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

    - by drJames
    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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  • C# underlying types of enums

    - by Marlon
    What is the point of having enum SomeEnum : byte // <---- { SomeValue = 0x01, ... } when you have to make a cast just to assign it to the same type of variable as the enums underlying type? byte b = (byte)SomeEnum.SomeValue;

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  • How to split and join array in C++?

    - by Richard Knop
    I have a byte array like this: lzo_bytep out; // my byte array size_t uncompressedImageSize = 921600; out = (lzo_bytep) malloc((uncompressedImageSize + uncompressedImageSize / 16 + 64 + 3)); wrkmem = (lzo_voidp) malloc(LZO1X_1_MEM_COMPRESS); // Now the byte array has 802270 bytes r = lzo1x_1_compress(imageData, uncompressedImageSize, out, &out_len, wrkmem); How can I split it into smaller parts under 65,535 bytes (the byte array is one large packet which I want to sent over UDP which has upper limit 65,535 bytes) and then join those small chunks back into a continuous array?

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  • Is the Google Annotations Gallery useful in production code?

    - by cafe
    I could actually see a use for the Google Annotations Gallery in real code: Stumble across code that somehow works beyond all reason? Life's short. Mark it with @Magic and move on: @Magic public static int negate(int n) { return new Byte((byte) 0xFF).hashCode() / (int) (short) '\uFFFF' * ~0 * Character.digit ('0', 0) * n * (Integer.MAX_VALUE * 2 + 1) / (Byte.MIN_VALUE >> 7) * (~1 | 1); } This is a serious question. Could this be used in an actual code review?

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  • Does the for foreach construct in java create a hard or soft copy?

    - by Doug
    Say I have the following piece of java code ArrayList<Double> myList = new Double[100]; for (Double x : myList) x = randomDouble(); Does this actually modify myList or just the dummy variable? I realize I should just try this code segment out, but I think this is the sort of thing I should be able to google or search for on this site, and several queries so far have turned up nothing useful.

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  • how to solve a weired swig python c++ interfacing type error

    - by user2981648
    I want to use swig to switch a simple cpp function to python and use "scipy.integrate.quadrature" function to calculate the integration. But python 2.7 reports a type error. Do you guys know what is going on here? Thanks a lot. Furthermore, "scipy.integrate.quad" runs smoothly. So is there something special for "scipy.integrate.quadrature" function? The code is in the following: File "testfunctions.h": #ifndef TESTFUNCTIONS_H #define TESTFUNCTIONS_H double test_square(double x); #endif File "testfunctions.cpp": #include "testfunctions.h" double test_square(double x) { return x * x; } File "swig_test.i" : /* File : swig_test.i */ %module swig_test %{ #include "testfunctions.h" %} /* Let's just grab the original header file here */ %include "testfunctions.h" File "test.py": import scipy.integrate import _swig_test print scipy.integrate.quadrature(_swig_test.test_square, 0., 1.) error info: UMD has deleted: _swig_test Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Python27\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 523, in runfile execfile(filename, namespace) File "D:\data\haitaliu\Desktop\Projects\swig_test\Release\test.py", line 4, in <module> print scipy.integrate.quadrature(_swig_test.test_square, 0., 1.) File "C:\Python27\lib\site-packages\scipy\integrate\quadrature.py", line 161, in quadrature newval = fixed_quad(vfunc, a, b, (), n)[0] File "C:\Python27\lib\site-packages\scipy\integrate\quadrature.py", line 61, in fixed_quad return (b-a)/2.0*sum(w*func(y,*args),0), None File "C:\Python27\lib\site-packages\scipy\integrate\quadrature.py", line 90, in vfunc return func(x, *args) TypeError: in method 'test_square', argument 1 of type 'double'

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  • How do I find the speed of an in-progress file upload in cURL?

    - by cinek1lol
    I'd like to know how to check out the speed of a file being uploaded in real time using the cURL library in C++. This is what I have written: void progress_func(void* ptr, double TotalToDownload, double NowDownloaded, double TotalToUpload,double NowUploaded) { cout<<NowUploaded<<endl; } //... int main() { //... curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, progress_func); } But the manual says that it shows average speed, but even this doesn't seem to work with me, because too mach fast is end. How to good write or A well-calculated?

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  • What is the equivalent of Java's .length for arrays in C#?

    - by Michael Loftus
    I'm new to C#, and I'm trying to convert this code from java into C#. static public double euclidean_2(double[] x, double[] y) { if (x.length != y.length) throw new RuntimeException("Arguments must have same number of dimensions."); double cumssq = 0.0; for (int i = 0; i < x.length; i++) cumssq += (x[i] - y[i]) * (x[i] - y[i]); return cumssq; } I know java uses .length but what is the equivalent in C# since I keep getting an error Thanks

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  • optimization math computation (multiplication and summing)

    - by wiso
    Suppose you want to compute the sum of the square of the differences of items: $\sum_{i=1}^{N-1} (x_i - x_{i+1})^2$, the simplest code (the input is std::vector<double> xs, the ouput sum2) is: double sum2 = 0.; double prev = xs[0]; for (vector::const_iterator i = xs.begin() + 1; i != xs.end(); ++i) { sum2 += (prev - (*i)) * (prev - (*i)); // only 1 - with compiler optimization prev = (*i); } I hope that the compiler do the optimization in the comment above. If N is the length of xs you have N-1 multiplications and 2N-3 sums (sums means + or -). Now suppose you know this variable: sum = $x_1^2 + x_N^2 + 2 sum_{i=2}^{N-1} x_i^2$ Expanding the binomial square: $sum_i^{N-1} (x_i-x_{i+1})^2 = sum - 2\sum_{i=1}^{N-1} x_i x_{i+1}$ so the code becomes: double sum2 = 0.; double prev = xs[0]; for (vector::const_iterator i = xs.begin() + 1; i != xs.end(); ++i) { sum2 += (*i) * prev; prev = (*i); } sum2 = -sum2 * 2. + sum; Here I have N multiplications and N-1 additions. In my case N is about 100. Well, compiling with g++ -O2 I got no speed up (I try calling the inlined function 2M times), why?

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  • VB6 Require some help with looping

    - by k80sg
    Hi, I am trying to convert a source from C++ to vb6: C++: static double mdArray[3][3]; static double mdArray2[3][3]; for (i = 0; i < 3; i++) for (j = 0; j < 3; j++) { double sum = 0; for(k = 0; k < 3; k++) sum = sum + mdArray[k][i] * mdArray[k][k]; mdArray2[i][j] = sum } VB6: dim mdArray(0 to 2, 0 to 2) as integer dim mdArray2(0 to 2, 0 to 2) as integer for i = 0 to 2 for j = 0 to 2 dim a as double sum = 0 for k = 0 to 2 sum = sum + mdArray(k,i) * mdArray(k,j) mdArray2(i,j) = sum Next Next Next Will the vb6 version yield the same result as the C++ version? Thanks.

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  • How to pass a file (read from Java) most effectively to a native method?

    - by soc
    Hi, I have approx. 30000 files (1MB each) which I want to put into a native method, which requires just an byte array and the size of it as arguments. I looked through some examples and benchmarks (like http://nadeausoftware.com/articles/2008/02/java_tip_how_read_files_quickly) but all of them do some other fancy things. Basically I don't care about the contents of the file, I don't want to access something in that file or the byte array or do anything else with it. I just want to put a file into a native method which accepts an byte array as fast as possible. At the moment I'm using RandomAccessFile, but that's horribly slow (10MB/s). Is there anything like byte[] readTheWholeFile(File file){ ... } which I could put into native void fancyCMethod(readTheWholeFile(myFile), myFile.length()) What would you suggest?

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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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  • how to use ByteArrayOutputStream and DataOutputStream simultaneously (Java)

    - by Manuel
    Hi! I'm having quite a problem here, and I think it is because I don't understand very much how I should use the API provided by Java. I need to write an int and a byte[] into a byte[] I thought of using a DataOutputStream to solve the data writing with writeInt(int i) and write(byte[] b), and to be able to put that into a byte array, I should use ByteArrayOutputStream's method toByteArray(). I understand that this classes use the Wrapper pattern, so I had two options: DataOutputStream w = new DataOutputStream(new ByteArrayOutputStream()); or ByteArrayOutputStream w = new ByteArrayOutputStream(new DataOutputStream()); but in both cases, I "loose" a method. in the first case, I can't access the toByteArray method, and in the second, I can't access the writeInt method. How should I use this classes together?

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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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  • DWORD to bytes using bitwise shift operators

    - by Dave18
    I can't get it to work correctly. #include <windows.h> int main() { DWORD i = 6521; BYTE first = i >> 32; BYTE second = i >> 24; BYTE third = i >> 16; BYTE fourth = i >> 8; i = (((DWORD)fourth) << 24) | (((DWORD)third) << 16) | (((DWORD)second) << 8) | first; }

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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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  • Sending Images over Sockets in C

    - by Takkun
    I'm trying to send an image file through a TCP socket in C, but the image isn't being reassembled correctly on the server side. I was wondering if anyone can point out the mistake? I know that the server is receiving the correct file size and it constructs a file of that size, but it isn't an image file. Client //Get Picture Size printf("Getting Picture Size\n"); FILE *picture; picture = fopen(argv[1], "r"); int size; fseek(picture, 0, SEEK_END); size = ftell(picture); //Send Picture Size printf("Sending Picture Size\n"); write(sock, &size, sizeof(size)); //Send Picture as Byte Array printf("Sending Picture as Byte Array\n"); char send_buffer[size]; while(!feof(picture)) { fread(send_buffer, 1, sizeof(send_buffer), picture); write(sock, send_buffer, sizeof(send_buffer)); bzero(send_buffer, sizeof(send_buffer)); } Server //Read Picture Size printf("Reading Picture Size\n"); int size; read(new_sock, &size, sizeof(1)); //Read Picture Byte Array printf("Reading Picture Byte Array\n"); char p_array[size]; read(new_sock, p_array, size); //Convert it Back into Picture printf("Converting Byte Array to Picture\n"); FILE *image; image = fopen("c1.png", "w"); fwrite(p_array, 1, sizeof(p_array), image); fclose(image);

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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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  • How do I convert a number (as a String) to an array of bytes in Java?

    - by user1795595
    I'm creating a method specific method for a java project i'm working on. The UML given specifies the return type to be of static byte[] that accepts the arguments (String, byte) So far, looks like this: public static byte[] convertNumToDigitArray(String number, byte numDigits) { } This method is supposed to convert a number (as a String) to an array of bytes. The ordering must go from most to least significant digits. For example, if the number String is “732” then index 0 of the array should contain 7. The last argument (numDigits) should match the length of the string passed in. How do I do this?

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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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  • 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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  • 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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  • 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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  • 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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