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  • And now for a complete change of direction from C++ function pointers

    - by David
    I am building a part of a simulator. We are building off of a legacy simulator, but going in different direction, incorporating live bits along side of the simulated bits. The piece I am working on has to, effectively route commands from the central controller to the various bits. In the legacy code, there is a const array populated with an enumerated type. A command comes in, it is looked up in the table, then shipped off to a switch statement keyed by the enumerated type. The type enumeration has a choice VALID_BUT_NOT_SIMULATED, which is effectively a no-op from the point of the sim. I need to turn those no-ops into commands to actual other things [new simulated bits| live bits]. The new stuff and the live stuff have different interfaces than the old stuff [which makes me laugh about the shill job that it took to make it all happen, but that is a topic for a different discussion]. I like the array because it is a very apt description of the live thing this chunk is simulating [latching circuits by row and column]. I thought that I would try to replace the enumerated types in the array with pointers to functions and call them directly. This would be in lieu of the lookup+switch.

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  • Object Oriented vs Relational Databases

    - by Dan
    Objects oriented databases seem like a really cool idea to me, no need to worry about mapping your domain model to your database model, no messing around with sql or ORM tools. The way I understand it, relational DBs offer some advantages when there is massive amounts of data, and searching an indexing need to be done. To my mind 99% of websites are not massive, and enterprise issues never need to be thought about, so why arn't OO DBs more widely used?

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  • DRY'er Object Initialization in Ruby

    - by Trevoro
    Hi, Is there a more 'DRY' way to do the following in ruby? #!/usr/bin/env ruby class Volume attr_accessor :name, :size, :type, :owner, :date_created, :date_modified, :iscsi_target, :iscsi_portal SYSTEM = 0 DATA = 1 def initialize(args={:type => SYSTEM}) @name = args[:name] @size = args[:size] @type = args[:type] @owner = args[:owner] @iscsi_target = args[:iscsi_target] @iscsi_portal = args[:iscsi_portal] end def inspect return {:name => @name, :size => @size, :type => @type, :owner => @owner, :date_created => @date_created, :date_modified => @date_modified, :iscsi_target => @iscsi_target, :iscsi_portal => @iscsi_portal } end def to_json self.inspect.to_json end end

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  • [Perl] Use a Module / Object which is defined in the same file

    - by Robert S. Barnes
    I need to define some modules and use them all in the same file. No, I can't change the requirement. I would like to do something like the following: { package FooObj; sub new { ... } sub add_data { ... } } { package BarObj; use FooObj; sub new { ... # BarObj "has a" FooObj my $self = ( myFoo => FooObj->new() ); ... } sub some_method { ... } } my $bar = BarObj->new(); However, this results in the message: Can't locate FooObj.pm in @INC ... BEGIN failed... How do I get this to work?

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  • Xpath help function

    - by NA
    Hi i have a document from which i am trying to extract a date. But the problem is within the node along with the date their is some text too. Something like <div class="postHeader"> Posted on July 20, 2009 9:22 PM PDT </div> From this tag i just want the date item not the Posted on text. something like ./xhtml:div[@class = 'postHeader'] is getting everything. and to be precise, the document i have is basically a nodelist of this elements for eg i will get 10 nodes of these elements with different date values but to be worse the problem is sometime inside these tags some random other tags also pops us like anchors etc. Can i write a universal expath which will just get the date out of the div tag?

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  • Function pointers uasage

    - by chaitanyavarma
    Hi All, Why these two codes give the same output, Case - 1: #include <stdio.h> typedef void (*mycall) (int a ,int b); void addme(int a,int b); void mulme(int a,int b); void subme(int a,int b); main() { mycall x[10]; x[0] = &addme; x[1] = &subme; x[2] = &mulme; (x[0])(5,2); (x[1])(5,2); (x[2])(5,2); } void addme(int a, int b) { printf("the value is %d\n",(a+b)); } void mulme(int a, int b) { printf("the value is %d\n",(a*b)); } void subme(int a, int b) { printf("the value is %d\n",(a-b)); } Output: the value is 7 the value is 3 the value is 10 Case -2 : #include <stdio.h> typedef void (*mycall) (int a ,int b); void addme(int a,int b); void mulme(int a,int b); void subme(int a,int b); main() { mycall x[10]; x[0] = &addme; x[1] = &subme; x[2] = &mulme; (*x[0])(5,2); (*x[1])(5,2); (*x[2])(5,2); } void addme(int a, int b) { printf("the value is %d\n",(a+b)); } void mulme(int a, int b) { printf("the value is %d\n",(a*b)); } void subme(int a, int b) { printf("the value is %d\n",(a-b)); } Output: the value is 7 the value is 3 the value is 10

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  • Function pointers usage

    - by chaitanyavarma
    Hi All, Why these two codes give the same output, Case 1: #include <stdio.h> typedef void (*mycall) (int a ,int b); void addme(int a,int b); void mulme(int a,int b); void subme(int a,int b); main() { mycall x[10]; x[0] = &addme; x[1] = &subme; x[2] = &mulme; (x[0])(5,2); (x[1])(5,2); (x[2])(5,2); } void addme(int a, int b) { printf("the value is %d\n",(a+b)); } void mulme(int a, int b) { printf("the value is %d\n",(a*b)); } void subme(int a, int b) { printf("the value is %d\n",(a-b)); } Output: the value is 7 the value is 3 the value is 10 Case 2 : #include <stdio.h> typedef void (*mycall) (int a ,int b); void addme(int a,int b); void mulme(int a,int b); void subme(int a,int b); main() { mycall x[10]; x[0] = &addme; x[1] = &subme; x[2] = &mulme; (*x[0])(5,2); (*x[1])(5,2); (*x[2])(5,2); } void addme(int a, int b) { printf("the value is %d\n",(a+b)); } void mulme(int a, int b) { printf("the value is %d\n",(a*b)); } void subme(int a, int b) { printf("the value is %d\n",(a-b)); } Output: the value is 7 the value is 3 the value is 10

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  • Python OOP - object has no attribute

    - by user1744269
    I am attempting to learn how to program. I really do want to learn how to program; I love the building and design aspect of it. However, in Java and Python, I have tried and failed with programs as they pertain to objects, classes, methods.. I am trying to develop some code for a program, but im stumped. I know this is a simple error. However I am lost! I am hoping someone can guide me to a working program, but also help me learn (criticism is not only expected, but APPRECIATED). class Converter: def cTOf(self, numFrom): numFrom = self.numFrom numTo = (self.numFrom * (9/5)) + 32 print (str(numTo) + ' degrees Farenheit') return numTo def fTOc(self, numFrom): numFrom = self.numFrom numTo = ((numFrom - 32) * (5/9)) return numTo convert = Converter() numFrom = (float(input('Enter a number to convert.. '))) unitFrom = input('What unit would you like to convert from.. ') unitTo = input('What unit would you like to convert to.. ') if unitFrom == ('celcius'): convert.cTOf(numFrom) print(numTo) input('Please hit enter..') if unitFrom == ('farenheit'): convert.fTOc(numFrom) print(numTo) input('Please hit enter..')

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  • for (Object object : list) [java] construction

    - by EugeneP
    My question, is, whether the sequence of elements picked from a list will always be the same, is this construction behaviour is deterministic for java "List"s - descendants of java.util.List 2) question, if I use for(Object o: list) construction and inside the loop's body increment a variable, will it be the index of list's elements? So, how it goes through list's elements, from 0 to size()-1 or chaotically? List.get(i) will always return this element? 3) question ( I suppose for the 2-nd question the answer will be negative, so:) for (int i=0; i < list.size(); i++) { } is the best way if I need to save the index of an element and later get it back from a list by its id?

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  • Java: Object Array assignment in for loop

    - by Hackster
    I am trying to use Dijkstra's algorithm to find the shortest path from a specific vertex (v0) to the rest of them. That is solved and works well with this code from this link below: http://en.literateprograms.org/index.php?title=Special:DownloadCode/Dijkstra%27s_algorithm_(Java)&oldid=15444 I am having trouble with assigning the Edge array in a for loop from the user input, as opposed to hard-coding it like it is here. Any help assigning a new edge to Edge[] adjacencies from each vertex? Keeping in mind it could be 1 or multiple edges. class Vertex implements Comparable<Vertex> { public final String name; public Edge[] adjacencies; public double minDistance = Double.POSITIVE_INFINITY; public Vertex previous; public Vertex(String argName) { name = argName; } public String toString() { return name; } public int compareTo(Vertex other){ return Double.compare(minDistance, other.minDistance); } } class Edge{ public final Vertex target; public final double weight; public Edge(Vertex argTarget, double argWeight){ target = argTarget; weight = argWeight; } } public static void main(String[] args) { Vertex v[] = new Vertex[3]; Vertex v[0] = new Vertex("Harrisburg"); Vertex v[1] = new Vertex("Baltimore"); Vertex v[2] = new Vertex("Washington"); v0.adjacencies = new Edge[]{ new Edge(v[1], 1), new Edge(v[2], 3) }; v1.adjacencies = new Edge[]{ new Edge(v[0], 1), new Edge(v[2], 1),}; v2.adjacencies = new Edge[]{ new Edge(v[0], 3), new Edge(v[1], 1) }; Vertex[] vertices = { v0, v1, v2}; /*Three vertices with weight: V0 connects (V1,1),(V2,3) V1 connects (V0,1),(V2,1) V2 connects (V1,1),(V2,3) */ computePaths(v0); for (Vertex v : vertices){ System.out.println("Distance to " + v + ": " + v.minDistance); List<Vertex> path = getShortestPathTo(v); System.out.println("Path: " + path); } } } The above code works well in finding the shortest path from v0 to all the other vertices. The problem occurs when assigning the new edge[] to edge[] adjacencies. For example this does not produce the correct output: for (int i = 0; i < total_vertices; i++){ s = br.readLine(); char[] line = s.toCharArray(); for (int j = 0; j < line.length; j++){ if(j % 4 == 0 ){ //Input: vertex weight vertex weight: 1 1 2 3 int vert = Integer.parseInt(String.valueOf(line[j])); int w = Integer.parseInt(String.valueOf(line[j+2])); v[i].adjacencies = new Edge[] {new Edge(v[vert], w)}; } } } As opposed to this: v0.adjacencies = new Edge[]{ new Edge(v[1], 1), new Edge(v[2], 3) }; How can I take the user input and make an Edge[], to pass it to adjacencies? The problem is it could be 0 edges or many. Any help would be much appreciated Thanks!

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  • Accessing Node of an XML object

    - by Lizard
    I am trying to access certain pieces of data from an xml file, here is the problem. ###XML FILE <products> <product> .... .... </product> <product> .... .... </product> etc... </products> I know that the piece of data I need is in ($products->product->myProdNode) I have this mapping (and many others) stored in my database as a string e.g.'product->prodCode' or 'product->dedscriptions->short_desc' How can I access this data by using the strings stored in my database. Thanks for you help in advance!

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  • Best method to select an object from another unknown jQuery object

    - by Yosi
    Lets say I have a jQuery object/collection stored in a variable named obj, which should contain a DOM element with an id named target. I don't know in advance if target will be a child in obj, i.e.: obj = $('<div id="parent"><div id="target"></div></div>'); or if obj equals target, i.e.: obj = $('<div id="target"></div>'); or if target is a top-level element inside obj, i.e.: obj = $('<div id="target"/><span id="other"/>'); I need a way to select target from obj, but I don't know in advance when to use .find and when to use .filter. What would be the fastest and/or most concise method of extracting target from obj? What I've come up with is: var $target = obj.find("#target").add(obj.filter("#target")); UPDATE I'm adding solutions to a JSPERF test page to see which one is the best. Currently my solution is still the fastest. Here is the link, please run the tests so that we'll have more data: http://jsperf.com/jquery-selecting-objects

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  • Creating a new object destroys an older object with different name in C++

    - by Mikael
    First question here! So, I am having some problems with pointers in Visual C++ 2008. I'm writing a program which will control six cameras and do some processing on them so to clean things up I have created a Camera Manager class. This class handles all operations which will be carried out on all the cameras. Below this is a Camera class which interacts with each individual camera driver and does some basic image processing. Now, the idea is that when the manager is initialised it creates two cameras and adds them to a vector so that I can access them later. The catch here is that when I create the second camera (camera2) the first camera's destructor is called for some reason, which then disconnects the camera. Normally I'd assume that the problem is somewhere in the Camera class, but in this case everything works perfectly as long as I don't create the camera2 object. What's gone wrong? CameraManager.h: #include "stdafx.h" #include <vector> #include "Camera.h" class CameraManager{ std::vector<Camera> cameras; public: CameraManager(); ~CameraManager(); void CaptureAll(); void ShowAll(); }; CameraManager.cpp: #include "stdafx.h" #include "CameraManager.h" CameraManager::CameraManager() { printf("Camera Manager: Initializing\n"); [...] Camera *camera1 = new Camera(NodeInfo,1, -44,0,0); cameras.push_back(*camera1); // Adding the following two lines causes camera1's destructor to be called. Why? Camera *camera2 = new Camera(NodeInfo,0, 44,0,0); cameras.push_back(*camera2); printf("Camera Manager: Ready\n"); }

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  • Most efficient way of checking if Date object and Calendar object are in the same month

    - by Indigenuity
    I am working on a project that will run many thousands of comparisons between dates to see if they are in the same month, and I am wondering what the most efficient way of doing it would be. This isn't exactly what my code looks like, but here's the gist: List<Date> dates = getABunchOfDates(); Calendar month = Calendar.getInstance(); for(int i = 0; i < numMonths; i++) { for(Date date : dates) { if(sameMonth(month, date) .. doSomething } month.add(Calendar.MONTH, -1); } Creating a new Calendar object for every date seems like a pretty hefty overhead when this comparison will happen thousands of times, soI kind of want to cheat a bit and use the deprecated method Date.getMonth() and Date.getYear() public static boolean sameMonth(Calendar month, Date date) { return month.get(Calendar.YEAR) == date.getYear() && month.get(Calendar.MONTH) == date.getMonth(); } I'm pretty close to just using this method, since it seems to be the fastest, but is there a faster way? And is this a foolish way, since the Date methods are deprecated? Note: This project will always run with Java 7

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  • Passing null child object from parent object to a partial view

    - by Mike
    I have an object which contains models for my ASP.NET MVC web app. The Model that is being passed into the view has sub models for "gadgets" on that particular view. Each of these sub models gets passed to a partial view (gadget). The problem is when I have a null model in the view model. See example below. View Model: public class FooBarHolder() { public FooBar1 FooBar1 { get; set; } public FooBar2 FooBar2 { get; set; } } We pass FooBarHolder into the view and inside the view we make calls such as <% Html.RenderPartial("Foo", Model.FooBar1); %> <% Html.RenderPartial("Foo2", Model.FooBar2); %> Now say for instance that Model.FooBar2 was null. What I am experiencing from the strongly typed partial view is an error that says "This view expected a model of type FooBar2 but got a model of type FooBarHolder." Why is this happening instead of just passing in a null?

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  • C# Function Inheritance--Use Child Class Vars with Base Class Function

    - by Sean O'Connor
    Good day, I have a fairly simple question to experienced C# programmers. Basically, I would like to have an abstract base class that contains a function that relies on the values of child classes. I have tried code similar to the following, but the compiler complains that SomeVariable is null when SomeFunction() attempts to use it. Base class: public abstract class BaseClass { protected virtual SomeType SomeVariable; public BaseClass() { this.SomeFunction(); } protected void SomeFunction() { //DO SOMETHING WITH SomeVariable } } A child class: public class ChildClass:BaseClass { protected override SomeType SomeVariable=SomeValue; } Now I would expect that when I do: ChildClass CC=new ChildClass(); A new instance of ChildClass should be made and CC would run its inherited SomeFunction using SomeValue. However, this is not what happens. The compiler complains that SomeVariable is null in BaseClass. Is what I want to do even possible in C#? I have used other managed languages that allow me to do such things, so I certain I am just making a simple mistake here. Any help is greatly appreciated, thank you.

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  • How do I create a partial function with generics in scala?

    - by Matteo Caprari
    Hello. I'm trying to write a performance measurements library for Scala. My idea is to transparently 'mark' sections so that the execution time can be collected. Unfortunately I wasn't able to bend the compiler to my will. An admittedly contrived example of what I have in mind: // generate a timing function val myTimer = mkTimer('myTimer) // see how the timing function returns the right type depending on the // type of the function it is passed to it val act = actor { loop { receive { case 'Int => val calc = myTimer { (1 to 100000).sum } val result = calc + 10 // calc must be Int self reply (result) case 'String => val calc = myTimer { (1 to 100000).mkString } val result = calc + " String" // calc must be String self reply (result) } Now, this is the farthest I got: trait Timing { def time[T <: Any](name: Symbol)(op: => T) :T = { val start = System.nanoTime val result = op val elapsed = System.nanoTime - start println(name + ": " + elapsed) result } def mkTimer[T <: Any](name: Symbol) : (() => T) => () => T = { type c = () => T time(name)(_ : c) } } Using the time function directly works and the compiler correctly uses the return type of the anonymous function to type the 'time' function: val bigString = time('timerBigString) { (1 to 100000).mkString("-") } println (bigString) Great as it seems, this pattern has a number of shortcomings: forces the user to reuse the same symbol at each invocation makes it more difficult to do more advanced stuff like predefined project-level timers does not allow the library to initialize once a data structure for 'timerBigString So here it comes mkTimer, that would allow me to partially apply the time function and reuse it. I use mkTimer like this: val myTimer = mkTimer('aTimer) val myString= myTimer { (1 to 100000).mkString("-") } println (myString) But I get a compiler error: error: type mismatch; found : String required: () => Nothing (1 to 100000).mkString("-") I get the same error if I inline the currying: val timerBigString = time('timerBigString) _ val bigString = timerBigString { (1 to 100000).mkString("-") } println (bigString) This works if I do val timerBigString = time('timerBigString) (_: String), but this is not what I want. I'd like to defer typing of the partially applied function until application. I conclude that the compiler is deciding the return type of the partial function when I first create it, chosing "Nothing" because it can't make a better informed choice. So I guess what I'm looking for is a sort of late-binding of the partially applied function. Is there any way to do this? Or maybe is there a completely different path I could follow? Well, thanks for reading this far -teo

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  • How to call a prototyped function from within the prototyped "class"?

    - by Jorge
    function FakeClass(){}; FakeClass.prototype.someMethod = function(){}; FakeClass.prototype.otherMethod = function(){ //need to call someMethod() here. } I need to call someMethod from otherMethod, but apparently it doesn't work. If i build it as a single function (not prototyped), i can call it, but calling a prototyped does not work. How can i do it as if i was treating the function just like a class method?

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  • Arcball 3D camera - how to convert from camera to object coordinates

    - by user38873
    I have checked multiple threads before posting, but i havent been able to figure this one out. Ok so i have been following this tutorial, but im not using glm, ive been implementing everything up until now, like lookat etc. http://en.wikibooks.org/wiki/OpenGL_Programming/Modern_OpenGL_Tutorial_Arcball So i can rotate with the click and drag of the mouse, but when i rotate 90º degrees around Y and then move the mouse upwards or donwwards, it rotates on the wrong axis, this problem is demonstrated on this part of the tutorial An extra trick is converting the rotation axis from camera coordinates to object coordinates. It's useful when the camera and object are placed differently. For instace, if you rotate the object by 90° on the Y axis ("turn its head" to the right), then perform a vertical move with your mouse, you make a rotation on the camera X axis, but it should become a rotation on the Z axis (plane barrel roll) for the object. By converting the axis in object coordinates, the rotation will respect that the user work in camera coordinates (WYSIWYG). To transform from camera to object coordinates, we take the inverse of the MV matrix (from the MVP matrix triplet). What i have to do acording to the tutorial is convert my axis_in_camera_coordinates to object coordinates, and the rotation is done well, but im confused on what matrix i use to do just that. The tutorial talks about converting the axis from camera to object coordinates by using the inverse of the MV. Then it shows these 3 lines of code witch i havent been able to understand. glm::mat3 camera2object = glm::inverse(glm::mat3(transforms[MODE_CAMERA]) * glm::mat3(mesh.object2world)); glm::vec3 axis_in_object_coord = camera2object * axis_in_camera_coord; So what do i aply to my calculated axis?, the inverse of what, i supose the inverse of the model view? So my question is how do you transform camera axis to object axis. Do i apply the inverse of the lookat matrix? My code: if (cur_mx != last_mx || cur_my != last_my) { va = get_arcball_vector(last_mx, last_my); vb = get_arcball_vector( cur_mx, cur_my); angle = acos(min(1.0f, dotProduct(va, vb)))*20; axis_in_camera_coord = crossProduct(va, vb); axis.x = axis_in_camera_coord[0]; axis.y = axis_in_camera_coord[1]; axis.z = axis_in_camera_coord[2]; axis.w = 1.0f; last_mx = cur_mx; last_my = cur_my; } Quaternion q = qFromAngleAxis(angle, axis); Matrix m; qGLMatrix(q,m); vi = mMultiply(m, vi); up = mMultiply(m, up); ViewMatrix = ogLookAt(vi.x, vi.y, vi.z,0,0,0,up.x,up.y,up.z);

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  • Function inside .profile results in no log-in

    - by bioShark
    I've created a custom function in my .profile, and I've added right at the bottom, after my custom aliases : # custom functions function eclipse-gtk { cd ~/development/eclipse-juno ./eclipse_wb.sh & cd - } The function starts a custom version of my eclipse. After I've added it, because I didn't wanted to log-out/log-in, I've reloaded my profile with the command: . ~/.profile and then I've tested my function by calling eclipse-gtk and it worked without any issue. Today when I booted, I couldn't log in. After providing my password, in a few seconds I was back at the log-in screen. Dropping to command line using CTR + ALT + F1, I've commented out the function in my .profile and the log-in was possible without any issue. My question is, what did I do wrong when I wrote the function? And if there is something wrong, why did it work yesterday after reloading the profile. Thanks in advance. Using: Ubuntu 12.04

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