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  • Speed comparison - Template specialization vs. Virtual Function vs. If-Statement

    - by Person
    Just to get it out of the way... Premature optimization is the root of all evil Make use of OOP etc. I understand. Just looking for some advice regarding the speed of certain operations that I can store in my grey matter for future reference. Say you have an Animation class. An animation can be looped (plays over and over) or not looped (plays once), it may have unique frame times or not, etc. Let's say there are 3 of these "either or" attributes. Note that any method of the Animation class will at most check for one of these (i.e. this isn't a case of a giant branch of if-elseif). Here are some options. 1) Give it boolean members for the attributes given above, and use an if statement to check against them when playing the animation to perform the appropriate action. Problem: Conditional checked every single time the animation is played. 2) Make a base animation class, and derive other animations classes such as LoopedAnimation and AnimationUniqueFrames, etc. Problem: Vtable check upon every call to play the animation given that you have something like a vector<Animation>. Also, making a separate class for all of the possible combinations seems code bloaty. 3) Use template specialization, and specialize those functions that depend on those attributes. Like template<bool looped, bool uniqueFrameTimes> class Animation. Problem: The problem with this is that you couldn't just have a vector<Animation> for something's animations. Could also be bloaty. I'm wondering what kind of speed each of these options offer? I'm particularly interested in the 1st and 2nd option because the 3rd doesn't allow one to iterate through a general container of Animations. In short, what is faster - a vtable fetch or a conditional?

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  • Percentage function for a group based on another group.

    - by Jeff O
    I have two grouping levels in a report. Group A can have a Percentage() of the entire report and so can Group B, but I would like to know the Percentage() of Group A of Group B. Even if I code it, it seems like once the inner and outer groups have created their footers, I can't go back to to the inner group and set it's value. Example: Group A Total 50 Group A percentage of Report Total = 33% Group A Percentage of Group B Total = 33% but I want 50% Group B Total 100 Group B Percentage of Report Total = 66% Report Total 150

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  • Write a function int mystrlen(char *s) that returns the number of characters in a string wuthout str

    - by henry
    heres what i did, i just have ne error that i cant figure out. int mystrlen(char string[]) { char string1[LENGHT], string2[LENGHT]; int len1, len2; char newstring[LENGHT*2]; printf("enter first string:\n"); len1 = mystrlen(string1); printf("enter second string:\n"); len2 = mystrlen(string2); if(len1 == EOF || len2 == EOF) exit(1); strcpy(newstring, string1); strcat(newstring, string2); printf("%s\n", newstring); return 0;

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  • How to decide if a parameter is the click event

    - by sameold
    I have a function which can be called by either a click event or directly. When I call it directly, I need pass it a data parameter, so I've defined the function to accept a parameter to account for the direct call with the parameter. function myFunc(param){ } Within the function, I need to differentiate whether the function was called directly or from the click event, so what I thought I could simply check if param is set. If it's set, then the function is called directly. If it's not set, then it's called from the click event. The problem is that a click event by default passes an event object. So even when the function is called by the click event, param won't be null. So is there a way to check whether the param passed is the click event?

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  • Variable scope problem in JavaScript

    - by dfjhdfjhdf
    I declare a variable with the var word inside a function that handles Ajax requests, then later on in the function I have another function that should change the value of the variable but - my problem - it fails. How to settle the problem down? Here's similiar code I use: function sendRuest(someargums) { /* some code */ var the_variable; /* some code */ //here's that other function request.onreadystatechange = function() { if (request.readyState == 4) { switch (request.status) { case 200: //here the variable should be changed the_variable = request.responseXML; /* a lot of code */ //somewhere here the function closes } return the_variable; } var data = sendRequest(someargums); //and trying to read the data I get the undefined value

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  • Call methods on native Javascript types without wrapping with ()

    - by Anurag
    In Javascript, we can call methods on string literals directly without enclosing it within round brackets. But not for other types such as numbers, or functions. It is a syntax error, but is there a reason as to why the Javascript lexer needs these other types to be enclosed in round brackets? For example, if we extend Number, String, and Function with an alert method and try calling this method on the literals, it's a SyntaxError for Number and Function, while it works for a String. function alertValue() { alert(this); } Number.prototype.alert = alertValue; String.prototype.alert = alertValue; Function.prototype.alert = alertValue; We can call alert directly on a string object: "someStringLiteral".alert() // alerts someStringLiteral but it's a SyntaxError on numbers, and functions. 7.alert(); function() {}.alert(); To work with these types, we have to enclose it within brackets: (7).alert(); // alerts "7" (function() {}).alert(); // alerts "function() {}"

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  • How can one enforce calling a base class function after derived class constructor?

    - by Mike Elkins
    I'm looking for a clean C++ idiom for the following situation: class SomeLibraryClass { public: SomeLibraryClass() { /* start initialization */ } void addFoo() { /* we are a collection of foos */ } void funcToCallAfterAllAddFoos() { /* Making sure this is called is the issue */ } }; class SomeUserClass : public SomeLibraryClass { public: SomeUserClass() { addFoo(); addFoo(); addFoo(); // SomeUserClass has three foos. } }; class SomeUserDerrivedClass : public SomeUserClass { public: SomeUserDerrivedClass() { addFoo(); // This one has four foos. } }; So, what I really want is for SomeLibraryClass to enforce the calling of funcToCallAfterAllAddFoos at the end of the construction process. The user can't put it at the end of SomeUserClass::SomeUserClass(), that would mess up SomeUserDerrivedClass. If he puts it at the end of SomeUserDerrivedClass, then it never gets called for SomeUserClass. To further clarify what I need, imagine that /* start initialization */ acquires a lock, and funcToCallAfterAllAddFoos() releases a lock. The compiler knows when all the initializations for an object are done, but can I get at that information by some nice trick?

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  • Custom events and event pooling in jQuery - What's the point?

    - by Nick Lowman
    I've been reading about custom events in jQuery and why they should be used but I'm still clearly missing the point. There is a very good article I read here that has the following code example; function UpdateOutput() { var name = $('#txtName').val(); var address = $('#txtAddress').val(); var city = $('#txtCity').val(); $('#output').html(name + ' ' + address + ' ' + city); } $(document).bind('NAME_CHANGE ADDRESS_CHANGE CITY_CHANGE', function() { UpdateOutput(); }); $('#txtAddress').keyup(function() { $(document).trigger('ADDRESS_CHANGE'); }); $('#txtCity').keyup(function() { $(document).trigger('CITY_CHANGE'); }); Can someone tell me why I just don't call the UpdateOutput() function directly? It would still work exactly the same way, i.e. $('#txtAddress').keyup(function() { UpdateOutput() }); $('#txtCity').keyup(function() { UpdateOutput() }); Many thanks

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  • how do i design a high pass filters in matlab without using the builtin function?

    - by noura
    hello everyone, i'm just not sure how to draw the frequency response (H) of the high pass filter? after drawing the frequency response i can get the b coefficient by taking the ifft of (H). so yeah, for a low pass filter, with a cutoff frequency of say pi/2 : the frequency response code will be H = exp(-1*j*w*4).*(((0 <= w) & (w<= pi/2)) | ((2*pi - pi/2 <= w) & (w<=2*pi)); sincr the response is "1" between 0 and pi/2 and between (2*pi - pi/2) and 2*pi. can you help me write H for a high pass filter? thanx in advance.

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  • How to implement a private virtual function within derived classes?

    - by Dane
    Hi, I know why I want to use private virtual functions, but how exactly can I implement them? For example: class Base{ [...] private: virtual void func() = 0; [...] } class Derived1: puplic Base{ void func() { //short implementation is ok here } } class Derived2: puplic Base{ void func(); //long implementation elsewhere (in cpp file) } [...] void Derived2::func() { //long implementation } The first version is ok but not always possible. Isn't the second version simply name hiding? How do you define the Base::func() of Derived2, if you cannot do it within the class declaration of Dereived2? Thanks

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  • PHP & bash; Linux; Compile my own function

    - by flienteen
    Hi. I would like to make my own program but I have no idea how.. for example I want to make a typical 'Hello $user' program. So.. +-- hi ¦   +-- hi.sh ¦   +-- hi_to.sh hi.sh #!/bin/bash ~/hi/hi_to.sh $1 hi_to.sh #!/usr/bin/php <?php echo "\nHellO ".$argv[1]."\n"; ?> Run it in terminal: me:~/hi ? ./hi.sh User HellO User and my question is: how to compile all this files into one bash program?

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  • Haskell: Why is it saying my function type is off?

    - by linkmaster03
    I wrote a little Haskell program to find the area of a triangle, primarily to practice custom types, but it keeps throwing the following error on compile: areafinder.hs:7:4: Couldn't match expected type 'Triangle' against inferred type 'm b' In a stmt of a 'do' expression: putStr "Base: " In the expression: do { putStr "Base: "; baseStr I'm not sure where 'm b' comes from, so I'm at a loss here. Why is it throwing this error, and what can I do to fix it? Here is my code: module Main where data Triangle = Triangle Double Double -- base, height getTriangle :: Triangle getTriangle = do putStr "Base: " baseStr Double calcTriangle (Triangle base height) = base * height main = putStrLn ("Area = " ++ show (calcTriangle getTriangle)) Thanks. :)

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  • Where do I put all these function-like #defines, in C?

    - by Tristan
    I'm working with an embedded system, and I'm ending up with a ton of HW-interfacing #define functions. I want to put all of these into a separate file (for OOP-ness), but I don't know the best way to #include that. Do I just put them all into a .c file, then include that? Seems silly to put these in a .h file.

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  • Does template class/function specialization improves compilation/linker speed?

    - by Stormenet
    Suppose the following template class is heavily used in a project with mostly int as typename and linker speed is noticeably slower since the introduction of this class. template <typename T> class MyClass { void Print() { std::cout << m_tValue << std::endl;; } T m_tValue; } Will defining a class specialization benefit compilation speed? eg. void MyClass<int>::Print() { std::cout << m_tValue << std::endl; }

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  • Is it bad practice to declare an array mid-function...

    - by Maximus
    In C, which would be more proper... void MyFunction() { int* array; int size; //do a bunch of stuff size = 10; array = (int*)(sizeof(int)*size); //do more stuff... //no longer need array... free(array); } Or is something like this okay? void MyFunction() { int size; //do a bunch of stuff size = 10; array[size]; //do more stuff... } The malloc uses the heap instead of the stack, so I suppose if you know size is going to be very large you'd want to malloc... but if you're quite certain size will be small enough, would the second method be reasonable?

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  • Telerik ASP.NET MVC2 Grid Delete Function with compound key.

    - by Dani
    I have a grid with a compound key: OrderId, ItemID. When I update the grid - the public ActionResult UpdateItemGridAjax(int OrderID, string ItemID) Gets both values from the grid. When I delete a row I get only the first one: public ActionResult DeleteItemGridAjax(int OrderID, string ItemID) Why is it happens and how can I get the ItemId value of the deleted row ? Grid Definition: <%= Html.Telerik().Grid<ItemsInOrderPOCO>() .Name("ItemsInOrderGrid") .DataKeys(dataKeys => { dataKeys.Add(e => e.OrderID); dataKeys.Add(e => e.ItemID); }) .ToolBar(commands => commands.Insert()) .DataBinding(dataBinding => { dataBinding.Ajax() //Ajax binding .Select("SelectItemGridAjax", "Orders", new { OrderID = Model.myOrder.OrderID }) .Insert("InsertItemGridAjax", "Orders", new { OrderID = Model.myOrder.OrderID }) .Update("UpdateItemGridAjax", "Orders") .Delete("DeleteItemGridAjax", "Orders"); }) .Columns(c => { c.Bound(o => o.ItemID); c.Bound(o => o.OrderID).Column.Visible = false; c.Bound(o => o.ItemDescription); c.Bound(o => o.NumOfItems); c.Bound(o => o.CostOfItem); c.Bound(o => o.TotalCost); c.Bound(o => o.SupplyDate); c.Command(commands => { commands.Edit(); commands.Delete(); }).Width(180).Title("Upadte"); })

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  • What hack can I use to suppress an unused function warning?

    - by Yuval A
    Consider a private method which is called from JNI and not used otherwise, generating a compiler warning about an unused method: private void someMethodCalledOnlyFromJNI() { // WARNING: method is never used // .... } This is some legacy code in Java 1.4 - so no dice on @SuppressWarnings. What hack would you use to suppress this compiler warning?

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