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• C++ domain specific embedded language operators

  - by aaa

  hi. In numerical oriented languages (Matlab, Fortran) range operator and semantics is very handy when working with multidimensional data. For example: A(i:j,k,:n) // represents two-dimensional slice B(i:j,0:n) of A at index k unfortunately C++ does not have range operator (:). of course it can be emulated using range/slice functor, but semantics is less clean than Matlab. I am prototyping matrix/tensor domain language in C++ and am wondering if there any options to reproduce range operator. I still would like to rely on C++/prprocessor framework exclusively. So far I have looked through boost wave which might be an suitable option. is there any other means to introduce new operators to C++ DSL?

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• Potential problems porting to different architectures

  - by Brendan Long

  I'm writing a Linux program that currently compiles and works fine on x86 and x86_64, and now I'm wondering if there's anything special I'll need to do to make it work on other architectures. What I've heard is that for cross platform code I should: Don't assume anything about the size of a pointer, int or size_t Don't make assumptions about byte order (I don't do any bit shifting -- I assume gcc will optimize my power of two multiplication/division for me) Don't use assembly blocks (obvious) Make sure your libraries work (I'm using SQLite, libcurl and Boost, which all seem pretty cross-platform) Is there anything else I need to worry about? I'm not currently targeting any other architectures, but I expect to support ARM at some point, and I figure I might as well make it work on any architecture if I can. Also, regarding my second point about byte order, do I need to do anything special with text input? I read files with getline(), so it seems like that should be done automatically as well.

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• C++ Thread Safe Integer

  - by Paul Ridgway

  Hello everyone, I have currently created a C++ class for a thread safe integer which simply stores an integer privately and has public get a set functions which use a boost::mutex to ensure that only one change at a time can be applied to the integer. Is this the most efficient way to do it, I have been informed that mutexes are quite resource intensive? The class is used a lot, very rapidly so it could well be a bottleneck... Googleing C++ Thread Safe Integer returns unclear views and oppinions on the thread safety of integer operations on different architectures. Some say that a 32bit int on a 32bit arch is safe, but 64 on 32 isn't due to 'alignment' Others say it is compiler/OS specific (which I don't doubt). I am using Ubuntu 9.10 on 32 bit machines, some have dual cores and so threads may be executed simultaneously on different cores in some cases and I am using GCC 4.4's g++ compiler. Thanks in advance...

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• How might one implement FileTimeToSystemTime?

  - by Billy ONeal

  Hello :) I'm writing a simple wrapper around the Win32 FILETIME structure. boost::datetime has most of what I want, except I need whatever date type I end up using to interpolate with Windows APIs without issues. To that end, I've decided to write my own things for doing this -- most of the operations aren't all that complicated. I'm implementing the TimeSpan - like type at this point, but I'm unsure how I'd implement FileTimeToSystemTime. I could just use the system's built-in FileTimeToSystemTime function, except FileTimeToSystemTime cannot handle negative dates -- I need to be able to represent something like "-12 seconds". How should something like this be implemented? Billy3

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• Getting meaningful error messages from fstream's in C++

  - by Hassan Syed

  What is the best way to get meaningful file access error messages, in a portable way from std::fstreams ? The primitiveness of badbits and failbits is getting to be bit annoying. I have written my own exception hierarchies against win32 and POSIX before, and that was far more flexible than the way the STL does it. I am getting "basic::ios_clear" as an error message from the what method of a downcasted catch (std::exception) of a fstream which has exceptions enabled. This doesn't mean much to me, although I do know what the problem is I'd like my program to be a tad more informative so that when I start deployment a few months later my life will be easier. Is there anything in Boost to extract meaningful messages out of the ofstream's implementation cross platform and cross STL implementation ?

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• Json problem with Page Method call on IE 8.

  - by ProfK

  I have the following code that populates a select element with values from an ajax call, via a Page Method. In FF, the code works perfectly, in IE8 I get the error: 'ResourceList[...].id' is null or not an object. What can I look at here? function readShift(jsonString) { var shiftInfo = Sys.Serialization.JavaScriptSerializer.deserialize(jsonString); var listItems = ""; listItems += "<option value='0'>[Unassigned]</option>"; for (var i = 0; i < shiftInfo.ResourceList.length; i++) { listItems += "<option value='" + shiftInfo.ResourceList[i].id + "'>" + shiftInfo.ResourceList[i].name + "</option>"; } $("#" + resourceListId).html(listItems); };

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• When to trash hashmap contents to avoid performance degradation?

  - by Jack

  Hello, I'm woking on Java with a large (millions) hashmap that is actually built with a capacity of 10.000.000 and a load factor of .75 and it's used to cache some values since cached values become useless with time (not accessed anymore) but I can't remove useless ones while on the way I would like to entirely empty the cache when its performance starts to degrade. How can I decide when it's good to do it? For example, with 10 millions capacity and .75 should I empty it when it reaches 7.5 millions of elements? Because I tried various threshold values but I would like to have an analytic one. I've already tested the fact that emping it when it's quite full is a boost for perfomance (first 2-3 algorithm iterations after the wipe just fill it back, then it starts running faster than before the wipe) Thanks

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• Apache thrift, struct contain itself

  - by mamu

  I am looking into thrift for serialization of data. But Document says cyclic structs - Structs can only contain structs that have been declared before it. A struct also cannot contain itself One of our requirement is Struct A List of Child items Items(Items are Struct A ) So reading requirement i can't have Struct within itself at any level? can i have it in cyclic model as i have it above. Struct is not member of Struct directly but it has some other member and it contains struct. Their document is not so well descriptive. Is it possible in Thrift? Does protobuf supports it?

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• what this `^` mean here in solr

  - by Rahul Mehta

  I am confuse her but i want to clear my doubt. I think it is stupid question but i want to know. Use a TokenFilter that outputs two tokens (one original and one lowercased) for each input token. For queries, the client would need to expand any search terms containing upper case characters to two terms, one lowercased and one original. The original search term may be given a boost, although it may not be necessary given that a match on both terms will produce a higher score. text:NeXT ==> (text:NeXT^10 OR text:next) what this ^ mean here . http://wiki.apache.org/solr/SolrRelevancyCookbook#Relevancy_and_Case_Matching

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• C++ build systems

  - by flo

  I will start a new C++ project (it may have some C components as well) soon and I am looking for a modern, industrial-strength (i.e. non-beta) build system. The software will be created by several developers in 3-5 years and will run on Linux (Mac OS X and Windows might be supported later). I am looking for something that has better comprehensibility, ease-of-use and maintainability than e.g. make but is still powerful enough to handle a complex project. Open source software is preferred. I started looking into Boost.Build, CMake, Maven and SCons so far and liked features and concepts of all of those, but I'm lacking the experience to make a decision for a large project.

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• LALR(1) or GLR on Windows - Alternatives to Bison++ / Flex++ that are current?

  - by mrjoltcola

  I have been using the same version of bison++ (1.21-8) and flex++ (2.3.8-7) since 2002. I'm not looking for an alternative to LALR(1) or GLR at this time, just looking for the most current options. Is anyone aware of any later ports of these than the original that aren't Cygwin dependent? What are other folks using in Windows environments for C++ compiler development (besides ANTLR or Boost.spirit)? Commercial options are ok, if you have firsthand experience. I do need to compile on Linux as well.

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• How do you debug c/c++ source code in linux using emacs?

  - by vmihai

  Hello all, I am using emacs and autotools, to write and compile c/c++ sources on linux. I am using gdb via GUD in emacs. I have defined for convenience: F7:compile, F10:gud-next, F11:gud-step, F5:gud-cont, F9:gud-tbreak, F8:gud-until, F4:gud-print. I am mainly interested in debugging c/c++ source code on linux from emacs and I would like to get the most gdb can give. Unfortunately I am using only F4 which prints the variable under cursor. So my question is how do you guys debug the source code ? What programs do you use ? What key bindings (functionality) do you use mostly ? What do you need the debugger to do for you ? If you do weird stuff it doesn't matter. I would like to know everything to boost my speed a bit here. Thanks in advance. Mihai

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• Passing an object as a parameter to a windows service

  - by user220723

  Is there some way to pass an object to a windows service? I know the method myServiceController.Star(string[] arg) but i need to pass a more complex object than a string array. Actually, i don't need the object to be passed as a parameter, what i really needs is that the service can use an object created in a windows forms application. I've tried using System.Web.Script.Serialization.JavaScriptSerializer.Serialize method to convert the object into a Json but i couldn't because the object contains a circular reference. I also tried using pointers, but i couldn't becouse it is a managed type object. Any idea what can i do?

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• Ravendb 960 does not honor JsonIgnore with property of Dictionary<string, object>

  - by David Robbins

  Does JsonIgnore not work when a property has data? I have the followin class: public class SomeObject { public string Name { get; set; } public DateTime Created { get; set; } public List<string> ErrorList { get; set; } [JsonIgnore] public Dictionary<string, object> Parameters { get; set; } public SomeObject() { this.ErrorList = new List<string>(); this.Parameters = new Dictionary<string, object>(); } } My expectation was that JsonIgnore would exclude properties from De- / Serialization. My RavenDB document has data. Am I missing something?

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• Function template accepting nothing less than a bidirectional iterator or a pointer

  - by san

  I need a function template that accepts two iterators that could be pointers. If the two arguments are random_access iterators I want the return type to be an object of std::iterator<random_access_iterator_tag, ...> type else a std::iterator<bidirectional_iterator_tag, ...> type. I also want the code to refuse compilation if the arguments are neither a bidirectional iterator, nor a pointer. I cannot have dependency on third party libraries e.g. Boost Could you help me with the signature of this function so that it accepts bidirectional iterators as well as pointers, but not say input_iterator, output_iterator, forward_iterators. One partial solution I can think of is the following template<class T> T foo( T iter1, T iter2) { const T tmp1 = reverse_iterator<T>(iter1); const T tmp2 = reverse_iterator<T>(iter2); // do something } The idea is that if it is not bidirectional the compiler will not let me construct a reverse_iterator from it.

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• What to do with missing fields in sunspot-rails?

  - by chrismealy

  I'm using sunspot/rails version 2. It's working great, but I can't figure out how to handle missing fields. If I don't have latitude and longitude this code will map it to 0,0 (near Africa): searchable do text :resume, :stored => true text :city, :boost => 5 latlon(:geo) { Sunspot::Util::Coordinates.new(latitude, longitude) } end I tried using two search blocks, each with a different conditional, but sunspot just uses the first searchable block. What I want to happen is for things missing locations to still be searchable, just not by location.

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• How to return Json from WCF Service?

  - by Zinoo

  Hi, I have the piece of code below of a template Ajax enabled WCF service. What can i do to make it return JSon instead of XML? thanks. using System; using System.Linq; using System.Runtime.Serialization; using System.ServiceModel; using System.ServiceModel.Activation; [ServiceContract(Namespace = "WCFServiceEight")] [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)] public class CostService { // Add [WebGet] attribute to use HTTP GET [OperationContract] [WebGet] public double CostOfSandwiches(int quantity) { return 1.25 * quantity; } }

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• Cookie Value not available, why?

  - by Camran

  I have tested this on my development computer, but now I have uploaded everything to the production server and I cant read out the value of the cookie. I think the problem lies in the Serialization and Unserialization. if (isset($_COOKIE['watched_ads'])){ $expir = time()+1728000; //20 days $ad_arr = unserialize($_COOKIE['watched_ads']); // HERE IS THE PROBLEM $arr_elem = count($ad_arr); if (in_array($ad_id, $ad_arr) == FALSE){ if ($arr_elem>10){ array_shift($ad_arr); } $ad_arr[]=$ad_id; setcookie('watched_ads', serialize($ad_arr), $expir, '/'); } } When I echo this: count($ad_arr) I receive the expected nr, 1 in this case, so there is a value there. But when I echo the value: echo $ad_arr[0]; I get nothing. Completely blank. No text at all. Anybody have a clue? if you need more info about something let me know...

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• Options for header in raw byte file.

  - by Tim

  I have a large raw data file (up to 1GB) which contains raw samples from a USB data logger. I need to store extra information relating to the file (sample rate, description, trigger point, last seek position etc) and was looking into adding this as a some sort of header. The header file should ideally be human readable and flexible so I've so far ruled out some sort of binary serialization into a header. I also want to avoid two separate files as they could end up separated when copied or backed up. I remembered somebody telling me that newer *.*x Microsoft Office documents are actually a number of files in a zip. Is there a simple way to achieve this? Could I still keep the quick seek times to the raw file?

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• FastCGI, PHP, Sendmail, and Codeigniter

  - by Kyle J. Dye

  Hi Everyone. I am experiencing an odd issue. I just switched to FastCGI (Apache) because of the big performance boost. Everything is working great, except when I attempt to use sendmail (Codeigniter Class or just raw PHP). I have tested with and without CI and still get a 500 internal server error when trying to send. Could this be getting caused by a discrepency in how FastCGI utilizes sendmail? Has anyone else experienced this issue? Also, the email will send, it just errors afterwards. Please let me know a solution if you have one! Thanks! :)

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• Is there an easy way in Python to wait until certain condition is true?

  - by Checkers

  I need to wait in a script until a certain number of conditions become true? I know I can roll my own eventing using condition variables and friends, but I don't want to go through all the trouble of implementing it, since some object property changes come from external thread in a wrapped C++ library (Boost.Python), so I can't just hijack __setattr__ in a class and put a condition variable there, which leaves me with either trying to create and signal a Python condition variable from C++, or wrap a native one and wait on it in Python, both of which sound fiddly, needlessly complicated and boring. Is there an easier way to do it, barring continuous polling of the condition? Ideally it would be along the lines of res = wait_until(lambda: some_predicate, timeout) if (not res): print 'timed out'

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• Matrix multiplication using Matrix Template library (MTL 4)

  - by Lxc

  The program is as following: #include <iostream> #include <boost/numeric/mtl/mtl.hpp> using namespace mtl; int main(int argc, char* argv[]) { dense_vector<double> a(5,1.0); dense_vector<double> b(5,2.0); a * trans(b); } I want to calculate a * trans(b), but there is a compling error :C2893. Will someone help me? Thanks a lot!

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• Deserialising Json to derived types in Asp.Net Web API

  - by IoChaos

  I'm calling a method of my WebAPI sending a json that I would like to match (or bind) with a model. In the controller I have a method like: public Result Post([ModelBinder(typeof(CustomModelBinder))]MyClass model); 'MyClass', wich is given as a parameter is an abstract class. I would like that at, depending of the type of json passed, the correct inherited class is instantiated. To achieve it, I'm trying to implement a custom binder. The problem is that (I don't know if it's very basic but I can't find anything) I don't know how to retrieve the raw Json (or better, some kind of serialization) that comes in the request. I see: actionContext.Request.Content But all methods are exposed as async. I don't know who this fits with passing the generate model to the controller method... Thanks a lot!

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• Need some explanation about MS Ajax using PageMethods

  - by Ahmed Said

  I have a project that uses PageMethods to call functions on the server. The server functions (written in C#) return the values as array of strings, without doing any kind of serialization and in the client side (from Js) the accessing of the return values is by using static variable called arguments. I found that sometimes for some users (cases are not repro) sometimes an exception occured "WebServiceFailedException the server method 'Foo' returned invalid data. the 'd' property is missing from JSON." Some searching on google I found that people are serializing the return values using DataContractJsonSerializer class and in js accessing the return value using one of the callback function Example: function OnRequestComplete(result, userContext, methodName) { var Person = eval('(' + result + ')'); alert(Person.Forename); alert(Person.Surname); } So is the first technique is correct? or what?

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• Data persistance with BufferedReader and PrintWriter?

  - by Nazgulled

  I have this simple application with a couple of classes which are all related. There's one, the main one, for which there is only one instance of. I need to save save and load that using a text stream. My instructor requirement is BufferedReader to load the stream and PrintWriter to save it. But is this even possible? To persist a data object/class with a text stream? I know how to do it with and object, using serialization. But I don't see how am I supposed to do it using text streams. Suggestions?

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