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  • Simplest way to mix sequences of types with iostreams?

    - by Kylotan
    I have a function void write<typename T>(const T&) which is implemented in terms of writing the T object to an ostream, and a matching function T read<typename T>() that reads a T from an istream. I am basically using iostreams as a plain text serialisation format, which obviously works fine for most built-in types, although I'm not sure how to effectively handle std::strings just yet. I'd like to be able to write out a sequence of objects too, eg void write<typename T>(const std::vector<T>&) or an iterator based equivalent (although in practice, it would always be used with a vector). However, while writing an overload that iterates over the elements and writes them out is easy enough to do, this doesn't add enough information to allow the matching read operation to know how each element is delimited, which is essentially the same problem that I have with a single std::string. Is there a single approach that can work for all basic types and std::string? Or perhaps I can get away with 2 overloads, one for numerical types, and one for strings? (Either using different delimiters or the string using a delimiter escaping mechanism, perhaps.)

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  • Improve performance writing 10 million records to text file using windows service

    - by user1039583
    I'm fetching more than 10 millions of records from database and writing to a text file. It takes hours of time to complete this operation. Is there any option to use TPL features here? It would be great if someone could get me started implementing this with the TPL. using (FileStream fStream = new FileStream("d:\\file.txt", FileMode.OpenOrCreate, FileAccess.ReadWrite)) { BufferedStream bStream = new BufferedStream(fStream); TextWriter writer = new StreamWriter(bStream); for (int i = 0; i < 100000000; i++) { writer.WriteLine(i); } bStream.Flush(); writer.Flush(); // empty buffer; fStream.Flush(); }

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  • Does my GetEnumerator cause a deadlock?

    - by Scott Chamberlain
    I am starting to write my first parallel applications. This partitioner will enumerate over a IDataReader pulling chunkSize records at a time from the data-source. TLDR; version private object _Lock = new object(); public IEnumerator GetEnumerator() { var infoSource = myInforSource.GetEnumerator(); //Will this cause a deadlock if two threads lock (_Lock) //use the enumator at the same time? { while (infoSource.MoveNext()) { yield return infoSource.Current; } } } full code protected class DataSourcePartitioner<object[]> : System.Collections.Concurrent.Partitioner<object[]> { private readonly System.Data.IDataReader _Input; private readonly int _ChunkSize; public DataSourcePartitioner(System.Data.IDataReader input, int chunkSize = 10000) : base() { if (chunkSize < 1) throw new ArgumentOutOfRangeException("chunkSize"); _Input = input; _ChunkSize = chunkSize; } public override bool SupportsDynamicPartitions { get { return true; } } public override IList<IEnumerator<object[]>> GetPartitions(int partitionCount) { var dynamicPartitions = GetDynamicPartitions(); var partitions = new IEnumerator<object[]>[partitionCount]; for (int i = 0; i < partitionCount; i++) { partitions[i] = dynamicPartitions.GetEnumerator(); } return partitions; } public override IEnumerable<object[]> GetDynamicPartitions() { return new ListDynamicPartitions(_Input, _ChunkSize); } private class ListDynamicPartitions : IEnumerable<object[]> { private System.Data.IDataReader _Input; int _ChunkSize; private object _ChunkLock = new object(); public ListDynamicPartitions(System.Data.IDataReader input, int chunkSize) { _Input = input; _ChunkSize = chunkSize; } public IEnumerator<object[]> GetEnumerator() { while (true) { List<object[]> chunk = new List<object[]>(_ChunkSize); lock(_Input) { for (int i = 0; i < _ChunkSize; ++i) { if (!_Input.Read()) break; var values = new object[_Input.FieldCount]; _Input.GetValues(values); chunk.Add(values); } if (chunk.Count == 0) yield break; } var chunkEnumerator = chunk.GetEnumerator(); lock(_ChunkLock) //Will this cause a deadlock? { while (chunkEnumerator.MoveNext()) { yield return chunkEnumerator.Current; } } } } IEnumerator IEnumerable.GetEnumerator() { return ((IEnumerable<object[]>)this).GetEnumerator(); } } } I wanted IEnumerable object it passed back to be thread safe (the MSDN example was so I am assuming PLINQ and TPL could need it) will the lock on _ChunkLock near the bottom help provide thread safety or will it cause a deadlock? From the documentation I could not tell if the lock would be released on the yeld return. Also if there is built in functionality to .net that will do what I am trying to do I would much rather use that. And if you find any other problems with the code I would appreciate it.

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  • Where are the readonly/const in .NET?

    - by acidzombie24
    In C++ you'll see void func(const T& t) everywhere. However, i havent seen anything similar in .NET. Why? I have notice a nice amount of parameters using struct. But i see no functions with readonly/const. In fact now that i tried it i couldnt use those keywords to make a function that promises to not modify a list being passed in. Is there no way to promise the caller that this function will never modify the contents of list? Is there no way to say to call code and say this list should never be modified? (I know i can clone the list or look at documentation but i like compile errors sometime)

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  • How should open source libraries be used on Windows?

    - by Jason Owen
    There are many open-source libraries that can be compiled with Visual Studio. I'm porting a program from Linux to Windows, but it depends on a number of libraries. I don't know what the best practices regarding libraries are on Windows. On Linux, these libraries are typically part of the distribution. To use sqlite on Debian, for example, you need only to install libsqlite3-dev and the include files and libraries (both static and dynamic) are automatically installed and available to your program. If you need a different version than your distribution supplies, you can compile it in your home directory, install it to ~/include and ~/lib, and set the appropriate environment variables so that your compiler includes those directories in its search path. What is the best way to use libraries that are distributed as source on Windows? If I link dynamically rather than statically, is there an easy way to copy required DLLs into the output directory to ease redistribution (assuming license requirements are met)?

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  • Java Double entry table

    - by Tom
    Hi, Does anyone know a double entry table implementation in java I can download ? I need to do something like this 1 2 3 _______ a| x y z b| h l m c| o a k table.get(a,1) would return x Of course, it should use any Object as key, value, etc Thanks in advance

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  • Why should I use PropertyProxyValidator? ASP.NET

    - by user102533
    I understand thatthe PropertyProxyValidator integrates with the ASP.NET UI. But, it cannot do client side validation. How would it be any different from throwing in a label in the UI and populating the errors on the server side? Also, If I am using Validation Application Block, what approaches do you suggest for client side validation if I don't want to duplicate rules on server and client side?

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  • Makefile option/rule to handle missing/removed source files

    - by b3nj1
    http://stackoverflow.com/questions/239004/need-a-makefile-dependency-rule-that-can-handle-missing-files gives some pointers on how to handle removed source files for generating .o files. I'm using gcc/g++, so adding the -MP option when generating dependencies works great for me, until I get to the link stage with my .a file... What about updating archives/libraries when input sources go away? This works OK for me, but is there a cleaner way (ie, something as straightforward as the g++ -MP option)? #BUILD_DIR is my target directory (includes Debug/Release and target arch) #SRC_OUTS are my .o files LIBATLS_HAS = $(shell nm ${BUILD_DIR}/libatls.a | grep ${BUILD_DIR} | sed -e 's/.*(//' -e 's/).*://') LIBATLS_REMOVE = $(filter-out $(notdir ${SRC_OUTS}), ${LIBATLS_HAS}) ${BUILD_DIR}/libatls.a: ${BUILD_DIR}/libatls.a(${SRC_OUTS}) ifneq ($(strip ${LIBATLS_REMOVE}),) $(AR) -d $@ ${LIBATLS_REMOVE} endif

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  • How can I merge two Linq IEnumerable<T> queries without running them?

    - by makerofthings7
    How do I merge a List<T> of TPL-based tasks for later execution? public async IEnumerable<Task<string>> CreateTasks(){ /* stuff*/ } My assumption is .Concat() but that doesn't seem to work: void MainTestApp() // Full sample available upon request. { List<string> nothingList = new List<string>(); nothingList.Add("whatever"); cts = new CancellationTokenSource(); delayedExecution = from str in nothingList select AccessTheWebAsync("", cts.Token); delayedExecution2 = from str in nothingList select AccessTheWebAsync("1", cts.Token); delayedExecution = delayedExecution.Concat(delayedExecution2); } /// SNIP async Task AccessTheWebAsync(string nothing, CancellationToken ct) { // return a Task } I want to make sure that this won't spawn any task or evaluate anything. In fact, I suppose I'm asking "what logically executes an IQueryable to something that returns data"? Background Since I'm doing recursion and I don't want to execute this until the correct time, what is the correct way to merge the results if called multiple times? If it matters I'm thinking of running this command to launch all the tasks var AllRunningDataTasks = results.ToList(); followed by this code: while (AllRunningDataTasks.Count > 0) { // Identify the first task that completes. Task<TableResult> firstFinishedTask = await Task.WhenAny(AllRunningDataTasks); // ***Remove the selected task from the list so that you don't // process it more than once. AllRunningDataTasks.Remove(firstFinishedTask); // TODO: Await the completed task. var taskOfTableResult = await firstFinishedTask; // Todo: (doen't work) TrustState thisState = (TrustState)firstFinishedTask.AsyncState; // TODO: Update the concurrent dictionary with data // thisState.QueryStartPoint + thisState.ThingToSearchFor Interlocked.Decrement(ref thisState.RunningDirectQueries); Interlocked.Increment(ref thisState.CompletedDirectQueries); if (thisState.RunningDirectQueries == 0) { thisState.TimeCompleted = DateTime.UtcNow; } }

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  • MooTools Problem in IE with Request

    - by trobrock
    I have this class method in a mootools class: getData : function(){ var r = new Request.JSON({ url : this.container.getAttribute('data-url'), method : 'post', onSuccess : function(j){ this.cards = j; this.prepareQuiz(); }.bind(this) }).send(); }, In any browser aside from IE this works fine, but in IE I get a this.cards is not defined in a method that occurs after the this.prepareQuiz method does it's stuff. I narrowed the problem to this section by adding an if ($defined(this.cards)) before the this.prepareQuiz call and if I just keep refreshing the page 1 out of every 5 or so times it will work. So the this.cards variable is not being set some of the time for some reason. Why would this happen?

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  • What library can I use to do simple, lightweight message passing?

    - by Mike
    I will be starting a project which requires communication between distributed nodes(the project is in C++). I need a lightweight message passing library to pass very simple messages(basically just strings of text) between nodes. The library must have the following characteristics: No external setup required. I need to be able to get everything up-and-running in my code - I don't want to require the user to install any packages or edit any configuration files(other than a list of IP addresses and ports to connect to). The underlying protocol which the library uses must be TCP(or if it is UDP, the library must guarantee the eventual receipt of the message). The library must be able to send and receive arbitrarily large strings(think up to 3GB+). The library needn't support any security mechanisms, fault tolerance, or encryption - I just need it to be fast, simple, and easy to use. I've considered MPI, but concluded it would require too much setup on the user's machine for my project. What library would you recommend for such a project? I would roll my own, but due to time constraints, I don't think that will be feasible.

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  • Should I consider memmove() O(n) or O(1) ?

    - by Andrei Ciobanu
    Hello, this may be a silly question, but I want to calculate the complexity of one of my algorithms, and I am not sure what complexity to consider for the memmove() function. Can you please help / explain ? void * memmove ( void * destination, const void * source, size_t num ); So is the complexity O(num) or O(1). I suppose it's O(num), but I am not sure as I lack for now the understanding of what's going on under the hood.

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  • Lexer written in Javascript?

    - by Phobis
    I have a project where a user needs to define a set of instructions for a ui that is completely written in javascript. I need to have the ability to parse a string of instructions and then translate them into instructions. Is there any libraries out there for parsing that are 100% javascript? Or a generator that will generate in javascript? Thanks!

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  • System("pause"); - Why is it wrong?

    - by Faken
    Here's a question that I don't quite understand: The command, System("pause"); is taught to new programmers as a way to pause a program and wait for a keyboard input to continue. However, it seems to be frowned on by many veteran programmers as something that should not be done in varying degrees. Some people say it is fine to use. Some say it is only to be used when you are locked in your room and no one is watching. Some say that they will personally come to your house and kill you if you use it. I, myself am a new programmer with no formal programming training. I use it because I was taught to use it. What I don't understand is that if it is not something to be used, then why was I taught to use it? Or, on the flip side, is it really not that bad after all? What are your thoughts on this subject?

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  • Have to put files in static_dir but need to read them afterwards

    - by SanjamX
    I just started using google app engine. In order to use templates, I'm using jinja2. I want to add images dynamically after I set the width and height of the img tag. I used PIL in order to read the image size and put the one I want. However when I open the image with PIL, I need it not to be in a static_dir and to put the image in the img tag, I need it to be in the static_dir. As a testing solution I've copied the folder to see if I get results and I did. But as you can see having each image saved twice is kind of bad.

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  • using asp.net membership provider in a dll

    - by Keith Barrows
    I've used Membership Providers in web apps over the last several years. I now have a new "request" for an internal project at work. They would like a service (not a web service) to do a quick authenticate against. Basically, exposing the ValidateUser(UserName, Password) method... I am building this in a DLL that will sit with our internal web site. What is the best approach to make this work? The DLL will not reference the web app and the web app will reference the DLL. How do I make the DLL aware of the Membership Provider? TIA PS: If this has been answered elsewhere please direct me to that... EDIT: I found an article on using ASP.NET Membership with WinForms and/or WPF applications. Unfortunately, these depend on an app.config file. A DLL appears to not use the app.config once published. If I am wrong, please set me straight! The article is here: http://aspalliance.com/1595_Client_Application_Services__Part_1.all

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  • What can you do in C without "std" includes? Are they part of "C," or just libraries?

    - by Chris Cooper
    I apologize if this is a subjective or repeated question. It's sort of awkward to search for, so I wasn't sure what terms to include. What I'd like to know is what the basic foundation tools/functions are in C when you don't include standard libraries like stdio and stdlib. What could I do if there's no printf(), fopen(), etc? Also, are those libraries technically part of the "C" language, or are they just very useful and effectively essential libraries?

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