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  • Structs inside #define in C++

    - by Adam Smith
    Being pretty new to C++, I don't quite understand some instructions I encounter such as: #ifndef BOT_H_ #define BOT_H_ #include "State.h" /* This struct represents your bot in the game of Ants */ struct Bot { State state; Bot(); void playGame(); //plays a single game of Ants void makeMoves(); //makes moves for a single turn void endTurn(); //indicates to the engine that it has made its moves }; #endif //BOT_H_ What I don't understand is the "#ifndef BOT_H_" and the "#define -- #endif" From what I gather, it defines a constant BOT_H_ if it's not already defined when the precompiler looks at it. I don't actually get how the struct inside it is a constant and how it is going to let me access the functions inside it. I also don't see why we're doing it this way? I used C++ a while back and I wasn't using .h files, so it might be something easy I'm missing.

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  • Cannot use String.Empty as a default value for an optional parameter in C# - then what's the point?

    - by Mikeyg36
    I am reading Effective C# by Bill Wagner. In Item 14 - Minimize Duplicate Initialization Logic, he shows the following example of using the new optional parameters feature in a constructor: public MyClass(int initialCount = 0, string name = "") Notice that he used "" instead of string.Empty. He comments: You'll note [in an example above] that the second constructor specified "" for the default value on the name parameter, rather than the more customary string.Empty. That's because string.Empty is not a compile-time constant. It is a static property defined in the string class. Because it is not a compile constant, you cannot use it for the default value for a parameter. If we cannot use the string.Empty static in all situations, then doesn't that defeat the purpose of it? I thought that we would use it to be sure that we have a system-independent means of referring to the empty string. Is my understanding wrong? Thanks.

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  • C++: Define simple string?

    - by Jason
    This thing is really wracking my mind. I'm learning C++ and I wanted to define a constant that I can use in another function, A short answer on how to do this will be fine.. Lets say at the beginning of my code I want to define this constant: //After #includes bool OS = 1; //1 = linux if (OS) { const ??? = "clear"; } else { const ??? = "cls"; } I don't know what type to use to define the "clear" string... I'm so confused. Later on I want to use it within a function: int foo() { system(::cls); //:: for global return 0; } How would I define the string up top, and use the string down below? I heard char only had one character and things... I'm not sure how to use , since it says it's converting string into const char or something.

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  • STL deque accessing by index is O(1)?

    - by jasonline
    I've read that accessing elements by position index can be done in constant time in a STL deque. As far as I know, elements in a deque may be stored in several non-contiguous locations, eliminating safe access through pointer arithmetic. For example: abc-defghi-jkl-mnop The elements of the deque above consists of a single character. The set of characters in one group indicate it is allocated in contiguous memory (e.g. abc is in a single block of memory, defhi is located in another block of memory, etc.). Can anyone explain how accessing by position index can be done in constant time, especially if the element to be accessed is in the second block? Or does a deque have a pointer to the group of blocks? Update: Or is there any other common implementation for a deque?

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  • Reference table values in a war against magic numbers

    - by Alex N.
    This question bugged me for years now and can't seem to find good solution still. I working in PHP and Java but it sounds like this maybe language-agnostic :) Say we have a standard status reference table that holds status ids for some kind of entity. Further let's assume the table will have just 5 values, and will remain like this for a long time, maybe edited occasionally with addition of a new status. When you fetch a row and need to see what status it is you have 2 options(as I see it at least) - put it straight ID values(magic numbers that is) or use a named constant. Latter seem much cleaner, the question though is where those named constants should leave? In a model class? In a class that uses this particular constant? Somewhere else?

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  • What are the implications of using static const instead of #define?

    - by Simon Elliott
    gcc complains about this: #include <stdio.h> static const int YY = 1024; extern int main(int argc, char*argv[]) { static char x[YY]; } $ gcc -c test1.c test1.c: In function main': test1.c:5: error: storage size of x' isn't constant test1.c:5: error: size of variable `x' is too large Remove the “static” from the definition of x and all is well. I'm not exactly clear what's going on here: surely YY is constant? I had always assumed that the "static const" approach was preferable to "#define". Is there any way of using "static const" in this situation?

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  • In WPF XAML how can I concatenate 2 constants so I can use pre-define paths?

    - by toaster24
    I'm new to XAML, so presume I'm missing something simple. I want to replace the path part of the source path with a c# constant for easier path management, for example I have: <Image Source="/Images/Themes/Buttons/MyPicture.png" /> and in another class I have my constant defined: public static readonly string UriImagesButtons = "/Images/Big/PNG/"; I want to have something along the lines of: <Image Source="{static:UriImagesButtons + MyPicture.png}" /> This means that I can change the path globally at a stroke if the need arises. What's the syntax to do this?

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  • Why the actionscript 3.0 snippet below failed to import Button and TextInput?

    - by user198729
    package { import fl.controls.Button; import fl.controls.TextInput; public class MinRecord extends Sprite { private var recordBtn:Button; private var stopBtn:Button; private var textInput:TextInput; ... When I run it reports: Type was not found or was not a compile-time constant: Button. Type was not found or was not a compile-time constant: TextInput. Can someone point out what's wrong here?

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  • Xampp error on windows

    - by Deepak Kumar
    My problem is when i use xampp i see many error and when i use my web it has no error Notice: Undefined index: action in C:\xampp\htdocs\xyz\index.php on line 3 Notice: Undefined index: usNick in C:\xampp\htdocs\xyz\config.php on line 11 Notice: Use of undefined constant setname - assumed 'setname' in C:\xampp\htdocs\xyz\config.php on line 31 Notice: Use of undefined constant setname - assumed 'setname' in C:\xampp\htdocs\xyz\config.php on line 31 Notice: Undefined index: usNick in C:\xampp\htdocs\xyz\config.php on line 34 Notice: A session had already been started - ignoring session_start() in C:\xampp\htdocs\xyz\data.php on line 2 Notice: Undefined index: r in C:\xampp\htdocs\xyz\data.php on line 4 Notice: Undefined index: ucNick in C:\xampp\htdocs\xyz\data.php on line 8 I have tried many time changing things in Setting, Security, Privileges etc but nothing changed, I want to know if im missing something out Thanks

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  • Define classes for a datatable structure - ORM

    - by user424493
    I have existing tables - I have following datatables : ActivityTable(Key ActivityId) - which lists the identifier for various activity ProcessTable (identified by ProcessId) - which lists down which activites(ActivityId) are to be carried out along with their order(StepNum). Some of the activities are marked constant with in a process, that is they will have same data, ir-respective of there run environment. RunTable(Key RunConfigurationId) - that identifies the project name and Process Id Then data for each activity is stored is stored in their individual tables Activity_A, Activity_B,Activity_C so on it uses a combination of RunConfigurationId,ProcessId and stepNum. For the activities which are constant we use a RunConfigurationId= -100. Can anybody help me out how I can map something like this in classes using inheritence regards

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  • Scope of Constants in Ruby Modules

    - by user204078
    I'm having a little problem with constant scope in mixin modules. Let's say I have something like this module Auth USER_KEY = "user" unless defined? USER_KEY def authorize user_id = session[USER_KEY] def end The USER_KEY constant should default to "user" unless it's already defined. Now I might mix this into a couple of places, but in one of those places the USER_KEY needs to be different, so we might have something like this class ApplicationController < ActionController::Base USER_KEY = "my_user" include Auth def test_auth authorize end end I would expect that USER_KEY would be "my_user" when used in authorize, since it's already defined, but it's still "user", taken from the modules definition of USER_KEY. Anyone have any idea how to get authorize to use the classes version of USER_KEY?

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  • Using inheritance with multiple files in Ruby

    - by Preethi Jain
    I am new to Ruby . I have a question with respect to using Inheritence in Ruby . I have a class called as Doggy inside a file named Doggy.rb class Doggy def bark puts "Vicky is barking" end end I have written another class named Puppy in another file named puppy.rb class Puppy < Doggy end puts Doggy.new.bark I am getting this Error: Puppy.rb:1:in `<main>': uninitialized constant Doggy (NameError) Is it mandatory to have these classes (Doggy and Puppy ) inside a single file only? Edited As per the suggestions , i have tried using require and require_relative as shown , but still i am getting below Error Puppy.rb:1:in `<main>': uninitialized constant Doggy (NameError) class Puppy < Doggy end require_relative 'Doggy.rb' puts Doggy.new.bark

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  • Good Design for Initialization of Static Array

    - by jplot
    I have a question regarding good design in C++. I have a class A, and all objects of this class use an integer array of constant values (they should share the same array, as their values are constant). The array needs to be computed (just once) before any object A. I thought about having another class B which contains the integer array as a static member, an init() method which would fill this array according to some formula and a static boolean flag initialized (if this variable if true then the init() method would do nothing), but I'm not sure this is the best way to solve my design issue. So my question is, what would be a good design/way to accomplish this ? Thanks in advance.

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  • GDC 2012: The Bleeding Edge of Open Web Tech

    GDC 2012: The Bleeding Edge of Open Web Tech (Pre-recorded GDC content) Web browsers from mobile to desktop devices are in a constant state of growth enabling ever richer and pervasive games. This presentation by Google software engineer Vincent Scheib focuses on the latest developments in client side web technologies, such as Web Sockets, WebGL, File API, Mouse Lock, Gamepads, Web Audio API and more. Speaker: Vincent Scheib From: GoogleDevelopers Views: 1279 31 ratings Time: 48:33 More in Science & Technology

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  • What is the usage of Splay Trees in the real world?

    - by Meena
    I decided to learn about balanced search trees, so I picked 2-3-4 and splay trees. What are the examples of splay trees usage in the real world? In this Cornell: http://www.cs.cornell.edu/courses/cs3110/2009fa/recitations/rec-splay.html I read that splay trees are 'A good example is a network router'. But from rest of the explanation seams like network routers use hash tables and not splay trees since the lookup time is constant instead of O(log n).

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  • Using IComparable<T> Interface

    - by Pawan_Mishra
    Level : Beginner to Intermediate C# language has constantly evolved over a constant period of time.Each new version introduced new features which changed the way we programmed and solved the problems. Whether it was introduction of generics in C# 2.0 , LINQ in C# 3.0 or concept of dynamic programming in C# 4.0 , each of them had or will have greater impact on our programming style.As a developer we don’t have much option but to evolve and redefine our self in this constantly changing environment...(read more)

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  • const vs. readonly for a singleton

    - by GlenH7
    First off, I understand there are folk who oppose the use of singletons. I think it's an appropriate use in this case as it's constant state information, but I'm open to differing opinions / solutions. (See The singleton pattern and When should the singleton pattern not be used?) Second, for a broader audience: C++/CLI has a similar keyword to readonly with initonly, so this isn't strictly a C# type question. (Literal field versus constant variable in C++/CLI) Sidenote: A discussion of some of the nuances on using const or readonly. My Question: I have a singleton that anchors together some different data structures. Part of what I expose through that singleton are some lists and other objects, which represent the necessary keys or columns in order to connect the linked data structures. I doubt that anyone would try to change these objects through a different module, but I want to explicitly protect them from that risk. So I'm currently using a "readonly" modifier on those objects*. I'm using readonly instead of const with the lists as I read that using const will embed those items in the referencing assemblies and will therefore trigger a rebuild of those referencing assemblies if / when the list(s) is/are modified. This seems like a tighter coupling than I would want between the modules, but I wonder if I'm obsessing over a moot point. (This is question #2 below) The alternative I see to using "readonly" is to make the variables private and then wrap them with a public get. I'm struggling to see the advantage of this approach as it seems like wrapper code that doesn't provide much additional benefit. (This is question #1 below) It's highly unlikely that we'll change the contents or format of the lists - they're a compilation of things to avoid using magic strings all over the place. Unfortunately, not all the code has converted over to using this singleton's presentation of those strings. Likewise, I don't know that we'd change the containers / classes for the lists. So while I normally argue for the encapsulations advantages a get wrapper provides, I'm just not feeling it in this case. A representative sample of my singleton public sealed class mySingl { private static volatile mySingl sngl; private static object lockObject = new Object(); public readonly Dictionary<string, string> myDict = new Dictionary<string, string>() { {"I", "index"}, {"D", "display"}, }; public enum parms { ABC = 10, DEF = 20, FGH = 30 }; public readonly List<parms> specParms = new List<parms>() { parms.ABC, parms.FGH }; public static mySingl Instance { get { if(sngl == null) { lock(lockObject) { if(sngl == null) sngl = new mySingl(); } } return sngl; } } private mySingl() { doSomething(); } } Questions: Am I taking the most reasonable approach in this case? Should I be worrying about const vs. readonly? is there a better way of providing this information?

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  • BizTalk 2009 - Creating a Custom Functoid Library

    - by StuartBrierley
    If you find that you have a need to created multiple Custom Functoids you may also choose to create a Custom Functoid Library - a single project containing many custom functoids.  As previsouly discussed, the Custom Functoid Wizard can be used to create a project with a new custom functoid inside.  But what if you want to extend this project to include more custom functoids and create your Custom Functoid Library?  First create a Custom Functoid Library project and your first Custom Functoid using the Custom Functoid Wizard. When you open your Custom Functoid Library project in Visual Studio you will see that it contains your custom functoid class file along with its resource file.  One of the items this resource file contains is the ID of the the custom functoid.  Each custom functoid needs a unique ID that is over 6000.  When creating a Custom Functoid Library I would first suggest that you delete the ID from this resource file and instead create a _FunctoidIDs class containing constants for each of your custom functoids.  In this way you can easily see which custom functoid IDs are assigned to which custom functoid and which ID is next in the sequence of availability: namespace MyCompany.BizTalk.Functoids.TestFunctoids {     class _FunctoidIDs     {         public const int TestFunctoid                       = 6001;     } } You will then need to update the base() function in your existing functoid class to reference these constant values rather than the current resource file. From:    int functoidID;    // This has to be a number greater than 6000    functoidID = System.Convert.ToInt32(resmgr.GetString("FunctoidId"));    this.ID = functoidID; To: this.ID = _FunctoidIDs.TestFunctoid; To create a new custom functoid you can copy the existing custom functoid, renaming the resultant class file as appropriate.  Once it is renamed you will need to change the Class name, ResourceName reference and Base function name in the class code to those of your new custom functoid.  You will also need to create a new constant value in the _FunctoidIDs class and update the ID reference in your code to match this.  Assuming that you need some different functionalty from your new  customfunctoid you will need to check or amend the following in your functoid class file: Min and Max connections Functoid Category Input and Output connection types The parameters and functionality of the Execute function To change the appearance of you new custom functoid you will need to check or amend the following in the functoid resource file: Name Description Tooltip Exception Icon You can change the String values by double clicking the resource file and amending the value fields in the string table. To amend the functoid icon you will need to create a 16x16 bitmap image.  Once you have saved this you are then ready to import it into the functoid resource file.  In Visual Studio change the resource view to images, right click the icon and choose import from file. You have now completed your new custom functoid and created a Custom Functoid Library.  You can test your new library of functoids by building the project, copying the resultant DLL to C:\Program Files\Microsoft BizTalk Server 2009\Developer Tools\Mapper Extensions and then resetting the toolbox in Visual Studio.

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  • How to efficiently render resizable GUI elements in DirectX?

    - by PolGraphic
    I wonder what would be most efficient way to render the GUI elements. When we're talking about constant-size elements (that can still be moving), the textures' atlas seems to be good. But what with the resizeable elements? Let's say the panel (with textured borders)? Is there any better way than just render 9 rectangles with textures on them (I guess one texture and different textures coordinates for left-top corner, border, middle etc. used in shader)?

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  • Smooth animation when using fixed time step

    - by sythical
    I'm trying to implement the game loop where the physics is independent from rendering but my animation isn't as smooth as I would like it to be and it seems to periodically jump. Here is my code: // alpha is used for interpolation double alpha = 0, counter_old_time = 0; double accumulator = 0, delta_time = 0, current_time = 0, previous_time = 0; unsigned frame_counter = 0, current_fps = 0; const unsigned physics_rate = 40, max_step_count = 5; const double step_duration = 1.0 / 40.0, accumulator_max = step_duration * 5; // information about the circ;e (position and velocity) int old_pos_x = 100, new_pos_x = 100, render_pos_x = 100, velocity_x = 60; previous_time = al_get_time(); while(true) { current_time = al_get_time(); delta_time = current_time - previous_time; previous_time = current_time; accumulator += delta_time; if(accumulator > accumulator_max) { accumulator = accumulator_max; } while(accumulator >= step_duration) { if(new_pos_x > 1330) velocity_x = -15; else if(new_pos_x < 70) velocity_x = 15; old_pos_x = new_pos_x; new_pos_x += velocity_x; accumulator -= step_duration; } alpha = accumulator / static_cast<double>(step_duration); render_pos_x = old_pos_x + (new_pos_x - old_pos_x) * alpha; al_clear_to_color(al_map_rgb(20, 20, 40)); // clears the screen al_draw_textf(font, al_map_rgb(255, 255, 255), 20, 20, 0, "current_fps: %i", current_fps); // print fps al_draw_filled_circle(render_pos_x, 400, 15, al_map_rgb(255, 255, 255)); // draw circle // I've added this to test how the program will behave when rendering takes // considerably longer than updating the game. al_rest(0.008); al_flip_display(); // swaps the buffers frame_counter++; if(al_get_time() - counter_old_time >= 1) { current_fps = frame_counter; frame_counter = 0; counter_old_time = al_get_time(); } } I have added a pause during the rendering part because I wanted to see how the code would behave when a lot of rendering is involved. Removing it makes the animation smooth but then I'll have to make sure that I don't let the frame rate drop too much and that doesn't seem like a good solution. I've been trying to fix this for a week and have had no luck so I'd be very grateful if someone can read through my code. Thank you! Edit: I added the following code to work out the actual velocity (pixels per second) of the ball each time the ball is rendered and surprisingly it's not constant so I'm guessing that's the issue. I'm not sure why it's not constant. alpha = accumulator / static_cast<double>(step_duration); render_pos_x = old_pos_x + (new_pos_x - old_pos_x) * alpha; cout << (render_pos_x - old_render_pos) / delta_time << endl; old_render_pos = render_pos_x;

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