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  • OpenGLES - Rendering a background image only once and not wiping it

    - by chaosbeaker
    Hello, first time asking a question here but been watching others answers for a while. My own question is one for improving the performance of my program. Currently I'm wiping the viewFrameBuffer on each pass through my program and then rendering the background image first followed by the rest of my scene. I was wondering how I go about rendering the background image once, and only wiping the rest of the scene for updating/re-rendering. I tried using a seperate buffer but I'm not sure how to present this new buffer to the render buffer. // Set the current EAGLContext and bind to the framebuffer. This will direct all OGL commands to the // framebuffer and the associated renderbuffer attachment which is where our scene will be rendered [EAGLContext setCurrentContext:context]; glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer); // Define the viewport. Changing the settings for the viewport can allow you to scale the viewport // as well as the dimensions etc and so I'm setting it for each frame in case we want to change i glViewport(0, 0, screenBounds.size.width , screenBounds.size.height); // Clear the screen. If we are going to draw a background image then this clear is not necessary // as drawing the background image will destroy the previous image glClearColor(0.0f, 1.0f, 0.0f, 1.0f); glClear(GL_COLOR_BUFFER_BIT); // Setup how the images are to be blended when rendered. This could be changed at different points during your // render process if you wanted to apply different effects glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); switch (currentViewInt) { case 1: { [background render:CGPointMake(240, 0) fromTopLeftBottomRightCenter:@"Bottom"]; // Other Rendering Code }} // Bind to the renderbuffer and then present this image to the current context glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer); [context presentRenderbuffer:GL_RENDERBUFFER_OES]; Hopefully by solving this I'll also be able to implement another buffer just for rendering particles as I can set them to always use a black background as their alpha source. Any help is greatly appreciated

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  • Why does this program take up so much memory?

    - by Adrian
    I am learning Objective-C. I am trying to release all of the memory that I use. So, I wrote a program to test if I am doing it right: #import <Foundation/Foundation.h> #define DEFAULT_NAME @"Unknown" @interface Person : NSObject { NSString *name; } @property (copy) NSString * name; @end @implementation Person @synthesize name; - (void) dealloc { [name release]; [super dealloc]; } - (id) init { if (self = [super init]) { name = DEFAULT_NAME; } return self; } @end int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; Person *person = [[Person alloc] init]; NSString *str; int i; for (i = 0; i < 1e9; i++) { str = [NSString stringWithCString: "Name" encoding: NSUTF8StringEncoding]; person.name = str; [str release]; } [person release]; [pool drain]; return 0; } I am using a mac with snow leopard. To test how much memory this is using, I open Activity Monitor at the same time that it is running. After a couple of seconds, it is using gigabytes of memory. What can I do to make it not use so much?

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  • Optimizing a shared buffer in a producer/consumer multithreaded environment

    - by Etan
    I have some project where I have a single producer thread which writes events into a buffer, and an additional single consumer thread which takes events from the buffer. My goal is to optimize this thing for a single machine to achieve maximum throughput. Currently, I am using some simple lock-free ring buffer (lock-free is possible since I have only one consumer and one producer thread and therefore the pointers are only updated by a single thread). #define BUF_SIZE 32768 struct buf_t { volatile int writepos; volatile void * buffer[BUF_SIZE]; volatile int readpos;) }; void produce (buf_t *b, void * e) { int next = (b->writepos+1) % BUF_SIZE; while (b->readpos == next); // queue is full. wait b->buffer[b->writepos] = e; b->writepos = next; } void * consume (buf_t *b) { while (b->readpos == b->writepos); // nothing to consume. wait int next = (b->readpos+1) % BUF_SIZE; void * res = b->buffer[b->readpos]; b->readpos = next; return res; } buf_t *alloc () { buf_t *b = (buf_t *)malloc(sizeof(buf_t)); b->writepos = 0; b->readpos = 0; return b; } However, this implementation is not yet fast enough and should be optimized further. I've tried with different BUF_SIZE values and got some speed-up. Additionaly, I've moved writepos before the buffer and readpos after the buffer to ensure that both variables are on different cache lines which resulted also in some speed. What I need is a speedup of about 400 %. Do you have any ideas how I could achieve this using things like padding etc?

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  • MySQL get point in time totals from related tables

    - by batfastad
    Hi everyone We have an order book and invoicing system and I've been tasked with trying to output monthly rolling totals from these tables. But I don't know really where to start with this. I think there's some SQL syntax that I don't even know about yet. I'm familiar with INNER/LEFT/JOINS and GROUP BY etc but grouping by date is confusing since I don't know how to limit the data to only the current date that's being grouped by at that point. I think this will involve joining the tables to themselves or possibly a sub-select. I always thought it best to avoid sub-selects apart from when absolutely necessary. Basically the system has 3 tables orders: order_id, currency, order_stamp orders_lines: order_line_id, invoice_id, order_id, price invoices: invoice_id, invoice_stamp order_stamp and invoice_stamp are UTC unix timestamps stored as integers, not MySQL timestamps. I'm trying to get a listing by year/month showing the total of current unbilled orders (sum of price), at that point in time. Current orders are ones where order_stamp is less than or equal to 00:00 on the 1st of the month. Unbilled orders are ones where invoice_stamp is null or invoice_stamp is greater than 00:00 on the 1st of the month. At that point in time there may not be a related invoice yet and invoice_id might be null. Anyone got any suggestions on what I should join to what and what I need to group by? Cheers, B

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  • How to make an AJAX call immediately on document loading

    - by Ankur
    I want to execute an ajax call as soon as a document is loaded. What I am doing is loading a string that contains data that I will use for an autocomplete feature. This is what I have done, but it is not calling the servlet. I have removed the calls to the various JS scripts to make it clearer. I have done several similar AJAX calls in my code but usually triggered by a click event, I am not sure what the syntax for doing it as soon as the document loads, but I thought this would be it (but it's not): <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <script type="text/javascript"> $(document).ready(function(){ $.ajax({ type: "GET", url: "AutoComplete", dataType: 'json', data: queryString, success: function(data) { var dataArray = data; alert(dataArray); } }); $("#example").autocomplete(dataArray); }); </script> <title></title> </head> <body> API Reference: <form><input id="example"> (try "C" or "E")</form> </body> </html>

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  • Can some tell me why I am seg faulting in this simple C program?

    - by user299648
    I keep on getting seg faulted after I end my first for loop, and for the life of me I don't why. The file I'm scanning is just 18 strings in 18 lines. I thinks the problem is the way I'm mallocing the double pointer called picks, but I don't know exactly why. I'm am only trying to scanf strings that are less than 15 chars long, so I don't see the problem. Can someone please help. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_LENGTH 100 int main( int argc,char *argv[] ) { char* string = malloc( 15*sizeof(char) ); char** picks = malloc(15*sizeof(char*)); FILE* pick_file = fopen( argv[l], "r" ); int num_picks; for( num_picks=0 ; fgets( string, MAX_LENGTH, pick_file ) != NULL ; num_picks++ ) { scanf( "%s", picks+num_picks ); } //this is where i seg fault int x; for(x=0; x<num_picks;x++) printf("s\n", picks+x); }

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  • jQuery: one-liner for removing all children but one

    - by user1352530
    HTML code is: <li> <a href="#" /> <ul> <li> <a href="#"/> </li> </ul> </li> I want to delete any node under $(this) = li that is not a link. If there are more than one link, just the first one is saved, and if there are links inside the ul tag, they are not included because they are descendants and no childrens. Something like this (I am cloning and outputting html): $(this).clone().remove('not(a:first)').html(); //Assuming remove looks for "a" as a first child Does not work, so I try with this: $(this).clone().children().remove('not(a:first)').parent().html(); Does not work so I try with this: $(this).clone().remove('not(>a:first)').html(); I need the original element as a reference after removal for chaining more operations EDIT: Ok! Second one works with a little syntax correction as some appointed (:not( instead of not() but I would like to know if there is any other solution similar to the third line so I don't have to do children().remove().parent(). Thank you!

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  • For a set of sql-queries, how do you determine which result-set contains a certain row?

    - by ManBugra
    I have a set of sql - queries: List<String> queries = ... queries[0] = "select id from person where ..."; ... queries[8756] = "select id from person where ..."; Each query selects rows from the same table 'person'. The only difference is the where-clause. Table 'person' looks like this: id | name | ... many other columns How can i determine which queries will contain a certain person in their subset? For example: List<Integer> matchingQueries = magicMethod(queries, [23,45]); The list obtained by 'magicMethod' filters all sql queries present in the list 'queries' (defined above) and returns only those that contain either the person with id 23 OR a person with id 45. Why i need it: I am dealing with an application that contains products and categories where the categories are sql queries that define which products belong to them (queries stored in a table also). Now i have a requirement where an admin has to see all categories an item belongs to immediately after the item was created. Btw, over 8.000 categories defined (so far, more to come). language and db: java && postgreSQL Thanks,

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  • Spring MVC: How to get the remaining path after the controller path?

    - by Willis Blackburn
    I've spent over an hour trying to find the answer to this question, which seems like it should reflect a common use case, but I can't figure it out! Basically I am writing a file-serving controller using Spring MVC. The URLs are of the format http://www.bighost.com/serve/the/path/to/the/file.jpg, in which the part after "/serve" is the path to the requested file, which may have an arbitrary number of path segments. I have a controller like this: @Controller class ServerController { @RequestMapping(value = "/serve/???") public void serve(???) { } } What I am trying to figure out is: What do I use in place of "???" to make this work? I have two theories about how this should work. The first theory is that I could replace the first "???" in the RequestMapping with a path variable placeholder that has some special syntax meaning "capture to the end of the path." If a regular placeholder looks like "{path}" then maybe I could use "{path:**}" or "{path:/}" or something like that. Then I could use a @PathVariable annotation to refer to the path variable in the second "???". The other theory is that I could replace the first "???" with "**" (match anything) and that Spring would give me an API to obtain the remainder of the path (the part matching the "**"). But I can't find such an API. Thanks for any help you can provide!

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  • Namespace constraint with generic class decleration

    - by SomeGuy
    Good afternoon people, I would like to know if (and if so how) it is possible to define a namespace as a constraint parameter in a generic class declaration. What I have is this: namespace MyProject.Models.Entities <-- Contains my classes to be persisted in db namespace MyProject.Tests.BaseTest <-- Obvious i think Now the decleration of my 'BaseTest' class looks like so; public class BaseTest<T> This BaseTest does little more (at the time of writing) than remove all entities that were added to the database during testing. So typically I will have a test class declared as: public class MyEntityRepositoryTest : BaseTest<MyEntity> What i would LIKE to do is something similar to the following: public class BaseTest<T> where T : <is of the MyProject.Models.Entities namespace> Now i am aware that it would be entirely possible to simply declare a 'BaseEntity' class from which all entities created within the MyProject.Models.Entities namespace will inherit from; public class BaseTest<T> where T : MyBaseEntity but...I dont actually need to, or want to. Plus I am using an ORM and mapping entities with inheritance, although possible, adds a layer of complexity that is not required. So, is it possible to constrain a generic class parameter to a namespace and not a specific type ? Thank you for your time.

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  • How to access global variable in a view in Ruby on Rails?

    - by ben
    I have a User model. I have a Session controller, in which I have a global user variable that is assigned as follows: $user = User.authenticate(params[:session][:email], params[:session][:password]) (I've made user global just to try to solve this problem, so if there's a better way please let me know!) I need to use the email of the logged in user as a parameter to send to Flex part of my website. At the moment I'm creating the link as follows: <%= link_to "secondpage", secondpage_path(:email => @session.$user.email) But I'm getting the following error: compile error /Users/benhartney/rails_projects/talk/app/views/layouts/_header.html.erb:12: syntax error, unexpected tGVAR ..._path(:email = @session.$user.email) ).to_s); @output_buffe... There's also a little arrow pointing at $user If I remove the $ from $user, I get this error: undefined method `user' for nil:NilClass If I remove the (:email => @session.user.email) part, everything works fine, so I think all of the code except for this is ok. Can anyone tell me what I'm doing wrong? Thanks for reading!

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  • OpenGL Nothing will Display

    - by m00st
    Why can't I get anything to display with this code? #include <iostream> #include "GL/glfw.h" #ifndef MAIN #define MAIN #include "GL/gl.h" #include "GL/glu.h" #endif using namespace std; void display(); int main() { int running = GL_TRUE; glfwInit(); if( !glfwOpenWindow( 640,480, 0,0,0,0,0,0, GLFW_WINDOW ) ) { glfwTerminate(); return 0; } while( running ) { //GL Code here display(); glfwSwapBuffers(); // Check if ESC key was pressed or window was closed running = !glfwGetKey( GLFW_KEY_ESC ) && glfwGetWindowParam( GLFW_OPENED ); } glfwTerminate(); return 0; } void display() { glClearColor(0, 0,0, 0.0f); glClear(GL_COLOR_BUFFER_BIT); glLoadIdentity(); gluLookAt(0, 0, 5, 0.0, 0.0, 0.0, 0, 1, 0); glScalef(1.0f, 1.0f, 1.0f); glTranslatef(0, 0, -2); glBegin(GL_POLYGON); glColor3f(1.0, 0.2, 0.2); glVertex3f(0.25, 0.25, 0.0); glVertex3f(0.75, 0.25, 0.0); glVertex3f(0.75, 0.75, 0.0); glVertex3f(0.25, 0.75, 0.0); glEnd(); glFlush(); }

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  • How to write to a text file in pipe delimited format from SQL Server / ASP.Net?

    - by NJTechGuy
    I have a text file which needs to be constantly updated (regular intervals). All I want is the syntax and possibly some code that outputs data from a SQL Server database using ASP.Net. The code I have so far is : <%@ Import Namespace="System.IO" %> <script language="vb" runat="server"> sub Page_Load(sender as Object, e as EventArgs) Dim FILENAME as String = Server.MapPath("Output.txt") Dim objStreamWriter as StreamWriter ' If Len(Dir$(FILENAME)) > 0 Then Kill(FILENAME) objStreamWriter = File.AppendText(FILENAME) objStreamWriter.WriteLine("A user viewed this demo at: " & DateTime.Now.ToString()) objStreamWriter.Close() Dim objStreamReader as StreamReader objStreamReader = File.OpenText(FILENAME) Dim contents as String = objStreamReader.ReadToEnd() lblNicerOutput.Text = contents.Replace(vbCrLf, "<br>") objStreamReader.Close() end sub </script> <asp:label runat="server" id="lblNicerOutput" Font-Name="Verdana" /> With PHP, it is a breeze, but with .Net I have no clue. If you could help me with the database connectivity and how to write the data in pipe delimited format to an Output.txt file, that had be awesome. Thanks guys!

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  • mysterical error

    - by Görkem Buzcu
    i get "customer_service_simulator.exe stopped" error, but i dont know why? this is my c programming project and i have limited time left before deadline. the code is: #include <stdio.h> #include <stdlib.h> #include<time.h> #define FALSE 0 #define TRUE 1 /*A Node declaration to store a value, pointer to the next node and a priority value*/ struct Node { int priority; //arrival time int val; //type int wait_time; int departure_time; struct Node *next; }; Queue Record that will store the following: size: total number of elements stored in the list front: it shows the front node of the queue (front of the queue) rear: it shows the rare node of the queue (rear of the queue) availability: availabity of the teller struct QueueRecord { struct Node *front; struct Node *rear; int size; int availability; }; typedef struct Node *niyazi; typedef struct QueueRecord *Queue; Queue CreateQueue(int); void MakeEmptyQueue(Queue); void enqueue(Queue, int, int); int QueueSize(Queue); int FrontOfQueue(Queue); int RearOfQueue(Queue); niyazi dequeue(Queue); int IsFullQueue(Queue); int IsEmptyQueue(Queue); void DisplayQueue(Queue); void sorteddequeue(Queue); void sortedenqueue(Queue, int, int); void tellerzfunctionz(Queue *, Queue, int, int); int main() { int system_clock=0; Queue waitqueue; int exit, val, priority, customers, tellers, avg_serv_time, sim_time,counter; char command; waitqueue = CreateQueue(0); srand(time(NULL)); fflush(stdin); printf("Enter number of customers, number of tellers, average service time, simulation time\n:"); scanf("%d%c %d%c %d%c %d",&customers, &command,&tellers,&command,&avg_serv_time,&command,&sim_time); fflush(stdin); Queue tellerarray[tellers]; for(counter=0;counter<tellers;counter++){ tellerarray[counter]=CreateQueue(0); //burada teller sayisi kadar queue yaratiyorum } for(counter=0;counter<customers;counter++){ priority=1+(int)rand()%sim_time; //this will generate the arrival time sortedenqueue(waitqueue,1,priority); //here i put the customers in the waiting queue } tellerzfunctionz(tellerarray,waitqueue,tellers,customers); DisplayQueue(waitqueue); DisplayQueue(tellerarray[0]); DisplayQueue(tellerarray[1]); // waitqueue-> printf("\n\n"); system("PAUSE"); return 0; } /*This function initialises the queue*/ Queue CreateQueue(int maxElements) { Queue q; q = (struct QueueRecord *) malloc(sizeof(struct QueueRecord)); if (q == NULL) printf("Out of memory space\n"); else MakeEmptyQueue(q); return q; } /*This function sets the queue size to 0, and creates a dummy element and sets the front and rear point to this dummy element*/ void MakeEmptyQueue(Queue q) { q->size = 0; q->availability=0; q->front = (struct Node *) malloc(sizeof(struct Node)); if (q->front == NULL) printf("Out of memory space\n"); else{ q->front->next = NULL; q->rear = q->front; } } /*Shows if the queue is empty*/ int IsEmptyQueue(Queue q) { return (q->size == 0); } /*Returns the queue size*/ int QueueSize(Queue q) { return (q->size); } /*Shows the queue is full or not*/ int IsFullQueue(Queue q) { return FALSE; } /*Returns the value stored in the front of the queue*/ int FrontOfQueue(Queue q) { if (!IsEmptyQueue(q)) return q->front->next->val; else { printf("The queue is empty\n"); return -1; } } /*Returns the value stored in the rear of the queue*/ int RearOfQueue(Queue q) { if (!IsEmptyQueue(q)) return q->rear->val; else { printf("The queue is empty\n"); return -1; } } /*Displays the content of the queue*/ void DisplayQueue(Queue q) { struct Node *pos; pos=q->front->next; printf("Queue content:\n"); printf("-->Priority Value\n"); while (pos != NULL) { printf("--> %d\t %d\n", pos->priority, pos->val); pos = pos->next; } } void enqueue(Queue q, int element, int priority){ if(IsFullQueue(q)){ printf("Error queue is full"); } else{ q->rear->next=(struct Node *)malloc(sizeof(struct Node)); q->rear=q->rear->next; q->rear->next=NULL; q->rear->val=element; q->rear->priority=priority; q->size++; } } void sortedenqueue(Queue q, int val, int priority) { struct Node *insert,*temp; insert=(struct Node *)malloc(sizeof(struct Node)); insert->val=val; insert->priority=priority; temp=q->front; if(q->size==0){ enqueue(q, val, priority); } else{ while(temp->next!=NULL && temp->next->priority<insert->priority){ temp=temp->next; } //printf("%d",temp->priority); insert->next=temp->next; temp->next=insert; q->size++; if(insert->next==NULL){ q->rear=insert; } } } niyazi dequeue(Queue q) { niyazi del; niyazi deli; del=(niyazi)malloc(sizeof(struct Node)); deli=(niyazi)malloc(sizeof(struct Node)); if(IsEmptyQueue(q)){ printf("Queue is empty!"); return NULL; } else { del=q->front->next; q->front->next=del->next; deli->val=del->val; deli->priority=del->priority; free(del); q->size--; return deli; } } void sorteddequeue(Queue q) { struct Node *temp; struct Node *min; temp=q->front->next; min=q->front; int i; for(i=1;i<q->size;i++) { if(temp->next->priority<min->next->priority) { min=temp; } temp=temp->next; } temp=min->next; min->next=min->next->next; free(temp); if(min->next==NULL){ q->rear=min; } q->size--; } void tellerzfunctionz(Queue *a, Queue b, int c, int d){ int i; int value=0; int priority; niyazi temp; temp=(niyazi)malloc(sizeof(struct Node)); if(c==1){ for(i=0;i<d;i++){ temp=dequeue(b); sortedenqueue((*(a)),temp->val,temp->priority); } } else{ for(i=0;i<d;i++){ while(b->front->next->val==1){ if((*(a+value))->availability==1){ temp=dequeue(b); sortedenqueue((*(a+value)),temp->val,temp->priority); (*(a+value))->rear->val=2; } else{ value++; } } } } } //end of the program

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  • ISO C++ forbids declaration of 'QPushButton' with no type in QT Creator

    - by Mohit Deshpande
    I am running QT Creator on a Linux Ubuntu 9.10 machine. I just got started with QT Creator, and I was going through the tutorials when this error popped up while I was trying to build my project: "ISO C++ forbids declaration of 'QPushButton' with no type". This problem appears in my header file: #ifndef MAINWINDOW_H #define MAINWINDOW_H #include <QtGui/QWidget> namespace Ui { class MainWindow; } class MainWindow : public QWidget { Q_OBJECT public: MainWindow(QWidget *parent = 0); ~MainWindow(); public slots: void addContact(); void submitContact(); void cancel(); private: Ui::MainWindow *ui; QPushButton *addButton; QPushButton *submitButton; QPushButton *cancelButton; QLineEdit *nameLine; QTextEdit *addressText; QMap<QString, QString> contacts; QString oldName; QString oldAddress; }; #endif // MAINWINDOW_H

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  • Concept: Is mongo right for applying schemas?

    - by Jan
    I am currently in charge of checking wether it is valuable for one of our upcoming products to be developed on mongo. Without going too much into detail, I'll try to explain, what the app does. The app simply has "entities". These entities are technical stuff, like cell phones, TVs, Laptops, tablet pcs, and so forth. Of course, a cell phone has other attributes than a Tablet PCs and a Laptop has even other attributes, like RAM, CPU, display size and so on. Now I want to have something that we wanna call a scheme: We define that we need to have saved the display size, amount of ram size of flash devices, processor type, processor speed and so on for tablet pcs. For cell phone we might save display size, GSM, Edge, 3g, 4g, processor, ram, touch screen technology, bla bla bla. I think you got it :) What I want to realize is, that each "category" has a schema and when one of the system's users enters a new product (let's say the new iphone 4), the app constructs the form to be filled out with the appropriate attributes. So far it sounds nice and should not be a problem with mongo. But now the tough for which I could not find a clean solution.... An attribute modeled in mongo looks like: { _id: 1234456, name: "Attribute name", type: 0, "description" } But what to do, if i need this attribute in several languages, like: { en: {name: "Attribute name", type: 0, "description"}, de: {name: "Name des Attributs, type: 0, "Beschreibung"} } I also need to ensure that the german attribute gets updated as soon as the english gets updated, for instance when type changes from 0 to 1. Any ideas on that?

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  • memcmp,strcmp,strncmp in C

    - by el10780
    I wrote this small piece of code in C to test memcmp() strncmp() strcmp() functions in C. Here is the code that I wrote: #include <stdio.h> #include <stdlib.h> #include <string.h> int main(int argc, char** argv) { char *word1="apple",*word2="atoms"; if (strncmp(word1,word2,5)==0) printf("strncmp result.\n"); if (memcmp(word1,word2,5)==0) printf("memcmp result.\n"); if (strcmp(word1,word2)==0) printf("strcmp result.\n"); } Can somebody explain me the differences because I am confused with these three functions?My main problem is that I have a file in which I tokenize its line of it,the problem is that when I tokenize the word "atoms" in the file I have to stop the process of tokenizing.I first tried strcmp() but unfortunately when it reached to the point where the word "atoms" were placed in the file it didn't stop and it continued,but when I used either the memcmp() or the strncmp() it stopped and I was happy.But then I thought,what if there will be a case in which there is one string in which the first 5 letters are a,t,o,m,s and these are being followed by other letters.Unfortunately,my thoughts were right as I tested it using the above code by initializing word1 to "atomsaaaaa" and word2 to atoms and memcmp() and strncmp() in the if statements returned 0.On the other hand strcmp() it didn't.It seems that I must use strcmp(). I have done google searches but I got more confused as I have seen sites and other forums to define these three differently.If it is possible for someone to give me correct explanations/definitions so I can use them correctly in my source code,I would be really grateful.

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  • C system calls open / read / write / close problem.

    - by Andrei Ciobanu
    Hello, given the following code (it's supposed to write "hellowolrd" in a "helloworld" file, and then read the text): #include <fcntl.h> #include <sys/types.h> #include <sys/stat.h> #define FNAME "helloworld" int main(){ int filedes, nbytes; char buf[128]; /* Creates a file */ if((filedes=open(FNAME, O_CREAT | O_EXCL | O_WRONLY | O_APPEND, S_IRUSR | S_IWUSR)) == -1){ write(2, "Error1\n", 7); } /* Writes hellow world to file */ if(write(filedes, FNAME, 10) != 10) write(2, "Error2\n", 7); /* Close file */ close(filedes); if((filedes = open(FNAME, O_RDONLY))==-1) write(2, "Error3\n", 7); /* Prints file contents on screen */ if((nbytes=read(filedes, buf, 128)) == -1) write(2, "Error4\n", 7); if(write(1, buf, nbytes) != nbytes) write(2, "Error5\n", 7); /* Close rile afte read */ close(filedes); return (0); } The first time i run the program, the output is: helloworld After that every time I to run the program, the output is: Error1 Error2 helloworld I don't understand why the text isn't appended, as I've specified the O_APPEND file. Is it because I've included O_CREAT ? It the file is already created, shouldn't O_CREAT be ignored ?

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  • Division by zero: Undefined Behavior or Implementation Defined in C and/or C++ ?

    - by SiegeX
    Regarding division by zero, the standards say: C99 6.5.5p5 - The result of the / operator is the quotient from the division of the first operand by the second; the result of the % operator is the remainder. In both operations, if the value of the second operand is zero, the behavior is undefined. C++03 5.6.4 - The binary / operator yields the quotient, and the binary % operator yields the remainder from the division of the first expression by the second. If the second operand of / or % is zero the behavior is undefined. If we were to take the above paragraphs at face value, the answer is clearly Undefined Behavior for both languages. However, if we look further down in the C99 standard we see the following paragraph which appears to be contradictory(1): C99 7.12p4 - The macro INFINITY expands to a constant expression of type float representing positive or unsigned infinity, if available; Do the standards have some sort of golden rule where Undefined Behavior cannot be superseded by a (potentially) contradictory statement? Barring that, I don't think it's unreasonable to conclude that if your implementation defines the INFINITY macro, division by zero is defined to be such. However, if your implementation does not define such a macro, the behavior is Undefined. I'm curious what the consensus on this matter for each of the two languages. Would the answer change if we are talking about integer division int i = 1 / 0 versus floating point division float i = 1.0 / 0.0 ? Note (1) The C++03 standard talks about the library which includes the INFINITY macro.

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  • NHibernate query against the key field of a dictionary (map)

    - by Carl Raymond
    I have an object model where a Calendar object has an IDictionary<MembershipUser, Perms> called UserPermissions, where MembershipUser is an object, and Perms is a simple enumeration. This is in the mapping file for Calendar as <map name="UserPermissions" table="CalendarUserPermissions" lazy="true" cascade="all"> <key column="CalendarID"/> <index-many-to-many class="MembershipUser" column="UserGUID" /> <element column="Permissions" type="CalendarPermission" not-null="true" /> </map> Now I want to execute a query to find all calendars for which a given user has some permission defined. The permission is irrelevant; I just want a list of the calendars where a given user is present as a key in the UserPermissions dictionary. I have the username property, not a MembershipUser object. How do I build that using QBC (or HQL)? Here's what I've tried: ISession session = SessionManager.CurrentSession; ICriteria calCrit = session.CreateCriteria<Calendar>(); ICriteria userCrit = calCrit.CreateCriteria("UserPermissions.indices"); userCrit.Add(Expression.Eq("Username", username)); return calCrit.List<Calendar>(); This constructed invalid SQL -- the WHERE clause contained WHERE membership1_.Username = @p0 as expected, but the FROM clause didn't include the MemberhipUsers table. Also, I really had to struggle to learn about the .indices notation. I found it by digging through the NHibernate source code, and saw that there's also .elements and some other dotted notations. Where's a reference to the allowed syntax of an association path? I feel like what's above is very close, and just missing something simple.

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  • Issue with Callback method and maintaining CultureInfo and ASP.Net HttpRuntime

    - by Little Larry Sellers
    Hi All, Here is my issue. I am working on an E-commerce solution that is deployed to multiple European countries. We persist all exceptions within the application to SQL Server and I have found that there are records in the DB that have a DateTime in the future! We define the culture in the web.config, for example pt-PT, and the format expected is DD-MM-YYYY. After debugging I found the issue with these 'future' records in the DB is because of Callback methods we use. For example, in our Caching architecture we use Callbacks, as such - CacheItemRemovedCallback ReloadCallBack = new CacheItemRemovedCallback(OnRefreshRequest); When I check the current threads CultureInfo, on these Callbacks it is en-US instead of pt-PT and also the HttpContext is null. If an exception occurs on the Callback our exception manager reports it as MM-DD-YYYY and thus it is persisted to SQL Server incorrectly. Unfortunately, in the exception manager code, we use DateTime.Now, which is fine if it is not a callback. I can't change this code to be culture specific due to it being shared across other verticals. So, why don't callbacks into ASP.Net maintain context? Is there any way to maintain it on this callback thread? What are the best practices here? Thanks.

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  • boost::python string-convertible properties

    - by Checkers
    I have a C++ class, which has the following methods: class Bar { ... const Foo& getFoo() const; void setFoo(const Foo&); }; where class Foo is convertible to std::string (it has an implicit constructor from std::string and an std::string cast operator). I define a Boost.Python wrapper class, which, among other things, defines a property based on previous two functions: class_<Bar>("Bar") ... .add_property( "foo", make_function( &Bar::getFoo, return_value_policy<return_by_value>()), &Bar::setFoo) ... I also mark the class as convertible to/from std::string. implicitly_convertible<std::string, Foo>(); implicitly_convertible<Foo, std::string>(); But at runtime I still get a conversion error trying to access this property: TypeError: No to_python (by-value) converter found for C++ type: Foo How to achieve the conversion without too much boilerplate of wrapper functions? (I already have all the conversion functions in class Foo, so duplication is undesirable.

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  • Ruby: how does constant-lookup work in instance_eval/class_eval?

    - by Alan O'Donnell
    I'm working my way through Pickaxe 1.9, and I'm a bit confused by constant-lookup in instance/class_eval blocks. I'm using 1.9.2. It seems that Ruby handles constant-lookup in *_eval blocks the same way it does method-lookup: look for a definition in receiver.singleton_class (plus mixins); then in receiver.singleton_class.superclass (plus mixins); then continue up the eigenchain until you get to #<Class:BasicObject>; whose superclass is Class; and then up the rest of the ancestor chain (including Object, which stores all the constants you define at the top-level), checking for mixins along the way Is this correct? The Pickaxe discussion is a bit terse. Some examples: class Foo CONST = 'Foo::CONST' class << self CONST = 'EigenFoo::CONST' end end Foo.instance_eval { CONST } # => 'EigenFoo::CONST' Foo.class_eval { CONST } # => 'EigenFoo::CONST', not 'Foo::CONST'! Foo.new.instance_eval { CONST } # => 'Foo::CONST' In the class_eval example, Foo-the-class isn't a stop along Foo-the-object's ancestor chain! And an example with mixins: module M CONST = "M::CONST" end module N CONST = "N::CONST" end class A include M extend N end A.instance_eval { CONST } # => "N::CONST", because N is mixed into A's eigenclass A.class_eval { CONST } # => "N::CONST", ditto A.new.instance_eval { CONST } # => "M::CONST", because A.new.class, A, mixes in M

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  • Java Trying to get a line of source from a website

    - by dsta
    I'm trying to get one line of source from a website and then I'm returning that line back to main. I keep on getting an error at the line where I define InputStream in. Why am I getting an error at this line? public class MP3LinkRetriever { private static String line; public static void main(String[] args) { String link = "www.google.com"; String line = ""; while (link != "") { link = JOptionPane.showInputDialog("Please enter the link"); try { line = Connect(link); } catch(Exception e) { } JOptionPane.showMessageDialog(null, "MP3 Link: " + parseLine(line)); String text = line; Toolkit.getDefaultToolkit( ).getSystemClipboard() .setContents(new StringSelection(text), new ClipboardOwner() { public void lostOwnership(Clipboard c, Transferable t) { } }); JOptionPane.showMessageDialog(null, "Link copied to your clipboard"); } } public static String Connect(String link) throws Exception { String strLine = null; InputStream in = null; try { URL url = new URL(link); HttpURLConnection uc = (HttpURLConnection) url.openConnection(); in = new BufferedInputStream(uc.getInputStream()); Reader re = new InputStreamReader(in); BufferedReader r = new BufferedReader(re); int index = -1; while ((strLine = r.readLine()) != null && index == -1) { index = strLine.indexOf("<source src"); } } finally { try { in.close(); } catch (Exception e) { } } return strLine; } public static String parseLine(String line) { line = line.replace("<source", ""); line = line.replace(" src=", ""); line = line.replace("\"", ""); line = line.replace("type=", ""); line = line.replace("audio/mpeg", ""); line = line.replace(">", ""); return line; } }

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  • how to store a file handle in perl class

    - by Haiyuan Zhang
    please look at the following code first. #! /usr/bin/perl package foo; sub new { my $pkg = shift; my $self = {}; my $self->{_fd} = undef; bless $self, $pkg; return $self; } sub Setfd { my $self = shift; my $fd = shift; $self_->{_fd} = $fd; } sub write { my $self = shift; print $self->{_fd} "hello word"; } my $foo = new foo; My intention is to store a file handle within a class using hash. the file handle is undefined at first, but can be initilized afterwards by calling Setfd function. then write can be called to actually write string "hello word" to a file indicated by the file handle, supposed that the file handle is the result of a success "write" open. but, perl compiler just complains that there are syntax error in the "print" line. can anyone of you tells me what's wrong here? thanks in advance.

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