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  • Obtain container type from (its) iterator type in C++ (STL)

    - by KRao
    It is easy given a container to get the associated iterators, example: std::vector<double>::iterator i; //An iterator to a std::vector<double> I was wondering if it is possible, given an iterator type, to deduce the type of the "corresponding container" (here I am assuming that for each container there is one and only one (non-const) iterator). More precisely, I would like a template metafunction that works with all STL containers (without having to specialize it manually for each single container) such that, for example: ContainerOf< std::vector<double>::iterator >::type evaluates to std::vector<double> Is it possible? If not, why? Thank you in advance for any help!

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  • Html.Editor() helper in ASP.NET MVC 3 does not work as expected with array in model

    - by SlimShaggy
    In my ASP.NET MVC 3 application I have classes like the following: public class Localization<T> { public int VersionID { get; set; } public T Value { get; set; } ... } public class Localizable<T> { public Localization<T>[] Name { get; set; } ... } Then, I have the following view: @model dynamic ... @for (int i = 0; i < VersionCount; i++) { ... @Html.Editor(string.Format("Name[{0}.Value", i)) ... } Now, when I display this view, passing a subclass of Localizable<string> as the model, the textboxes for the strings are rendered, but they are empty. If I replace @Html.Editor(string.Format("Name[{0}.Value", i)) with @InputExtensions.TextBox(Html, string.Format("Name[{0}].Value", i), Model.Name[i].Value), the textboxes are correctly filled with values from the model. However, using TextBox instead of Editor is not an option for me, because I want to use different editor templates for different types of T. So, what am I doing wrong, or is it a bug in MVC, and is there any workaround?

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  • How can I get the JSON array data from nsstring or byte in xcode 4.2?

    - by user1471568
    I'm trying to get values from nsdata class and doesn't work. here is my JSON data. { "count": 3, "item": [{ "id": "1", "latitude": "37.556811", "longitude": "126.922015", "imgUrl": "http://175.211.62.15/sample_res/1.jpg", "found": false }, { "id": "3", "latitude": "37.556203", "longitude": "126.922629", "imgUrl": "http://175.211.62.15/sample_res/3.jpg", "found": false }, { "id": "2", "latitude": "37.556985", "longitude": "126.92286", "imgUrl": "http://175.211.62.15/sample_res/2.jpg", "found": false }] } and here is my code -(NSDictionary *)getDataFromItemList { NSData *dataBody = [[NSData alloc] initWithBytes:buffer length:sizeof(buffer)]; NSDictionary *iTem = [[NSDictionary alloc]init]; iTem = [NSJSONSerialization JSONObjectWithData:dataBody options:NSJSONReadingMutableContainers error:nil]; NSLog(@"id = %@",[iTem objectForKey:@"id"]); //for Test output = [[NSString alloc] initWithBytes:buffer length:rangeHeader.length encoding:NSUTF8StringEncoding]; NSLog(@"%@",output); return iTem; } how can I access every value in the JSON? Please help me.

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  • How do I get a array to just count how many numbers there are instead of counting the value of each number?

    - by Chad Loos
    //This is the output of the program *** start of 276 2D Arrays_03.cpp program *** Number Count Total 1 3 3 2 6 9 3 15 24 4 6 30 5 9 39 *** end of 276 2D Arrays_03.cpp program *** #include <iostream> #include <string> #include <iomanip> using namespace std; const int COLUMN_SIZE = 13; int main(void) { const int ROW_SIZE = 3; const int COUNT_SIZE = 5; void countValues(const int[][COLUMN_SIZE], const int, int[]); void display(const int [], const int); int numbers[ROW_SIZE][COLUMN_SIZE] = {{1, 3, 4, 5, 3, 2, 3, 5, 3, 4, 5, 3, 2}, {2, 1, 3, 4, 5, 3, 2, 3, 5, 3, 4, 5, 3}, {3, 4, 5, 3, 2, 1, 3, 4, 5, 3, 2, 3, 5}}; int counts[COUNT_SIZE] = {0}; string choice; cout << "*** start of 276 2D Arrays_03.cpp program ***" << endl; cout << endl; countValues(numbers, ROW_SIZE, counts); display(counts, COUNT_SIZE); cout << endl; cout << endl; cout << "*** end of 276 2D Arrays_03.cpp program ***" << endl << endl; cin.get(); return 0; } // end main() This is the function where I need to count each of the values. I know how to sum rows and cols, but I'm not quite sure of the code to just tally the values themselves. void countValues(const int numbers[][COLUMN_SIZE], const int ROW_SIZE, int counts[]) This is what I have so far. { for (int index = 0; index < ROW_SIZE; index++) counts[index]; {

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  • need help with some basic java.

    - by Racket
    Hi, I'm doing the first chapter exercises on my Java book and I have been stuck for a problem for a while now. I'll print the question, prompt/read a double value representing a monetary amount. Then determine the fewest number of each bill and coin needed to represent that amount, starting with the highest (assume that a ten dollar bill is the maximum size needed). For example, if the value entered is 47,63 (forty-seven dollars and sixty-three cents), and the program should print the equivalent amount as: 4 ten dollar bills 1 five dollar bills 2 one dollar bills 2 quarters 1 dimes 0 nickels 3 pennies" etc. I'm doing an example exactly as they said in order to get an idea, as you will see in the code. Nevertheless, I managed to print 4 dollars, and I can't figure out how to get "1 five dollar", only 7 dollars (see code). Please, don't do the whole code for me. I just need some advice in regards to what I said. Thank you. import java.util.Scanner; public class PP29 { public static void main (String[] args) { Scanner sc = new Scanner (System.in); int amount; double value; double test1; double quarter; System.out.println("Enter \"double\" value: "); value = sc.nextDouble(); amount = (int) value / 10; // 47,63 / 10 = 4. int amount2 = (int) value % 10; // 47 - 40 = 7 quarter = value * 100; // 47,63 * 100 = 4736 int sum = (int) quarter % 100; // 4763 / 100 => 4763-4700 = 63. System.out.println(amount); System.out.println(amount2); } }

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  • Templated derived class in CRTP (Curiously Recurring Template Pattern)

    - by Butterwaffle
    Hi, I have a use of the CRTP that doesn't compile with g++ 4.2.1, perhaps because the derived class is itself a template? Does anyone know why this doesn't work or, better yet, how to make it work? Sample code and the compiler error are below. Source: foo.C #include <iostream> using namespace std; template<typename X, typename D> struct foo; template<typename X> struct bar : foo<X,bar<X> > { X evaluate() { return static_cast<X>( 5.3 ); } }; template<typename X> struct baz : foo<X,baz<X> > { X evaluate() { return static_cast<X>( "elk" ); } }; template<typename X, typename D> struct foo : D { X operator() () { return static_cast<D*>(this)->evaluate(); } }; template<typename X, typename D> void print_foo( foo<X,D> xyzzx ) { cout << "Foo is " << xyzzx() << "\n"; } int main() { bar<double> br; baz<const char*> bz; print_foo( br ); print_foo( bz ); return 0; } Compiler errors foo.C: In instantiation of ‘foo<double, bar<double> >’: foo.C:8: instantiated from ‘bar<double>’ foo.C:30: instantiated from here foo.C:18: error: invalid use of incomplete type ‘struct bar<double>’ foo.C:8: error: declaration of ‘struct bar<double>’ foo.C: In instantiation of ‘foo<const char*, baz<const char*> >’: foo.C:13: instantiated from ‘baz<const char*>’ foo.C:31: instantiated from here foo.C:18: error: invalid use of incomplete type ‘struct baz<const char*>’ foo.C:13: error: declaration of ‘struct baz<const char*>’

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  • Rotation in a Vector2d class in Java

    - by wanstein
    I've been working on this for one hour, just can't get it. I have a Vector2d class: public class Vector2d { public double x = 0.0; public double y = 0.0; .... } This vector class has a rotate() method which is causing me trouble. The first snippet seems to make the x and y values smaller and smaller. The second one works just fine! Am I missing something simple here? public void rotate(double n) { this.x = (this.x * Math.cos(n)) - (this.y * Math.sin(n)); this.y = (this.x * Math.sin(n)) + (this.y * Math.cos(n)); } This works: public void rotate(double n) { rx = (this.x * Math.cos(n)) - (this.y * Math.sin(n)); ry = (this.x * Math.sin(n)) + (this.y * Math.cos(n)); x = rx; y = ry; } I just can't spot any difference there

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  • Safe way of iterating over an array or dictionary and deleting entries?

    - by mystify
    I've heard that it is a bad idea to do something like this. But I am sure there is some rule of thumb which can help to get that right. When I iterate over an NSMutableDictionary or NSMutableArray often I need to get rid of entries. Typical case: You iterate over it, and compare the entry against something. Sometimes the result is "don't need anymore" and you have to remove it. But doing so affects the index of all the rows, doesn't it? So how could I safely iterate over it without accidently exceeding bounds or jumping over an element that hasn't been checked?

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  • Why does the order of the loops affect performance when iterating over a 2D array? [closed]

    - by Mark
    Possible Duplicate: Which of these two for loops is more efficient in terms of time and cache performance Below are two programs that are almost identical except that I switched the i and j variables around. They both run in different amounts of time. Could someone explain why this happens? Version 1 #include <stdio.h> #include <stdlib.h> main () { int i,j; static int x[4000][4000]; for (i = 0; i < 4000; i++) { for (j = 0; j < 4000; j++) { x[j][i] = i + j; } } } Version 2 #include <stdio.h> #include <stdlib.h> main () { int i,j; static int x[4000][4000]; for (j = 0; j < 4000; j++) { for (i = 0; i < 4000; i++) { x[j][i] = i + j; } } }

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  • Getting Frequency Components with FFT

    - by ruhig brauner
    so I was able to solv my last problem but i stubmled upon the next already. So I want to make a simple spectrogram but in oder to do so I want to understand how FFT-libaries work and what they actually calculate and return. (FFT and Signal Processing is the number 1 topic I will get into as soon as I have time but right now, I only have time for some programming exercises in the evening. ;) ) Here I just summarized the most important parts: int framesPerSecond; int samplesPerSecond; int samplesPerCycle; // right now i want to refresh the spectogram every DoubleFFT_1D fft; WAVReader audioIn; double audioL[], audioR[]; double fftL[], fftR[]; ..... framesPerSecond = 30; audioIn= new WAVReader("Strobe.wav"); int samplesPerSecond = (int)audioIn.GetSampleRate(); samplesPerCycle = (int)(audioIn.GetSampleRate()/framesPerSecond); audioL = new double[samplesPerCycle*2]; audioR = new double[samplesPerCycle*2]; fftL = new double[samplesPerCycle]; fftR = new double[samplesPerCycle]; for(int i = 0; i < samplesPerCycle; i++) { // don't even know why,... fftL[i] = 0; fftR[i] = 0; } fft = new DoubleFFT_1D(samplesPerCycle); ..... for(int i = 0; i < samplesPerCycle; i++) { audioIn.GetStereoSamples(temp); audioL[i]=temp[0]; audioR[i]=temp[1]; } fft.realForwardFull(audioL); //still stereo fft.realForwardFull(audioR); System.out.println("Check"); for(int i = 0; i < samplesPerCycle; i++) { //storing the magnitude in the fftL/R arrays fftL[i] = Math.sqrt(audioL[2*i]*audioL[2*i] + audioL[2*i+1]*audioL[2*i+1]); fftR[i] = Math.sqrt(audioR[2*i]*audioR[2*i] + audioR[2*i+1]*audioR[2*i+1]); } So the question is, if I want to know, what frequencys are in the sampled signal, how do I calculate them? (When I want to print the fftL / fftR arrays, I get some exponential formes at both ends of the array.) Thx :)

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  • WPF: Trying to add a class to Window.Resources Again

    - by user3952846
    I did exactly the same thing, but still the same error is occurring: "The tag 'CenterToolTipConverter' does not exist in XML namespace 'clr-namespace:WpfApplication1;assembly=WpfApplication1'. Line 12 Position 10." CenterToolTipConverter.cs namespace WpfApplication1 { public class CenterToolTipConverter : IMultiValueConverter { public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture) { if (values.FirstOrDefault(v => v == DependencyProperty.UnsetValue) != null) { return double.NaN; } double placementTargetWidth = (double)values[0]; double toolTipWidth = (double)values[1]; return (placementTargetWidth / 2.0) - (toolTipWidth / 2.0); } public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture) { throw new NotSupportedException(); } } } MainWindow.xaml <Window x:Class="WpfApplication1.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:WpfApplication1;assembly=WpfApplication1" Title="MainWindow" Height="350" Width="525"> <Window.Resources> <local:CenterToolTipConverter x:Key="myCenterToolTipConverter"/> </Window.Resources> </Window> What am I doing wrong? Thanks in advance!!!

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  • what is the accepted naming convention for int, string, array, list, object, etc...

    - by RJ
    The company I work for now uses a set naming convention for their C# variables such as iSomeName for int, sSomeName for string, aSomeName for arrays, bSomeName for boolean, dSomeName for datetime and so on. My previous employer did not use the i, s, a, b and d prefixes and just named the variables a good understandable name. My impression is that these prefixes lost favor a while ago and from what I read it is not the current trend. It seems fine to me either way as long as the variable is descriptive enough to understand what it is doing but I was wondering what the now-a-day accepted practice is for naming variables?

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  • function takes only half of the inputs

    - by gcc
    /*-> struct sam set_of_data[4] -<*/ int main (void) {int k=0; for(i=0;i<4;++i) { {char nm; double thelow,theupp; double numbers[200]; scanf("%c %lf %lf",&nm ,&thelow ,&theupp); for(k=0;scanf("%lf",&numbers[k])!=0;++k) ; set_of_data[i]=construct_struct(nm,thelow,theupp,numbers,k); } ; } .. /* helper function to construct data structure*/ sam_t construct_struct(char name,double thelow,double theupp,double *numbers,int k) { stored_name_t stn; stn.name=name; stn.the_lower_limit=thelow; stn.the_upper_limit=theupp; for(i=0 ; i<k && numbers[k]!='\n' && numbers[k]!='\0' ; ++i) stn.numbers[k]=numbers[k]; return stn; } these two funtion takes only half of the inputs(lines starting with D and B didnot be taken,why? inputs: C 3.25 18. 0.01 .01 .02 .04 .08 .02 .02 .05 .065 .08 .1 .13 .2 .05 .04 .04 .03 .01 .005 .0 A 0 7.5 .054 .031 .016 .008 .116 .124 .147 .155 .039 .023 .016 .008 .124 .062 .031 .016 .008 .008 .008 .006 D -1.5 0.5 .012 .025 .05 .1 .1 .1 .025 .012 0 0 0 .012 .025 .1 .2 .1 .05 .039 .025 .025 B 1 3 .117 .058 .029 .015 .007 .007 .007 .015 .022 .029 .036 .044 .051 .058 .066 .073 .080 .088 .095 .103

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  • Stop functions in 5 minutes if they dont end running

    - by george mano
    I want to add a feature in my project. I have 2 functions running in a for-loop because I want to find the solution of the functions in random arrays. I also have an function that makes random arrays. In each loop the array that is made by the random_array fun are the input of the 2 functions. The 2 functions print solutions in the screen , they dont return an argument. int main(){ for (i=0;i<50 i++) { arr1=ramdom_array(); func1(arr1) func2(arr1) } } I need to stop the functions running if they have not ended in 5 minutes. I have thought that I have to put in the functions something like this : void func1(array<array<int,4>,4> initial) { while (5minutes_not_passed) { //do staff if(solution==true) break; } } But I dont know what to put in the 5minutes_not_passed. the declaration of the functions are like this: void func1(array<array<int,4>,4> initial) void func2(array<array<int,4>,4> initial) I have found that I can use the thread library but I dont think meshing up with threads in a good idea. I believe something like a timer is needed. Note that the functions sometimes might end before 5 minutes.

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  • Is it possible to pass arithmatic operators to a method in java?

    - by user349611
    Right now I'm going to have to write a method that looks like this: public String Calculate(String Operator, Double Operand1, Double Operand2) { if (Operator.equals("+")) { return String.valueOf(Operand1 + Operand2); } else if (Operator.equals("-")) { return String.valueOf(Operand1 - Operand2); } else if (Operator.equals("*")) { return String.valueOf(Operand1 * Operand2); } else { return "error..."; } } It would be nice if I could write the code more like this: public String Calculate(String Operator, Double Operand1, Double Operand2) { return String.valueOf(Operand1 Operator Operand2); } So Operator would replace the Arithmetic Operators (+, -, *, /...) Does anyone know if something like this is possible in java?

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  • Is object clearing/array deallocation really necessary in VB6/VBA (Pros/Cons?)

    - by Oorang
    Hello, A lot of what I have learned about VB I learned from using Static Code Analysis (Particularly Aivosto's Project Analyzer). And one one of things it checks for is whether or not you cleared all objects and arrays. I used to just do this blindly because PA said so. But now that I know a little bit more about the way VB releases resources, it seems to me that these things should be happening automatically. Is this a legacy feature from pre VB6, or is there a reason why you should explicitly set objects back to nothing and use Erase on arrays?

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  • Better variant of getting the output dinamically-allocated array from the function?

    - by Raigomaru
    Here is to variants. First: int n = 42; int* some_function(int* input) { int* result = new int[n]; // some code return result; } void main() { int* input = new int[n]; int* output = some_function(input); delete[] input; delete[] output; } Here the function returns the memory, allocated inside the function. Second variant: int n = 42; void some_function(int* input, int* output) { // some code } void main() { int* input = new int[n]; int* output = new int[n]; some_function(input, output); delete[] input; delete[] output; } Here the memory is allocated outside the function. Now I use the first variant. But I now that many built-in c++ functions use the second variant. The first variant is more comfortable (in my opinion). But the second one also has some advantages (you allocate and delete memory in the same block). Maybe it's a silly question but what variant is better and why?

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  • How to define an array inside a function in C?

    - by Arunav Dev
    So in my source file I have the folowin function: void update(state* old_state, state* measurement, uint32_t size) { state new_state[size]; //some function using measurement and old_state and returning the result in newstate arm_fadd_32(measurement,old_state,newstate,size); // rest of the code } Now the compiler throws an error saying that error#28:expression must have a constant value. I think it's due to the fact that even though inside the method the size local variable is not changing the compiler is expecting a constant while defining the size. I have tried the following: int const a = size; and then tried to reinitialize it says constant value is not known. I did some research in internet and it appears that there is no easier way without using malloc, which I don't want to since I am using the code for some embedded application. Is there a way to avoid this problem without really using malloc? Thanks in advance guys!

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  • C++ methods which take templated classes as argument.

    - by Nils
    I have a templated class Vector<class T, int N> Where T is the type of the components (double for example) and n the number of components (so N=3 for a 3D vector) Now I want to write a method like double findStepsize(Vector<double,2> v) {..} I want to do this also for three and higher dimensional vectors. Of course I could just introduce further methods for higher dimensions, but the methods would have a lot of redundant code, so I want a more generic solution. Is there a way to create a method which takes a templated class without further specializing it (in this case without specifying T or N)? Like double findStepsize(Vector<T,N> v) ?

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