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• forkpty - socket

  - by Alexxx

  Hi, I'm trying to develop a simple "telnet/server" daemon which have to run a program on a new socket connection. This part working fine. But I have to associate my new process to a pty, because this process have some terminal capabilities (like a readline). The code I've developped is (where socketfd is the new socket file descriptor for the new input connection) : int masterfd, pid; const char *prgName = "..."; char *arguments[10] = ....; if ((pid = forkpty(&masterfd, NULL, NULL, NULL)) < 0) perror("FORK"); else if (pid) return pid; else { close(STDOUT_FILENO); dup2(socketfd, STDOUT_FILENO); close(STDIN_FILENO); dup2(socketfd, STDIN_FILENO); close(STDERR_FILENO); dup2(socketfd, STDERR_FILENO); if (execvp(prgName, arguments) < 0) { perror("execvp"); exit(2); } } With that code, the stdin / stdout / stderr file descriptor of my "prgName" are associated to the socket (when looking with ls -la /proc/PID/fd), and so, the terminal capabilities of this process doesn't work. A test with a connection via ssh/sshd on the remote device, and executing "localy" (under the ssh connection) prgName, show that the stdin/stdout/stderr fd of this process "prgName" are associated to a pty (and so the terminal capabilities of this process are working fine). What I am doing wrong? How to associate my socketfd with the pty (created by forkpty) ? Thank Alex

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• ObjC: Alloc instance of Class and performing selectors on it leads to __CFRequireConcreteImplementat

  - by Arakyd

  Hi, I'm new to Objective-C and I'd like to abstract my database access using a model class like this: @interface LectureModel : NSMutableDictionary { } -(NSString*)title; -(NSDate*)begin; ... @end I use the dictionary methods setValue:forKey: to store attributes and return these in the getters. Now I want to read these models from a sqlite database by using the Class dynamically. + (NSArray*)findBySQL:(NSString*)sql intoModelClass:(Class)modelClass { NSMutableArray* models = [[[NSMutableArray alloc] init] autorelease]; sqlite3* db = sqlite3_open(...); sqlite3_stmt* result = NULL; sqlite3_prepare_v2(db, [sql UTF8String], -1, &result, NULL); while(sqlite3_step(result) == SQLITE_ROW) { id modelInstance = [[modelClass alloc] init]; for (int i = 0; i < sqlite3_column_count(result); ++i) { NSString* key = [NSString stringWithUTF8String:sqlite3_column_name(result, i)]; NSString* value = [NSString stringWithUTF8String:(const char*)sqlite3_column_text(result, i)]; if([modelInstance respondsToSelector:@selector(setValue:forKey:)]) [modelInstance setValue:value forKey:key]; } [models addObject:modelInstance]; } sqlite3_finalize(result); sqlite3_close(db); return models; } Funny thing is, the respondsToSelector: works, but if I try (in the debugger) to step over [modelInstance setValue:value forKey:key], it will throw an exception, and the stacktrace looks like: #0 0x302ac924 in ___TERMINATING_DUE_TO_UNCAUGHT_EXCEPTION___ #1 0x991d9509 in objc_exception_throw #2 0x302d6e4d in __CFRequireConcreteImplementation #3 0x00024d92 in +[DBManager findBySQL:intoModelClass:] at DBManager.m:114 #4 0x0001ea86 in -[FavoritesViewController initializeTableData:] at FavoritesViewController.m:423 #5 0x0001ee41 in -[FavoritesViewController initializeTableData] at FavoritesViewController.m:540 #6 0x305359da in __NSFireDelayedPerform #7 0x302454a0 in CFRunLoopRunSpecific #8 0x30244628 in CFRunLoopRunInMode #9 0x32044c31 in GSEventRunModal #10 0x32044cf6 in GSEventRun #11 0x309021ee in UIApplicationMain #12 0x00002988 in main at main.m:14 So, what's wrong with this? Presumably I'm doing something really stupid and just don't see it... Many thanks in advance for your answers, Arakyd :..

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• Query on simple C++ threadpool implementation

  - by ticketman

  Stackoverflow has been a tremendous help to me and I'd to give something back to the community. I have been implementing a simple threadpool using the tinythread C++ portable thread library, using what I have learnt from Stackoverflow. I am new to thread programming, so not that comfortable with mutexes, etc. I have a question best asked after presenting the code (which runs quite well under Linux): // ThreadPool.h class ThreadPool { public: ThreadPool(); ~ThreadPool(); // Creates a pool of threads and gets them ready to be used void CreateThreads(int numOfThreads); // Assigns a job to a thread in the pool, but doesn't start the job // Each SubmitJob call will use up one thread of the pool. // This operation can only be undone by calling StartJobs and // then waiting for the jobs to complete. On completion, // new jobs may be submitted. void SubmitJob( void (*workFunc)(void *), void *workData ); // Begins execution of all the jobs in the pool. void StartJobs(); // Waits until all jobs have completed. // The wait will block the caller. // On completion, new jobs may be submitted. void WaitForJobsToComplete(); private: enum typeOfWorkEnum { e_work, e_quit }; class ThreadData { public: bool ready; // thread has been created and is ready for work bool haveWorkToDo; typeOfWorkEnum typeOfWork; // Pointer to the work function each thread has to call. void (*workFunc)(void *); // Pointer to work data void *workData; ThreadData() : ready(false), haveWorkToDo(false) { }; }; struct ThreadArgStruct { ThreadPool *threadPoolInstance; int threadId; }; // Data for each thread ThreadData *m_ThreadData; ThreadPool(ThreadPool const&); // copy ctor hidden ThreadPool& operator=(ThreadPool const&); // assign op. hidden // Static function that provides the function pointer that a thread can call // By including the ThreadPool instance in the void * parameter, // we can use it to access other data and methods in the ThreadPool instance. static void ThreadFuncWrapper(void *arg) { ThreadArgStruct *threadArg = static_cast<ThreadArgStruct *>(arg); threadArg->threadPoolInstance->ThreadFunc(threadArg->threadId); } // The function each thread calls void ThreadFunc( int threadId ); // Called by the thread pool destructor void DestroyThreadPool(); // Total number of threads available // (fixed on creation of thread pool) int m_numOfThreads; int m_NumOfThreadsDoingWork; int m_NumOfThreadsGivenJobs; // List of threads std::vector<tthread::thread *> m_ThreadList; // Condition variable to signal each thread has been created and executing tthread::mutex m_ThreadReady_mutex; tthread::condition_variable m_ThreadReady_condvar; // Condition variable to signal each thread to start work tthread::mutex m_WorkToDo_mutex; tthread::condition_variable m_WorkToDo_condvar; // Condition variable to signal the main thread that // all threads in the pool have completed their work tthread::mutex m_WorkCompleted_mutex; tthread::condition_variable m_WorkCompleted_condvar; }; cpp file: // // ThreadPool.cpp // #include "ThreadPool.h" // This is the thread function for each thread. // All threads remain in this function until // they are asked to quit, which only happens // when terminating the thread pool. void ThreadPool::ThreadFunc( int threadId ) { ThreadData *myThreadData = &m_ThreadData[threadId]; std::cout << "Hello world: Thread " << threadId << std::endl; // Signal that this thread is ready m_ThreadReady_mutex.lock(); myThreadData->ready = true; m_ThreadReady_condvar.notify_one(); // notify the main thread m_ThreadReady_mutex.unlock(); while(true) { //tthread::lock_guard<tthread::mutex> guard(m); m_WorkToDo_mutex.lock(); while(!myThreadData->haveWorkToDo) // check for work to do m_WorkToDo_condvar.wait(m_WorkToDo_mutex); // if no work, wait here myThreadData->haveWorkToDo = false; // need to do this before unlocking the mutex m_WorkToDo_mutex.unlock(); // Do the work switch(myThreadData->typeOfWork) { case e_work: std::cout << "Thread " << threadId << ": Woken with work to do\n"; // Do work myThreadData->workFunc(myThreadData->workData); std::cout << "#Thread " << threadId << ": Work is completed\n"; break; case e_quit: std::cout << "Thread " << threadId << ": Asked to quit\n"; return; // ends the thread } // Now to signal the main thread that my work is completed m_WorkCompleted_mutex.lock(); m_NumOfThreadsDoingWork--; // Unsure if this 'if' would make the program more efficient // if(NumOfThreadsDoingWork == 0) m_WorkCompleted_condvar.notify_one(); // notify the main thread m_WorkCompleted_mutex.unlock(); } } ThreadPool::ThreadPool() { m_numOfThreads = 0; m_NumOfThreadsDoingWork = 0; m_NumOfThreadsGivenJobs = 0; } ThreadPool::~ThreadPool() { if(m_numOfThreads) { DestroyThreadPool(); delete [] m_ThreadData; } } void ThreadPool::CreateThreads(int numOfThreads) { // Check a thread pool has already been created if(m_numOfThreads > 0) return; m_NumOfThreadsGivenJobs = 0; m_NumOfThreadsDoingWork = 0; m_numOfThreads = numOfThreads; m_ThreadData = new ThreadData[m_numOfThreads]; ThreadArgStruct threadArg; for(int i=0; i<m_numOfThreads; ++i) { threadArg.threadId = i; threadArg.threadPoolInstance = this; // Creates the thread and save in a list so we can destroy it later m_ThreadList.push_back( new tthread::thread( ThreadFuncWrapper, (void *)&threadArg ) ); // It takes a little time for a thread to get established. // Best wait until it gets established before creating the next thread. m_ThreadReady_mutex.lock(); while(!m_ThreadData[i].ready) // Check if thread is ready m_ThreadReady_condvar.wait(m_ThreadReady_mutex); // If not, wait here m_ThreadReady_mutex.unlock(); } } // Adds a job to the batch, but doesn't start the job void ThreadPool::SubmitJob(void (*workFunc)(void *), void *workData) { // Check that the thread pool has been created if(!m_numOfThreads) return; if(m_NumOfThreadsGivenJobs >= m_numOfThreads) return; m_ThreadData[m_NumOfThreadsGivenJobs].workFunc = workFunc; m_ThreadData[m_NumOfThreadsGivenJobs].workData = workData; std::cout << "Submitted job " << m_NumOfThreadsGivenJobs << std::endl; m_NumOfThreadsGivenJobs++; } void ThreadPool::StartJobs() { // Check that the thread pool has been created // and some jobs have been assigned if(!m_numOfThreads || !m_NumOfThreadsGivenJobs) return; // Set 'haveworkToDo' flag for all threads m_WorkToDo_mutex.lock(); for(int i=0; i<m_NumOfThreadsGivenJobs; ++i) m_ThreadData[i].haveWorkToDo = true; m_NumOfThreadsDoingWork = m_NumOfThreadsGivenJobs; // Reset this counter so we can resubmit jobs later m_NumOfThreadsGivenJobs = 0; // Notify all threads they have work to do m_WorkToDo_condvar.notify_all(); m_WorkToDo_mutex.unlock(); } void ThreadPool::WaitForJobsToComplete() { // Check that a thread pool has been created if(!m_numOfThreads) return; m_WorkCompleted_mutex.lock(); while(m_NumOfThreadsDoingWork > 0) // Check if all threads have completed their work m_WorkCompleted_condvar.wait(m_WorkCompleted_mutex); // If not, wait here m_WorkCompleted_mutex.unlock(); } void ThreadPool::DestroyThreadPool() { std::cout << "Ask threads to quit\n"; m_WorkToDo_mutex.lock(); for(int i=0; i<m_numOfThreads; ++i) { m_ThreadData[i].haveWorkToDo = true; m_ThreadData[i].typeOfWork = e_quit; } m_WorkToDo_condvar.notify_all(); m_WorkToDo_mutex.unlock(); // As each thread terminates, catch them here for(int i=0; i<m_numOfThreads; ++i) { tthread::thread *t = m_ThreadList[i]; // Wait for thread to complete t->join(); } m_numOfThreads = 0; } Example of usage: (this calculates pi-squared/6) struct CalculationDataStruct { int inputVal; double outputVal; }; void LongCalculation( void *theSums ) { CalculationDataStruct *sums = (CalculationDataStruct *)theSums; int terms = sums->inputVal; double sum; for(int i=1; i<terms; i++) sum += 1.0/( double(i)*double(i) ); sums->outputVal = sum; } int main(int argc, char** argv) { int numThreads = 10; // Create pool ThreadPool threadPool; threadPool.CreateThreads(numThreads); // Create thread workspace CalculationDataStruct sums[numThreads]; // Set up jobs for(int i=0; i<numThreads; i++) { sums[i].inputVal = 3000*(i+1); threadPool.SubmitJob(LongCalculation, &sums[i]); } // Run the jobs threadPool.StartJobs(); threadPool.WaitForJobsToComplete(); // Print results for(int i=0; i<numThreads; i++) std::cout << "Sum of " << sums[i].inputVal << " terms is " << sums[i].outputVal << std::endl; return 0; } Question: In the ThreadPool::ThreadFunc method, would better performance be obtained if the following if statement if(NumOfThreadsDoingWork == 0) was included? Also, I'd be grateful of criticisms and ways to improve the code. At the same time, I hope the code is of use to others.

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• valgrind complains doing a very simple strtok in c

  - by monkeyking

  Hi I'm trying to tokenize a string by loading an entire file into a char[] using fread. For some strange reason it is not always working, and valgrind complains in this very small sample program. Given an input like test.txt first second And the following program #include <stdio.h> #include <string.h> #include <stdlib.h> #include <sys/stat.h> //returns the filesize in bytes size_t fsize(const char* fname){ struct stat st ; stat(fname,&st); return st.st_size; } int main(int argc, char *argv[]){ FILE *fp = NULL; if(NULL==(fp=fopen(argv[1],"r"))){ fprintf(stderr,"\t-> Error reading file:%s\n",argv[1]); return 0; } char buffer[fsize(argv[1])]; fread(buffer,sizeof(char),fsize(argv[1]),fp); char *str = strtok(buffer," \t\n"); while(NULL!=str){ fprintf(stderr,"token is:%s with strlen:%lu\n",str,strlen(str)); str = strtok(NULL," \t\n"); } return 0; } compiling like gcc test.c -std=c99 -ggdb running like ./a.out test.txt thanks

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• Generic allocator class without variadic templates?

  - by rainer

  I am trying to write a generic allocator class that does not really release an object's memory when it is free()'d but holds it in a queue and returns a previously allocated object if a new one is requested. Now, what I can't wrap my head around is how to pass arguments to the object's constructor when using my allocator (at least without resorting to variadic templates, that is). The alloc() function i came up with looks like this: template <typename... T> inline T *alloc(const &T... args) { T *p; if (_free.empty()) { p = new T(args...); } else { p = _free.front(); _free.pop(); // to call the ctor of T, we need to first call its DTor p->~T(); p = new( p ) T(args...); } return p; } Still, I need the code to be compatible with today's C++ (and older versions of GCC that do not support variadic templates). Is there any other way to go about passing an arbitrary amount of arguments to the objects constructor?

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• Vector of pointers to base class, odd behaviour calling virtual functions

  - by Ink-Jet

  I have the following code #include <iostream> #include <vector> class Entity { public: virtual void func() = 0; }; class Monster : public Entity { public: void func(); }; void Monster::func() { std::cout << "I AM A MONSTER" << std::endl; } class Buddha : public Entity { public: void func(); }; void Buddha::func() { std::cout << "OHMM" << std::endl; } int main() { const int num = 5; // How many of each to make std::vector<Entity*> t; for(int i = 0; i < num; i++) { Monster m; Entity * e; e = &m; t.push_back(e); } for(int i = 0; i < num; i++) { Buddha b; Entity * e; e = &b; t.push_back(e); } for(int i = 0; i < t.size(); i++) { t[i]->func(); } return 0; } However, when I run it, instead of each class printing out its own message, they all print the "Buddha" message. I want each object to print its own message: Monsters print the monster message, Buddhas print the Buddha message. What have I done wrong?

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• Threadsafe binding with DispatcherObject.CheckAccess()

  - by maffe

  Hi, according to this, I can achieve threadsafety with large overhead. I wrote the following class and use it. It works fine. public abstract class BindingBase : DispatcherObject, INotifyPropertyChanged, INotifyPropertyChanging { private string _displayName; private const string NameDisplayName = "DisplayName"; /// /// The display name for the gui element which bound this instance. It can be used for localization. /// public string DisplayName { get { return _displayName; } set { NotifyPropertyChanging(NameDisplayName); _displayName = value; NotifyPropertyChanged(NameDisplayName); } } protected BindingBase() {} protected BindingBase(string displayName) { DisplayName = displayName; } public event PropertyChangedEventHandler PropertyChanged; public event PropertyChangingEventHandler PropertyChanging; protected void NotifyPropertyChanged(string name) { if (PropertyChanged == null) return; if (CheckAccess()) PropertyChanged.Invoke(this, new PropertyChangedEventArgs(name)); else Dispatcher.BeginInvoke(DispatcherPriority.Normal, (Action) (() = NotifyPropertyChanged(name))); } protected void NotifyPropertyChanging(string name) { if (PropertyChanging == null) return; if (CheckAccess()) PropertyChanging.Invoke(this, new PropertyChangingEventArgs(name)); else Dispatcher.BeginInvoke(DispatcherPriority.Normal, (Action) (() = NotifyPropertyChanging(name))); } } So is there a reason, why I've never found something like that? Are there any issues I should be aware off? Regards

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• Possible mem leak?

  - by LCD Fire

  I'm new to the concept so don't be hard on me. why doesn't this code produce a destructor call ? The names of the classes are self-explanatory. The SString will print a message in ~SString(). It only prints one destructor message. int main(int argc, TCHAR* argv[]) { smart_ptr<SString> smt(new SString("not lost")); new smart_ptr<SString>(new SString("but lost")); return 0; } Is this a memory leak? The impl. for smart_ptr is from here edited: //copy ctor smart_ptr(const smart_ptr<T>& ptrCopy) { m_AutoPtr = new T(ptrCopy.get()); } //overloading = operator smart_ptr<T>& operator=(smart_ptr<T>& ptrCopy) { if(m_AutoPtr) delete m_AutoPtr; m_AutoPtr = new T(*ptrCopy.get()); return *this; }

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• QT: I've inherited from QTreeView. I've inherited from QStandardItem. How do i Style the items?

  - by San Jacinto

  My Google skills must be failing me today. I've inherited from QTreeView to create a TreeView that stores a QStandardItemModel instead of a QAbstractItemModel. I have also inherited from QStandardItem to create a class to store my data in an item as is necessary. I've successfully inserted my derived QStandardItem into my derived QTreeView's QStandardItemModel. Now the trouble is, I can't figure out how to style it. I know that QTreeView has a setStyleSheet(QString) member, but I can't seem to get it working. It may be as simple as I'm not styling the correct attribute. Any pointers would be appreciated. Thanks. For clarity, here are my class defs. class SurveyTreeItem : public QStandardItem { public: SurveyTreeItem(); SurveyTreeItem( const QString & text ); ~SurveyTreeItem(); }; class StandardItemModelTreeView : public QTreeView { public: StandardItemModelTreeView(QWidget* parent = 0); ~StandardItemModelTreeView(); QStandardItemModel* getStandardItemModel(); }; I've tried the following StyleSheets: StandardTreeView::Item { font: 87 12pt 'Arial Black'; } StandardTreeView::QStandardItem { font: 87 12pt 'Arial Black'; } QTreeView::QStandardItem { font: 87 12pt 'Arial Black'; } QTreeView::Item { font: 87 12pt 'Arial Black'; } QTreeView::SurveyTreeItem { font: 87 12pt 'Arial Black'; } StandardTreeView::SurveyTreeItem { font: 87 12pt 'Arial Black'; }

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• Preparing a MySQL INSERT/UPDATE statement with DEFAULT values

  - by Raveren

  Quoting MySQL INSERT manual - same goes for UPDATE: Use the keyword DEFAULT to set a column explicitly to its default value. This makes it easier to write INSERT statements that assign values to all but a few columns, because it enables you to avoid writing an incomplete VALUES list that does not include a value for each column in the table. Otherwise, you would have to write out the list of column names corresponding to each value in the VALUES list. So in short if I write INSERT INTO table1 (column1,column2) values ('value1',DEFAULT); A new row with column2 set as its default value - whatever it may be - is inserted. However if I prepare and execute a statement in PHP: $statement = $pdoObject-> prepare("INSERT INTO table1 (column1,column2) values (?,?)"); $statement->execute(array('value1','DEFAULT')); The new row will contain 'DEFAULT' as its text value - if the column is able to store text values. Now I have written an abstraction layer to PDO (I needed it) and to get around this issue am considering to introduce a const DEFAULT_VALUE = "randomstring"; So I could execute statements like this: $statement->execute(array('value1',mysql::DEFAULT_VALUE)); And then in method that does the binding I'd go through values that are sent to be bound and if some are equal to self::DEFAULT_VALUE, act accordingly. I'm pretty sure there's a better way to do this. Has someone else encountered similar situations?

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• Facade Design Patterns and Subclassing

  - by Code Sherpa

  Hi. I am using a facade design pattern for a C# program. The program basically looks like this... public class Api { #region Constants private const int version = 1; #endregion #region Private Data private XProfile _profile; private XMembership _membership; private XRoles _role; #endregion Private Data public Api() { _membership = new XMembership(); _profile = new XProfile(); _role = new XRoles(); } public int GetUserId(string name) { return _membership.GetIdByName(name); } } Now, as I would like subclass my methods into three categories: Role, Profile, and Member. This will be easier on the developers eye because both Profile and Membership expose a lot of methods that look similar (and a few by Role). For example, getting a user's ID would look like: int _id = Namespace.Api.Member.GetUserId("Henry222"); Can somebody "illustrate" how subclassing should work in this case to achieve the effect I am looking for? Thanks in advance.

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• Help me create a Firefox extension (Javascript XPCOM Component)

  - by Johnny Grass

  I've been looking at different tutorials and I know I'm close but I'm getting lost in implementation details because some of them are a little bit dated and a few things have changed since Firefox 3. I have already written the javascript for the firefox extension, now I need to make it into an XPCOM component. This is the functionality that I need: My Javascript file is simple, I have two functions startServer() and stopServer. I need to run startServer() when the browser starts and stopServer() when firefox quits. Edit: I've updated my code with a working solution (thanks to Neil). The following is in MyExtension/components/myextension.js. Components.utils.import("resource://gre/modules/XPCOMUtils.jsm"); const CI = Components.interfaces, CC = Components.classes, CR = Components.results; // class declaration function MyExtension() {} MyExtension.prototype = { classDescription: "My Firefox Extension", classID: Components.ID("{xxxx-xxxx-xxx-xxxxx}"), contractID: "@example.com/MyExtension;1", QueryInterface: XPCOMUtils.generateQI([CI.nsIObserver]), // add to category manager _xpcom_categories: [{ category: "profile-after-change" }], // start socket server startServer: function () { /* socket initialization code */ }, // stop socket server stopServer: function () { /* stop server */ }, observe: function(aSubject, aTopic, aData) { var obs = CC["@mozilla.org/observer-service;1"].getService(CI.nsIObserverService); switch (aTopic) { case "quit-application": this.stopServer(); obs.removeObserver(this, "quit-application"); break; case "profile-after-change": this.startServer(); obs.addObserver(this, "quit-application", false); break; default: throw Components.Exception("Unknown topic: " + aTopic); } } }; var components = [MyExtension]; function NSGetModule(compMgr, fileSpec) { return XPCOMUtils.generateModule(components); }

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• Empty data problem - data layer or DAL?

  - by luckyluke

  I designing the new App now and giving the following question a lot of thought. I consume a lot of data from the warehouse, and the entities have a lot of dictionary based values (currency, country, tax-whatever data) - dimensions. I cannot be assured though that there won't be nulls. So I am thinking: create an empty value in each of teh dictionaries with special keyID - ie. -1 do the ETL (ssis) do the correct stuff and insert -1 where it needs to let the DAL know that -1 is special (Static const whatever thing) don't care in the code to check for nullness of dictionary entries because THEY will always have a value But maybe I should be thinking: import data AS IS let the DAL do the thinking using empty record Pattern still don't care in the code because business layer will have what it needs from DAL. I think is more of a approach thing but maybe i am missing something important here... What do You think? Am i clear? Please don't confuse it with empty record problem. I do use emptyCustomer think all the time and other defaults too.

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• Operator issues with cout

  - by BSchlinker

  I have a simple package class which is overloaded so I can output package data simply with cout << packagename. I also have two data types, name which is a string and shipping cost with a double. protected: string name; string address; double weight; double shippingcost; ostream &operator<<( ostream &output, const Package &package ) { output << "Package Information ---------------"; output << "Recipient: " << package.name << endl; output << "Shipping Cost (including any applicable fees): " << package.shippingcost; The problem is occurring with the 4th line (output << "Recipient:...). I'm receiving the error "no operator "<<" matches these operands". However, line 5 is fine. I'm guessing this has to do with the data type being a string for the package name. Any ideas?

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• Issue with clipping rectangles and back to front rendering

  - by Milo

  Here is my problem. My rendering algorithm renders from back to front. But logically, clipping rectangles need to be applied from front to back. Hence why the following does not work: void AguiWidgetManager::recursiveRender(const AguiWidget *root) { //recursively calls itself to render widgets from back to front AguiWidget* nonConstRoot = (AguiWidget*)root; if(!nonConstRoot->isVisable()) { return; } //push the clipping rectangle if(nonConstRoot->isClippingChildren()) { graphicsContext->pushClippingRect(nonConstRoot->getClippingRectangle()); } if(nonConstRoot->isEnabled()) { nonConstRoot->paint(AguiPaintEventArgs(true,graphicsContext)); for(std::vector<AguiWidget*>::const_iterator it = root->getPrivateChildBeginIterator(); it != root->getPrivateChildEndIterator(); ++it) { recursiveRender(*it); } for(std::vector<AguiWidget*>::const_iterator it = root->getChildBeginIterator(); it != root->getChildEndIterator(); ++it) { recursiveRender(*it); } } else { nonConstRoot->paint(AguiPaintEventArgs(false,graphicsContext)); for(std::vector<AguiWidget*>::const_iterator it = root->getPrivateChildBeginIterator(); it != root->getPrivateChildEndIterator(); ++it) { recursiveRenderDisabled(*it); } for(std::vector<AguiWidget*>::const_iterator it = root->getChildBeginIterator(); it != root->getChildEndIterator(); ++it) { recursiveRenderDisabled(*it); } } //release clipping rectangle if(nonConstRoot->isClippingChildren()) { graphicsContext->popClippingRect(); } } I could ofcourse go to the top of the tree, then apply clipping rectangles inward until I get to the currently rendered widget, but that would involve lots of clipping rectangles @ 60 frames per second. I want to minimize calls to pushing and popping rectangles. What could I do, Thanks

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• Can you force a crash if a write occurs to a given memory location with finer than page granularity?

  - by Joseph Garvin

  I'm writing a program that for performance reasons uses shared memory (alternatives have been evaluated, and they are not fast enough for my task, so suggestions to not use it will be downvoted). In the shared memory region I am writing many structs of a fixed size. There is one program responsible for writing the structs into shared memory, and many clients that read from it. However, there is one member of each struct that clients need to write to (a reference count, which they will update atomically). All of the other members should be read only to the clients. Because clients need to change that one member, they can't map the shared memory region as read only. But they shouldn't be tinkering with the other members either, and since these programs are written in C++, memory corruption is possible. Ideally, it should be as difficult as possible for one client to crash another. I'm only worried about buggy clients, not malicious ones, so imperfect solutions are allowed. I can try to stop clients from overwriting by declaring the members in the header they use as const, but that won't prevent memory corruption (buffer overflows, bad casts, etc.) from overwriting. I can insert canaries, but then I have to constantly pay the cost of checking them. Instead of storing the reference count member directly, I could store a pointer to the actual data in a separate mapped write only page, while keeping the structs in read only mapped pages. This will work, the OS will force my application to crash if I try to write to the pointed to data, but indirect storage can be undesirable when trying to write lock free algorithms, because needing to follow another level of indirection can change whether something can be done atomically. Is there any way to mark smaller areas of memory such that writing them will cause your app to blow up? Some platforms have hardware watchpoints, and maybe I could activate one of those with inline assembly, but I'd be limited to only 4 at a time on 32-bit x86 and each one could only cover part of the struct because they're limited to 4 bytes. It'd also make my program painful to debug ;)

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• How to invalidate cache when benchmarking?

  - by Michael Buen

  I have this code, that when swapping the order of UsingAs and UsingCast, their performance also swaps. using System; using System.Diagnostics; using System.Linq; using System.IO; class Test { const int Size = 30000000; static void Main() { object[] values = new MemoryStream[Size]; UsingAs(values); UsingCast(values); Console.ReadLine(); } static void UsingCast(object[] values) { Stopwatch sw = Stopwatch.StartNew(); int sum = 0; foreach (object o in values) { if (o is MemoryStream) { var m = (MemoryStream)o; sum += (int)m.Length; } } sw.Stop(); Console.WriteLine("Cast: {0} : {1}", sum, (long)sw.ElapsedMilliseconds); } static void UsingAs(object[] values) { Stopwatch sw = Stopwatch.StartNew(); int sum = 0; foreach (object o in values) { if (o is MemoryStream) { var m = o as MemoryStream; sum += (int)m.Length; } } sw.Stop(); Console.WriteLine("As: {0} : {1}", sum, (long)sw.ElapsedMilliseconds); } } Outputs: As: 0 : 322 Cast: 0 : 281 When doing this... UsingCast(values); UsingAs(values); ...Results to this: Cast: 0 : 322 As: 0 : 281 When doing just this... UsingAs(values); ...Results to this: As: 0 : 322 When doing just this: UsingCast(values); ...Results to this: Cast: 0 : 322 Aside from running them independently, how to invalidate the cache so the second code being benchmarked won't receive the cached memory of first code? Benchmarking aside, just loved the fact that modern processors do this caching magic :-)

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• How to properly implement cheat codes?

  - by Axarydax

  Hi, what would be the best way to implement kind of cheat codes in general? I have WinForms application in mind, where a cheat code would unlock an easter egg, but the implementation details are not relevant. The best approach that comes to my mind is to keep index for each code - let's consider famous DOOM codes - IDDQD and IDKFA, in a fictional C# app. string[] CheatCodes = { "IDDQD", "IDKFA"}; int[] CheatIndexes = { 0, 0 }; const int CHEAT_COUNT = 2; void KeyPress(char c) { for (int i = 0; i < CHEAT_COUNT; i++) //for each cheat code { if (CheatCodes[i][CheatIndexes[i]] == c) { //we have hit the next key in sequence if (++CheatIndexes[i] == CheatCodes[i].Length) //are we in the end? { //Do cheat work MessageBox.Show(CheatCodes[i]); //reset cheat index so we can enter it next time CheatIndexes[i] = 0; } } else //mistyped, reset cheat index CheatIndexes[i] = 0; } } Is this the right way to do it?

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• Output iterator's value_type

  - by wilhelmtell

  The STL commonly defines an output iterator like so: template<class Cont> class insert_iterator : public iterator<output_iterator_tag,void,void,void,void> { // ... Why do output iterators define value_type as void? It would be useful for an algorithm to know what type of value it is supposed to output. For example, a function that translates a URL query "key1=value1&key2=value2&key3=value3" into any container that holds key-value strings elements. template<typename Ch,typename Tr,typename Out> void parse(const std::basic_string<Ch,Tr>& str, Out result) { std::basic_string<Ch,Tr> key, value; // loop over str, parse into p ... *result = typename iterator_traits<Out>::value_type(key, value); } The SGI reference page of value_type hints this is because it's not possible to dereference an output iterator. But that's not the only use of value_type: I might want to instantiate one in order to assign it to the iterator.

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• how to know location of return address on stack c/c++

  - by Dr Deo

  i have been reading about a function that can overwrite its return address. void foo(const char* input) { char buf[10]; //What? No extra arguments supplied to printf? //It's a cheap trick to view the stack 8-) //We'll see this trick again when we look at format strings. printf("My stack looks like:\n%p\n%p\n%p\n%p\n%p\n% p\n\n"); //%p ie expect pointers //Pass the user input straight to secure code public enemy #1. strcpy(buf, input); printf("%s\n", buf); printf("Now the stack looks like:\n%p\n%p\n%p\n%p\n%p\n%p\n\n"); } It was sugggested that this is how the stack would look like Address of foo = 00401000 My stack looks like: 00000000 00000000 7FFDF000 0012FF80 0040108A <-- We want to overwrite the return address for foo. 00410EDE Question: -. Why did the author arbitrarily choose the second last value as the return address of foo()? -. Are values added to the stack from the bottom or from the top? apart from the function return address, what are the other values i apparently see on the stack? ie why isn't it filled with zeros Thanks.

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• AuthorizationExecuteWithPrivileges and osascript failing

  - by cygnl7

  I'm attempting to execute an uninstaller (written in AppleScript) through AuthorizationExecuteWithPrivileges. I'm setting up my rights after creating an empty auth ref like so: char *tool = "/usr/bin/osascript"; AuthorizationItem items = {kAuthorizationRightExecute, strlen(tool), tool, 0}; AuthorizationRights rights = {sizeof(items)/sizeof(AuthorizationItem), &items}; AuthorizationFlags flags = kAuthorizationFlagDefaults | kAuthorizationFlagExtendRights | kAuthorizationFlagPreAuthorize | kAuthorizationFlagInteractionAllowed; status = AuthorizationCopyRights(authorizationRef, &rights, NULL, flags, NULL); Later I call: status = AuthorizationExecuteWithPrivileges(authorizationRef, tool, kAuthorizationFlagDefaults, (char *const *)args, NULL); On Snow Leopard this works fine, but on Leopard I get the following in syslog.log: Apr 19 15:30:09 hostname /usr/bin/osascript[39226]: OpenScripting.framework - 'gdut' event blocked in process with mixed credentials (issetugid=0 uid=501 euid=0 gid=20 egid=20) Apr 19 15:30:12: --- last message repeated 1 time --- ... Apr 19 15:30:12 hostname [0x0-0x2e92e9].com.example.uninstaller[39219]: /var/folders/vm/vmkIi0nYG8mHMrllaXaTgk+++TI/-Tmp-/TestApp_tmpfiles/Uninstall.scpt: Apr 19 15:30:12 hostname [0x0-0x2e92e9].com.example.uninstaller[39219]: execution error: «constant afdmasup» doesn’t understand the «event earsffdr» message. (-1708) Am I going about this all wrong? I just want to run the equivalent of "sudo /usr/bin/osascript ..."

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• objective-c 2.0 properties and 'retain'

  - by Adam

  Stupid question, but why do we need to use 'retain' when declaring a property? Doesn't it get retained anyway when it's assigned something? Looking at this example, it seems that an object is automatically retained when alloc'ed, so what's the point? #import "Fraction.h" #import <stdio.h> int main( int argc, const char *argv[] ) { Fraction *frac1 = [[Fraction alloc] init]; Fraction *frac2 = [[Fraction alloc] init]; // print current counts printf( "Fraction 1 retain count: %i\n", [frac1 retainCount] ); printf( "Fraction 2 retain count: %i\n", [frac2 retainCount] ); // increment them [frac1 retain]; // 2 [frac1 retain]; // 3 [frac2 retain]; // 2 // print current counts printf( "Fraction 1 retain count: %i\n", [frac1 retainCount] ); printf( "Fraction 2 retain count: %i\n", [frac2 retainCount] ); // decrement [frac1 release]; // 2 [frac2 release]; // 1 // print current counts printf( "Fraction 1 retain count: %i\n", [frac1 retainCount] ); printf( "Fraction 2 retain count: %i\n", [frac2 retainCount] ); // release them until they dealloc themselves [frac1 release]; // 1 [frac1 release]; // 0 [frac2 release]; // 0 ¦output Fraction 1 retain count: 1 Fraction 2 retain count: 1 Fraction 1 retain count: 3 Fraction 2 retain count: 2 Fraction 1 retain count: 2 Fraction 2 retain count: 1 Deallocing fraction Deallocing fraction This is driving me crazy!

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• Warning: passing Argument 1 of "sqlite3_bind_text" from incompatible pointer type" What should I do

  - by Amarpreet

  Hi All, i am pretty new in iphone development. I have created one function to insert data into database. The code compiles successfully. But when comes to statement sqlite3_bind_text(sqlStatement, 1, [s UTF8String], -1, SQLITE_TRANSIENT); it does not do anything but hangs AND in warning it says "passing Argument 1 of "sqlite3_bind_text" from incompatible pointer type"" for all statements in Red colour The same code i am using to fetch the data from database and its working on other viewController. Below in the code. Its pretty straightforward. Please help guys. -(void) SaveData: (NSString *)FirstName: (NSString *)LastName: (NSString *)State: (NSString *)Street: (NSString *)PostCode { databaseName = @"Zen.sqlite"; NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDire ctory, NSUserDomainMask,YES); NSString *documentsDir=[documentPaths objectAtIndex:0]; databasePath=[documentsDir stringByAppendingPathComponent:databaseName]; sqlite3 *database; if(sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) { const char *sqlStatement = "insert into customers (FirstName, LastName, State, Street, PostCode) values(?, ?, ?, ?, ?)"; sqlite3_stmt *compiledStatement; sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL); sqlite3_bind_text(sqlStatement, 1, [FirstName UTF8String], -1, SQLITE_TRANSIENT); sqlite3_bind_text(sqlStatement,2,[LastName UTF8String],-1,SQLITE_TRANSIENT); sqlite3_bind_text(sqlStatement,3,[State UTF8String],-1,SQLITE_TRANSIENT); sqlite3_bind_text(sqlStatement,4,[Street UTF8String],-1,SQLITE_TRANSIENT); sqlite3_bind_text(sqlStatement,5,[PostCode UTF8String],-1,SQLITE_TRANSIENT); sqlite3_step(sqlStatement); sqlite3_finalize(compiledStatement); } sqlite3_close(database); }

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• Passenger error message I can't figure out

  - by Sam Kong

  Hi, I am testing Rails 3 on DreamHost which just installed Rails 3. I created a simple controller and it failed. Browser shows 500 error (Internal Server Error) and the log shows the following message. Could not find i18n-0.5.0 in any of the sources Try running `bundle install`. *** Exception EOFError in spawn manager (Unexpected end-of-file detected.) (process 17951): from /dh/passenger/lib/phusion_passenger/utils.rb:306:in `unmarshal_and_raise_errors' from /dh/passenger/lib/phusion_passenger/rack/application_spawner.rb:71:in `spawn_application' from /dh/passenger/lib/phusion_passenger/rack/application_spawner.rb:41:in `spawn_application' from /dh/passenger/lib/phusion_passenger/spawn_manager.rb:159:in `spawn_application' from /dh/passenger/lib/phusion_passenger/spawn_manager.rb:287:in `handle_spawn_application' from /dh/passenger/lib/phusion_passenger/abstract_server.rb:352:in `__send__' from /dh/passenger/lib/phusion_passenger/abstract_server.rb:352:in `main_loop' from /dh/passenger/lib/phusion_passenger/abstract_server.rb:196:in `start_synchronously' from /dh/passenger/bin/passenger-spawn-server:61 [ pid=13245 file=ext/apache2/Hooks.cpp:727 time=2010-12-24 12:13:38.287 ]: Unexpected error in mod_passenger: Cannot spawn application '/home/cp_rails3/sites/rails3.codepremise.com': The spawn server has exited unexpectedly. Backtrace: in 'virtual boost::shared_ptr<Passenger::Application::Session> Passenger::ApplicationPoolServer::Client::get(const Passenger::PoolOptions&)' (ApplicationPoolServer.h:471) in 'int Hooks::handleRequest(request_rec*)' (Hooks.cpp:523) It runs fine in console (app.get "url") and also ok with "rails server". What's wrong? Thanks. Sam

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• Boost Spirit and Lex parser problem

  - by bpw1621

  I've been struggling to try and (incrementally) modify example code from the documentation but with not much different I am not getting the behavior I expect. Specifically, the "if" statement fails when (my intent is that) it should be passing (there was an "else" but that part of the parser was removed during debugging). The assignment statement works fine. I had a "while" statement as well which had the same problem as the "if" statement so I am sure if I can get help to figure out why one is not working it should be easy to get the other going. It must be kind of subtle because this is almost verbatim what is in one of the examples. #include <iostream> #include <fstream> #include <string> #define BOOST_SPIRIT_DEBUG #include <boost/config/warning_disable.hpp> #include <boost/spirit/include/qi.hpp> #include <boost/spirit/include/lex_lexertl.hpp> #include <boost/spirit/include/phoenix_operator.hpp> #include <boost/spirit/include/phoenix_statement.hpp> #include <boost/spirit/include/phoenix_container.hpp> namespace qi = boost::spirit::qi; namespace lex = boost::spirit::lex; inline std::string read_from_file( const char* infile ) { std::ifstream instream( infile ); if( !instream.is_open() ) { std::cerr << "Could not open file: \"" << infile << "\"" << std::endl; exit( -1 ); } instream.unsetf( std::ios::skipws ); return( std::string( std::istreambuf_iterator< char >( instream.rdbuf() ), std::istreambuf_iterator< char >() ) ); } template< typename Lexer > struct LangLexer : lex::lexer< Lexer > { LangLexer() { identifier = "[a-zA-Z][a-zA-Z0-9_]*"; number = "[-+]?(\\d*\\.)?\\d+([eE][-+]?\\d+)?"; if_ = "if"; else_ = "else"; this->self = lex::token_def<> ( '(' ) | ')' | '{' | '}' | '=' | ';'; this->self += identifier | number | if_ | else_; this->self( "WS" ) = lex::token_def<>( "[ \\t\\n]+" ); } lex::token_def<> if_, else_; lex::token_def< std::string > identifier; lex::token_def< double > number; }; template< typename Iterator, typename Lexer > struct LangGrammar : qi::grammar< Iterator, qi::in_state_skipper< Lexer > > { template< typename TokenDef > LangGrammar( const TokenDef& tok ) : LangGrammar::base_type( program ) { using boost::phoenix::val; using boost::phoenix::ref; using boost::phoenix::size; program = +block; block = '{' >> *statement >> '}'; statement = assignment | if_stmt; assignment = ( tok.identifier >> '=' >> expression >> ';' ); if_stmt = ( tok.if_ >> '(' >> expression >> ')' >> block ); expression = ( tok.identifier[ qi::_val = qi::_1 ] | tok.number[ qi::_val = qi::_1 ] ); BOOST_SPIRIT_DEBUG_NODE( program ); BOOST_SPIRIT_DEBUG_NODE( block ); BOOST_SPIRIT_DEBUG_NODE( statement ); BOOST_SPIRIT_DEBUG_NODE( assignment ); BOOST_SPIRIT_DEBUG_NODE( if_stmt ); BOOST_SPIRIT_DEBUG_NODE( expression ); } qi::rule< Iterator, qi::in_state_skipper< Lexer > > program, block, statement; qi::rule< Iterator, qi::in_state_skipper< Lexer > > assignment, if_stmt; typedef boost::variant< double, std::string > expression_type; qi::rule< Iterator, expression_type(), qi::in_state_skipper< Lexer > > expression; }; int main( int argc, char** argv ) { typedef std::string::iterator base_iterator_type; typedef lex::lexertl::token< base_iterator_type, boost::mpl::vector< double, std::string > > token_type; typedef lex::lexertl::lexer< token_type > lexer_type; typedef LangLexer< lexer_type > LangLexer; typedef LangLexer::iterator_type iterator_type; typedef LangGrammar< iterator_type, LangLexer::lexer_def > LangGrammar; LangLexer lexer; LangGrammar grammar( lexer ); std::string str( read_from_file( 1 == argc ? "boostLexTest.dat" : argv[1] ) ); base_iterator_type strBegin = str.begin(); iterator_type tokenItor = lexer.begin( strBegin, str.end() ); iterator_type tokenItorEnd = lexer.end(); std::cout << std::setfill( '*' ) << std::setw(20) << '*' << std::endl << str << std::endl << std::setfill( '*' ) << std::setw(20) << '*' << std::endl; bool result = qi::phrase_parse( tokenItor, tokenItorEnd, grammar, qi::in_state( "WS" )[ lexer.self ] ); if( result ) { std::cout << "Parsing successful" << std::endl; } else { std::cout << "Parsing error" << std::endl; } return( 0 ); } Here is the output of running this (the file read into the string is dumped out first in main) ******************** { a = 5; if( a ){ b = 2; } } ******************** <program> <try>{</try> <block> <try>{</try> <statement> <try></try> <assignment> <try></try> <expression> <try></try> <success>;</success> <attributes>(5)</attributes> </expression> <success></success> <attributes>()</attributes> </assignment> <success></success> <attributes>()</attributes> </statement> <statement> <try></try> <assignment> <try></try> <fail/> </assignment> <if_stmt> <try> if(</try> <fail/> </if_stmt> <fail/> </statement> <fail/> </block> <fail/> </program> Parsing error

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