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  • C++ Exception Handling

    - by user1413793
    So I was writing some code and I noticed that apart from syntactical, type, and other compile-time errors, C++ does not throw any other exceptions. So I decided to test this out with a very trivial program: #include<iostream> int main() { std::count<<5/0<<std::endl; return 1 } When I compiled it using g++, g++ gave me a warning saying I was dividing by 0. But it still compiled the code. Then when I ran it, it printed some really large arbitrary number. When I want to know is, how does C++ deal with exceptions? Integer division by 0 should be a very trivial example of when an exception should be thrown and the program should terminate. Do I have to essentially enclose my entire program in a huge try block and then catch certain exceptions? I know in Python when an exception is thrown, the program will immediately terminate and print out the error. What does C++ do? Are there even runtime exceptions which stop execution and kill the program?

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  • Assembly keep getting seg fault when working with stack [migrated]

    - by user973917
    I'm trying to learn assembly and have found that I keep getting segfaults when trying to push/pop data off of the stack. I've read a few guides and know how the stack works and how to work with the stack; but don't know why I keep getting the error. Can someone help? segment .data myvar: db "hello world", 0xA0, 0 myvarL: equ $-myvar segment .text global _start _start: push ebp mov ebp, esp push myvarL push myvar call _hworld _hworld: mov eax, 4 mov ebx, 1 mov ecx, [ebp+4] mov edx, [ebp+8] pop ebp int 0x80 ret I'm assuming that the +4 is 32 bits, then +8 is 64 bits. It isn't really clear to me why this way is being done on some of the guides I've read. I would assume that myvar is 13 bits?

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  • Cost of creating exception compared to cost of logging it

    - by Sebastien Lorber
    Hello, Just wonder how much cost to raise a java exception (or to call native fillInStackTrace() of Throwable) compared to what it cost to log it with log4j (in a file, with production hard drive)... Asking myself, when exceptions are raised, does it worth to often log them even if they are not necessary significant... (i work in a high load environment) Thanks

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  • Tracking the user function that threw the exception

    - by makerofthings7
    I've been given a large application with only one try..catch at the outer most level. This application also throws exceptions all the time, and is poorly documented. Is there any pattern I can implement that will tell me what user method is being called, the exception being thrown, and also the count of exceptions? I'm thinking of using a dictionary with reflection to get the needed information, but I'm not sure if this will work. What do you think?

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  • How do I implement a fibonacci sequence in java using try/catch logic?

    - by Lars Flyger
    I know how to do it using simple recursion, but in order to complete this particular assignment I need to be able to accumulate on the stack and throw an exception that holds the answer in it. So far I have: public static int fibo(int index) { int sum = 0; try { fibo_aux(index, 1, 1); } catch (IntegerException me) { sum = me.getIntValue(); } return sum; } fibo_aux is supposed to throw an IntegerException (which holds the value of the answer that is retireved via getIntValue) and accumulates the answer on the stack, but so far I can't figure it out. Can anyone help?

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  • Where is this exception caught and handled?

    - by Zaki
    In some code I've been reading, I've come across this : class Someclass { public static void main(String[] args) throws IOException { //all other code here...... } } If main() throws an exception, in this case its an IOException, where is it caught and handled?

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  • calculater by using reverse polish notation and using a stack

    - by programmer
    hello everyone I have a segmentation fault ,can you help please? if i have this operater "3 5 +" that mean 3+5 and like "9 8 * 5 + 4 + sin", "sin(((9*8)+5)+4)" so my idea is check if the first and second are numbers and push theem in the stack then when i have operator i pop the numbers and make the calculation then push the answer again. ` typedef struct st_node { float val; struct st_node *next; } t_node; typedef t_node t_stack; // a function to allocate memory for a stack and returns the stack t_stack* fnewCell() { t_stack* ret; ret = (t_stack*) malloc(sizeof(t_stack)); return ret; } // a function to allocate memory for a stack, fills it with value v and pointer n , and returns the stack t_stack* fnewCellFilled(float v, t_stack* n) { t_stack* ret; ret = fnewCell(); ret->val = v; ret->next =n; return ret; } //function to initialize stack void initstack(t_stack** stack) { fnewCellFilled(0,NULL); } // add new cell void insrtHead(t_stack** head,float val) { *head = fnewCellFilled(val,*head); } //function to push the value v into the stack s void push(t_stack **s, float val) { insrtHead(s,val); } //function to pop a value from the stack and returns it int pop(t_stack **s) { t_stack* tmp; int ret; tmp = (*s)->next; ret = (*s)->val; free(*s); (*s) = tmp; return ret; } int isempty (t_stack *t) { return t == NULL; } //function to transfer a string(str) to int (value) //returns -1 when success , i otherwise int str2int(char *str,int *value) { int i; *value = 0; int sign=(str[0]=='-' ? -1 : 1); for(i=(str[0]=='-' ? 1 : 0);str[i]!=0;i++) { if(!(str[i]>=48 && str[i]<=57)) // Ascii char 0 to 9 return i; *value= *value*10+(str[i]-48); } *value = *value * sign; return -1; } //a function that takes a string, transfer it into integer and make operation using a stack void function(t_stack *stack, char *str) { char x[10]=" "; int y,j,i=0,z; printf("++\n"); if(str[i] != '\0') { strcpy(x, strtok(str, " ")); z= str2int(x, &y); if(z == -1) { push(&stack,y); i=i+2; } } while(str[i] != '\0') { strcpy(x, strtok(NULL, " ")); z= str2int(x, &y); if(z == -1) { printf("yes %d",y); push(&stack,y); i=i+2; } else { y=pop(&stack); j=pop(&stack); if(x[0] == '+' ) push(&stack,y+j); else if (x[0] == '-' ) push(&stack,j-y); else if(x[0] == '*' ) push(&stack,j*y); else if(x[0] == '/') push (&stack ,j/y); } } } int main() { t_stack *s; initstack(&s); char *str="3 5 +"; function(s,str); return 0; } `

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  • Getting the innermost .NET Exception

    - by Rick Strahl
    Here's a trivial but quite useful function that I frequently need in dynamic execution of code: Finding the innermost exception when an exception occurs, because for many operations (for example Reflection invocations or Web Service calls) the top level errors returned can be rather generic. A good example - common with errors in Reflection making a method invocation - is this generic error: Exception has been thrown by the target of an invocation In the debugger it looks like this: In this case this is an AJAX callback, which dynamically executes a method (ExecuteMethod code) which in turn calls into an Amazon Web Service using the old Amazon WSE101 Web service extensions for .NET. An error occurs in the Web Service call and the innermost exception holds the useful error information which in this case points at an invalid web.config key value related to the System.Net connection APIs. The "Exception has been thrown by the target of an invocation" error is the Reflection APIs generic error message that gets fired when you execute a method dynamically and that method fails internally. The messages basically says: "Your code blew up in my face when I tried to run it!". Which of course is not very useful to tell you what actually happened. If you drill down the InnerExceptions eventually you'll get a more detailed exception that points at the original error and code that caused the exception. In the code above the actually useful exception is two innerExceptions down. In most (but not all) cases when inner exceptions are returned, it's the innermost exception that has the information that is really useful. It's of course a fairly trivial task to do this in code, but I do it so frequently that I use a small helper method for this: /// <summary> /// Returns the innermost Exception for an object /// </summary> /// <param name="ex"></param> /// <returns></returns> public static Exception GetInnerMostException(Exception ex) { Exception currentEx = ex; while (currentEx.InnerException != null) { currentEx = currentEx.InnerException; } return currentEx; } This code just loops through all the inner exceptions (if any) and assigns them to a temporary variable until there are no more inner exceptions. The end result is that you get the innermost exception returned from the original exception. It's easy to use this code then in a try/catch handler like this (from the example above) to retrieve the more important innermost exception: object result = null; string stringResult = null; try { if (parameterList != null) // use the supplied parameter list result = helper.ExecuteMethod(methodToCall,target, parameterList.ToArray(), CallbackMethodParameterType.Json,ref attr); else // grab the info out of QueryString Values or POST buffer during parameter parsing // for optimization result = helper.ExecuteMethod(methodToCall, target, null, CallbackMethodParameterType.Json, ref attr); } catch (Exception ex) { Exception activeException = DebugUtils.GetInnerMostException(ex); WriteErrorResponse(activeException.Message, ( HttpContext.Current.IsDebuggingEnabled ? ex.StackTrace : null ) ); return; } Another function that is useful to me from time to time is one that returns all inner exceptions and the original exception as an array: /// <summary> /// Returns an array of the entire exception list in reverse order /// (innermost to outermost exception) /// </summary> /// <param name="ex">The original exception to work off</param> /// <returns>Array of Exceptions from innermost to outermost</returns> public static Exception[] GetInnerExceptions(Exception ex) {     List<Exception> exceptions = new List<Exception>();     exceptions.Add(ex);       Exception currentEx = ex;     while (currentEx.InnerException != null)     {         exceptions.Add(ex);     }       // Reverse the order to the innermost is first     exceptions.Reverse();       return exceptions.ToArray(); } This function loops through all the InnerExceptions and returns them and then reverses the order of the array returning the innermost exception first. This can be useful in certain error scenarios where exceptions stack and you need to display information from more than one of the exceptions in order to create a useful error message. This is rare but certain database exceptions bury their exception info in mutliple inner exceptions and it's easier to parse through them in an array then to manually walk the exception stack. It's also useful if you need to log errors and want to see the all of the error detail from all exceptions. None of this is rocket science, but it's useful to have some helpers that make retrieval of the critical exception info trivial. Resources DebugUtils.cs utility class in the West Wind Web Toolkit© Rick Strahl, West Wind Technologies, 2005-2011Posted in CSharp  .NET  

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  • Trace File Source Adapter

    The Trace File Source adapter is a useful addition to your SSIS toolbox.  It allows you to read 2005 and 2008 profiler traces stored as .trc files and read them into the Data Flow.  From there you can perform filtering and analysis using the power of SSIS. There is no need for a SQL Server connection this just uses the trace file. Example Usages Cache warming for SQL Server Analysis Services Reading the flight recorder Find out the longest running queries on a server Analyze statements for CPU, memory by user or some other criteria you choose Properties The Trace File Source adapter has two properties, both of which combine to control the source trace file that is read at runtime. SQL Server 2005 and SQL Server 2008 trace files are supported for both the Database Engine (SQL Server) and Analysis Services. The properties are managed by the Editor form or can be set directly from the Properties Grid in Visual Studio. Property Type Description AccessMode Enumeration This property determines how the Filename property is interpreted. The values available are: DirectInput Variable Filename String This property holds the path for trace file to load (*.trc). The value is either a full path, or the name of a variable which contains the full path to the trace file, depending on the AccessMode property. Trace Column Definition Hopefully the majority of you can skip this section entirely, but if you encounter some problems processing a trace file this may explain it and allow you to fix the problem. The component is built upon the trace management API provided by Microsoft. Unfortunately API methods that expose the schema of a trace file have known issues and are unreliable, put simply the data often differs from what was specified. To overcome these limitations the component uses  some simple XML files. These files enable the trace column data types and sizing attributes to be overridden. For example SQL Server Profiler or TMO generated structures define EventClass as an integer, but the real value is a string. TraceDataColumnsSQL.xml  - SQL Server Database Engine Trace Columns TraceDataColumnsAS.xml    - SQL Server Analysis Services Trace Columns The files can be found in the %ProgramFiles%\Microsoft SQL Server\100\DTS\PipelineComponents folder, e.g. "C:\Program Files\Microsoft SQL Server\100\DTS\PipelineComponents\TraceDataColumnsSQL.xml" "C:\Program Files\Microsoft SQL Server\100\DTS\PipelineComponents\TraceDataColumnsAS.xml" If at runtime the component encounters a type conversion or sizing error it is most likely due to a discrepancy between the column definition as reported by the API and the actual value encountered. Whilst most common issues have already been fixed through these files we have implemented specific exception traps to direct you to the files to enable you to fix any further issues due to different usage or data scenarios that we have not tested. An example error that you can fix through these files is shown below. Buffer exception writing value to column 'Column Name'. The string value is 999 characters in length, the column is only 111. Columns can be overridden by the TraceDataColumns XML files in "C:\Program Files\Microsoft SQL Server\100\DTS\PipelineComponents\TraceDataColumnsAS.xml". Installation The component is provided as an MSI file which you can download and run to install it. This simply places the files on disk in the correct locations and also installs the assemblies in the Global Assembly Cache as per Microsoft’s recommendations. You may need to restart the SQL Server Integration Services service, as this caches information about what components are installed, as well as restarting any open instances of Business Intelligence Development Studio (BIDS) / Visual Studio that you may be using to build your SSIS packages. Finally you will have to add the transformation to the Visual Studio toolbox manually. Right-click the toolbox, and select Choose Items.... Select the SSIS Data Flow Items tab, and then check the Trace File Source transformation in the Choose Toolbox Items window. This process has been described in detail in the related FAQ entry for How do I install a task or transform component? We recommend you follow best practice and apply the current Microsoft SQL Server Service pack to your SQL Server servers and workstations. Please note that the Microsoft Trace classes used in the component are not supported on 64-bit platforms. To use the Trace File Source on a 64-bit host you need to ensure you have the 32-bit (x86) tools available, and the way you execute your package is setup to use them, please see the help topic 64-bit Considerations for Integration Services for more details. Downloads Trace Sources for SQL Server 2005 -- Trace Sources for SQL Server 2008 Version History SQL Server 2008 Version 2.0.0.382 - SQL Sever 2008 public release. (9 Apr 2009) SQL Server 2005 Version 1.0.0.321 - SQL Server 2005 public release. (18 Nov 2008) -- Screenshots

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  • Trace File Source Adapter

    The Trace File Source adapter is a useful addition to your SSIS toolbox.  It allows you to read 2005 and 2008 profiler traces stored as .trc files and read them into the Data Flow.  From there you can perform filtering and analysis using the power of SSIS. There is no need for a SQL Server connection this just uses the trace file. Example Usages Cache warming for SQL Server Analysis Services Reading the flight recorder Find out the longest running queries on a server Analyze statements for CPU, memory by user or some other criteria you choose Properties The Trace File Source adapter has two properties, both of which combine to control the source trace file that is read at runtime. SQL Server 2005 and SQL Server 2008 trace files are supported for both the Database Engine (SQL Server) and Analysis Services. The properties are managed by the Editor form or can be set directly from the Properties Grid in Visual Studio. Property Type Description AccessMode Enumeration This property determines how the Filename property is interpreted. The values available are: DirectInput Variable Filename String This property holds the path for trace file to load (*.trc). The value is either a full path, or the name of a variable which contains the full path to the trace file, depending on the AccessMode property. Trace Column Definition Hopefully the majority of you can skip this section entirely, but if you encounter some problems processing a trace file this may explain it and allow you to fix the problem. The component is built upon the trace management API provided by Microsoft. Unfortunately API methods that expose the schema of a trace file have known issues and are unreliable, put simply the data often differs from what was specified. To overcome these limitations the component uses  some simple XML files. These files enable the trace column data types and sizing attributes to be overridden. For example SQL Server Profiler or TMO generated structures define EventClass as an integer, but the real value is a string. TraceDataColumnsSQL.xml  - SQL Server Database Engine Trace Columns TraceDataColumnsAS.xml    - SQL Server Analysis Services Trace Columns The files can be found in the %ProgramFiles%\Microsoft SQL Server\100\DTS\PipelineComponents folder, e.g. "C:\Program Files\Microsoft SQL Server\100\DTS\PipelineComponents\TraceDataColumnsSQL.xml" "C:\Program Files\Microsoft SQL Server\100\DTS\PipelineComponents\TraceDataColumnsAS.xml" If at runtime the component encounters a type conversion or sizing error it is most likely due to a discrepancy between the column definition as reported by the API and the actual value encountered. Whilst most common issues have already been fixed through these files we have implemented specific exception traps to direct you to the files to enable you to fix any further issues due to different usage or data scenarios that we have not tested. An example error that you can fix through these files is shown below. Buffer exception writing value to column 'Column Name'. The string value is 999 characters in length, the column is only 111. Columns can be overridden by the TraceDataColumns XML files in "C:\Program Files\Microsoft SQL Server\100\DTS\PipelineComponents\TraceDataColumnsAS.xml". Installation The component is provided as an MSI file which you can download and run to install it. This simply places the files on disk in the correct locations and also installs the assemblies in the Global Assembly Cache as per Microsoft’s recommendations. You may need to restart the SQL Server Integration Services service, as this caches information about what components are installed, as well as restarting any open instances of Business Intelligence Development Studio (BIDS) / Visual Studio that you may be using to build your SSIS packages. Finally you will have to add the transformation to the Visual Studio toolbox manually. Right-click the toolbox, and select Choose Items.... Select the SSIS Data Flow Items tab, and then check the Trace File Source transformation in the Choose Toolbox Items window. This process has been described in detail in the related FAQ entry for How do I install a task or transform component? We recommend you follow best practice and apply the current Microsoft SQL Server Service pack to your SQL Server servers and workstations. Please note that the Microsoft Trace classes used in the component are not supported on 64-bit platforms. To use the Trace File Source on a 64-bit host you need to ensure you have the 32-bit (x86) tools available, and the way you execute your package is setup to use them, please see the help topic 64-bit Considerations for Integration Services for more details. Downloads Trace Sources for SQL Server 2005 -- Trace Sources for SQL Server 2008 Version History SQL Server 2008 Version 2.0.0.382 - SQL Sever 2008 public release. (9 Apr 2009) SQL Server 2005 Version 1.0.0.321 - SQL Server 2005 public release. (18 Nov 2008) -- Screenshots

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  • Java: immutable Stack?

    - by HH
    I chose to use Stacks and Tables before knowing Collections has immutable empty things only for Set, Map and List. Because the size of table does not change after its init: Integer[] table = new Intger[0] I can use the zero-witdh table as an empty table. But I cannot use final or empty Stack to get immutable Stack: No immutability to Stack with Final import java.io.*; import java.util.*; public class TestStack{ public static void main(String[] args) { final Stack<Integer> test = new Stack<Integer>(); Stack<Integer> test2 = new Stack<Integer>(); test.push(37707); test2.push(80437707); //WHY is there not an error to remove an elment // from FINAL stack? System.out.println(test.pop()); System.out.println(test2.pop()); } } Java Api 5 for list interface shows that Stack is an implementing class for list and arraylist, here. The java.coccurrent pkg does not have any immutable Stack data structure. From Stack to some immutable data structure How to get immutable Stack data structure? Can I box it with list? Should I switch my current implementatios from stacks to Lists to get immutable? Which immutable data structure is Very fast with about similar exec time as Stack?

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  • How to implement exception chaining in PHP

    - by Josef Sábl
    Constructor for PHP's exception has third parameter, documentation says: $previous: The previous exception used for the exception chaining. But I can't make it work. My code looks like this: try { throw new Exception('Exception 1', 1001); } catch (Exception $ex) { throw new Exception('Exception 2', 1002, $ex); } I expect Exception 2 to be thrown and I expect that it will have Exception 1 attached. But all I get is: Fatal error: Wrong parameters for Exception([string $exception [, long $code ]]) in ... What am I doing wrong?

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  • Installing a new hardware enablement (HWE) stack in 64 bit Ubuntu

    - by Alexey
    I'd like to install 13.10 (Saucy) hardware enablement (HWE) stack to my Ubuntu 12.04 (64-bit) because I need a newer Linux kernel. This wiki page explains what "hardware enablement stacks" are. Among other things it says: Only the -generic x86 kernel flavor ... will be supported... Also, this answer says: ...This is only recommended for x86 hardware installations... Is x86 here synonymous to 32-bit/i386 architecture (but not 64-bit/AMD64), or is it i386/AMD64 (but not ARM)? Can I install this "hardware enablement stack" in a 64-bit/AMD64 Ubuntu? Will it be supported with future updates?

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  • Migrating from SQL Trace to Extended Events

    - by extended_events
    In SQL Server codenamed “Denali” we are moving our diagnostic tracing capabilities forward by building a system on top of Extended Events. With every new system you face the specter of migration which is always a bit of a hassle. I’m obviously motivated to see everyone move their diagnostic tracing systems over to the new extended events based system, so I wanted to make sure we lowered the bar for the migration process to help ease your trials. In my initial post on Denali CTP 1 I described a couple tables that we created that will help map the existing SQL Trace Event Classes to the equivalent Extended Events events. In this post I’ll describe the tables in a bit more details, explain the relationship between the SQL Trace objects (Event Class & Column) and Extended Event objects (Events & Actions) and at the end provide some sample code for a managed stored procedure that will take an existing SQL Trace session (eg. a trace that you can see in sys.Traces) and converts it into event session DDL. Can you relate? In some ways, SQL Trace and Extended Events is kind of like the Standard and Metric measuring systems in the United States. If you spend too much time trying to figure out how to convert between the two it will probably make your head hurt. It’s often better to just use the new system without trying to translate between the two. That said, people like to relate new things to the things they’re comfortable with, so, with some trepidation, I will now explain how these two systems are related to each other. First, some terms… SQL Trace is made up of Event Classes and Columns. The Event Class occurs as the result of some activity in the database engine, for example, SQL:Batch Completed fires when a batch has completed executing on the server. Each Event Class can have any number of Columns associated with it and those Columns contain the data that is interesting about the Event Class, such as the duration or database name. In Extended Events we have objects named Events, EventData field and Actions. The Event (some people call this an xEvent but I’ll stick with Event) is equivalent to the Event Class in SQL Trace since it is the thing that occurs as the result of some activity taking place in the server. An  EventData field (from now on I’ll just refer to these as fields) is a piece of information that is highly correlated with the event and is always included as part of the schema of an Event. An Action is something that can be associated with any Event and it will cause some additional “action” to occur when ever the parent Event occurs. Actions can do a number of different things for example, there are Actions that collect additional data and, take memory dumps. When mapping SQL Trace onto Extended Events, Columns are covered by a combination of both fields and Actions. Knowing exactly where a Column is covered by a field and where it is covered by an Action is a bit of an art, so we created the mapping tables to make you an Artist without the years of practice. Let me draw you a map. Event Mapping The table dbo.trace_xe_event_map exists in the master database with the following structure: Column_name Type trace_event_id smallint package_name nvarchar xe_event_name nvarchar By joining this table sys.trace_events using trace_event_id and to the sys.dm_xe_objects using xe_event_name you can get a fair amount of information about how Event Classes are related to Events. The most basic query this lends itself to is to match an Event Class with the corresponding Event. SELECT     t.trace_event_id,     t.name [event_class],     e.package_name,     e.xe_event_name FROM sys.trace_events t INNER JOIN dbo.trace_xe_event_map e     ON t.trace_event_id = e.trace_event_id There are a couple things you’ll notice as you peruse the output of this query: For the most part, the names of Events are fairly close to the original Event Class; eg. SP:CacheMiss == sp_cache_miss, and so on. We’ve mostly stuck to a one to one mapping between Event Classes and Events, but there are a few cases where we have combined when it made sense. For example, Data File Auto Grow, Log File Auto Grow, Data File Auto Shrink & Log File Auto Shrink are now all covered by a single event named database_file_size_change. This just seemed like a “smarter” implementation for this type of event, you can get all the same information from this single event (grow/shrink, Data/Log, Auto/Manual growth) without having multiple different events. You can use Predicates if you want to limit the output to just one of the original Event Class measures. There are some Event Classes that did not make the cut and were not migrated. These fall into two categories; there were a few Event Classes that had been deprecated, or that just did not make sense, so we didn’t migrate them. (You won’t find an Event related to mounting a tape – sorry.) The second class is bigger; with rare exception, we did not migrate any of the Event Classes that were related to Security Auditing using SQL Trace. We introduced the SQL Audit feature in SQL Server 2008 and that will be the compliance and auditing feature going forward. Doing this is a very deliberate decision to support separation of duties for DBAs. There are separate permissions required for SQL Audit and Extended Events tracing so you can assign these tasks to different people if you choose. (If you’re wondering, the permission for Extended Events is ALTER ANY EVENT SESSION, which is covered by CONTROL SERVER.) Action Mapping The table dbo.trace_xe_action_map exists in the master database with the following structure: Column_name Type trace_column_id smallint package_name nvarchar xe_action_name nvarchar You can find more details by joining this to sys.trace_columns on the trace_column_id field. SELECT     c.trace_column_id,     c.name [column_name],     a.package_name,     a.xe_action_name FROM sys.trace_columns c INNER JOIN    dbo.trace_xe_action_map a     ON c.trace_column_id = a.trace_column_id If you examine this list, you’ll notice that there are relatively few Actions that map to SQL Trace Columns given the number of Columns that exist. This is not because we forgot to migrate all the Columns, but because much of the data for individual Event Classes is included as part of the EventData fields of the equivalent Events so there is no need to specify them as Actions. Putting it all together If you’ve spent a bunch of time figuring out the inner workings of SQL Trace, and who hasn’t, then you probably know that the typically set of Columns you find associated with any given Event Class in SQL Profiler is not fix, but is determine by the contents of the table sys.trace_event_bindings. We’ve used this table along with the mapping tables to produce a list of Event + Action combinations that duplicate the SQL Profiler Event Class definitions using the following query, which you can also find in the Books Online topic How To: View the Extended Events Equivalents to SQL Trace Event Classes. USE MASTER; GO SELECT DISTINCT    tb.trace_event_id,    te.name AS 'Event Class',    em.package_name AS 'Package',    em.xe_event_name AS 'XEvent Name',    tb.trace_column_id,    tc.name AS 'SQL Trace Column',    am.xe_action_name as 'Extended Events action' FROM (sys.trace_events te LEFT OUTER JOIN dbo.trace_xe_event_map em    ON te.trace_event_id = em.trace_event_id) LEFT OUTER JOIN sys.trace_event_bindings tb    ON em.trace_event_id = tb.trace_event_id LEFT OUTER JOIN sys.trace_columns tc    ON tb.trace_column_id = tc.trace_column_id LEFT OUTER JOIN dbo.trace_xe_action_map am    ON tc.trace_column_id = am.trace_column_id ORDER BY te.name, tc.name As you might imagine, it’s also possible to map an existing trace definition to the equivalent event session by judicious use of fn_trace_geteventinfo joined with the two mapping tables. This query extracts the list of Events and Actions equivalent to the trace with ID = 1, which is most likely the Default Trace. You can find this query, along with a set of other queries and steps required to migrate your existing traces over to Extended Events in the Books Online topic How to: Convert an Existing SQL Trace Script to an Extended Events Session. USE MASTER; GO DECLARE @trace_id int SET @trace_id = 1 SELECT DISTINCT el.eventid, em.package_name, em.xe_event_name AS 'event'    , el.columnid, ec.xe_action_name AS 'action' FROM (sys.fn_trace_geteventinfo(@trace_id) AS el    LEFT OUTER JOIN dbo.trace_xe_event_map AS em       ON el.eventid = em.trace_event_id) LEFT OUTER JOIN dbo.trace_xe_action_map AS ec    ON el.columnid = ec.trace_column_id WHERE em.xe_event_name IS NOT NULL AND ec.xe_action_name IS NOT NULL You’ll notice in the output that the list doesn’t include any of the security audit Event Classes, as I wrote earlier, those were not migrated. But wait…there’s more! If this were an infomercial there’d by some obnoxious guy next to me blogging “Well Mike…that’s pretty neat, but I’m sure you can do more. Can’t you make it even easier to migrate from SQL Trace?”  Needless to say, I’d blog back, in an overly excited way, “You bet I can' obnoxious blogger side-kick!” What I’ve got for you here is a Extended Events Team Blog only special – this tool will not be sold in any store; it’s a special offer for those of you reading the blog. I’ve wrapped all the logic of pulling the configuration information out of an existing trace and and building the Extended Events DDL statement into a handy, dandy CLR stored procedure. Once you load the assembly and register the procedure you just supply the trace id (from sys.traces) and provide a name for the event session. Run the procedure and out pops the DDL required to create an equivalent session. Any aspects of the trace that could not be duplicated are included in comments within the DDL output. This procedure does not actually create the event session – you need to copy the DDL out of the message tab and put it into a new query window to do that. It also requires an existing trace (but it doesn’t have to be running) to evaluate; there is no functionality to parse t-sql scripts. I’m not going to spend a bunch of time explaining the code here – the code is pretty well commented and hopefully easy to follow. If not, you can always post comments or hit the feedback button to send us some mail. Sample code: TraceToExtendedEventDDL   Installing the procedure Just in case you’re not familiar with installing CLR procedures…once you’ve compile the assembly you can load it using a script like this: -- Context to master USE master GO -- Create the assembly from a shared location. CREATE ASSEMBLY TraceToXESessionConverter FROM 'C:\Temp\TraceToXEventSessionConverter.dll' WITH PERMISSION_SET = SAFE GO -- Create a stored procedure from the assembly. CREATE PROCEDURE CreateEventSessionFromTrace @trace_id int, @session_name nvarchar(max) AS EXTERNAL NAME TraceToXESessionConverter.StoredProcedures.ConvertTraceToExtendedEvent GO Enjoy! -Mike

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  • How to simulate inner exception in C++

    - by Siva Chandran
    Basically I want to simulate .NET Exception.InnerException in C++. I want to catch exception from bottom layer and wrap it with another exception and throw again to upper layer. The problem here is I don't know how to wrap the catched exception inside another exception. struct base_exception : public std::exception { std::exception& InnerException; base_exception() : InnerException(???) { } // <---- what to initialize with base_exception(std::exception& innerException) : InnerException(innerException) { } }; struct func1_exception : public base_exception { const char* what() const throw() { return "func1 exception"; } }; struct func2_exception : public base_exception { const char* what() const throw() { return "func2 exception"; } }; void func2() { throw func2_exception(); } void func1() { try { func2(); } catch(std::exception& e) { throw func2_exception(e); // <--- is this correct? will the temporary object will be alive? } } int main(void) { try { func1(); } catch(base_exception& e) { std::cout << "Got exception" << std::endl; std::cout << e.what(); std::cout << "InnerException" << std::endl; std::cout << e.InnerException.what(); // <---- how to make sure it has inner exception ? } } In the above code listing I am not sure how to initialize the "InnerException" member when there is no inner exception. Also I am not sure whether the temporary object that is thrown from func1 will survive even after func2 throw?

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  • Strengthening code with possibly useless exception handling

    - by rdurand
    Is it a good practice to implement useless exception handling, just in case another part of the code is not coded correctly? Basic example A simple one, so I don't loose everybody :). Let's say I'm writing an app that will display a person's information (name, address, etc.), the data being extracted from a database. Let's say I'm the one coding the UI part, and someone else is writing the DB query code. Now imagine that the specifications of your app say that if the person's information is incomplete (let's say, the name is missing in the database), the person coding the query should handle this by returning "NA" for the missing field. What if the query is poorly coded and doesn't handle this case? What if the guy who wrote the query handles you an incomplete result, and when you try to display the informations, everything crashes, because your code isn't prepared to display empty stuff? This example is very basic. I believe most of you will say "it's not your problem, you're not responsible for this crash". But, it's still your part of the code which is crashing. Another example Let's say now I'm the one writing the query. The specifications don't say the same as above, but that the guy writing the "insert" query should make sure all the fields are complete when adding a person to the database to avoid inserting incomplete information. Should I protect my "select" query to make sure I give the UI guy complete informations? The questions What if the specifications don't explicitly say "this guy is the one in charge of handling this situation"? What if a third person implements another query (similar to the first one, but on another DB) and uses your UI code to display it, but doesn't handle this case in his code? Should I do what's necessary to prevent a possible crash, even if I'm not the one supposed to handle the bad case? I'm not looking for an answer like "(s)he's the one responsible for the crash", as I'm not solving a conflict here, I'd like to know, should I protect my code against situations it's not my responsibility to handle? Here, a simple "if empty do something" would suffice. In general, this question tackles redundant exception handling. I'm asking it because when I work alone on a project, I may code 2-3 times a similar exception handling in successive functions, "just in case" I did something wrong and let a bad case come through.

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  • .NET Single Line Logging (ala Trace.Write/WriteLine) using Instrumentation.Logging

    - by KnownColor
    Hello Everyone, My question is whether it is possible to get line/multiline (very unsure of correct term for this) behaviour of the Trace.Write and Trace.WriteLine methods but using the Microsoft Instrumentation Logging framework in .NET 2.0. Desired Output Hello World! Oh Hai. What I Currently Have Trace.Write("Hello "); Trace.WriteLine("World!"); Trace.Write("Oh Hai."); I would prefer to use instrumentation to log rather than writing to a log file using Debug.Trace. EDIT: By Instrumentation Logging I mean using a 'loggingConfiguration' block in my App.config and writing Log Entries using using Microsoft.Practices.EnterpriseLibrary.Logging.Logger.Write(LogEntry logEntry); Microsoft.Practices.EnterpriseLibrary.Logging.Configuration.FlatFileTraceListenerData, Microsoft.Practices.EnterpriseLibrary.Logging, Version=2.0.0.0 for example. Ta, KnownColor

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  • ASP.NET Web API Exception Handling

    - by Fredrik N
    When I talk about exceptions in my product team I often talk about two kind of exceptions, business and critical exceptions. Business exceptions are exceptions thrown based on “business rules”, for example if you aren’t allowed to do a purchase. Business exceptions in most case aren’t important to log into a log file, they can directly be shown to the user. An example of a business exception could be "DeniedToPurchaseException”, or some validation exceptions such as “FirstNameIsMissingException” etc. Critical Exceptions are all other kind of exceptions such as the SQL server is down etc. Those kind of exception message need to be logged and should not reach the user, because they can contain information that can be harmful if it reach out to wrong kind of users. I often distinguish business exceptions from critical exceptions by creating a base class called BusinessException, then in my error handling code I catch on the type BusinessException and all other exceptions will be handled as critical exceptions. This blog post will be about different ways to handle exceptions and how Business and Critical Exceptions could be handled. Web API and Exceptions the basics When an exception is thrown in a ApiController a response message will be returned with a status code set to 500 and a response formatted by the formatters based on the “Accept” or “Content-Type” HTTP header, for example JSON or XML. Here is an example:   public IEnumerable<string> Get() { throw new ApplicationException("Error!!!!!"); return new string[] { "value1", "value2" }; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } The response message will be: HTTP/1.1 500 Internal Server Error Content-Length: 860 Content-Type: application/json; charset=utf-8 { "ExceptionType":"System.ApplicationException","Message":"Error!!!!!","StackTrace":" at ..."} .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The stack trace will be returned to the client, this is because of making it easier to debug. Be careful so you don’t leak out some sensitive information to the client. So as long as you are developing your API, this is not harmful. In a production environment it can be better to log exceptions and return a user friendly exception instead of the original exception. There is a specific exception shipped with ASP.NET Web API that will not use the formatters based on the “Accept” or “Content-Type” HTTP header, it is the exception is the HttpResponseException class. Here is an example where the HttpReponseExcetpion is used: // GET api/values [ExceptionHandling] public IEnumerable<string> Get() { throw new HttpResponseException(new HttpResponseMessage(HttpStatusCode.InternalServerError)); return new string[] { "value1", "value2" }; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } The response will not contain any content, only header information and the status code based on the HttpStatusCode passed as an argument to the HttpResponseMessage. Because the HttpResponsException takes a HttpResponseMessage as an argument, we can give the response a content: public IEnumerable<string> Get() { throw new HttpResponseException(new HttpResponseMessage(HttpStatusCode.InternalServerError) { Content = new StringContent("My Error Message"), ReasonPhrase = "Critical Exception" }); return new string[] { "value1", "value2" }; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The code above will have the following response:   HTTP/1.1 500 Critical Exception Content-Length: 5 Content-Type: text/plain; charset=utf-8 My Error Message .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } The Content property of the HttpResponseMessage doesn’t need to be just plain text, it can also be other formats, for example JSON, XML etc. By using the HttpResponseException we can for example catch an exception and throw a user friendly exception instead: public IEnumerable<string> Get() { try { DoSomething(); return new string[] { "value1", "value2" }; } catch (Exception e) { throw new HttpResponseException(new HttpResponseMessage(HttpStatusCode.InternalServerError) { Content = new StringContent("An error occurred, please try again or contact the administrator."), ReasonPhrase = "Critical Exception" }); } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Adding a try catch to every ApiController methods will only end in duplication of code, by using a custom ExceptionFilterAttribute or our own custom ApiController base class we can reduce code duplicationof code and also have a more general exception handler for our ApiControllers . By creating a custom ApiController’s and override the ExecuteAsync method, we can add a try catch around the base.ExecuteAsync method, but I prefer to skip the creation of a own custom ApiController, better to use a solution that require few files to be modified. The ExceptionFilterAttribute has a OnException method that we can override and add our exception handling. Here is an example: using System; using System.Diagnostics; using System.Net; using System.Net.Http; using System.Web.Http; using System.Web.Http.Filters; public class ExceptionHandlingAttribute : ExceptionFilterAttribute { public override void OnException(HttpActionExecutedContext context) { if (context.Exception is BusinessException) { throw new HttpResponseException(new HttpResponseMessage(HttpStatusCode.InternalServerError) { Content = new StringContent(context.Exception.Message), ReasonPhrase = "Exception" }); } //Log Critical errors Debug.WriteLine(context.Exception); throw new HttpResponseException(new HttpResponseMessage(HttpStatusCode.InternalServerError) { Content = new StringContent("An error occurred, please try again or contact the administrator."), ReasonPhrase = "Critical Exception" }); } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Note: Something to have in mind is that the ExceptionFilterAttribute will be ignored if the ApiController action method throws a HttpResponseException. The code above will always make sure a HttpResponseExceptions will be returned, it will also make sure the critical exceptions will show a more user friendly message. The OnException method can also be used to log exceptions. By using a ExceptionFilterAttribute the Get() method in the previous example can now look like this: public IEnumerable<string> Get() { DoSomething(); return new string[] { "value1", "value2" }; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } To use the an ExceptionFilterAttribute, we can for example add the ExceptionFilterAttribute to our ApiControllers methods or to the ApiController class definition, or register it globally for all ApiControllers. You can read more about is here. Note: If something goes wrong in the ExceptionFilterAttribute and an exception is thrown that is not of type HttpResponseException, a formatted exception will be thrown with stack trace etc to the client. How about using a custom IHttpActionInvoker? We can create our own IHTTPActionInvoker and add Exception handling to the invoker. The IHttpActionInvoker will be used to invoke the ApiController’s ExecuteAsync method. Here is an example where the default IHttpActionInvoker, ApiControllerActionInvoker, is used to add exception handling: public class MyApiControllerActionInvoker : ApiControllerActionInvoker { public override Task<HttpResponseMessage> InvokeActionAsync(HttpActionContext actionContext, System.Threading.CancellationToken cancellationToken) { var result = base.InvokeActionAsync(actionContext, cancellationToken); if (result.Exception != null && result.Exception.GetBaseException() != null) { var baseException = result.Exception.GetBaseException(); if (baseException is BusinessException) { return Task.Run<HttpResponseMessage>(() => new HttpResponseMessage(HttpStatusCode.InternalServerError) { Content = new StringContent(baseException.Message), ReasonPhrase = "Error" }); } else { //Log critical error Debug.WriteLine(baseException); return Task.Run<HttpResponseMessage>(() => new HttpResponseMessage(HttpStatusCode.InternalServerError) { Content = new StringContent(baseException.Message), ReasonPhrase = "Critical Error" }); } } return result; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } You can register the IHttpActionInvoker with your own IoC to resolve the MyApiContollerActionInvoker, or add it in the Global.asax: GlobalConfiguration.Configuration.Services.Remove(typeof(IHttpActionInvoker), GlobalConfiguration.Configuration.Services.GetActionInvoker()); GlobalConfiguration.Configuration.Services.Add(typeof(IHttpActionInvoker), new MyApiControllerActionInvoker()); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   How about using a Message Handler for Exception Handling? By creating a custom Message Handler, we can handle error after the ApiController and the ExceptionFilterAttribute is invoked and in that way create a global exception handler, BUT, the only thing we can take a look at is the HttpResponseMessage, we can’t add a try catch around the Message Handler’s SendAsync method. The last Message Handler that will be used in the Wep API pipe-line is the HttpControllerDispatcher and this Message Handler is added to the HttpServer in an early stage. The HttpControllerDispatcher will use the IHttpActionInvoker to invoke the ApiController method. The HttpControllerDipatcher has a try catch that will turn ALL exceptions into a HttpResponseMessage, so that is the reason why a try catch around the SendAsync in a custom Message Handler want help us. If we create our own Host for the Wep API we could create our own custom HttpControllerDispatcher and add or exception handler to that class, but that would be little tricky but is possible. We can in a Message Handler take a look at the HttpResponseMessage’s IsSuccessStatusCode property to see if the request has failed and if we throw the HttpResponseException in our ApiControllers, we could use the HttpResponseException and give it a Reason Phrase and use that to identify business exceptions or critical exceptions. I wouldn’t add an exception handler into a Message Handler, instead I should use the ExceptionFilterAttribute and register it globally for all ApiControllers. BUT, now to another interesting issue. What will happen if we have a Message Handler that throws an exception?  Those exceptions will not be catch and handled by the ExceptionFilterAttribute. I found a  bug in my previews blog post about “Log message Request and Response in ASP.NET WebAPI” in the MessageHandler I use to log incoming and outgoing messages. Here is the code from my blog before I fixed the bug:   public abstract class MessageHandler : DelegatingHandler { protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) { var corrId = string.Format("{0}{1}", DateTime.Now.Ticks, Thread.CurrentThread.ManagedThreadId); var requestInfo = string.Format("{0} {1}", request.Method, request.RequestUri); var requestMessage = await request.Content.ReadAsByteArrayAsync(); await IncommingMessageAsync(corrId, requestInfo, requestMessage); var response = await base.SendAsync(request, cancellationToken); var responseMessage = await response.Content.ReadAsByteArrayAsync(); await OutgoingMessageAsync(corrId, requestInfo, responseMessage); return response; } protected abstract Task IncommingMessageAsync(string correlationId, string requestInfo, byte[] message); protected abstract Task OutgoingMessageAsync(string correlationId, string requestInfo, byte[] message); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   If a ApiController throws a HttpResponseException, the Content property of the HttpResponseMessage from the SendAsync will be NULL. So a null reference exception is thrown within the MessageHandler. The yellow screen of death will be returned to the client, and the content is HTML and the Http status code is 500. The bug in the MessageHandler was solved by adding a check against the HttpResponseMessage’s IsSuccessStatusCode property: public abstract class MessageHandler : DelegatingHandler { protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) { var corrId = string.Format("{0}{1}", DateTime.Now.Ticks, Thread.CurrentThread.ManagedThreadId); var requestInfo = string.Format("{0} {1}", request.Method, request.RequestUri); var requestMessage = await request.Content.ReadAsByteArrayAsync(); await IncommingMessageAsync(corrId, requestInfo, requestMessage); var response = await base.SendAsync(request, cancellationToken); byte[] responseMessage; if (response.IsSuccessStatusCode) responseMessage = await response.Content.ReadAsByteArrayAsync(); else responseMessage = Encoding.UTF8.GetBytes(response.ReasonPhrase); await OutgoingMessageAsync(corrId, requestInfo, responseMessage); return response; } protected abstract Task IncommingMessageAsync(string correlationId, string requestInfo, byte[] message); protected abstract Task OutgoingMessageAsync(string correlationId, string requestInfo, byte[] message); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } If we don’t handle the exceptions that can occur in a custom Message Handler, we can have a hard time to find the problem causing the exception. The savior in this case is the Global.asax’s Application_Error: protected void Application_Error() { var exception = Server.GetLastError(); Debug.WriteLine(exception); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } I would recommend you to add the Application_Error to the Global.asax and log all exceptions to make sure all kind of exception is handled. Summary There are different ways we could add Exception Handling to the Wep API, we can use a custom ApiController, ExceptionFilterAttribute, IHttpActionInvoker or Message Handler. The ExceptionFilterAttribute would be a good place to add a global exception handling, require very few modification, just register it globally for all ApiControllers, even the IHttpActionInvoker can be used to minimize the modifications of files. Adding the Application_Error to the global.asax is a good way to catch all unhandled exception that can occur, for example exception thrown in a Message Handler.   If you want to know when I have posted a blog post, you can follow me on twitter @fredrikn

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  • Catching a nested-in-template exception [C++]

    - by Karol
    Hello, I have a problem with writing a catch clause for an exception that is a class nested in a template. To be more specific, I have a following definition of the template and exception: /** Generic stack implementation. Accepts std::list, std::deque and std::vector as inner container. */ template < typename T, template < typename Element, typename = std::allocator<Element> > class Container = std::deque > class stack { public: class StackEmptyException { }; ... /** Returns value from the top of the stack. Throws StackEmptyException when the stack is empty. */ T top() const; ... } I have a following template method that I want exception to catch: template <typename Stack> void testTopThrowsStackEmptyExceptionOnEmptyStack() { Stack stack; std::cout << "Testing top throws StackEmptyException on empty stack..."; try { stack.top(); } catch (Stack::StackEmptyException) { // as expected. } std::cout << "success." << std::endl; } When I compile it (-Wall, -pedantic) I get the following error: In function ‘void testTopThrowsStackEmptyExceptionOnEmptyStack()’: error: expected type-specifier error: expected unqualified-id before ‘)’ token === Build finished: 2 errors, 0 warnings === Thanks in advance for any help! What is interesting, if the stack implementation was not a template, then the compiler would accept the code as it is.

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  • How are exceptions allocated on the stack caught beyond their scope?

    - by John Doe
    In the following code, the stack-based variable 'ex' is thrown and caught in a function beyond the scope in which ex was declared. This seems a bit strange to me, since (AFAIK) stack-based variables cannot be used outside the scope in which they were declared (the stack is unwound). void f() { SomeKindOfException ex(...); throw ex; } void g() { try { f(); } catch (SomeKindOfException& ex) { //Handling code... } } I've added a print statement to SomeKindOfException's destructor and it shows that ex is destructed once it goes out of scope in f() but then it's caught in g() and destructed again once it goes out of scope there as well. Any help?

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