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• How to implement B+ Tree for file systems ?

  - by user312544

  I have a text file which contains some info on extents about all the files in the file system, like below C:\Program Files\abcd.txt 12345 100 23456 200 C:\Program Files\bcde.txt 56789 50 26746 300 ... Now i have another binary which tries to find out about extents for all the files. Now currently i am using linear search to find extent info for the files in the above mentioned text file. This is a time consuming process. Is there a better way of coding this ? Like Implementing any good data structure like BTree. If B+ Tree is used what is the key, branch factor i need to use ?

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• Digital clocking systems/software? (employee clocking)

  - by Bill

  How does a digital clocking system deal with user error such as someone forgetting to clock out or someone erroneously entering their code causing them to clock someone else in/out (who might not even be on the schedule that day). Its obvious there could be issues of dishonesty, but what about human error?

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• How to convert value of Generic Type Argument to a concrete type?

  - by Aleksey Bieneman

  I am trying to convert the value of the generic type parameter T value into integer after making sure that T is in fact integer: public class Test { void DoSomething<T>(T value) { var type = typeof(T); if (type == typeof(int)) { int x = (int)value; // Error 167 Cannot convert type 'T' to 'int' int y = (int)(object)value; // works though boxing and unboxing } } } Although it works through boxing and unboxing, this is an additional performance overhead and i was wandering if there's a way to do it directly. Thank you!

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• Web Control added in .master control type not found in child page

  - by turtle

  I have a Web Site project, and within it I have a user Web Control defined in an ascx file. The control is added to the Site.Master, and it shows up correctly on the page and everything is fine. I need to override some of the control's fields on one of the pages that derive from Site.Master. // In OnLoad: MyControlName control = (MyControlName) Page.Master.GetBaseMasterPage().FindControl("controlID")); The issue is that MyControlName doesn't register as a valid Type on the child page. If I add a second instance of the control to the child page directly, the above works as needed, but if the control isn't placed directly on the page, and instead is only defined in the master page, the type is undefined. The control is not in a namespace, and is defined within the project, so I don't know why it is having such an issue location the appropriate type. If I put a breakpoint in the OnLoad, the type listed for the control is ASP.my_control_name_ascx, but using that does not work either. Why can't the child class reference the correct type? Can I fix this? Thanks!

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• Function return type style

  - by JB

  I'm learning c++0x, at least the parts supported by the Visual C++ Express 2010 Beta. This is a question about style rather than how it works. Perhaps it's too early for style and good practice to have evolved yet for a standard that isn't even released yet... In c++0x you can define the return type of a method using - type at the end of the function instead of putting the type at the start. I believe this change in syntax is required due to lambdas and some use cases of the new decltype keyword, but you can use it anywhere as far as I know. // Old style int add1(int a, int b) { return a + b; } // New style return type auto add2(int a, int b) -> int { return a + b; } My question really then, is given that some functions will need to be defined in the new way is it considered good style to define all functions in this way for consistency? Or should I stick to only using it when necessary?

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• Problem with incomplete type while trying to detect existence of a member function

  - by abir

  I was trying to detect existence of a member function for a class where the function tries to use an incomplete type. The typedef is struct foo; typedef std::allocator<foo> foo_alloc; The detection code is struct has_alloc { template<typename U,U x> struct dummy; template<typename U> static char check(dummy<void* (U::*)(std::size_t),&U::allocate>*); template<typename U> static char (&check(...))[2]; const static bool value = (sizeof(check<foo_alloc>(0)) == 1); }; So far I was using incomplete type foo with std::allocator without any error on VS2008. However when I replaced it with nearly an identical implementation as template<typename T> struct allocator { T* allocate(std::size_t n) { return (T*)operator new (sizeof(T)*n); } }; it gives an error saying that as T is incomplete type it has problem instantiating allocator<foo> because allocate uses sizeof. GCC 4.5 with std::allocator also gives the error, so it seems during detection process the class need to be completely instantiated, even when I am not using that function at all. What I was looking for is void* allocate(std::size_t) which is different from T* allocate(std::size_t). My questions are (I have three questions, but as they are correlated , so I thought it is better not to create three separate questions). Why MS std::allocator doesn't check for incomplete type foo while instantiating? Are they following any trick which can be implemented ? Why the compiler need to instantiate allocator<T> to check the existence of the function when sizeof is not used as sfinae mechanism to remove/add allocate in the overload resolutions set? It should be noted that, if I remove the generic implementation of allocate leaving the declaration only, and specialized it for foo afterwards such as struct foo{}; template< struct allocator { foo* allocate(std::size_t n) { return (foo*)operator new (sizeof(foo)*n); } }; after struct has_alloc it compiles in GCC 4.5 while gives error in VS2008 as allocator<T> is already instantiated and explicit specialization for allocator<foo> already defined. Is it legal to use nested types for an std::allocator of incomplete type such as typedef foo_alloc::pointer foo_pointer; ? Though it is practically working for me, I suspect the nested types such as pointer may depend on completeness of type it takes. It will be good to know if there is any possible way to typedef such types as foo_pointer where the type pointer depends on completeness of foo. NOTE : As the code is not copy paste from editor, it may have some syntax error. Will correct it if I find any. Also the codes (such as allocator) are not complete implementation, I simplified and typed only the portion which I think useful for this particular problem.

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• Embedded systems linux

  - by bhaskaragr29

  I want to make final year project so i want a two way interface device one connect to server and other connect to ouput display device..like television. whats are the rquirements i need....and how do i this.

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• Allocation of IP Address in Ad hoc systems

  - by Kasturi

  Me and my friends play Age of Empires every weekend and create an Ad-hoc network each time before playing. But each time we all get the SAME IP Address even if a new ad-hoc network is created. Is this something to do with the Game's algorithm or does the laptop remember our previous IP Address. EDIT: What is the algorithm that is used to distribute the IP Addresses? If the algorithm uses random function how come same IP addresses are being allocated.

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• Custom Content-Type for File in Rails 'public' Folder

  - by Kevin Sylvestre

  For assets stored in the 'public' folder of a ruby-on-rails application is it possible to change the 'Content-Type' when running 'script/server'? For example, I am attempting to create an HTML5 application supporting offline mode, and have an 'offline.manifest'. When I run: curl -I localhost:3000/offline.mainfest The following header information is returned: HTTP/1.1 200 OK ... Content-Type: text/plain ... However, HTML5 specifications require: HTTP/1.1 200 OK ... Content-Type: text/cache-manifest ...

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• C++ choose function by return type.

  - by anon

  I realize standard C++ only picks functions by argument type, not return type. I.e I can do something like: void func(int); void func(double); but not double func(); int func(); Where in the former, it's clear, in the latter, it's ambigious. Are there any extensions that lets me tell C++ to pick which function to use also by return type? Thanks!

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• How to implement table-per-concrete-type using entity framework

  - by SDReyes

  Hello Guys! I'm mapping a set of tables that share a common set of fields: So as you can see I'm using a table-per-concrete-type strategy to map the inheritance. But... I have not could to relate them to an abstract type containing these common properties. It's possible to do it using EF? BONUS: The only non documented Entity Data Model Mapping Scenario is Table-per-concrete-type inheritance http://msdn.microsoft.com/en-us/library/cc716779.aspx : P

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• LINQ TO SQL, Dynamic query with DATE type fields

  - by acanthus

  Hello, I'm building a query with the LINQ dynamic library so I don't know how many potential parameters will I have and I get an error when trying to query DATE type fields: Operator '=' incompatible with operand types 'DateTime' and 'String' When I step through the debugger in the Dynamic.cs it shows that the value is of type string and the field is of type date so the problem is obvious but I have no idea how to approach it. Any ideas? BR

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• how to get the type of input?

  - by Trez

  How to get the type of input in the form? for example: <input type="text" value="123" name="username" /> the return type should be "text". Any ideas?

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• safe structures embedded systems

  - by user405633

  I have a packet from a server which is parsed in an embedded system. I need to parse it in a very efficient way, avoiding memory issues, like overlapping, corrupting my memory and others variables. The packet has this structure "String A:String B:String C". As example, here the packet received is compounded of three parts separated using a separator ":", all these parts must be accesibles from an structure. Which is the most efficient and safe way to do this. A.- Creating an structure with attributes (partA, PartB PartC) sized with a criteria based on avoid exceed this sized from the source of the packet, and attaching also an index with the length of each part in a way to avoid extracting garbage, this part length indicator could be less or equal to 300 (ie: part B). typedef struct parsedPacket_struct { char partA[2];int len_partA; char partB[300];int len_partB; char partC[2];int len_partC; }parsedPacket; The problem here is that I am wasting memory, because each structure should copy the packet content to each the structure, is there a way to only save the base address of each part and still using the len_partX.

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• Mapping to a different view based on child type

  - by Ryan Burnham

  So i have a situation where i have common base type but i need to map to a different view based on the child type. It looks like i can use a generic mapping class to handle the inheritance http://geekswithblogs.net/nharrison/archive/2010/07/09/inheriting-a-class-map-in-fluent-nhibernate.aspx But how can i conditionally map to a different view based on the child type? I see an EntityType property but it says its obsolete and will be made private in the next version. As an example i have a base class of ContactInfo is standard between contact types but the values come from different places depending on the contact type, this I'll handle through the sql view.

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• singledispatch in class, how to dispatch self type

  - by yanxinyou

  Using python3.4. Here I want use singledispatch to dispatch different type in __mul__ method . The code like this : class Vector(object): ## some code not paste @functools.singledispatch def __mul__(self, other): raise NotImplementedError("can't mul these type") @__mul__.register(int) @__mul__.register(object) # Becasue can't use Vector , I have to use object def _(self, other): result = Vector(len(self)) # start with vector of zeros for j in range(len(self)): result[j] = self[j]*other return result @__mul__.register(Vector) # how can I use the self't type @__mul__.register(object) # def _(self, other): pass # need impl As you can see the code , I want support Vector*Vertor , This has Name error Traceback (most recent call last): File "p_algorithms\vector.py", line 6, in <module> class Vector(object): File "p_algorithms\vector.py", line 84, in Vector @__mul__.register(Vector) # how can I use the self't type NameError: name 'Vector' is not defined The question may be How Can I use class Name a Type in the class's method ? I know c++ have font class statement . How python solve my problem ? And it is strange to see result = Vector(len(self)) where the Vector can be used in method body .

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• How to convert string to any type

  - by DJPB

  Hi there I want to convert a string to a generic type I have this: string inputValue = myTxtBox.Text; PropertyInfo propInfo = typeof(MyClass).GetProperty(myPropertyName); Type propType = propInfo.PropertyType; object propValue = ????? I want to convert 'inputString' to the type of that property, to check if it's compatible how can I do that? tks

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• system-wide hook for 64-bit operating systems

  - by strDisplayName

  Hey everybody I want to perform a system-wide hook (using SetWindowHook) on a 64bit operating system. I know that 64bit processes (= proc64) can load only 64bit dlls (= dll64) and 32bit processes (= proc32) can load only 32bit dlls (= dll32). Currently I am planning to call SetWindowHook twice, once with dll32 and once with dll64, expecting that proc64s will load dll64 and proc32s will load dll32 (while dll32 for proc64s and dll64 for proc32s will fail). Is that the correct way to do that, or is there a "more correct" way to do that? Thanks! :-)

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• GDI+ on 64bit systems

  - by LaZe

  Our system uses a lot of large Bitmaps (System.Drawing.Bitmap) and sometimes we run out of memory and gets a "Parameter is not valid" error. This makes sense, since it can be difficult to allocate large continuous chunk of memory. So the question is... If we upgraded the system to 64bit, would this problem go away?

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• Sorting and displaying a custom QVariant type.

  - by Kranar

  Hello, I have a custom type I'd like to use with QVariant but I don't know how to get the QVariant to display in a table or have it sort in a QSortFilterProxyModel. I register the type with Q_DECLARE_METATYPE and wrote streaming operators registered via qRegisterMetaTypeStreamOperators but for whatever reason when I use the type with a table model, it doesn't display anything and it doesn't sort. I should specify that this custom type can not be modified. It has a copy and default constructor, but I can not go in and modify the source code to get it to work with QVariant. Is there a way of non-intrusively getting the behaviour I'd like?

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• What type of objects can be sent back to an action Method using HTML.HIDDEN()

  - by Richard77

  Hello, 1)Let's say I've this form: <%Using(Html.BeginForm()){%> <% = Html.Hidden("myObject", (cast to the appropriate type)ViewData["KeyForMyObject"]%> <input type = "submit" "Submit Object"> <%}%> 2) Here's the Action which's supposed to intercept the value of the object public ActionResult MyAction(Type myObject) { //Do Something with the object } Here's my question: What type of objects the Hidden field can support? In fact, when ViewData["KeyForMyObject"] contains a string, int, or bool, myAction is able to retrieve the value. But, when it comes to objects, such as List, and dictionary, nothing happens. When I debug to check the local values, I see null for Type myObject in the MyMethod. So what are the rules in MVC when it comes to a List or Dictionary? ================================= EDIT To make things simpler, can I write something like this <% = Html.Hidden("contactDic", (Dictionary<string, string>) ViewData["contacts"])%> and expect to retrieve the dictionary in the action Method like this public ActionResult myMethod(Dictionary<string, string> contactDic) { //Do something with the dictionary } Thanks for Helping

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• Inferring type from method generics

  - by ng

  I am from a Java background and I am looking from the equivalent in c# for the following. public interface Reader { <T> T read(Class<? extends T> type); } Such that I can do the following, constraining the parameter and inferring the return type. Cat cat = reader.read(Cat.class); Dog dog = reader.read(Dog.class); I was hoping something like this would work in c# but I am not sure it will. public interface Reader { T Read<T>(); } And and do this. public class TypeReader : Reader { public T Read<T>() { Type type = T.GetType(); ... } } Is something like this even possible in c#?

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• Incompatible pointer type

  - by Boffin

  Hello. I have the function with following signature: void box_sort(int**, int, int) and variable of following type: int boxes[MAX_BOXES][MAX_DIMENSIONALITY+1] When I am calling the function box_sort(boxes, a, b) GCC gives me two warnings: 103.c:79: warning: passing argument 1 of ‘box_sort’ from incompatible pointer type (string where i am calling the function) 103.c:42: note: expected ‘int **’ but argument is of type ‘int (*)[11] (string where the function is defined) The question is why? Whether int x[][] and int** x (and actually int* x[]) are not the same types in C?

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• Using generic type from other generic parameter

  - by DEHAAS

  Hi, I have a question about .net generics. Consider the following code: public class Test<TKey> { TKey Key { get; set; } } public class Wrapper<TValue, TKey> where TValue : Test<TKey> { public TValue Value { get; set; } } Now, when using this code, I could do something like this: Wrapper<Test<int>, int> wrapper = new Wrapper<Test<int>, int>(); The int type parameter has to be provided twice. Is it possible to modify the Wrapper definition, to require TValue to be a generic type, and use this 'nested' generic type parameter insted of the TKey type parameter?

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• Objective C - creating concrete class instances from base class depending upon type

  - by indiantroy

  Just to give a real world example, say the base class is Vehicle and concrete classes are TwoWheeler and FourWheeler. Now the type of the vehicle - TwoWheeler or FourWheeler, is decided by the base class Vehicle. When I create an instance of TwoWheeler/FourWheeler using alloc-init method, it calls the super implementation like below to set the value of common properties defined in the Vehicle class and out of these properties one of them is type that actually decides if the type is TwoWheeler or FourWheeler. if (self = [super initWithDictionary:dict]){ [self setOtherAttributes:dict]; return self; } Now when I get a collection of vehicles some of them could be TwoWheeler and others will be FourWheeler. Hence I cannot directly create an instance of TwoWheeler or FourWheeler like this Vehicle *v = [[TwoWheeler alloc] initWithDictionary:dict]; Is there any way I can create an instance of base class and once I know the type, create an instance of child class depending upon type and return it. With the current implementation, it would result in infinite loop because I call super implementation from concrete class. What would be the perfect design to handle this scenario when I don't know which concrete class should be instantiated beforehand?

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