EXC BAD ACCESS signal received

Question

When deploying the application to the device  the program will quit after a few cycles with the following error   Program received signal   EXC BAD ACCESS     The program runs without any issue on the iPhone simulator  it will also debug and run as long as I step through the instructions one at a time  As soon as I let it run again  I will hit the EXC BAD ACCESS signal   In this particular case  it happened to be an error in the accelerometer code  It would not execute within the simulator  which is why it did not throw any errors  However  it would execute once deployed to the device   Most of the answers to this question deal with the general EXC BAD ACCESS error  so I will leave this open as a catch-all for the dreaded Bad Access error   EXC BAD ACCESS is typically thrown as the result of an illegal memory access  You can find more information in the answers below   Have you encountered the EXC BAD ACCESS signal before  and how did you deal with it

User · Answer

When you have infinite recursion  I think you can also have this error  This was a case for me

User · Answer

I ve been debuging  and refactoring code to solve this error for the last four hours  A post above led me to see the problem   Property before    startPoint     DataPoint alloc  init    startPoint   DataPointList objectAtIndex  0   x   startPoint x - 10     EXC BAD ACCESS   Property after    startPoint     DataPoint alloc  init    startPoint     DataPointList objectAtIndex  0  retain     Goodbye EXC BAD ACCESS  Thank you so much for your answer   I ve been struggling with this problem all day   You re awesome

User · Answer

NSAssert   calls to validate method parameters is pretty handy for tracking down and avoiding passing nils as well

User · Answer

Not a complete answer  but one specific situation where I ve received this is when trying to access an object that  died  because I tried to use autorelease   netObjectDefinedInMyHeader      MyNetObject alloc  init  autorelease     So for example  I was actually passing this as an object to  notify   registered it as a listener  observer  whatever idiom you like  but it had already died once the notification was sent and I d get the EXC BAD ACCESS  Changing it to   MyNetObject alloc  init  and releasing it later as appropriate solved the error    Another reason this may happen is for example if you pass in an object and try to store it   myObjectDefinedInHeader   aParameterObjectPassedIn    Later when trying to access myObjectDefinedInHeader you may get into trouble  Using   myObjectDefinedInHeader    aParameterObjectPassedIn retain     may be what you need  Of course these are just a couple of examples of what I ve ran into and there are other reasons  but these can prove elusive so I mention them  Good luck

User · Answer

In my experience  this is generally caused by an illegal memory access   Check all pointers  especially object pointers  to make sure they re initialized   Make sure your MainWindow xib file  if you re using one  is set up properly  with all the necessary connections   If none of that on-paper checking turns anything up  and it doesn t happen when single-stepping  try to locate the error with NSLog   statements  sprinkle your code with them  moving them around until you isolate the line that s causing the error   Then set a breakpoint on that line and run your program   When you hit the breakpoint  examine all the variables  and the objects in them  to see if anything doesn t look like you expect I d especially keep an eye out for variables whose object class is something you didn t expect   If a variable is supposed to contain a UIWindow but it has an NSNotification in it instead  the same underlying code error could be manifesting itself in a different way when the debugger isn t in operation

User · Answer

I forgot to return self in an init-Method

User · Answer

NSAssert   calls to validate method parameters is pretty handy for tracking down and avoiding passing nils as well

User · Answer

In my experience  this is generally caused by an illegal memory access   Check all pointers  especially object pointers  to make sure they re initialized   Make sure your MainWindow xib file  if you re using one  is set up properly  with all the necessary connections   If none of that on-paper checking turns anything up  and it doesn t happen when single-stepping  try to locate the error with NSLog   statements  sprinkle your code with them  moving them around until you isolate the line that s causing the error   Then set a breakpoint on that line and run your program   When you hit the breakpoint  examine all the variables  and the objects in them  to see if anything doesn t look like you expect I d especially keep an eye out for variables whose object class is something you didn t expect   If a variable is supposed to contain a UIWindow but it has an NSNotification in it instead  the same underlying code error could be manifesting itself in a different way when the debugger isn t in operation

User · Answer

NSAssert   calls to validate method parameters is pretty handy for tracking down and avoiding passing nils as well

User · Answer

I just spent a couple hours tracking an EXC BAD ACCESS and found NSZombies and other env vars didn t seem to tell me anything   For me  it was a stupid NSLog statement with format specifiers but no args passed   NSLog   Some silly log message   -        Fixed by  NSLog   Some silly log message   -     someObj1  someObj2

User · Answer

I find it useful to set a breakpoint on objc exception throw  That way the debugger should break when you get the EXC BAD ACCESS   Instructions can be found here DebuggingTechniques

User · Answer

A major cause of EXC BAD ACCESS is from trying to access released objects   To find out how to troubleshoot this  read this document  DebuggingAutoReleasePool  Even if you don t think you are  releasing auto-released objects   this will apply to you   This method works extremely well   I use it all the time with great success    In summary  this explains how to use Cocoa s NSZombie debugging class and the command line  malloc history  tool to find exactly what released object has been accessed in your code   Sidenote   Running Instruments and checking for leaks will not help troubleshoot EXC BAD ACCESS   I m pretty sure memory leaks have nothing to do with EXC BAD ACCESS  The definition of a leak is an object that you no longer have access to  and you therefore cannot call it   UPDATE  I now use Instruments to debug Leaks   From Xcode 4 2  choose Product- Profile and when Instruments launches  choose  Zombies

User · Answer

I find it useful to set a breakpoint on objc exception throw  That way the debugger should break when you get the EXC BAD ACCESS   Instructions can be found here DebuggingTechniques

User · Answer

This is an excellent thread  Here s my experience  I messed up with the retain assign keyword on a property declaration  I said    property  nonatomic  assign  IBOutlet UISegmentedControl  choicesControl   property  nonatomic  assign  IBOutlet UISwitch  africaSwitch   property  nonatomic  assign  IBOutlet UISwitch  asiaSwitch    where I should have said   property  nonatomic  retain  IBOutlet UISegmentedControl  choicesControl   property  nonatomic  retain  IBOutlet UISwitch  africaSwitch   property  nonatomic  retain  IBOutlet UISwitch  asiaSwitch

User · Answer

In my experience  this is generally caused by an illegal memory access   Check all pointers  especially object pointers  to make sure they re initialized   Make sure your MainWindow xib file  if you re using one  is set up properly  with all the necessary connections   If none of that on-paper checking turns anything up  and it doesn t happen when single-stepping  try to locate the error with NSLog   statements  sprinkle your code with them  moving them around until you isolate the line that s causing the error   Then set a breakpoint on that line and run your program   When you hit the breakpoint  examine all the variables  and the objects in them  to see if anything doesn t look like you expect I d especially keep an eye out for variables whose object class is something you didn t expect   If a variable is supposed to contain a UIWindow but it has an NSNotification in it instead  the same underlying code error could be manifesting itself in a different way when the debugger isn t in operation

User · Answer

From your description I suspect the most likely explanation is that you have some error in your memory management  You said you ve been working on iPhone development for a few weeks  but not whether you are experienced with Objective C in general  If you ve come from another background it can take a little while before you really internalise the memory management rules - unless you make a big point of it   Remember  anything you get from an allocation function  usually the static alloc method  but there are a few others   or a copy method  you own the memory too and must release it when you are done   But if you get something back from just about anything else including factory methods  e g   NSString stringWithFormat   then you ll have an autorelease reference  which means it could be released at some time in the future by other code - so it is vital that if you need to keep it around beyond the immediate function that you retain it  If you don t  the memory may remain allocated while you are using it  or be released but coincidentally still valid  during your emulator testing  but is more likely to be released and show up as bad access errors when running on the device   The best way to track these things down  and a good idea anyway  even if there are no apparent problems  is to run the app in the Instruments tool  especially with the Leaks option

User · Answer

How i deal with EXC BAD ACCESS  Sometimes i feel that when a EXC BAD ACCESS error is thrown xcode will show the error in the main m class giving no extra information of where the crash happens Sometimes    In those times we can set a Exceptional Breakpoint in Xcode so that when exception is caught a breakpoint will be placed and will directly intimate the user that crash has happened in that line

User · Answer

In my experience  this is generally caused by an illegal memory access   Check all pointers  especially object pointers  to make sure they re initialized   Make sure your MainWindow xib file  if you re using one  is set up properly  with all the necessary connections   If none of that on-paper checking turns anything up  and it doesn t happen when single-stepping  try to locate the error with NSLog   statements  sprinkle your code with them  moving them around until you isolate the line that s causing the error   Then set a breakpoint on that line and run your program   When you hit the breakpoint  examine all the variables  and the objects in them  to see if anything doesn t look like you expect I d especially keep an eye out for variables whose object class is something you didn t expect   If a variable is supposed to contain a UIWindow but it has an NSNotification in it instead  the same underlying code error could be manifesting itself in a different way when the debugger isn t in operation

User · Answer

XCode 4 and above  it has been made really simple with Instruments  Just run Zombies in Instruments  This tutorial explains it well  debugging exc bad access error xcode instruments

User · Answer

I encountered EXC BAD ACCESS on the iPhone only while trying to execute a C method that included a big array   The simulator was able to give me enough memory to run the code  but not the device  the array was a million characters  so it was a tad excessive       The EXC BAD ACCESS occurred just after entry point of the method  and had me confused for quite a while because it was nowhere near the array declaration   Perhaps someone else might benefit from my couple of hours of hair-pulling

User · Answer

Just to add another situation where this can happen   I had the code   NSMutableString  string   string   appendWithFormat   foo      Obviously I had forgotten to allocate memory for the string   NSMutableString  string     NSMutableString alloc  init    string   appendWithFormat   foo      fixes the problem

User · Answer

When you have infinite recursion  I think you can also have this error  This was a case for me

User · Answer

Hope you re releasing the  string  when you re done

User · Answer

I ve been debuging  and refactoring code to solve this error for the last four hours  A post above led me to see the problem   Property before  startPoint     DataPoint alloc  init    startPoint   DataPointList objectAtIndex  0         x   startPoint x - 10      EXC BAD ACCESS   Property after  startPoint     DataPoint alloc  init    startPoint     DataPointList objectAtIndex  0  retain     Goodbye EXC BAD ACCESS

User · Answer

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   I found this answer on iPhoneSDK

User · Answer

A major cause of EXC BAD ACCESS is from trying to access released objects   To find out how to troubleshoot this  read this document  DebuggingAutoReleasePool  Even if you don t think you are  releasing auto-released objects   this will apply to you   This method works extremely well   I use it all the time with great success    In summary  this explains how to use Cocoa s NSZombie debugging class and the command line  malloc history  tool to find exactly what released object has been accessed in your code   Sidenote   Running Instruments and checking for leaks will not help troubleshoot EXC BAD ACCESS   I m pretty sure memory leaks have nothing to do with EXC BAD ACCESS  The definition of a leak is an object that you no longer have access to  and you therefore cannot call it   UPDATE  I now use Instruments to debug Leaks   From Xcode 4 2  choose Product- Profile and when Instruments launches  choose  Zombies

User · Answer

Not a complete answer  but one specific situation where I ve received this is when trying to access an object that  died  because I tried to use autorelease   netObjectDefinedInMyHeader      MyNetObject alloc  init  autorelease     So for example  I was actually passing this as an object to  notify   registered it as a listener  observer  whatever idiom you like  but it had already died once the notification was sent and I d get the EXC BAD ACCESS  Changing it to   MyNetObject alloc  init  and releasing it later as appropriate solved the error    Another reason this may happen is for example if you pass in an object and try to store it   myObjectDefinedInHeader   aParameterObjectPassedIn    Later when trying to access myObjectDefinedInHeader you may get into trouble  Using   myObjectDefinedInHeader    aParameterObjectPassedIn retain     may be what you need  Of course these are just a couple of examples of what I ve ran into and there are other reasons  but these can prove elusive so I mention them  Good luck

User · Answer

NSAssert   calls to validate method parameters is pretty handy for tracking down and avoiding passing nils as well

User · Answer

I just had this problem  For me the reason was deleting a CoreData managed object ans trying to read it afterwards from another place

User · Answer

I got it because I wasn t using self performSegueWithIdentifier sender   and - void  prepareForSegue  UIstoryboardSegue    right

User · Answer

Don t forget the   symbol when creating strings  treating C-strings as NSStrings will cause EXC BAD ACCESS   Use this     Some String    Rather than this    Some String    PS - typically when populating contents of an array with lots of records

User · Answer

I ve been debuging  and refactoring code to solve this error for the last four hours  A post above led me to see the problem   Property before    startPoint     DataPoint alloc  init    startPoint   DataPointList objectAtIndex  0   x   startPoint x - 10     EXC BAD ACCESS   Property after    startPoint     DataPoint alloc  init    startPoint     DataPointList objectAtIndex  0  retain     Goodbye EXC BAD ACCESS  Thank you so much for your answer   I ve been struggling with this problem all day   You re awesome

User · Answer

Use the simple rule of  if you didn t allocate it or retain it  don t release it

User · Answer

Not a complete answer  but one specific situation where I ve received this is when trying to access an object that  died  because I tried to use autorelease   netObjectDefinedInMyHeader      MyNetObject alloc  init  autorelease     So for example  I was actually passing this as an object to  notify   registered it as a listener  observer  whatever idiom you like  but it had already died once the notification was sent and I d get the EXC BAD ACCESS  Changing it to   MyNetObject alloc  init  and releasing it later as appropriate solved the error    Another reason this may happen is for example if you pass in an object and try to store it   myObjectDefinedInHeader   aParameterObjectPassedIn    Later when trying to access myObjectDefinedInHeader you may get into trouble  Using   myObjectDefinedInHeader    aParameterObjectPassedIn retain     may be what you need  Of course these are just a couple of examples of what I ve ran into and there are other reasons  but these can prove elusive so I mention them  Good luck

User · Answer

Before you do anything  you should try   Product -  Clean  And run again  It worked for me  Otherwise  I would have wasted hours

User · Answer

Just to add  Lynda com has a fantastic DVD called     iPhone SDK Essential Training   and Chapter 6  Lesson 3 is all about EXEC BAD ACCESS and working with Zombies   It was great for me to understand  not just the error code but how can I use Zombies to get more info on the released object

User · Answer

An EXC BAD ACCESS signal is the result of passing an invalid pointer to a system call   I got one just earlier today with a test program on OS X - I was passing an uninitialized variable to pthread join    which was due to an earlier typo   I m not familiar with iPhone development  but you should double-check all your buffer pointers that you re passing to system calls   Crank up your compiler s warning level all the way  with gcc  use the -Wall and -Wextra options    Enable as many diagnostics on the simulator debugger as possible

User · Answer

The 2010 WWDC videos are available to any participants in the apple developer program  There s a great video   Session 311 - Advanced Memory Analysis with Instruments  that shows some examples of using zombies in instruments and debugging other memory problems   For a link to the login page click HERE

User · Answer

From your description I suspect the most likely explanation is that you have some error in your memory management  You said you ve been working on iPhone development for a few weeks  but not whether you are experienced with Objective C in general  If you ve come from another background it can take a little while before you really internalise the memory management rules - unless you make a big point of it   Remember  anything you get from an allocation function  usually the static alloc method  but there are a few others   or a copy method  you own the memory too and must release it when you are done   But if you get something back from just about anything else including factory methods  e g   NSString stringWithFormat   then you ll have an autorelease reference  which means it could be released at some time in the future by other code - so it is vital that if you need to keep it around beyond the immediate function that you retain it  If you don t  the memory may remain allocated while you are using it  or be released but coincidentally still valid  during your emulator testing  but is more likely to be released and show up as bad access errors when running on the device   The best way to track these things down  and a good idea anyway  even if there are no apparent problems  is to run the app in the Instruments tool  especially with the Leaks option

User · Answer

Forgot to take out a non-alloc d pointer from dealloc  I was getting the exc bad access on my rootView of a UINavigationController  but only sometimes  I assumed the problem was in the rootView because it was crashing halfway through its viewDidAppear    It turned out to only happen after I popped the view with the bad dealloc   release  and that was it    EXC BAD ACCESS   Switching to process 330  No memory available to program now  unsafe to call malloc  I thought it was a problem where I was trying to alloc    not where I was trying to release a non-alloc  D oh

User · Answer

An EXC BAD ACCESS signal is the result of passing an invalid pointer to a system call   I got one just earlier today with a test program on OS X - I was passing an uninitialized variable to pthread join    which was due to an earlier typo   I m not familiar with iPhone development  but you should double-check all your buffer pointers that you re passing to system calls   Crank up your compiler s warning level all the way  with gcc  use the -Wall and -Wextra options    Enable as many diagnostics on the simulator debugger as possible

User · Answer

Just to add another situation where this can happen   I had the code   NSMutableString  string   string   appendWithFormat   foo      Obviously I had forgotten to allocate memory for the string   NSMutableString  string     NSMutableString alloc  init    string   appendWithFormat   foo      fixes the problem

User · Answer

Even another possibility  using blocks in queues  it might easily happen that you try to access an object in another queue  that has already been de-allocated at this time  Typically when you try to send something to the GUI  If your exception breakpoint is being set at a strange place  then this might be the cause

User · Answer

I got it because I wasn t using self performSegueWithIdentifier sender   and - void  prepareForSegue  UIstoryboardSegue    right

User · Answer

How To Debug EXC BAD ACCESS  Check out the link above and do as it says     Just some quick instructions for using NSZombies  Run the application and after it fails  Should display  Interrupted  rather than  EXC BAD ACCESS     check the Console  Run   Console     there should be a message there now telling what object it was trying to access   -Ben

User · Answer

Don t forget the   symbol when creating strings  treating C-strings as NSStrings will cause EXC BAD ACCESS   Use this     Some String    Rather than this    Some String    PS - typically when populating contents of an array with lots of records

User · Answer

In my case it was caused tableview delete operation  This solution solved my bad access exception  https   stackoverflow com a 4186786 538408

User · Answer

Use the simple rule of  if you didn t allocate it or retain it  don t release it

User · Answer

In my case it was caused tableview delete operation  This solution solved my bad access exception  https   stackoverflow com a 4186786 538408

User · Answer

Even another possibility  using blocks in queues  it might easily happen that you try to access an object in another queue  that has already been de-allocated at this time  Typically when you try to send something to the GUI  If your exception breakpoint is being set at a strange place  then this might be the cause

User · Answer

The 2010 WWDC videos are available to any participants in the apple developer program  There s a great video   Session 311 - Advanced Memory Analysis with Instruments  that shows some examples of using zombies in instruments and debugging other memory problems   For a link to the login page click HERE

User · Answer

Before you do anything  you should try   Product -  Clean  And run again  It worked for me  Otherwise  I would have wasted hours

User · Answer

I ve been debuging  and refactoring code to solve this error for the last four hours  A post above led me to see the problem   Property before  startPoint     DataPoint alloc  init    startPoint   DataPointList objectAtIndex  0         x   startPoint x - 10      EXC BAD ACCESS   Property after  startPoint     DataPoint alloc  init    startPoint     DataPointList objectAtIndex  0  retain     Goodbye EXC BAD ACCESS

User · Answer

Just to add  Lynda com has a fantastic DVD called     iPhone SDK Essential Training   and Chapter 6  Lesson 3 is all about EXEC BAD ACCESS and working with Zombies   It was great for me to understand  not just the error code but how can I use Zombies to get more info on the released object

User · Answer

An EXC BAD ACCESS signal is the result of passing an invalid pointer to a system call   I got one just earlier today with a test program on OS X - I was passing an uninitialized variable to pthread join    which was due to an earlier typo   I m not familiar with iPhone development  but you should double-check all your buffer pointers that you re passing to system calls   Crank up your compiler s warning level all the way  with gcc  use the -Wall and -Wextra options    Enable as many diagnostics on the simulator debugger as possible

User · Answer

How To Debug EXC BAD ACCESS  Check out the link above and do as it says     Just some quick instructions for using NSZombies  Run the application and after it fails  Should display  Interrupted  rather than  EXC BAD ACCESS     check the Console  Run   Console     there should be a message there now telling what object it was trying to access   -Ben

User · Answer

Hope you re releasing the  string  when you re done

User · Answer

I just had this problem  For me the reason was deleting a CoreData managed object ans trying to read it afterwards from another place

User · Answer

I forgot to return self in an init-Method

User · Answer

How i deal with EXC BAD ACCESS  Sometimes i feel that when a EXC BAD ACCESS error is thrown xcode will show the error in the main m class giving no extra information of where the crash happens Sometimes    In those times we can set a Exceptional Breakpoint in Xcode so that when exception is caught a breakpoint will be placed and will directly intimate the user that crash has happened in that line

User · Answer

I encountered EXC BAD ACCESS on the iPhone only while trying to execute a C method that included a big array   The simulator was able to give me enough memory to run the code  but not the device  the array was a million characters  so it was a tad excessive       The EXC BAD ACCESS occurred just after entry point of the method  and had me confused for quite a while because it was nowhere near the array declaration   Perhaps someone else might benefit from my couple of hours of hair-pulling

User · Answer

An EXC BAD ACCESS signal is the result of passing an invalid pointer to a system call   I got one just earlier today with a test program on OS X - I was passing an uninitialized variable to pthread join    which was due to an earlier typo   I m not familiar with iPhone development  but you should double-check all your buffer pointers that you re passing to system calls   Crank up your compiler s warning level all the way  with gcc  use the -Wall and -Wextra options    Enable as many diagnostics on the simulator debugger as possible

User · Answer

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   I found this answer on iPhoneSDK

User · Answer

XCode 4 and above  it has been made really simple with Instruments  Just run Zombies in Instruments  This tutorial explains it well  debugging exc bad access error xcode instruments

User · Answer

Another method for catching EXC BAD ACCESS exceptions before they happen is the static analyzer  in XCode 4    Run the static analyzer with Product   Analyze  shift cmd B   Clicking on any messages generated by the analyzer will overlay a diagram on your source showing the sequence of retains releases of the offending object

User · Answer

Forgot to take out a non-alloc d pointer from dealloc  I was getting the exc bad access on my rootView of a UINavigationController  but only sometimes  I assumed the problem was in the rootView because it was crashing halfway through its viewDidAppear    It turned out to only happen after I popped the view with the bad dealloc   release  and that was it    EXC BAD ACCESS   Switching to process 330  No memory available to program now  unsafe to call malloc  I thought it was a problem where I was trying to alloc    not where I was trying to release a non-alloc  D oh

User · Answer

This is an excellent thread  Here s my experience  I messed up with the retain assign keyword on a property declaration  I said    property  nonatomic  assign  IBOutlet UISegmentedControl  choicesControl   property  nonatomic  assign  IBOutlet UISwitch  africaSwitch   property  nonatomic  assign  IBOutlet UISwitch  asiaSwitch    where I should have said   property  nonatomic  retain  IBOutlet UISegmentedControl  choicesControl   property  nonatomic  retain  IBOutlet UISwitch  africaSwitch   property  nonatomic  retain  IBOutlet UISwitch  asiaSwitch

User · Answer

Another method for catching EXC BAD ACCESS exceptions before they happen is the static analyzer  in XCode 4    Run the static analyzer with Product   Analyze  shift cmd B   Clicking on any messages generated by the analyzer will overlay a diagram on your source showing the sequence of retains releases of the offending object

User · Answer

From your description I suspect the most likely explanation is that you have some error in your memory management  You said you ve been working on iPhone development for a few weeks  but not whether you are experienced with Objective C in general  If you ve come from another background it can take a little while before you really internalise the memory management rules - unless you make a big point of it   Remember  anything you get from an allocation function  usually the static alloc method  but there are a few others   or a copy method  you own the memory too and must release it when you are done   But if you get something back from just about anything else including factory methods  e g   NSString stringWithFormat   then you ll have an autorelease reference  which means it could be released at some time in the future by other code - so it is vital that if you need to keep it around beyond the immediate function that you retain it  If you don t  the memory may remain allocated while you are using it  or be released but coincidentally still valid  during your emulator testing  but is more likely to be released and show up as bad access errors when running on the device   The best way to track these things down  and a good idea anyway  even if there are no apparent problems  is to run the app in the Instruments tool  especially with the Leaks option

User · Answer

I realize this was asked some time ago  but after reading this thread  I found the solution for XCode 4 2  Product -  Edit Scheme -  Diagnostics Tab -  Enable Zombie Objects  Helped me find a message being sent to a deallocated object

User · Answer

Not a complete answer  but one specific situation where I ve received this is when trying to access an object that  died  because I tried to use autorelease   netObjectDefinedInMyHeader      MyNetObject alloc  init  autorelease     So for example  I was actually passing this as an object to  notify   registered it as a listener  observer  whatever idiom you like  but it had already died once the notification was sent and I d get the EXC BAD ACCESS  Changing it to   MyNetObject alloc  init  and releasing it later as appropriate solved the error    Another reason this may happen is for example if you pass in an object and try to store it   myObjectDefinedInHeader   aParameterObjectPassedIn    Later when trying to access myObjectDefinedInHeader you may get into trouble  Using   myObjectDefinedInHeader    aParameterObjectPassedIn retain     may be what you need  Of course these are just a couple of examples of what I ve ran into and there are other reasons  but these can prove elusive so I mention them  Good luck

User · Answer

I realize this was asked some time ago  but after reading this thread  I found the solution for XCode 4 2  Product -  Edit Scheme -  Diagnostics Tab -  Enable Zombie Objects  Helped me find a message being sent to a deallocated object

User · Answer

From your description I suspect the most likely explanation is that you have some error in your memory management  You said you ve been working on iPhone development for a few weeks  but not whether you are experienced with Objective C in general  If you ve come from another background it can take a little while before you really internalise the memory management rules - unless you make a big point of it   Remember  anything you get from an allocation function  usually the static alloc method  but there are a few others   or a copy method  you own the memory too and must release it when you are done   But if you get something back from just about anything else including factory methods  e g   NSString stringWithFormat   then you ll have an autorelease reference  which means it could be released at some time in the future by other code - so it is vital that if you need to keep it around beyond the immediate function that you retain it  If you don t  the memory may remain allocated while you are using it  or be released but coincidentally still valid  during your emulator testing  but is more likely to be released and show up as bad access errors when running on the device   The best way to track these things down  and a good idea anyway  even if there are no apparent problems  is to run the app in the Instruments tool  especially with the Leaks option

User · Answer

I just spent a couple hours tracking an EXC BAD ACCESS and found NSZombies and other env vars didn t seem to tell me anything   For me  it was a stupid NSLog statement with format specifiers but no args passed   NSLog   Some silly log message   -        Fixed by  NSLog   Some silly log message   -     someObj1  someObj2

[ios] EXC_BAD_ACCESS signal received

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