C catching all exceptions

Question

Is there a c   equivalent of Java s  try             catch  Throwable t                I am trying to debug Java jni code that calls native windows functions and the virtual machine keeps crashing   The native code appears fine in unit testing and only seems to crash when called through jni   A generic exception catching mechanism would prove extremely useful

User · Answer

For the real problem about being unable to properly debug a program that uses JNI (or the bug does not appear when running it under a debugger):

In this case it often helps to add Java wrappers around your JNI calls (i.e. all native methods are private and your public methods in the class call them) that do some basic sanity checking (check that all "objects" are freed and "objects" are not used after freeing) or synchronization (just synchronize all methods from one DLL to a single object instance). Let the java wrapper methods log the mistake and throw an exception.

This will often help to find the real error (which surprisingly is mostly in the Java code that does not obey the semantics of the called functions causing some nasty double-frees or similar) more easily than trying to debug a massively parallel Java program in a native debugger...

If you know the cause, keep the code in your wrapper methods that avoids it. Better have your wrapper methods throw exceptions than your JNI code crash the VM...

User · Answer

Be aware   try           catch                    catches only language-level exceptions  other low-level exceptions errors like Access Violation and Segmentation Fault wont be caught

User · Answer

Let me just mention this here  the Java  try          catch  Exception e            may NOT catch all exceptions   I ve actually had this sort of thing happen before  and it s insantiy-provoking  Exception derives from Throwable   So literally  to catch everything  you DON T want to catch Exceptions  you want to catch Throwable   I know it sounds nitpicky  but when you ve spent several days trying to figure out where the  uncaught exception  came from in code that was surrounded by a try     catch  Exception e   block comes from  it sticks with you

User · Answer

try               catch                       Note that the     inside the catch is a real ellipsis  ie  three dots   However  because C   exceptions are not necessarily subclasses of a base Exception class  there isn t any way to actually see the exception variable that is thrown when using this construct

User · Answer

A generic exception catching mechanism   would prove extremely useful    Doubtful  You already know your code is broken  because it s crashing  Eating exceptions may mask this  but that ll probably just result in even nastier  more subtle bugs    What you really want is a debugger

User · Answer

Can you run your JNI-using Java application from a console window  launch it from a java command line  to see if there is any report of what may have been detected before the JVM was crashed   When running directly as a Java window application  you may be missing messages that would appear if you ran from a console window instead  Secondly  can you stub your JNI DLL implementation to show that methods in your DLL are being entered from JNI  you are returning properly  etc    Just in case the problem is with an incorrect use of one of the JNI-interface methods from the C   code  have you verified that some simple JNI examples compile and work with your setup   I m thinking in particular of using the JNI-interface methods for converting parameters to native C   formats and turning function results into Java types   It is useful to stub those to make sure that the data conversions are working and you are not going haywire in the COM-like calls into the JNI interface  There are other things to check  but it is hard to suggest any without knowing more about what your native Java methods are and what the JNI implementation of them is trying to do   It is not clear that catching an exception from the C   code level is related to your problem    You can use the JNI interface to rethrow the exception as a Java one  but it is not clear from what you provide that this is going to help

User · Answer

it is possible to do this by writing   try                 catch          lt  lt - catch all                   But there is a very not noticeable risk here  you can not find the exact type of error that has been thrown in the try block  so use this kind of catch when you are sure that no matter what the type of exception is  the program must persist in the way defined in the catch block

User · Answer

Let me just mention this here  the Java  try          catch  Exception e            may NOT catch all exceptions   I ve actually had this sort of thing happen before  and it s insantiy-provoking  Exception derives from Throwable   So literally  to catch everything  you DON T want to catch Exceptions  you want to catch Throwable   I know it sounds nitpicky  but when you ve spent several days trying to figure out where the  uncaught exception  came from in code that was surrounded by a try     catch  Exception e   block comes from  it sticks with you

User · Answer

Can you run your JNI-using Java application from a console window  launch it from a java command line  to see if there is any report of what may have been detected before the JVM was crashed   When running directly as a Java window application  you may be missing messages that would appear if you ran from a console window instead  Secondly  can you stub your JNI DLL implementation to show that methods in your DLL are being entered from JNI  you are returning properly  etc    Just in case the problem is with an incorrect use of one of the JNI-interface methods from the C   code  have you verified that some simple JNI examples compile and work with your setup   I m thinking in particular of using the JNI-interface methods for converting parameters to native C   formats and turning function results into Java types   It is useful to stub those to make sure that the data conversions are working and you are not going haywire in the COM-like calls into the JNI interface  There are other things to check  but it is hard to suggest any without knowing more about what your native Java methods are and what the JNI implementation of them is trying to do   It is not clear that catching an exception from the C   code level is related to your problem    You can use the JNI interface to rethrow the exception as a Java one  but it is not clear from what you provide that this is going to help

User · Answer

Someone should add that one cannot catch  crashes  in C   code  Those don t throw exceptions  but do anything they like  When you see a program crashing because of say a null-pointer dereference  it s doing undefined behavior  There is no std  null pointer exception  Trying to catch exceptions won t help there   Just for the case someone is reading this thread and thinks he can get the cause of the program crashes  A Debugger like gdb should be used instead

User · Answer

You can use   catch        but that is very dangerous   In his book Debugging Windows  John Robbins tells a war story about a really nasty bug that was masked by a catch      command   You re much better off catching specific exceptions   Catch whatever you think your try block might reasonably throw  but let the code throw an exception higher up if something really unexpected happens

User · Answer

try               catch                        will catch all C   exceptions  but it should be considered bad design   You can use c  11 s new current exception mechanism  but if you don t have the ability to use c  11  legacy code systems requiring a rewrite   then you have no named exception pointer to use  to get a message or name   You may want to add separate catch clauses for the various exceptions you can catch  and only catch everything at the bottom to record an unexpected exception   E g    try               catch  const std  exception amp  ex                 catch  const std  string amp  ex                 catch

User · Answer

try               catch                       Note that the     inside the catch is a real ellipsis  ie  three dots   However  because C   exceptions are not necessarily subclasses of a base Exception class  there isn t any way to actually see the exception variable that is thrown when using this construct

User · Answer

try               catch                        will catch all C   exceptions  but it should be considered bad design   You can use c  11 s new current exception mechanism  but if you don t have the ability to use c  11  legacy code systems requiring a rewrite   then you have no named exception pointer to use  to get a message or name   You may want to add separate catch clauses for the various exceptions you can catch  and only catch everything at the bottom to record an unexpected exception   E g    try               catch  const std  exception amp  ex                 catch  const std  string amp  ex                 catch

User · Answer

it is not possible  in C    to catch all exceptions in a portable manner  This is because some exceptions are not exceptions in a C   context  This includes things like division by zero errors and others  It is possible to hack about and thus get the ability to throw exceptions when these errors happen  but it s not easy to do and certainly not easy to get right in a portable manner   If you want to catch all STL exceptions  you can do  try         catch  const std  exception  amp e            Which will allow you do use e what    which will return a const char   which can tell you more about the exception itself  This is the construct that resembles the Java construct  you asked about  the most   This will not help you if someone is stupid enough to throw an exception that does not inherit from std  exception

User · Answer

it is not possible  in C    to catch all exceptions in a portable manner  This is because some exceptions are not exceptions in a C   context  This includes things like division by zero errors and others  It is possible to hack about and thus get the ability to throw exceptions when these errors happen  but it s not easy to do and certainly not easy to get right in a portable manner   If you want to catch all STL exceptions  you can do  try         catch  const std  exception  amp e            Which will allow you do use e what    which will return a const char   which can tell you more about the exception itself  This is the construct that resembles the Java construct  you asked about  the most   This will not help you if someone is stupid enough to throw an exception that does not inherit from std  exception

User · Answer

it is possible to do this by writing   try                 catch          lt  lt - catch all                   But there is a very not noticeable risk here  you can not find the exact type of error that has been thrown in the try block  so use this kind of catch when you are sure that no matter what the type of exception is  the program must persist in the way defined in the catch block

User · Answer

You can use   catch        but that is very dangerous   In his book Debugging Windows  John Robbins tells a war story about a really nasty bug that was masked by a catch      command   You re much better off catching specific exceptions   Catch whatever you think your try block might reasonably throw  but let the code throw an exception higher up if something really unexpected happens

User · Answer

In short  use catch       However  note that catch      is meant to be used in conjunction with throw  basically   try      foo   new Foo      bar   new Bar    catch               will catch all possible errors thrown          delete foo      delete bar      throw           throw the same error again to be handled somewhere else     This is the proper way to use catch

User · Answer

Well  if you would like to catch all exception to create a minidump for example     Somebody did the work on Windows   See http   www codeproject com Articles 207464 Exception-Handling-in-Visual-Cplusplus In the article  he explains how he found out how to catch all kind of exceptions and he provides code that works   Here is the list you can catch    SEH exception  terminate  unexpected  pure virtual method call  invalid parameter  new operator fault   SIGABR  SIGFPE  SIGILL  SIGINT  SIGSEGV  SIGTERM  Raised exception C   typed exception   And the usage  CCrashHandler ch  ch SetProcessExceptionHandlers       do this for one thread ch SetThreadExceptionHandlers       for each thred    By default  this creates a minidump in the current directory  crashdump dmp

User · Answer

Can you run your JNI-using Java application from a console window  launch it from a java command line  to see if there is any report of what may have been detected before the JVM was crashed   When running directly as a Java window application  you may be missing messages that would appear if you ran from a console window instead  Secondly  can you stub your JNI DLL implementation to show that methods in your DLL are being entered from JNI  you are returning properly  etc    Just in case the problem is with an incorrect use of one of the JNI-interface methods from the C   code  have you verified that some simple JNI examples compile and work with your setup   I m thinking in particular of using the JNI-interface methods for converting parameters to native C   formats and turning function results into Java types   It is useful to stub those to make sure that the data conversions are working and you are not going haywire in the COM-like calls into the JNI interface  There are other things to check  but it is hard to suggest any without knowing more about what your native Java methods are and what the JNI implementation of them is trying to do   It is not clear that catching an exception from the C   code level is related to your problem    You can use the JNI interface to rethrow the exception as a Java one  but it is not clear from what you provide that this is going to help

User · Answer

try               catch                        will catch all C   exceptions  but it should be considered bad design   You can use c  11 s new current exception mechanism  but if you don t have the ability to use c  11  legacy code systems requiring a rewrite   then you have no named exception pointer to use  to get a message or name   You may want to add separate catch clauses for the various exceptions you can catch  and only catch everything at the bottom to record an unexpected exception   E g    try               catch  const std  exception amp  ex                 catch  const std  string amp  ex                 catch

User · Answer

Be aware   try           catch                    catches only language-level exceptions  other low-level exceptions errors like Access Violation and Segmentation Fault wont be caught

User · Answer

A generic exception catching mechanism   would prove extremely useful    Doubtful  You already know your code is broken  because it s crashing  Eating exceptions may mask this  but that ll probably just result in even nastier  more subtle bugs    What you really want is a debugger

User · Answer

try               catch                        will catch all C   exceptions  but it should be considered bad design   You can use c  11 s new current exception mechanism  but if you don t have the ability to use c  11  legacy code systems requiring a rewrite   then you have no named exception pointer to use  to get a message or name   You may want to add separate catch clauses for the various exceptions you can catch  and only catch everything at the bottom to record an unexpected exception   E g    try               catch  const std  exception amp  ex                 catch  const std  string amp  ex                 catch

User · Answer

Someone should add that one cannot catch  crashes  in C   code  Those don t throw exceptions  but do anything they like  When you see a program crashing because of say a null-pointer dereference  it s doing undefined behavior  There is no std  null pointer exception  Trying to catch exceptions won t help there   Just for the case someone is reading this thread and thinks he can get the cause of the program crashes  A Debugger like gdb should be used instead

User · Answer

This is how you can reverse-engineer the exception type from within catch      should you need to  may be useful when catching unknown from a third party library  with GCC    include  lt iostream gt    include  lt exception gt   include  lt typeinfo gt   include  lt stdexcept gt   int main         try           throw         throw something           catch                    std  exception ptr p   std  current exception            std  clog  lt  lt  p   p   cxa exception type  - gt name      null    lt  lt  std  endl            return 1      and if you can afford using Boost you can make your catch section even simpler  on the outside  and potentially cross-platform  catch             std  clog  lt  lt  boost  current exception diagnostic information    lt  lt  std  endl

User · Answer

Someone should add that one cannot catch  crashes  in C   code  Those don t throw exceptions  but do anything they like  When you see a program crashing because of say a null-pointer dereference  it s doing undefined behavior  There is no std  null pointer exception  Trying to catch exceptions won t help there   Just for the case someone is reading this thread and thinks he can get the cause of the program crashes  A Debugger like gdb should be used instead

User · Answer

Let me just mention this here  the Java  try          catch  Exception e            may NOT catch all exceptions   I ve actually had this sort of thing happen before  and it s insantiy-provoking  Exception derives from Throwable   So literally  to catch everything  you DON T want to catch Exceptions  you want to catch Throwable   I know it sounds nitpicky  but when you ve spent several days trying to figure out where the  uncaught exception  came from in code that was surrounded by a try     catch  Exception e   block comes from  it sticks with you

User · Answer

Let me just mention this here  the Java  try          catch  Exception e            may NOT catch all exceptions   I ve actually had this sort of thing happen before  and it s insantiy-provoking  Exception derives from Throwable   So literally  to catch everything  you DON T want to catch Exceptions  you want to catch Throwable   I know it sounds nitpicky  but when you ve spent several days trying to figure out where the  uncaught exception  came from in code that was surrounded by a try     catch  Exception e   block comes from  it sticks with you

User · Answer

Well this really depends on the compiler environment  gcc does not catch these  Visual Studio and the last Borland that I used did   So the conclusion about crashes is that it depends on the quality of your development environment   The C   specification says that catch      must catch any exceptions  but it doesn t in all cases   At least from what I tried

User · Answer

For the real problem about being unable to properly debug a program that uses JNI (or the bug does not appear when running it under a debugger):

In this case it often helps to add Java wrappers around your JNI calls (i.e. all native methods are private and your public methods in the class call them) that do some basic sanity checking (check that all "objects" are freed and "objects" are not used after freeing) or synchronization (just synchronize all methods from one DLL to a single object instance). Let the java wrapper methods log the mistake and throw an exception.

This will often help to find the real error (which surprisingly is mostly in the Java code that does not obey the semantics of the called functions causing some nasty double-frees or similar) more easily than trying to debug a massively parallel Java program in a native debugger...

If you know the cause, keep the code in your wrapper methods that avoids it. Better have your wrapper methods throw exceptions than your JNI code crash the VM...

User · Answer

A generic exception catching mechanism   would prove extremely useful    Doubtful  You already know your code is broken  because it s crashing  Eating exceptions may mask this  but that ll probably just result in even nastier  more subtle bugs    What you really want is a debugger

User · Answer

Someone should add that one cannot catch  crashes  in C   code  Those don t throw exceptions  but do anything they like  When you see a program crashing because of say a null-pointer dereference  it s doing undefined behavior  There is no std  null pointer exception  Trying to catch exceptions won t help there   Just for the case someone is reading this thread and thinks he can get the cause of the program crashes  A Debugger like gdb should be used instead

User · Answer

You can use   catch        but that is very dangerous   In his book Debugging Windows  John Robbins tells a war story about a really nasty bug that was masked by a catch      command   You re much better off catching specific exceptions   Catch whatever you think your try block might reasonably throw  but let the code throw an exception higher up if something really unexpected happens

User · Answer

Well  if you would like to catch all exception to create a minidump for example     Somebody did the work on Windows   See http   www codeproject com Articles 207464 Exception-Handling-in-Visual-Cplusplus In the article  he explains how he found out how to catch all kind of exceptions and he provides code that works   Here is the list you can catch    SEH exception  terminate  unexpected  pure virtual method call  invalid parameter  new operator fault   SIGABR  SIGFPE  SIGILL  SIGINT  SIGSEGV  SIGTERM  Raised exception C   typed exception   And the usage  CCrashHandler ch  ch SetProcessExceptionHandlers       do this for one thread ch SetThreadExceptionHandlers       for each thred    By default  this creates a minidump in the current directory  crashdump dmp

User · Answer

You can use   catch        but that is very dangerous   In his book Debugging Windows  John Robbins tells a war story about a really nasty bug that was masked by a catch      command   You re much better off catching specific exceptions   Catch whatever you think your try block might reasonably throw  but let the code throw an exception higher up if something really unexpected happens

User · Answer

This is how you can reverse-engineer the exception type from within catch      should you need to  may be useful when catching unknown from a third party library  with GCC    include  lt iostream gt    include  lt exception gt   include  lt typeinfo gt   include  lt stdexcept gt   int main         try           throw         throw something           catch                    std  exception ptr p   std  current exception            std  clog  lt  lt  p   p   cxa exception type  - gt name      null    lt  lt  std  endl            return 1      and if you can afford using Boost you can make your catch section even simpler  on the outside  and potentially cross-platform  catch             std  clog  lt  lt  boost  current exception diagnostic information    lt  lt  std  endl

User · Answer

Can you run your JNI-using Java application from a console window  launch it from a java command line  to see if there is any report of what may have been detected before the JVM was crashed   When running directly as a Java window application  you may be missing messages that would appear if you ran from a console window instead  Secondly  can you stub your JNI DLL implementation to show that methods in your DLL are being entered from JNI  you are returning properly  etc    Just in case the problem is with an incorrect use of one of the JNI-interface methods from the C   code  have you verified that some simple JNI examples compile and work with your setup   I m thinking in particular of using the JNI-interface methods for converting parameters to native C   formats and turning function results into Java types   It is useful to stub those to make sure that the data conversions are working and you are not going haywire in the COM-like calls into the JNI interface  There are other things to check  but it is hard to suggest any without knowing more about what your native Java methods are and what the JNI implementation of them is trying to do   It is not clear that catching an exception from the C   code level is related to your problem    You can use the JNI interface to rethrow the exception as a Java one  but it is not clear from what you provide that this is going to help

User · Answer

In short  use catch       However  note that catch      is meant to be used in conjunction with throw  basically   try      foo   new Foo      bar   new Bar    catch               will catch all possible errors thrown          delete foo      delete bar      throw           throw the same error again to be handled somewhere else     This is the proper way to use catch

User · Answer

A generic exception catching mechanism   would prove extremely useful    Doubtful  You already know your code is broken  because it s crashing  Eating exceptions may mask this  but that ll probably just result in even nastier  more subtle bugs    What you really want is a debugger

User · Answer

try               catch                       Note that the     inside the catch is a real ellipsis  ie  three dots   However  because C   exceptions are not necessarily subclasses of a base Exception class  there isn t any way to actually see the exception variable that is thrown when using this construct

User · Answer

Well this really depends on the compiler environment  gcc does not catch these  Visual Studio and the last Borland that I used did   So the conclusion about crashes is that it depends on the quality of your development environment   The C   specification says that catch      must catch any exceptions  but it doesn t in all cases   At least from what I tried

User · Answer

try               catch                       Note that the     inside the catch is a real ellipsis  ie  three dots   However  because C   exceptions are not necessarily subclasses of a base Exception class  there isn t any way to actually see the exception variable that is thrown when using this construct

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