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  • error handling strategies in C?

    - by Leo
    Given the code below: typedef struct {int a;} test_t; arbitrary_t test_dosomething(test_t* test) { if (test == NULL) { //options: //1. print an error and let it crash //e.g. fprintf(stderr, "null ref at %s:%u", __FILE__, __LINE__); //2. stop the world //e.g. exit(1); //3. return (i.e. function does nothing) //4. attempt to re-init test } printf("%d", test->a); //do something w/ test } I want to get a compiler error if test is ever NULL, but I guess that's not possible in C. Since I need to do null checking at runtime, what option is the most proper way to handle it?

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  • Handling Input with Zend Framework outside MVC

    - by Pekka
    In a classic Zend Framework MVC setup, there seems to be access to a generic _request object from within the model/view/controller instance as outlined here: $this->_request->getPost('variablename'); is this request object somehow available in a non-MVC setup as well? If yes: how would I initialize and access it?

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  • Selecting items from events, as evenly spaced as possible

    - by Matt Warren
    If I have an event that happens 15 times a second (numbered 1 - 15), but I only want to process it 3 times I can choose [1], [6] and [11],. It's important that the events I process are as evenly spaced as possible and take into account wrap-around, i.e. the events are continuous 13, 14, 15, 1, 2, 3 etc. If I want 4 items the best I can do is [1], [5], [9] & [13]. Is there a general algorithm that will calculate which events I need to process given the total number of events (total) and the number to process (processAmount).

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  • Catching "NullPointerExceptions" in JavaScript

    - by Lenni
    I'm writing quite a bit of code in Prototype.js which returns null if a DOM-id wasn't found. $("someId").show(); If someId doesn't exist, a method will be called on null, which halts the entire program, in effect disabling all JS effects after the error. I could just check for null before executing such a statement, but this is getting tiring. I would like to catch an exception but I'm not sure which one its is. MDC lists the following ECMA Script error types: * Error * EvalError * RangeError * ReferenceError * SyntaxError * TypeError * URIError * DOMException * EventException * RangeException Also, do browsers have a unified way of dealing with a method call on null?

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  • Why does Perl's Net::Msmgr hang when I try to authenticate?

    - by codeholic
    There's Net::Msmgr module on CPAN. It's written clean and the code looks trustworthy at the first glance. However this module seems to be beta and there is little documentation and no tests :-/ Has anyone used this module in production? I haven't managed to make it run by now, because it requires all event loop processing to be done in the application and as I've already said there is little documentation and no working examples to study. That's where I've gone so far: #!/usr/bin/perl use strict; use warnings; use Event; use Net::Msmgr::Object; use Net::Msmgr::Session; use Net::Msmgr::User; use constant DEBUG => 511; use constant EVENT_TIMEOUT => 5; # seconds my ($username, $password) = qw/[email protected] my.password/; my $buddy = '[email protected]'; my $user = Net::Msmgr::User->new(user => $username, password => $password); my $session = Net::Msmgr::Session->new; $session->debug(DEBUG); $session->login_handler(\&login_handler); $session->user($user); my $conv; sub login_handler { my $self = shift; print "LOGIN\n"; $self->ui_state_nln; $conv = $session->ui_new_conversation; $conv->invite($buddy); } our %watcher; sub ConnectHandler { my ($connection) = @_; warn "CONNECT\n"; my $socket = $connection->socket; $watcher{$connection} = Event->io(fd => $socket, cb => [ $connection, '_recv_message' ], poll => 're', desc => 'recv_watcher', repeat => 1); } sub DisconnectHandler { my $connection = shift; print "DISCONNECT\n"; $watcher{$connection}->cancel; } $session->connect_handler(\&ConnectHandler); $session->disconnect_handler(\&DisconnectHandler); $session->Login; Event::loop(); That's what it outputs: Dispatch Server connecting to: messenger.hotmail.com:1863 Dispatch Server connected CONNECT Dispatch Server >>>VER 1 MSNP2 CVR0 --> VER 1 MSNP2 CVR0 Dispatch Server >>>USR 2 MD5 I [email protected] --> USR 2 MD5 I [email protected] Dispatch Server <<<VER 1 CVR0 <-- VER 1 CVR0 And that's all, here it hangs. The handler on login is not being triggered. What am I doing wrong?

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  • How can I process a form's events in another class in VB.NET?

    - by CowKingDeluxe
    Here's my code: Public Class Form1 End Class Public Class Form1Handler Inherits Form1 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click MsgBox("I") End Sub End Class I'm trying to get Form1Handler to process Form1's events automatically. How can I do this? Should I use a module instead? I'm doing this in VB 2010.

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  • Can you catch exceeded allocated memory error before it kills the script?

    - by kristovaher
    The thing is that I want to catch memory problems before they happen. I have a system that gets rows from database and casts the returned associative array to a variable, but I never know what the size of the database result is is or how much memory it will take once the database request is made. This means that my software can fail simply because memory is exceeded. But I want to avoid that somehow. One of the ways is to obviously make database requests that are smaller, but what if this is not possible or what if I do not know the size of data that is returned from database? Is it possible to 'catch' situations where memory use is exceeded in PHP? Something like this: $requestOk=memory_test(function(){ return doSomething(); }); if($requestOk){ // Memory seems fine // $requestOk now has the value from memory_test() function } else { // Function would have exceeded memory } I just find it problematic that my script can just die at any moment because of memory issues. From what I know, try-catch cannot be used here because it is a fatal error. Any help would be appreciated!

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  • Catching errors in ANTLR and finding parent

    - by Andreas
    I have found out that I can catch errors during parsing by overwriting displayRecognitionError, but how do I find the parent "node" of this error? ex. if I have the grammar: prog: stat expr; stat: STRING; expr: INTEGER; And give it the input "abc def". Then I will get an error at "def" which should be an integer. At this point I then want to get the parent which is "expr" (since it fails inside the INTEGER part) and it's parent "prog". Kind of like printing stack trace in java. I tried to look at the node from RecognitionException parsed to displayRecognitionError, but it is null, and using CommonErrorNode the parent is null. Should I maybe take a completely different approach?

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  • ASP.Net Treeview - Client side event handling (jQuery??)

    - by The Great Gonzo
    I have a Treeview (bog standard ASP.Net Treeview) that is bound to an Xml source which allows the user to navigate to various parts of our system. Nothing special.... However, I wanted to generate a breadcrumb for use in the main content area on the client side when the user clicks a node in the Treeview control. I know there are mechanisms available for breadcrumb generation (such as site maps) but for various reasons I need to do it when a node is clicked. So far hooking up a click event using the document ready function available as part of jQuery is easy. However, having spent sometime looking I can not see how I navigate back up the tree nodes to get to each parent nodes text value to build the breadcrumb. I have been playing with .parent(), .parents() and .closest() available via jQuery but don't seem to be getting anywhere. Has anyone done anything like this or can anyone provide a better method? Thanks in advance....

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  • Manipulating a NSTextField via AppleScript

    - by Garry
    A little side project I'm working on is a digital life assistant, much like project JARVIS. What I'm trying to do is speak to my mac, have my words translated to text and then have the text interpreted by my program. Currently, my app is very simple, consisting of a single window containing a single wrapped NSTextView. Using MacSpeech Dictate, When I say the custom command "Jeeves", MacSpeech ensures that my app is frontmost, highlights any text in the TextField and clears it, then presses the Return key to trigger the textDidEndEditing method of NSTextField. This is done via Applescript. MacSpeech then switches to dictation mode and the next sentence I say will appear in the NSTextField. What I can't figure out is how to signify that I have finished saying a command to my program. I could simply say another keyword like "execute" or something similar that would send an AppleScript return keystroke to my app (thereby triggering the textDidEndEditing event) but this is cumbersome. Is there a notification that happens when text is pasted into a NSTextField? Would a timer work that would fire after maybe three seconds once my program becomes frontmost (three seconds should be sufficient for me to say a command)? Thanks,

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  • Handling Corrupted JPEGs in C#

    - by ddango
    We have a process that pulls images from a remote server. Most of the time, we're good to go, the images are valid, we don't timeout, etc. However, every once and awhile we see this error similar to this: Unhandled Exception: System.Runtime.InteropServices.ExternalException: A generic error occurred in GDI+. at System.Drawing.Image.Save(Stream stream, ImageCodecInfo encoder, EncoderPa rameters encoderParams) at ConsoleApplication1.Program.Main(String[] args) in C:\images\ConsoleApplic ation1\ConsoleApplication1\Program.cs:line 24 After not being able to reproduce it locally, we looked closer at the image, and realized that there were artifacts, making us suspect corruption. Created an ugly little unit test with only the image in question, and was unable to reproduce the error on Windows 7 as was expected. But after running our unit test on Windows Server 2008, we see this error every time. Is there a way to specify non-strictness for jpegs when writing them? Some sort of check/fix we can use? Unit test snippet: var r = ReadFile("C:\\images\\ConsoleApplication1\\test.jpg"); using (var imgStream = new MemoryStream(r)) { using (var ms = new MemoryStream()) { var guid = Guid.NewGuid(); var fileName = "C:\\images\\ConsoleApplication1\\t" + guid + ".jpg"; Image.FromStream(imgStream).Save(ms, ImageFormat.Jpeg); using (FileStream fs = File.Create(fileName)) { fs.Write(ms.GetBuffer(), 0, ms.GetBuffer().Length); } } }

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  • Replacing objects, handling clones, dealing with write logs

    - by Alix
    Hi everyone, I'm dealing with a problem I can't figure out how to solve, and I'd love to hear some suggestions. [NOTE: I realise I'm asking several questions; however, answers need to take into account all of the issues, so I cannot split this into several questions] Here's the deal: I'm implementing a system that underlies user applications and that protect shared objects from concurrent accesses. The application programmer (whose application will run on top of my system) defines such shared objects like this: public class MyAtomicObject { // These are just examples of fields you may want to have in your class. public virtual int x { get; set; } public virtual List<int> list { get; set; } public virtual MyClassA objA { get; set; } public virtual MyClassB objB { get; set; } } As you can see they declare the fields of their class as auto-generated properties (auto-generated means they don't need to implement get and set). This is so that I can go in and extend their class and implement each get and set myself in order to handle possible concurrent accesses, etc. This is all well and good, but now it starts to get ugly: the application threads run transactions, like this: The thread signals it's starting a transaction. This means we now need to monitor its accesses to the fields of the atomic objects. The thread runs its code, possibly accessing fields for reading or writing. If there are accesses for writing, we'll hide them from the other transactions (other threads), and only make them visible in step 3. This is because the transaction may fail and have to roll back (undo) its updates, and in that case we don't want other threads to see its "dirty" data. The thread signals it wants to commit the transaction. If the commit is successful, the updates it made will now become visible to everyone else. Otherwise, the transaction will abort, the updates will remain invisible, and no one will ever know the transaction was there. So basically the concept of transaction is a series of accesses that appear to have happened atomically, that is, all at the same time, in the same instant, which would be the moment of successful commit. (This is as opposed to its updates becoming visible as it makes them) In order to hide the write accesses in step 2, I clone the accessed field (let's say it's the field list) and put it in the transaction's write log. After that, any time the transaction accesses list, it will actually be accessing the clone in its write log, and not the global copy everyone else sees. Like this, any changes it makes will be done to the (invisible) clone, not to the global copy. If in step 3 the commit is successful, the transaction should replace the global copy with the updated list it has in its write log, and then the changes become visible for everyone else at once. It would be something like this: myAtomicObject.list = updatedCloneOfListInTheWriteLog; Problem #1: possible references to the list. Let's say someone puts a reference to the global list in a dictionary. When I do... myAtomicObject.list = updatedCloneOfListInTheWriteLog; ...I'm just replacing the reference in the field list, but not the real object (I'm not overwriting the data), so in the dictionary we'll still have a reference to the old version of the list. A possible solution would be to overwrite the data (in the case of a list, empty the global list and add all the elements of the clone). More generically, I would need to copy the fields of one list to the other. I can do this with reflection, but that's not very pretty. Is there any other way to do it? Problem #2: even if problem #1 is solved, I still have a similar problem with the clone: the application programmer doesn't know I'm giving him a clone and not the global copy. What if he puts the clone in a dictionary? Then at commit there will be some references to the global copy and some to the clone, when in truth they should all point to the same object. I thought about providing a wrapper object that contains both the cloned list and a pointer to the global copy, but the programmer doesn't know about this wrapper, so they're not going to use the pointer at all. The wrapper would be like this: public class Wrapper<T> : T { // This would be the pointer to the global copy. The local data is contained in whatever fields the wrapper inherits from T. private T thisPtr; } I do need this wrapper for comparisons: if I have a dictionary that has an entry with the global copy as key, if I look it up with the clone, like this: dictionary[updatedCloneOfListInTheWriteLog] I need it to return the entry, that is, to think that updatedCloneOfListInTheWriteLog and the global copy are the same thing. For this, I can just override Equals, GetHashCode, operator== and operator!=, no problem. However I still don't know how to solve the case in which the programmer unknowingly inserts a reference to the clone in a dictionary. Problem #3: the wrapper must extend the class of the object it wraps (if it's wrapping MyClassA, it must extend MyClassA) so that it's accepted wherever an object of that class (MyClass) would be accepted. However, that class (MyClassA) may be final. This is pretty horrible :$. Any suggestions? I don't need to use a wrapper, anything you can think of is fine. What I cannot change is the write log (I need to have a write log) and the fact that the programmer doesn't know about the clone. I hope I've made some sense. Feel free to ask for more info if something needs some clearing up. Thanks so much!

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  • .net Attributes that handle exceptions - usage on a property accessor

    - by Mr AH
    Hi, well I know from my asp.net mvc experience that you can have attributes that handle exceptions (HandleErrorAttribute). As far as I can tell the Controller class has some OnException event which may be integral to this behaviour. However, I want to do something similar in my own code: dream example: public String MyProperty { [ExceptionBehaviour(typeof(FormatException), MyExEnum.ClearValue)] set { _thing.prop = Convert.ToThing(value); } } .... The code above obviously makes very little sense, but is close to the kind of thing I wish to do. I want the attribute on the property set accessor to catch some type of exception and then deal with this in some custom way (or even just swallow it). Any ideas guys?

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  • Detecting and handling third-party library filehandle leaks in Java

    - by tucuxi
    Is there any way to detect and handle whether a Java library is correctly releasing file-handles (via "close") from within a Java program that is using said library, short of having access to the actual library code and inserting the corresponding "finally close" statements? If detection is feasible, is there any way to close those file-handles without a reference to the Reader (or FileInputStream) that was reading the file?

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  • Better way to ignore exception type: multiple catch block vs. type querying

    - by HuBeZa
    There are situations that we like to ignore a specific exception type (commonly ObjectDisposedException). It can be achieved with those two methods: try { // code that throws error here: } catch (SpecificException) { /*ignore this*/ } catch (Exception ex) { // Handle exception, write to log... } or try { // code that throws error here: } catch (Exception ex) { if (ex is SpecificException) { /*ignore this*/ } else { // Handle exception, write to log... } } What are the pros and cons of this two methods (regarding performance, readability, etc.)?

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  • Google JavaScript CAPTCHA handling

    - by Sam
    I am using Google API's to provide maps on a web page, however, Google frequently prompts for a CAPTCHA (I only know this from going into Firebug, users just get a JavaScript error) for requests for its javascript API's (e.g. http://maps.google.co.uk/maps?file=api&v=2&key=xxxx). However, this prevents visitors from our network (a very large (UK wide) WAN) using Google Maps etc from using these sites with it on. This is likely due to the fact the IP is shared by many people, so Google sees it as spam. I don't see any way of contacting Google about this, so was wondering if there is any way of intercepting these failing JavaScript requests since they return a 403 status code? Perhaps by opening a new window, although that would not be user friendly (they will see the JavaScript after the CAPTCHA, so would be a cause of confusion and would need to refresh the page in question).

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  • Error debugging - Conversion from String to Double

    - by Jamie Taylor
    I'm doing some error debugging trying to get the errors on our website down to a minimum and there seems to be an error that is popping up quite a lot Conversion from string "" to type 'Double' is not valid. I'm unable to replicate this problem but I can see that it is happening. I've been looking through the code in one of the pages and strolled across this Dim varWeek As String If varWeek < 10 Then 'Do something' End If Could this be causing the problem as it is trying to see if a String is less than 10 which is an Integer? As I said before as I am unable to see this error in the first place so changing this to an Integer doesn't change anything on my system. Thanks.

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  • Handling Messages in Console Apps/DLLs in C++ Win32

    - by vsimon
    I would like to have the ability to process Win32 messages in a console app and/or inside a standalone DLL. I have been able to do it in .NET with the following article and it works great in C# inside a console app and standalone DLL http://msdn.microsoft.com/en-us/magazine/cc163417.aspx Is there a way to do the equivalent with C/C++ Win32 APIs? I have tried doing RegisterClassEx(...) and CreateWindow(...) even passing in HWND_MESSAGE to hWndParent but the trouble is that after the "invisible" window is created messages are not being processed probably due to the lack of a message pump. Where would the message pump go if you had a DLL entry point? I have tried creating another thread in a DLL and put while(GetMesage(..)) there but that did not work either. Any ideas?

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  • How can I intercept an exception occurred during serialization in WCF?

    - by bonomo
    I have a legit data object with all data contract / data member attributes. For some reason the WCF service crashes after the operation has completed and the result is passed as a return value. I believe it has something to do with WCF not being able to serialize that result properly. The test client doesn't say anything specific: The underlying connection was closed: The connection was closed unexpectedly. Server stack trace: at System.ServiceModel.Channels.HttpChannelUtilities.ProcessGetResponseWebException(WebException webException, HttpWebRequest request, HttpAbortReason abortReason) at System.ServiceModel.Channels.HttpChannelFactory.HttpRequestChannel.HttpChannelRequest.WaitForReply(TimeSpan timeout) at System.ServiceModel.Channels.RequestChannel.Request(Message message, TimeSpan timeout) at System.ServiceModel.Dispatcher.RequestChannelBinder.Request(Message message, TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation) at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message) Exception rethrown at [0]: at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg) at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type) at IFacade.PickSecurities(String pattern, Int32 atMost) at FacadeClient.PickSecurities(String pattern, Int32 atMost) Inner Exception: The underlying connection was closed: The connection was closed unexpectedly. at System.Net.HttpWebRequest.GetResponse() at System.ServiceModel.Channels.HttpChannelFactory.HttpRequestChannel.HttpChannelRequest.WaitForReply(TimeSpan timeout) I am in control of creating the instance of the service using a customized service host factory. I know I can set up trace listeners and check the logs, but it's a lot of hassle to do. So I would rather handle it explicitly on the server at the time it happens. So I how can I intercept that exception programmatically and return an appropriate fault meassage?

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  • Strange problem with Random Access Filing in C++

    - by sam
    This is a simple random access filing program . The problem arises where i want to write data randomly. If I write any where in the file the previous records are set to 0. the last 1 which is being entered currently holds the correct value all others =0. This is the code #include <iostream> #include<fstream> #include<string> using namespace std; class name { int id; int pass; public: void writeBlank(); void writedata(); void readdata(); void readall(); int getid() { return id; } int getpass() { return pass; } void setid(int i) { id=i; } void setpass(int p) { pass=p; } }; void name::writeBlank() { name person; person.setid(0); person.setpass(0); int i; ofstream out("pass.txt",ios::binary); if ( !out ) { cout << "File could not be opened." << endl; } for(i=0;i<10;i++) //make 10 records { cout<<"Put pointer is at: "<<out.tellp()<<endl; cout<<"Blank record "<<i<<" is: "<<person.getid()<<" "<<person.getpass()<<" and size: "<<sizeof(person)<<endl; cout<<"Put pointer is at: "<<out.tellp()<<endl; out.write(reinterpret_cast< const char * >(&person),sizeof(name)); } } void name::writedata() { ofstream out("pass.txt",ios::binary|ios::out); name n1; int iD,p; cout<<"ID?"; cin>>iD; n1.setid(iD); cout<<"Enter password"; cin>>p; n1.setpass(p); if (!out ) { cout << "File could not be opened." << endl; } out.seekp((n1.getid()-1)*sizeof(name),ios::beg); //pointer moves to desired location where we have to store password according to its ID(index) cout<<"File pointer is at: "<<out.tellp()<<endl; out.write(reinterpret_cast<const char*> (&n1), sizeof(name)); //write on that pointed location } void name::readall() { name n1; ifstream in("pass.txt",ios::binary); if ( !in ) { cout << "File could not be opened." << endl; } in.read( reinterpret_cast<char *>(&n1), sizeof(name) ); while ( !in.eof() ) { // display record cout<<endl<<"password at this index is:"<<n1.getpass()<<endl; cout<<"File pointer is at: "<<in.tellg()<<endl; // read next from file in.read( reinterpret_cast< char * >(&n1), sizeof(name)); } // end while } void name::readdata() { ifstream in("pass.txt",ios::binary); if ( !in ) { cout << "File could not be opened." << endl; } in.seekg((getid()-1)*sizeof(name)); //pointer moves to desired location where we have to read password according to its ID(index) cout<<"File pointer is at: "<<in.tellg()<<endl; in.read((char* )this,sizeof(name)); //reads from that pointed location cout<<endl<<"password at this index is:"<<getpass()<<endl; } int main() { name n1; cout<<"Enter 0 to write blank records"<<endl; cout<<"Enter 1 for new account"<<endl; cout<<"Enter 2 to login"<<endl; cout<<"Enter 3 to read all"<<endl; cout<<"Enter 9 to exit"<<endl; int option; cin>>option; while(option==0 || option==1 || option==2 || option==3) { if (option == 0) n1.writeBlank(); if(option==1) { /*int iD,p; cout<<"ID?"; cin>>iD; n1.setid(iD); cout<<"Enter password"; cin>>p; n1.setpass(p);*/ n1.writedata(); } int ind; if(option==2) { cout<<"Index?"; cin>>ind; n1.setid(ind); n1.readdata(); } if(option == 3) n1.readall(); cout<<"Enter 0 to write blank records"<<endl; cout<<"Enter 1 for new account"<<endl; cout<<"Enter 2 to login"<<endl; cout<<"Enter 3 to read all"<<endl; cout<<"Enter 9 to exit"<<endl; cin>>option; } } I Cant understand Y the previous records turn 0.

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