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  • Handling close-to-impossible collisions on should-be-unique values

    - by balpha
    There are many systems that depend on the uniqueness of some particular value. Anything that uses GUIDs comes to mind (eg. the Windows registry or other databases), but also things that create a hash from an object to identify it and thus need this hash to be unique. A hash table usually doesn't mind if two objects have the same hash because the hashing is just used to break down the objects into categories, so that on lookup, not all objects in the table, but only those objects in the same category (bucket) have to be compared for identity to the searched object. Other implementations however (seem to) depend on the uniqueness. My example (that's what lead me to asking this) is Mercurial's revision IDs. An entry on the Mercurial mailing list correctly states The odds of the changeset hash colliding by accident in your first billion commits is basically zero. But we will notice if it happens. And you'll get to be famous as the guy who broke SHA1 by accident. But even the tiniest probability doesn't mean impossible. Now, I don't want an explanation of why it's totally okay to rely on the uniqueness (this has been discussed here for example). This is very clear to me. Rather, I'd like to know (maybe by means of examples from your own work): Are there any best practices as to covering these improbable cases anyway? Should they be ignored, because it's more likely that particularly strong solar winds lead to faulty hard disk reads? Should they at least be tested for, if only to fail with a "I give up, you have done the impossible" message to the user? Or should even these cases get handled gracefully? For me, especially the following are interesting, although they are somewhat touchy-feely: If you don't handle these cases, what do you do against gut feelings that don't listen to probabilities? If you do handle them, how do you justify this work (to yourself and others), considering there are more probable cases you don't handle, like a supernonva?

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  • What exactly does it mean when $_FILES is empty?

    - by Mike
    I am working on an upload script and when testing my error checks, I attempted to upload a 17MB TIFF file. When I do this the $_FILES array is empty. The script works fine for what I need it to do, which is to upload JPEG files. My solution is to test if $_FILES is empty or not before continuing with the upload script. Can anybody explain why $_FILES is empty when a TIFF is attempted to be uploaded? Is my solution, to check if $_FILES is empty or not, an okay one?

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  • How to change FPU context in signal handler (C++/Linux)

    - by Henry Fané
    I wrote a signal handler to catch FPE errors. I need to continue execution even if this happens. I receive a ucontext_t as parameter, I can change the bad operand from 0 to another value but the FPU context is still bad and I run into an infinite loop ? Does someone already manupulate the ucontext_t structure on Linux ? I finally found a way to handle these situations by clearing the status flag of ucontext_t like this: ... const long int cFPUStatusFlag = 0x3F; aContext->uc_mcontext.fpregs->sw &= ~cFPUStatusFlag; ... 0x3F is negated to put 0 in the 6 bits of the status register of the FPU (x87). Doing this implies to check for FPE exceptions after calculation.

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  • Trying to write priority queue in Java but getting "Exception in thread "main" java.lang.ClassCastEx

    - by Dan
    For my data structure class, I am trying to write a program that simulates a car wash and I want to give fancy cars a higher priority than regular ones using a priority queue. The problem I am having has something to do with Java not being able to type cast "Object" as an "ArrayQueue" (a simple FIFO implementation). What am I doing wrong and how can I fix it? public class PriorityQueue<E> { private ArrayQueue<E>[] queues; private int highest=0; private int manyItems=0; public PriorityQueue(int h) { highest=h; queues = (ArrayQueue[]) new Object[highest+1]; <----problem is here } public void add(E item, int priority) { queues[priority].add(item); manyItems++; } public boolean isEmpty( ) { return (manyItems == 0); } public E remove() { E answer=null; int counter=0; do { if(!queues[highest-counter].isEmpty()) { answer = queues[highest-counter].remove(); counter=highest+1; } else counter++; }while(highest-counter>=0); return answer; } }

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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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  • jsp servlet exception: bean not found within scope.

    - by stu
    I'm getting this error: javax.servlet.ServletException: bean givingFormBean not found within scope on a page with this at the top. The class exists in the classpath, it worked this morning, and I don't get what not found within scope means. I've googled and googled and nothing useful came up.

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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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  • Why wouldn't I be able to establish a trust relationship for a SSL/TLS channel?

    - by Abe Miessler
    I have a piece of .NET code that is erroring out when it makes a call to HTTPWebRequest.GetRequestStream. Here is the error message: The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel. I've read a few things that suggest that I might need a certificate on the machine running the code, but i'm not sure if that's true or how to do it. If I need to get a certificate, how do I do it? Code: var request = (HttpWebRequest)HttpWebRequest.Create(requestUrl); //my url request.Method = StringUtilities.ConvertToString(httpMethod); // Set the http method GET, POST, etc. if (postData != null) { request.ContentLength = postData.Length; request.ContentType = contentType; using (var dataStream = request.GetRequestStream()) { dataStream.Write(postData, 0, postData.Length); } }

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  • Check for live Data Source Name Before proceeding

    - by n_kips
    Would it be ok to get a CF app to check for a valid database before proceeding to process that request? This is because there may be instances where the database server may be down or being upgraded, hence an error comes when a db dependant request is made. If there is no connection to the db server, the user can be safely redirected to a safe page. Or can cfcatch work? How can this check be done? Thank you.

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  • WCF net.tcp server disconnects - how to handle properly on client side?

    - by RoastedBattleSquirrel
    I'm stuck with a bit of an annoying problem right now. I've got a Silverlight 4 application (which runs OOB by default). It uses WCF with net.tcp as means of communicating with the server. The client uses a central instance of the wcf client proxy. As long as everything keeps running on the server side, everything's fine. If i kill the server in the middle of everything, i drown in an avalanche of exceptions on the client side (connection lost, channel faulted etc etc). Now i'm looking for a way to handle this in a clean and centralized way (if centralized is possible). The SL app has one central client object sitting in App.cs (public static MyClient Client { get;set;}), which gets initialized on application start. Any idea how to properly handle any connectivity problems on the client object?

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  • Exception if there is IBOutlet in view controller created by initWithNibName

    - by Kail
    When I create a Navigation-based application, the second view controller is created with initWithNibName, if I add a label onto the second view and connect it with IBOutlet in the second view controller. After I navigate to the second view by clicking table cell, and then back to the root view, the application aborts - send message retainCount to a freed object. I know this is caused by the IBOutlet label, which is retained, set nil in viewDidUnload and dealloc in dealloc. But I don't know why, and if I wanna still use IBOutlet, what can I do? Not dealloc it in viewcontroller's dealloc? Anybody could help? Thank you.

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  • C++ Storing variables and inheritance

    - by Kaa
    Hello Everyone, Here is my situation: I have an event driven system, where all my handlers are derived from IHandler class, and implement an onEvent(const Event &event) method. Now, Event is a base class for all events and contains only the enumerated event type. All actual events are derived from it, including the EventKey event, which has 2 fields: (uchar) keyCode and (bool)isDown. Here's the interesting part: I generate an EventKey event using the following syntax: Event evt = EventKey(15, true); and I ship it to the handlers: EventDispatch::sendEvent(evt); // void EventDispatch::sendEvent(const Event &event); (EventDispatch contains a linked list of IHandlers and calls their onEvent(const Event &event) method with the parameter containing the sent event. Now the actual question: Say I want my handlers to poll the events in a queue of type Event, how do I do that? x Dynamic pointers with reference counting sound like too big of a solution. x Making copies is more difficult than it sounds, since I'm only receiving a reference to a base type, therefore each time I would need to check the type of event, upcast to EventKey and then make a copy to store in a queue. Sounds like the only solution - but is unpleasant since I would need to know every single type of event and would have to check that for every event received - sounds like a bad plan. x I could allocate the events dynamically and then send around pointers to those events, enqueue them in the array if wanted - but other than having reference counting - how would I be able to keep track of that memory? Do you know any way to implement a very light reference counter that wouldn't interfere with the user? What do you think would be a good solution to this design? I thank everyone in advance for your time. Sincerely, Kaa

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  • Laravel - Mail class Exception

    - by Christian Giupponi
    I need to send email within my app and this is my code: if( $agent->save() ) { //Preparo la mail da inviare con i dati di login $data = [ 'nome' => $input['nome'], 'cognome' => $input['cognome'], 'email' => $input['email'], 'password' => $input['password'] ]; //ATTENZIONE //Questo è da rimuovere in produzione, finge di inviare la mail Mail::pretend(); //Recuero il template e passo alla funzione i dati Mail::send('emails.agents.registration', $data, function($message) use ($data) { $message->to( $data['email'], $data['nome'].' '.$data['cognome'] )->subject('Benvenuto!'); }); return Redirect::action('admin.agents.index')->with('positive_flash_message', 'Agente inserito correttamente.'); } As you can see I have use the Mail::pretend to avoid the email send in development, the problem is that I get this error every time I try to send an email: Undefined property: Illuminate\Mail\Message::$email (View: /var/www/progetti/app/views/emails/agents/registration.blade.php) nd this is my blade view: Email: {{ $message->email }} Password: {{ $message->password }} What's wrong with $message?

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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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  • handling javaScript alerts when running a selenium test?

    - by Mo
    Hi I am am running some selenium tests(ruby) on my web page and as i enter an invalid characters in to a text box i have the JavaScript throw a alert like so if(isNaN($(this).val()) || Number($(this).val().valueOf() <=0)){ alert("Please Enter A Number"); } how can i handle this alert when its made and close the pop up? i tried to use the wait_for_pop_up() and close() but i think that's only for browser pop up's and not JavaScript alerts. any ideas? thanks

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  • What is a good generic sibling control Javascript communication strategy?

    - by James
    I'm building a webpage that is composed of several controls, and trying to come up with an effective somewhat generic client side sibling control communication model. One of the controls is the menu control. Whenever an item is clicked in here I wanted to expose a custom client side event that other controls can subscribe to, so that I can achieve a loosely coupled sibling control communication model. To that end I've created a simple Javascript event collection class (code below) that acts as like a hub for control event registration and event subscription. This code certainly gets the job done, but my question is is there a better more elegant way to do this in terms of best practices or tools, or is this just a fools errand? /// Event collection object - acts as the hub for control communication. function ClientEventCollection() { this.ClientEvents = {}; this.RegisterEvent = _RegisterEvent; this.AttachToEvent = _AttachToEvent; this.FireEvent = _FireEvent; function _RegisterEvent(eventKey) { if (!this.ClientEvents[eventKey]) this.ClientEvents[eventKey] = []; } function _AttachToEvent(eventKey, handlerFunc) { if (this.ClientEvents[eventKey]) this.ClientEvents[eventKey][this.ClientEvents[eventKey].length] = handlerFunc; } function _FireEvent(eventKey, triggerId, contextData ) { if (this.ClientEvents[eventKey]) { for (var i = 0; i < this.ClientEvents[eventKey].length; i++) { var fn = this.ClientEvents[eventKey][i]; if (fn) fn(triggerId, contextData); } } } } // load new collection instance. var myClientEvents = new bsdClientEventCollection(); // register events specific to the control that owns it, this will be emitted by each respective control. myClientEvents.RegisterEvent("menu-item-clicked"); Here is the part where this code above is consumed by source and subscriber controls. // menu control $(document).ready(function() { $(".menu > a").click( function(event) { //event.preventDefault(); myClientEvents.FireEvent("menu-item-clicked", $(this).attr("id"), null); }); }); <div style="float: left;" class="menu"> <a id="1" href="#">Menu Item1</a><br /> <a id="2" href="#">Menu Item2</a><br /> <a id="3" href="#">Menu Item3</a><br /> <a id="4" href="#">Menu Item4</a><br /> </div> // event subscriber control $(document).ready(function() { myClientEvents.AttachToEvent("menu-item-clicked", menuItemChanged); myClientEvents.AttachToEvent("menu-item-clicked", menuItemChanged2); myClientEvents.AttachToEvent("menu-item-clicked", menuItemChanged3); }); function menuItemChanged(id, contextData) { alert('menuItemChanged ' + id); } function menuItemChanged2(id, contextData) { alert('menuItemChanged2 ' + id); } function menuItemChanged3(id, contextData) { alert('menuItemChanged3 ' + id); }

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  • Is there a browser-agnostic way to detect client-side script errors with Watin?

    - by Michael
    We're using WatiN to test our web portals. During the course of an E2E test, we'll occasionally see client-side script errors on the IE status bar. I'd like to chain a handler onto the script error event and record the error for later analysis and bug filing. Problem is, I don't know that there's a global script error event or how to chain into it. And if there's not a browser-agnostic way to accomplish this, I can create MyIE and MyFF subclasses but then this becomes two browser-specific questions. In essence, I'm thinking of something like this entirely made-up call: browser.ScriptEngine.SetCustomErrorHandler(LogScriptingError); ... where LogScriptErrors is my code that does the obvious. Many of our client-side scripting errors don't necessarily prevent the test from continuing (a pretty UI element didn't animate, for example, but the underlying form is still submittable), so I'd like to log the error and forge ahead in most cases.

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  • Python - from file to data structure?

    - by Seafoid
    Hi, I have large file comprising ~100,000 lines. Each line corresponds to a cluster and each entry within each line is a reference i.d. for another file (protein structure in this case), e.g. 1hgn 1dju 3nmj 8kfn 9opu 7gfb 4bui I need to read in the file as a list of lists where each line is a sublist, thus preserving the integrity of the cluster, e.g. nested_list = [['1hgn', '1dju', '3nmj', '8kfn'], ['9opu', '7gfb'], ['4bui']] My current code creates a nested list but the entries within each list are a single string and not comma separated. Therefore, I cannot splice the list with indices so easily. Any help greatly appreciated. Thanks, S :-)

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  • better way of handling nested list

    - by laspal
    Hi, I have list my_list = [ [1,2,3,4,5,6], [1,3,4],[34,56,56,56]] for item in my_list: var1,var2,var3,var4,var5,var6 = None if len(item) ==1: var1 = item[0] if len(item) == 2: var1 = item[0] var2 = item[1] if len(item) == 3: var1 = item[0] var2 = item[1] var3 = item[2] if len(item) == 4: var1 = item[0] var2 = item[1] var3 = item[2] var4 = item[3] fun(var1,var2,var3,var4,var5,var6) I have a function def fun(var1, var2 = None, var3 = None, var4 = None, var5=None, var6= None) Depending upon the values in my inner list. I am passing it to function. I hope I made it clear. Thanks

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  • Python - network buffer handling question...

    - by Patrick Moriarty
    Hi, I want to design a game server in python. The game will mostly just be passing small packets filled with ints, strings, and bytes stuffed into one message. As I'm using a different language to write the game, a normal packet would be sent like so: Writebyte(buffer, 5); // Delimit type of message Writestring(buffer, "Hello"); Sendmessage(buffer, socket); As you can see, it writes the bytes to the buffer, and sends the buffer. Is there any way to read something like this in python? I am aware of the struct module, and I've used it to pack things, but I've never used it to actually read something with mixed types stuck into one message. Thanks for the help.

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  • Exception when access inner class reflectively

    - by MikeJiang
    Hi Folk, Here is a sample java program. I wonder why the two approaches reslut different stories. Is it a bug or kind of bitter java feature? And I run the sample upon java 1.5 package test; public class TestOut{ public static void main(String[] args){ new TestIn();//it works Class.forName("test.TestOut$TestIn").newInstance();// throw IllegalAccessException } private static class TestIn{} }

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  • Java: Check what processes are bound to a port?

    - by bguiz
    Hi, I am developing an application in Netbeans, and it is using JavaDB. I can connect to it and execute queries without issues, but for some reason, the "Output - JavaDB Database Process" pane within Netbeans keeps displaying Security manager installed using the Basic server security policy. Could not listen on port 1527 on host localhost: java.net.BindException: Address already in use How do I find out what process is already using, or bound to that port? On Ubuntu Karmic, Netbeans 6.7.1

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