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• Compiler optimization causing the performance to slow down

  - by aJ

  I have one strange problem. I have following piece of code: template<clss index, class policy> inline int CBase<index,policy>::func(const A& test_in, int* srcPtr ,int* dstPtr) { int width = test_in.width(); int height = test_in.height(); double d = 0.0; //here is the problem for(int y = 0; y < height; y++) { //Pointer initializations //multiplication involving y //ex: int z = someBigNumber*y + someOtherBigNumber; for(int x = 0; x < width; x++) { //multiplication involving x //ex: int z = someBigNumber*x + someOtherBigNumber; if(soemCondition) { // floating point calculations } *dstPtr++ = array[*srcPtr++]; } } } The inner loop gets executed nearly 200,000 times and the entire function takes 100 ms for completion. ( profiled using AQTimer) I found an unused variable double d = 0.0; outside the outer loop and removed the same. After this change, suddenly the method is taking 500ms for the same number of executions. ( 5 times slower). This behavior is reproducible in different machines with different processor types. (Core2, dualcore processors). I am using VC6 compiler with optimization level O2. Follwing are the other compiler options used : -MD -O2 -Z7 -GR -GX -G5 -X -GF -EHa I suspected compiler optimizations and removed the compiler optimization /O2. After that function became normal and it is taking 100ms as old code. Could anyone throw some light on this strange behavior? Why compiler optimization should slow down performance when I remove unused variable ? Note: The assembly code (before and after the change) looked same.

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• Why `A & a = a` is valid?

  - by psaghelyi

  #include <iostream> #include <assert.h> using namespace std; struct Base { Base() : m_member1(1) {} Base(const Base & other) { assert(this != &other); // this should trigger m_member1 = other.m_member1; } int m_member1; }; struct Derived { Derived(Base & base) : m_base(m_base) {} // m_base(base) Base & m_base; }; void main() { Base base; Derived derived(base); cout << derived.m_base.m_member1 << endl; // crashes here } The above example is a synthesized version of a mistyped constructor. I used reference at the class member Derived::m_base because I wanted to make sure that the member will be initialized as the constructor had called. One problem is that nor GCC nor MSVC gives me a warning at m_base(m_base). But the more serious for me is that the assert finds everything fine and the application crashes later (sometimes far away from the mistake). Question: Is there any way to indicate such mistakes?

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• Encode and Decode using UTF-8 in iphone

  - by Ekra

  Hi friends, I wanted an example were in I can encode and then decode the same string using UTF-8. Encode and then Decode means I want to implement the method in 2 area were one can encode it and other is able to decode it. I have seen the API but I didnt get much success:- StringWithCString:encoding: stringWithUTF8String: stringWithCString:(const char *)cString encoding:(NSStringEncoding)enc; =================EDITED================= I have string as "øæ-test-2.txt" . when I am encoding it char *s = "øæ-test-2.txt"; NSString *enc = [NSString stringWithCString:s encoding:NSASCIIStringEncoding]; I am getting "øæ-test-2.txt" as output. Now I want to get back the original string back i.e. "øæ-test-2.txt" +++++++++EDITED+++++++++++++++++++ I am getting "øæ-test-2.txt" from server and I need "øæ-test-2.txt" by decoding it . I am able to get the output from the link below http://www.cafewebmaster.com/online_tools/utf_decode Please try to use the link and u will understand my concern. I need the solution on urgent basis. It would be highly appreciated if anyone can give some hint or tutorial in right direction. Regards

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• Calling unmanaged dll from C#. Take 2

  - by Charles Gargent

  I have written a c# program that calls a c++ dll that echoes the commandline args to a file When the c++ is called using the rundll32 command it displays the commandline args no problem, however when it is called from within the c# it doesnt. I asked this question to try and solve my problem, but I have modified it my test environment and I think it is worth asking a new question. Here is the c++ dll #include "stdafx.h" #include "stdlib.h" #include <stdio.h> #include <iostream> #include <fstream> using namespace std; BOOL APIENTRY DllMain( HANDLE hModule, DWORD ul_reason_for_call, LPVOID lpReserved ) { return TRUE; } extern "C" __declspec(dllexport) int WINAPI CMAKEX( HWND hwnd, HINSTANCE hinst, LPCSTR lpszCommandLine, DWORD dwReserved) { ofstream SaveFile("output.txt"); SaveFile << lpszCommandLine; SaveFile.close(); return 0; } Here is the c# app using System; using System.Collections.Generic; using System.Text; using System.Security.Cryptography; using System.Runtime.InteropServices; using System.Net; namespace nac { class Program { [DllImport("cmakca.dll", SetLastError = true, CharSet = CharSet.Unicode)] static extern bool CMAKEX(IntPtr hwnd, IntPtr hinst, string lpszCmdLine, int nCmdShow); static void Main(string[] args) { string cmdLine = @"/source_filename proxy-1.txt /backup_filename proxy.bak /DialRasEntry NULL /TunnelRasEntry DSLVPN /profile ""C:\Documents and Settings\Administrator\Application Data\Microsoft\Network\Connections\Cm\dslvpn.cmp"""; const int SW_SHOWNORMAL = 1; CMAKEX(IntPtr.Zero, IntPtr.Zero, cmdLine, SW_SHOWNORMAL).ToString(); } } } The output from the rundll32 command is rundll32 cmakex.dll,CMAKEX /source_filename proxy-1.txt /backup_filename proxy.bak /DialRasEntry NULL /TunnelRasEntry DSLVPN /profile ""C:\Documents and Settings\Administrator\Application Data\Microsoft\Network\Connections\Cm\dslvpn.cmp" /source_filename proxy-1.txt /backup_filename proxy.bak /DialRasEntry NULL /TunnelRasEntry DSLVPN /profile ""C:\Documents and Settings\Administrator\Application Data\Microsoft\Network\Connections\Cm\dslvpn.cmp" however the output when the c# app runs is /

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• Unknown Exception on trying to initialize the web service stub created by Axis C++

  - by Harsha Reddy

  Hi, I am trying out the sample calculator program given in the folder of axis c++. I am mainly interested in the client side. So I used the wsdl to create the stubs and my main is pretty much the same as given in the sample. However on executing the call Calculator ws (endpoint) I get an unknown exception "First-chance exception at 0x7c0024b9 in CalculatorClient.exe: 0xC0000005: Access violation reading location 0x00000000. First-chance exception at 0x7c812afb in CalculatorClient.exe: Microsoft C++ exception: [rethrow] at memory location 0x00000000.. Unhandled exception at 0x7c0024b9 in CalculatorClient.exe: 0xC0000005: Access violation reading location 0x00000000." and the exception causing code is Calculator::Calculator(const char* pchEndpointUri, AXIS_PROTOCOL_TYPE eProtocol) :Stub(pchEndpointUri, eProtocol) { } I had earlier tried to run a a webservice using Axis C++ but had received the same error. At that time my web service was a java ws on WAS. Then I later tried the calculator client (but this time I did not have any server hosting the ws as I just wanted to check if the Client could initialize). Is the problem caused due to the web service not being hosted on Apache in C++ (though I highly doubt it). Any help would be appreciated. Thanks, Harsha

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• How do I pass a callback function to sqlite3_exec on iOS 5.1?

  - by John Doh

  I am new to both xcode/iOS/Objective-C and sqlite. I am trying to teach myself the basics - and I would like to use the sqlite3 wrapper "sqlite3_exec" for a select query. For some reason, I can't find a simple example anywhere of someone doing this. Basically, the method has a parameter (the third one) for a callback function: int sqlite3_exec( sqlite3*, /* An open database */ const char *sql, /* SQL to be evaluated */ int (*callback)(void*,int,char**,char**), /* Callback function */ void *, /* 1st argument to callback */ char **errmsg /* Error msg written here */ ); That's fine. I'm no stranger to callbacks. However, I just can't seem to get the syntax down right. I took over one of the view controllers in my iPad (iOS 5.1) xcode (4.3) project, and made the changes shown below: #import "SecondViewController.h" #import "sqlite3.h" #import "AppState.h" @interface SecondViewController () @end @implementation SecondViewController - (int)myCallback:(void *)a_parm argc:(int)argc argv:(char **)argv column:(char **)column { return 0; } - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. //grab questionnaire names char *sql = "select * from QST2Main order by [Name]"; char *err = nil; sqlite3 *db = [[AppState sharedManager] getgCn]; sqlite3_exec(db, sql, myCallback, nil, &err); } Essentially, I want to run a query when this view first loads, to store some data for later use. But, XCode doesn't like the "myCallback" usage at the bottom there. It says: Undeclared Use of Identifier 'myCallback.' That method is declared in the header file, and I've even tried making it static. Nothing seems to make this error go away. I know I must be doing something fundamentally wrong here, but for the life of me I can't figure out what - I can't even find other code samples in this area that could help me figure out what I'm missing. Many thanks!

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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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• 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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• Visual C++ Testing problem

  - by JamesMCCullum

  Hi there I have installed VisualAssert and cFix. I have been using Visual Studio C++ and programming in CLI/C++. I have a working Chess Game Program that works perfectly by itself.....and I have been studying testing and have many examples(with tutorials) I have found on the net, that compile and run in Visual Studio..... But as soon as I try and implement those tests on my chess game......I get this problem.... This is what its telling me 1>------ Build started: Project: ChessRound1, Configuration: Debug Win32 ------ 1>Compiling... 1>stdafx.cpp 1>C:\Program Files\VisualAssert\include\cfixpe.h(137) : error C3641: 'CfixpCrtInitEmbedding' : invalid calling convention '__cdecl ' for function compiled with /clr:pure or /clr:safe 1>C:\Program Files\VisualAssert\include\cfixpe.h(235) : error C4394: 'CfixpCrtInitEmbeddingRegistration' : per-appdomain symbol should not be marked with __declspec(allocate) 1>C:\Program Files\VisualAssert\include\cfixpe.h(235) : error C2393: 'CfixpCrtInitEmbeddingRegistration' : per-appdomain symbol cannot be allocated in segment '.CRT$XCX' 1>C:\Program Files\VisualAssert\include\cfixpe.h(244) : error C2440: 'initializing' : cannot convert from 'void (__cdecl *)(void)' to 'const CFIX_CRT_INIT_ROUTINE' 1> Address of a function yields __clrcall calling convention in /clr:pure and /clr:safe; consider using __clrcall in target type 1>C:\Program Files\VisualAssert\include\cfixpe.h(137) : error C3641: 'CfixpCrtInitEmbedding' : invalid calling convention '__cdecl ' for function compiled with /clr:pure or /clr:safe 1>Build log was saved at "file://c:\Users\james\Documents\Visual Studio 2008\Projects\ChessRound1\ChessRound1\Debug\BuildLog.htm" 1>ChessRound1 - 4 error(s), 0 warning(s) ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== Any ideas what I'm doing wrong? Im working with windows forms and have a heap of cpp source files. Any help would be appreciated. Thanks

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• Instantiating class with custom allocator in shared memory

  - by recipriversexclusion

  I'm pulling my hair due to the following problem: I am following the example given in boost.interprocess documentation to instantiate a fixed-size ring buffer buffer class that I wrote in shared memory. The skeleton constructor for my class is: template<typename ItemType, class Allocator > SharedMemoryBuffer<ItemType, Allocator>::SharedMemoryBuffer( unsigned long capacity ){ m_capacity = capacity; // Create the buffer nodes. m_start_ptr = this->allocator->allocate(); // allocate first buffer node BufferNode* ptr = m_start_ptr; for( int i = 0 ; i < this->capacity()-1; i++ ) { BufferNode* p = this->allocator->allocate(); // allocate a buffer node } } My first question: Does this sort of allocation guarantee that the buffer nodes are allocated in contiguous memory locations, i.e. when I try to access the n'th node from address m_start_ptr + n*sizeof(BufferNode) in my Read() method would it work? If not, what's a better way to keep the nodes, creating a linked list? My test harness is the following: // Define an STL compatible allocator of ints that allocates from the managed_shared_memory. // This allocator will allow placing containers in the segment typedef allocator<int, managed_shared_memory::segment_manager> ShmemAllocator; //Alias a vector that uses the previous STL-like allocator so that allocates //its values from the segment typedef SharedMemoryBuffer<int, ShmemAllocator> MyBuf; int main(int argc, char *argv[]) { shared_memory_object::remove("MySharedMemory"); //Create a new segment with given name and size managed_shared_memory segment(create_only, "MySharedMemory", 65536); //Initialize shared memory STL-compatible allocator const ShmemAllocator alloc_inst (segment.get_segment_manager()); //Construct a buffer named "MyBuffer" in shared memory with argument alloc_inst MyBuf *pBuf = segment.construct<MyBuf>("MyBuffer")(100, alloc_inst); } This gives me all kinds of compilation errors related to templates for the last statement. What am I doing wrong?

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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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• 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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• 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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• 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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• How to create static method that evaluates local static variable once?

  - by Viet

  I have a class with static method which has a local static variable. I want that variable to be computed/evaluated once (the 1st time I call the function) and for any subsequent invocation, it is not evaluated anymore. How to do that? Here's my class: template< typename T1 = int, unsigned N1 = 1, typename T2 = int, unsigned N2 = 0, typename T3 = int, unsigned N3 = 0, typename T4 = int, unsigned N4 = 0, typename T5 = int, unsigned N5 = 0, typename T6 = int, unsigned N6 = 0, typename T7 = int, unsigned N7 = 0, typename T8 = int, unsigned N8 = 0, typename T9 = int, unsigned N9 = 0, typename T10 = int, unsigned N10 = 0, typename T11 = int, unsigned N11 = 0, typename T12 = int, unsigned N12 = 0, typename T13 = int, unsigned N13 = 0, typename T14 = int, unsigned N14 = 0, typename T15 = int, unsigned N15 = 0, typename T16 = int, unsigned N16 = 0> struct GroupAlloc { static const uint32_t sizeClass; static uint32_t getSize() { static uint32_t totalSize = 0; totalSize += sizeof(T1)*N1; totalSize += sizeof(T2)*N2; totalSize += sizeof(T3)*N3; totalSize += sizeof(T4)*N4; totalSize += sizeof(T5)*N5; totalSize += sizeof(T6)*N6; totalSize += sizeof(T7)*N7; totalSize += sizeof(T8)*N8; totalSize += sizeof(T9)*N9; totalSize += sizeof(T10)*N10; totalSize += sizeof(T11)*N11; totalSize += sizeof(T12)*N12; totalSize += sizeof(T13)*N13; totalSize += sizeof(T14)*N14; totalSize += sizeof(T15)*N15; totalSize += sizeof(T16)*N16; totalSize = 8*((totalSize + 7)/8); return totalSize; } };

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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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• Memory leak problem. iPhone SDK

  - by user326375

  Hello, i've got a problem, i cannot solve it, just recieving error: Program received signal: “0”. The Debugger has exited due to signal 10 (SIGBUS).The Debugger has exited due to signal 10 (SIGBUS). Here is some method, if i comment it out, problem goes aways - (void)loadTexture { const int num_tex = 10; glGenTextures(num_tex, &textures[0]); //TEXTURE #1 textureImage[0] = [UIImage imageNamed:@"wonder.jpg"].CGImage; //TEXTURE #2 textureImage[1] = [UIImage imageNamed:@"wonder.jpg"].CGImage; //TEXTURE #3 textureImage[2] = [UIImage imageNamed:@"wall_eyes.jpg"].CGImage; //TEXTURE #4 textureImage[3] = [UIImage imageNamed:@"wall.jpg"].CGImage; //TEXTURE #5 textureImage[4] = [UIImage imageNamed:@"books.jpg"].CGImage; //TEXTURE #6 textureImage[5] = [UIImage imageNamed:@"bush.jpg"].CGImage; //TEXTURE #7 textureImage[6] = [UIImage imageNamed:@"mushroom.jpg"].CGImage; //TEXTURE #8 textureImage[7] = [UIImage imageNamed:@"roots.jpg"].CGImage; //TEXTURE #9 textureImage[8] = [UIImage imageNamed:@"roots.jpg"].CGImage; //TEXTURE #10 textureImage[9] = [UIImage imageNamed:@"clean.jpg"].CGImage; for(int i=0; i<num_tex; i++) { NSInteger texWidth = CGImageGetWidth(textureImage[i]); NSInteger texHeight = CGImageGetHeight(textureImage[i]); GLubyte *textureData = (GLubyte *)malloc(texWidth * texHeight * 4); CGContextRef textureContext = CGBitmapContextCreate(textureData, texWidth, texHeight, 8, texWidth * 4, CGImageGetColorSpace(textureImage[i]), kCGImageAlphaPremultipliedLast); CGContextDrawImage(textureContext, CGRectMake(0.0, 0.0, (float)texWidth, (float)texHeight), textureImage[i]); CGContextRelease(textureContext); glBindTexture(GL_TEXTURE_2D, textures[i]); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, texWidth, texHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureData); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); free(textureData); } } anyone can help me with releasing/deleting objects in this method? Thanks.

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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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• 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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• 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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• 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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• 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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