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  • OpenCL - incremental summation during compute

    - by user1721997
    I'm absolutelly novice in OpenCL programming. For my app. (molecular simulaton) I wrote a kernel for calculate intermolecular potential of lennard-jones liquid. In this kernel I need to compute cumulative value of the potential of all particles with one: __kernel void Molsim(__global const float* inmatrix, __global float* fi, const int c, const float r1, const float r2, const float r3, const float rc, const float epsilon, const float sigma, const float h1, const float h23) { float fi0; float fi1; float d; unsigned int i = get_global_id(0); //number of particles (typically 2000) if(c!=i) { // potential before particle movement d=sqrt(pow((0.5*h1-fabs(0.5*h1-fabs(inmatrix[c*3]-inmatrix[i*3]))),2.0)+pow((0.5*h23-fabs(0.5*h23-fabs(inmatrix[c*3+1]-inmatrix[i*3+1]))),2.0)+pow((0.5*h23-fabs(0.5*h23-fabs(inmatrix[c*3+2]-inmatrix[i*3+2]))),2.0)); if(d<rc) { fi0=4.0*epsilon*(pow(sigma/d,12.0)-pow(sigma/d,6.0)); } else { fi0=0; } // potential after particle movement d=sqrt(pow((0.5*h1-fabs(0.5*h1-fabs(r1-inmatrix[i*3]))),2.0)+pow((0.5*h23-fabs(0.5*h23-fabs(r2-inmatrix[i*3+1]))),2.0)+pow((0.5*h23-fabs(0.5*h23-fabs(r3-inmatrix[i*3+2]))),2.0)); if(d<rc) { fi1=4.0*epsilon*(pow(sigma/d,12.0)-pow(sigma/d,6.0)); } else { fi1=0; } // cumulative difference of potentials fi[0]+=fi1-fi0; } } My problem is in the line: fi[0]+=fi1-fi0;. In the one-element vector fi[0] are wrong results. I read something about sum reduction, but I do not know how to do it during the calculation. Exist any simple solution of my problem?

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  • MySQL indexes: how do they work?

    - by bob-the-destroyer
    I'm a complete newbie with MySQL indexes. I have several MyISAM tables on MySQL 5.0x having utf8 charsets and collations with 100k+ records each. The primary keys are generally integer. Many columns on each table may have duplicate values. I need to quickly count, sum, average, or otherwise perform custom calculations on any number of fields in each table or joined on any number of others. I found this page giving an overview of MySQL index usage: http://dev.mysql.com/doc/refman/5.0/en/mysql-indexes.html, but I'm still not sure I'm using indexes right. Just when I think I've made the perfect index out of a collection of fields I want to calculate against, I get the "index must be under 1000 bytes" error. Can anyone explain how to most efficiently create and use indexes to speed up queries? Caveat: upgrading Mysql is not possible in this case. Using Navicat Light for db administration, but this app isn't required.

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  • Ok to use VirtualProtect to change resource in Delphi?

    - by user257188
    I'm working on a simple localization effort in D2010. I'm handling all strings on forms because ETM seems like overkill for my needs, as did other 3rd party tools... (although I'm not so sure at this point!) Is the code below for changing the Const.pas strings considered safe to change the button labels on standard message boxes? procedure HookResourceString(rs: PResStringRec; newStr: PChar); var oldprotect: DWORD; begin VirtualProtect(rs, SizeOf(rs^), PAGE_EXECUTE_READWRITE, @oldProtect); rs^.Identifier := Integer(newStr); VirtualProtect(rs, SizeOf(rs^), oldProtect, @oldProtect); end; const NewOK: PChar = 'New Ok'; NewCancel: PChar = 'New Cancel'; Procedure TForm.FormCreate; begin HookResourceString(@SMsgDlgOK, NewOK); HookResourceString(@SMsgDlgCancel, NewCancel); end;

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  • C++ password masking

    - by blaxc
    hi... i'm writing a code to receive password input. Below is my code... the program run well but the problem is other keys beside than numerical and alphabet characters also being read, for example delete, insert, and etc. can i know how can i avoid it? tq... string pw=""; char c=' '; while(c != 13) //Loop until 'Enter' is pressed { c = _getch(); if(c==13) break; if(c==8) { if(pw.size()!=0) //delete only if there is input { cout<<"\b \b"; pw.erase(pw.size()-1); } } if((c>47&&c<58)||(c>64&&c<91)||(c>96&&c<123)) //ASCii code for integer and alphabet { pw += c; cout << "*"; } }

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  • calculate intersection between two segments in a symmetric way

    - by Elazar Leibovich
    When using the usual formulas to calculate intersection between two 2D segments, ie here, if you round the result to an integer, you get non-symmetric results. That is, sometimes, due to rounding errors, I get that intersection(A,B)!=intersection(B,A). The best solution is to keep working with floats, and compare the results up to a certain precision. However, I must round the results to integers after calculating the intersection, I cannot keep working with floats. My best solution so far was to use some full order on the segments in the plane, and have intersection to always compare the smaller segment to the larger segment. Is there a better method? Am I missing something?

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  • Using stack defined in C++ stl

    - by cambr
    #include <stack> using namespace std; int main() { stack<int> s; int i; for (i = 0; i <= 10; i++) { s.push(i); } for (i = 0; i <= 10; i++) { printf("%d", s.pop()); } } Whats wrong with the code above? Error: In function `int main()': aggregate value used where an integer was expected

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  • RSA_sign and RSACryptoProvider.VerifySignature

    - by Miky D
    I'm trying to get up to speed on how to get some code that uses OpenSSL for cryptography, to play nice with another program that I'm writing in C#, using the Microsoft cryptography providers available in .NET. More to the point, I'm trying to have the C# program verify an RSA message signature generated by the OpenSSL code. The code that generates the signature looks something like this: // Code in C, using the OpenSSL RSA implementation char msgToSign[] = "Hello World"; // the message to be signed char signature[RSA_size(rsa)]; // buffer that will hold signature int slen = 0; // will contain signature size // rsa is an OpenSSL RSA context, that's loaded with the public/private key pair memset(signature, 0, sizeof(signature)); RSA_sign(NID_sha1 , (unsigned char*)msgToSign , strlen(msgToSign) , signature , &slen , rsa); // now signature contains the message signature // and can be verified using the RSA_verify counterpart // .. I would like to verify the signature in C# In C#, I would do the following: import the other side's public key into an RSACryptoServiceProvider object receive the message and it's signature try to verify the signature I've got the first two parts working (I've verified that the public key is loading properly because I managed to send an RSA encrypted text from the C# code to the OpenSSL code in C and successfully have it decrypted) In order to verify the signature in C#, I've tried using the: VerifySignature method of the RSACryptoServiceProvider but that didn't work. And digging around the internet I was only able to find some vague information pointing out that .NET uses a different method for generating the signature than OpenSSL does. So, does anybody know how to accomplish this?

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  • Complex sound handling (I.E. pitch change while looping)

    - by Matthew
    Hi everyone I've been meaning to learn Java for a while now (I usually keep myself in languages like C and Lua) but buying an android phone seems like an excellent time to start. now after going through the lovely set of tutorials and a while spent buried in source code I'm beginning to get the feel for it so what's my next step? well to dive in with a fully featured application with graphics, sound, sensor use, touch response and a full menu. hmm now there's a slight conundrum since i can continue to use cryptic references to my project or risk telling you what the application is but at the same time its going to make me look like a raving sci-fi nerd so bare with me for the brief... A semi-working sonic screwdriver (oh yes!) my grand idea was to make an animated screwdriver where sliding the controls up and down modulate the frequency and that frequency dictates the sensor data it returns. now I have a semi-working sound system but its pretty poor for what its designed to represent and I just wouldn't be happy producing a sub-par end product whether its my first or not. the problem : sound must begin looping when the user presses down on the control the sound must stop when the user releases the control when moving the control up or down the sound effect must change pitch accordingly if the user doesn't remove there finger before backing out of the application it must plate the casing of there device with gold (Easter egg ;P) now I'm aware of how monolithic the first 3 look and that's why I would really appreciate any help I can get. sorry for how bad this code looks but my general plan is to create the functional components then refine the code later, no good painting the walls if the roofs not finished. here's my user input, he set slide stuff is used in the graphics for the control @Override public boolean onTouchEvent(MotionEvent event) { //motion event for the screwdriver view if(event.getAction() == MotionEvent.ACTION_DOWN) { //make sure the users at least trying to touch the slider if (event.getY() > SonicSlideYTop && event.getY() < SonicSlideYBottom) { //power setup, im using 1.5 to help out the rate on soundpool since it likes 0.5 to 1.5 SonicPower = 1.5f - ((event.getY() - SonicSlideYTop) / SonicSlideLength); //just goes into a method which sets a private variable in my sound pool class thing mSonicAudio.setPower(1, SonicPower); //this handles the slides graphics setSlideY ( (int) event.getY() ); @Override public boolean onTouchEvent(MotionEvent event) { //motion event for the screwdriver view if(event.getAction() == MotionEvent.ACTION_DOWN) { //make sure the users at least trying to touch the slider if (event.getY() > SonicSlideYTop && event.getY() < SonicSlideYBottom) { //power setup, im using 1.5 to help out the rate on soundpool since it likes 0.5 to 1.5 SonicPower = 1.5f - ((event.getY() - SonicSlideYTop) / SonicSlideLength); //just goes into a method which sets a private variable in my sound pool class thing mSonicAudio.setPower(1, SonicPower); //this handles the slides graphics setSlideY ( (int) event.getY() ); //this is from my latest attempt at loop pitch change, look for this in my soundPool class mSonicAudio.startLoopedSound(); } } if(event.getAction() == MotionEvent.ACTION_MOVE) { if (event.getY() > SonicSlideYTop && event.getY() < SonicSlideYBottom) { SonicPower = 1.5f - ((event.getY() - SonicSlideYTop) / SonicSlideLength); mSonicAudio.setPower(1, SonicPower); setSlideY ( (int) event.getY() ); } } if(event.getAction() == MotionEvent.ACTION_UP) { mSonicAudio.stopLoopedSound(); SonicPower = 1.5f - ((event.getY() - SonicSlideYTop) / SonicSlideLength); mSonicAudio.setPower(1, SonicPower); } return true; } and here's where those methods end up in my sound pool class its horribly messy but that's because I've been trying a ton of variants to get this to work, you will also notice that I begin to hard code the index, again I was trying to get the methods to work before making them work well. package com.mattster.sonicscrewdriver; import java.util.HashMap; import android.content.Context; import android.media.AudioManager; import android.media.SoundPool; public class SoundManager { private float mPowerLvl = 1f; private SoundPool mSoundPool; private HashMap mSoundPoolMap; private AudioManager mAudioManager; private Context mContext; private int streamVolume; private int LoopState; private long mLastTime; public SoundManager() { } public void initSounds(Context theContext) { mContext = theContext; mSoundPool = new SoundPool(2, AudioManager.STREAM_MUSIC, 0); mSoundPoolMap = new HashMap<Integer, Integer>(); mAudioManager = (AudioManager)mContext.getSystemService(Context.AUDIO_SERVICE); streamVolume = mAudioManager.getStreamVolume(AudioManager.STREAM_MUSIC); } public void addSound(int index,int SoundID) { mSoundPoolMap.put(1, mSoundPool.load(mContext, SoundID, 1)); } public void playUpdate(int index) { if( LoopState == 1) { long now = System.currentTimeMillis(); if (now > mLastTime) { mSoundPool.play(mSoundPoolMap.get(1), streamVolume, streamVolume, 1, 0, mPowerLvl); mLastTime = System.currentTimeMillis() + 250; } } } public void stopLoopedSound() { LoopState = 0; mSoundPool.setVolume(mSoundPoolMap.get(1), 0, 0); mSoundPool.stop(mSoundPoolMap.get(1)); } public void startLoopedSound() { LoopState = 1; } public void setPower(int index, float mPower) { mPowerLvl = mPower; mSoundPool.setRate(mSoundPoolMap.get(1), mPowerLvl); } } ah ha! I almost forgot, that looks pretty ineffective but I omitted my thread which actuality updates it, nothing fancy it just calls : mSonicAudio.playUpdate(1); thanks in advance, Matthew

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  • CakePHP 'Cake is NOT able to connect to the database'

    - by kand
    I've looked at this post about a similar issue: CakePHP: Can't access MySQL database and I've tried everything they mentioned in there including: Changing my database.php so that the 'port' attribute for both $default and $test are the location of my mysqld.sock file Changing the 'port' attribute to the actual integer that represents the port in my my.cnf mysql config Changing the mysql socket locations in php.ini to the location of my mysqld.sock file I'm using ubuntu 11.04, apache 2.2.17, mysql 5.1.54, and CakePHP 1.3.10. My install of mysql and apache don't seem to match any conventions, as in, all the config files are there, they are all just in really weird places--I'm not sure why that is, but I've tried reinstalling both programs multiple times with the same results... At any rate, I can log into mysql from the terminal and use it normally, and apache is working because I can see the CakePHP default homepage. I just can't get it to change the message 'Cake is NOT able to connect to the database'. SOLVED: Figured it out, had to change php.ini so that extension_dir pointed to the correct directory and had to add a line extension=mysql.so.

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  • Reading a text file in c++

    - by Yavuz Karacabey
    string numbers; string fileName = "text.txt"; ifstream inputFile; inputFile.open(fileName.c_str(),ios_base::in); inputFile >> numbers; inputFile.close(); cout << numbers; And my text.txt file is: 1 2 3 4 5 basically a set of integers separated by tabs. The problem is the program only reads the first integer in the text.txt file and ignores the rest for some reason. If I remove the tabs between the integers it works fine, but with tabs between them, it won't work. What causes this? As far as I know it should ignore any white space characters or am I mistaken? If so is there a better way to get each of these numbers from the text file?

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  • Template metaprogram converting type to unique number

    - by daramarak
    I just started playing with metaprogramming and I am working on different tasks just to explore the domain. One of these was to generate a unique integer and map it to type, like below: int myInt = TypeInt<AClass>::value; I want to know if this is at all possible, and in that case how. Because although I have learned much about exploring this subject I still have failed to come up with an answer. (P.S. A yes/no answer is much more gratifying than a c++ solution that doesn't use metaprogramming, as this is the domain that I am exploring)

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  • Rails and MongoDB with MongoMapper

    - by FCastellanos
    I'm new to Rails development and I'm starting with MongoDB also. I have been following this Railscast tutorial about complex forms with Rails but I'm using MongoDB as my database. I'm having no problems inserting documents with it's childs and retrieving the data to the edit form, but when I try to update it I get this error undefined method `assert_valid_keys' for false:FalseClass this is my entity class class Project include MongoMapper::Document key :name, String, :required => true key :priority, Integer many :tasks after_update :save_tasks def task_attributes=(task_attributes) task_attributes.each do |attributes| if attributes[:id].blank? tasks.build(attributes) else task = tasks.detect { |t| t.id.to_s == attributes[:id].to_s } task.attributes = attributes end end end def save_tasks tasks.each do |t| t.save(false) end end end Does anyone knows whats happening here? Thanks

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  • Interesting interview question. .Net

    - by rahul
    Coding Problem NumTrans There is an integer K. You are allowed to add to K any of its divisors not equal to 1and K. The same operation can be applied to the resulting number and so on. Notice that starting from the number 4, we can reach any composite number by applying several such operations. For example, the number 24 can be reached starting from 4 using 5 operations: 468121824 You will solve a more general problem. Given integers n and m, return the minimal number of the described operations necessary to transform n into m. Return -1 if m can't be obtained from n. Definition Method signature: int GetLeastCount (int n, int m) Constraints N will be between 4 and 100000, inclusive. M will be between N and 100000, inclusive. Examples 1) 4 576 Returns: 14 The shortest order of operations is: 468121827365481108162243324432576 2) 8748 83462 Returns: 10 The shortest order of operations is: 874813122196832624439366590497873283106834488346083462 3) 4 99991 Returns: -1 The number 99991 can't be obtained because it’s prime!

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  • Resolving type parameter values passed to ancester type using reflection

    - by Tom Tucker
    I've asked a similar question before, but this one is much more challenging. How do I find a value of a specific type parameter that is passed to an ancestor class or an interface implemented by one of its ancestor classes using reflection? I basically need to write a method that looks like this. // Return the value of the type parameter at the index passed to the parameterizedClass from the clazz. Object getParameterValue(Class<?> clazz, Class<?> parameterizedClass, int index) For the example below, getParameterValue(MyClass.class, Map.class, 1) would return String.class public class Foo<K, V> implements Map<K, V>{ } public class Bar<V> extends Foo<Integer, V> { } public class MyClass extends Bar<String> { } Thanks!

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  • Simple dynamic memory allocation bug.

    - by M4design
    I'm sure you (pros) can identify the bug's' in my code, I also would appreciate any other comments on my code. BTW, the code crashes after I run it. #include <stdlib.h> #include <stdio.h> #include <stdbool.h> typedef struct { int x; int y; } Location; typedef struct { bool walkable; unsigned char walked; // number of times walked upon } Cell; typedef struct { char name[40]; // Name of maze Cell **grid; // 2D array of cells int rows; // Number of rows int cols; // Number of columns Location entrance; } Maze; Maze *maz_new() { int i = 0; Maze *mazPtr = (Maze *)malloc(sizeof (Maze)); if(!mazPtr) { puts("The memory couldn't be initilised, Press ENTER to exit"); getchar(); exit(-1); } else { // allocating memory for the grid mazPtr->grid = (Cell **) malloc((sizeof (Cell)) * (mazPtr->rows)); for(i = 0; i < mazPtr->rows; i++) mazPtr->grid[i] = (Cell *) malloc((sizeof (Cell)) * (mazPtr->cols)); } return mazPtr; } void maz_delete(Maze *maz) { int i = 0; if (maz != NULL) { for(i = 0; i < maz->rows; i++) free(maz->grid[i]); free(maz->grid); } } int main() { Maze *ptr = maz_new(); maz_delete(ptr); getchar(); return 0; } Thanks in advance.

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  • Are there any modern platforms with non-IEEE C/C++ float formats?

    - by Patrick Niedzielski
    Hi all, I am writing a video game, Humm and Strumm, which requires a network component in its game engine. I can deal with differences in endianness easily, but I have hit a wall in attempting to deal with possible float memory formats. I know that modern computers have all a standard integer format, but I have heard that they may not all use the IEEE standard for floating-point integers. Is this true? While certainly I could just output it as a character string into each packet, I would still have to convert to a "well-known format" of each client, regardless of the platform. The standard printf() and atod() would be inadequate. Please note, because this game is a Free/Open Source Software program that will run on GNU/Linux, *BSD, and Microsoft Windows, I cannot use any proprietary solutions, nor any single-platform solutions. Cheers, Patrick

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  • memory alignment issues with union

    - by confucius
    Hi all, Is there guarantee, that memory for this object will be properly aligned if we create this object of this type in stack? union my_union { int value; char bytes[4]; }; If we create char bytes[4] in stack and then try to cast it to integer there might be alignment problem. We can avoid that problem by creating it in heap, however, is there such guarantee for union objects? Logically there should be, but I would like to confirm. Thanks.

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  • Add two 32-bit integers in Assembler for use in VB6

    - by Emtucifor
    I would like to come up with the byte code in assembler (assembly?) for Windows machines to add two 32-bit longs and throw away the carry bit. I realize the "Windows machines" part is a little vague, but I'm assuming that the bytes for ADD are pretty much the same in all modern Intel instruction sets. I'm just trying to abuse VB a little and make some things faster. So... if the string "8A4C240833C0F6C1E075068B442404D3E0C20800" is the assembly code for SHL that can be "injected" into a VB6 program for a fast SHL operation expecting two Long parameters (we're ignoring here that 32-bit longs in VB6 are signed, just pretend they are unsigned), what is the hex string of bytes representing assembler instructions that will do the same thing to return the sum? The hex code above for SHL is, according to the author: mov eax, [esp+4] mov cl, [esp+8] shl eax, cl ret 8 I spit those bytes into a file and tried unassembling them in a windows command prompt using the old debug utility, but I figured out it's not working with the newer instruction set because it didn't like EAX when I tried assembling something but it was happy with AX. I know from comments in the source code that SHL EAX, CL is D3E0, but I don't have any reference to know what the bytes are for instruction ADD EAX, CL or I'd try it. I tried flat assembler and am not getting anything I can figure out how to use. I used it to assemble the original SHL code and got a very different result, not the same bytes. Help?

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  • Python Beginner: Selective Printing in loops

    - by Jonathan Straus
    Hi there. I'm a very new python user (had only a little prior experience with html/javascript as far as programming goes), and was trying to find some ways to output only intermittent numbers in my loop for a basic bicycle racing simulation (10,000 lines of biker positions would be pretty excessive :P). I tried in this loop several 'reasonable' ways to communicate a condition where a floating point number equals its integer floor (int, floor division) to print out every 100 iterations or so: for i in range (0,10000): i = i + 1 t = t + t_step #t is initialized at 0 while t_step is set at .01 acceleration_rider1 = (power_rider1 / (70 * velocity_rider1)) - (force_drag1 / 70) velocity_rider1 = velocity_rider1 + (acceleration_rider1 * t_step) position_rider1 = position_rider1 + (velocity_rider1 * t_step) force_drag1 = area_rider1 * (velocity_rider1 ** 2) acceleration_rider2 = (power_rider2 / (70 * velocity_rider1)) - (force_drag2 / 70) velocity_rider2 = velocity_rider2 + (acceleration_rider2 * t_step) position_rider2 = position_rider2 + (velocity_rider2 * t_step) force_drag2 = area_rider1 * (velocity_rider2 ** 2) if t == int(t): #TRIED t == t // 1 AND OTHER VARIANTS THAT DON'T WORK HERE:( print t, "biker 1", position_rider1, "m", "\t", "biker 2", position_rider2, "m"

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  • Reading a triangle of numbers into a 2d array of ints in Python

    - by Gabriel Silk
    I want to read a triangle of integer values from a file into a 2D array of ints using Python. The numbers would look like this: 75 95 64 17 47 82 18 35 87 10 20 04 82 47 65 ... The code I have so far is as follows: f = open('problem18.input', 'r') arr = [] for i in range(0, 15): arr.append([]) str = f.readline() a = str.split(' ') for tok in a: arr[i].append(int(tok[:2])) print arr I have a feeling this could be done in a tighter, more Pythonesque way. How would you do it?

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  • Creating an array & outputting its code definition for preloading

    - by user422318
    I want to create a 2d array that represents my 2d canvas. For each pixel, I will look up the value and then save an integer {0, 1, 2, 3, 4} as each element of the array. Unfortunately, this takes way too friggin' long to run each time I load the game. How can I write a script that creates this array for me and outputs the array code so I can just paste it in a js file and have it preloaded? (I'm prototyping a game, so I just need to run this for my test map or two.)

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  • MVP - asp.net - passing information via views - confused

    - by ekynox
    Hi, I've just started to play around with MVP in asp.net. One thing I quite cant figure out is how do I pass information, i.e. an integer variable from one view(webform) to another. Let's I have a customerlistView which is mapped to a customerlist.aspx page. From it I select a customer and it's record id. Say I want to display the customer's details in another view (i.e customerDetailView, customerdetail.aspx). How do I achieve that ? Does that mean customerlistView would call the presenter of the customerdetail and cause a page redirect ? Any ideas ? thanks

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  • Invalid conversion from int to int** C++

    - by user69514
    Not sure why I'm getting this error. I have the following: int* arr = new int[25]; int* foo(){ int* i; cout << "Enter an integer:"; cin >> *i; return i; } void test(int** myInt){ *myInt = foo(); } This call here is where I get the error: test(arr[0]); //here i get invalid conversion from int to int**

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  • recommended format to save time with MJD + BCD format in database

    - by pierr
    Hi, There is a time represented in MJD and BCD format with 5 bytes .I am wondering what is the recommended format to save this date-time in the sqlite database so that user can search against it ? My first attempt is to save it just as it is, that is a 5 bytes string. The user will use the same format to search and the result will be converted to unix time by the user with following code. However, later, I was suggested to save the time in the integer - the UTC time, for example. But I can not find a standard way to do the conversion. I feel this is a common issue and would like to hear your comments. time_t sidate_to_unixtime(unsigned char sidate[]) { int k = 0; struct tm tm; double mjd; /* check for the undefined value */ if ((sidate[0] == 0xff) && (sidate[1] == 0xff) && (sidate[2] == 0xff) && (sidate[3] == 0xff) && (sidate[4] == 0xff)) { return -1; } memset(&tm, 0, sizeof(tm)); mjd = (sidate[0] << 8) | sidate[1]; tm.tm_year = (int) ((mjd - 15078.2) / 365.25); tm.tm_mon = (int) (((mjd - 14956.1) - (int) (tm.tm_year * 365.25)) / 30.6001); tm.tm_mday = (int) mjd - 14956 - (int) (tm.tm_year * 365.25) - (int) (tm.tm_mon * 30.6001); if ((tm.tm_mon == 14) || (tm.tm_mon == 15)) k = 1; tm.tm_year += k; tm.tm_mon = tm.tm_mon - 2 - k * 12; tm.tm_sec = bcd_to_integer(sidate[4]); tm.tm_min = bcd_to_integer(sidate[3]); tm.tm_hour = bcd_to_integer(sidate[2]); return mktime(&tm); }

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  • Delphi Performance: Case Versus If

    - by Andreas Rejbrand
    I guess there might be some overlapping with previous SO questions, but I could not find a Delphi-specific question on this topic. Suppose that you want to check if an unsigned 32-bit integer variable "MyAction" is equal to any of the constants ACTION1, ACTION2, ... ACTIONn, where n is - say 1000. I guess that, besides being more elegant, case MyAction of ACTION1: {code}; ACTION2: {code}; ... ACTIONn: {code}; end; if much faster than if MyAction = ACTION1 then // code else if MyAction = ACTION2 then // code ... else if MyAction = ACTIONn then // code; I guess that the if variant takes time O(n) to complete (i.e. to find the right action) if the right action ACTIONi has a high value of i, whereas the case variant takes a lot less time (O(1)?). Am I correct that switch is much faster? Am I correct that the time required to find the right action in the switch case actually is independent of n? I.e. is it true that it does not really take any longer to check a million cases than to check 10 cases? How, exactly, does this work?

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