceException: Object reference not set to an object.
Source Error:
Line 56: posts.Add(post);
On a more serious note, what are the first things you look for when you see the
yellow screen of death? Half the time the debug trace isn't actually telling you what the problem is (understandable I guess).
I must admit, I still use Response.Write more than I should. I just get lazy going through the debugger. What techniques do you use to debug the problem?
If I'm unable to identify/resolve the issue using the error message that the page presents to me, I will typically try to use the Windows Event Viewer to help me identify what is causing the issue.
For example, SharePoint errors are sometimes far less than descriptive. So, I'll combine what I'm seeing on the Y.S.O.D. with error messages from the Event Viewer to help me narrow down the cause.
I will do my best to ask a co-worker or other associate that I think might have some experience that might help. If I'm still unable to identify the cause, I will resort to Google armed with all the information.
Here's how I try to reduce the number of YSODs. One of the first things I do when starting work on an app is to create a custom exception class.
Add properties such as the SQL
statement being run. Two display
message text fields, one for display
to users, one for display to
developers (in debug mode) Who is
the logged-in user. Get all the form
variables so you know what they were
trying to enter.
Log the errors somewhere (event log
is good, if you can access the web
server; logging to the database is
less successful when so many
exceptions are inability to access
the database).
Create code in the MasterPage or web page base class Page Error events and Application Error events to do the logging.
Create a custom error page. When in
debug mode, the custom error page
displays everything. When not in
debug mode (production), display
only selected properties of the
custom exception.
Investing the time up front to do this will save you many hours of anguish later.
I usually do my debugging on my local machine with the Cassini web server (comes with VS 2005/2008). If I see an exception on my QA or, heaven forbid, my production box it's usually because I forgot to update my connection strings so that they point to the QA/production database instead of my local machine.
In other cases, I've found the stack traces to be very helpful in determining where to provide breakpoints so I step through it in the debugger and examine the data at runtime. The only time I've written any debugging information on the page was when trying to find some performance issues that I couldn't replicate on my developer instance. In this case I wrote some hidden fields that contained timing information about various parts of the render process.
the error info provided, assuming you are in debug mode, will give you information as to what line the error actually occurred on, along with the lines of code leading up to the error. This info should give you a good start on defining where to set your break points for debugging.
I was once in your shoes many moons ago, using response.write for debugging. Once you start using the IDE and debugger as it's intended you'll find yourself pulling out less hair and getting to the solutions much faster.
Also, opening up the immediate window while debugging is gonna make your life even more happy.
Use a decent logging framework such as log4net, and be liberal in your use of DEBUG-level logging.
It's essentially a neater version of your Response.Write approach, which can be left in your production code and "switched on" when required.