C++ :: Access Objects From Another Thread
Jun 25, 2013
I have the following code below. I am getting a memory access violation when accessing cmd->query_string in the loop function. The loop() function is running in another thread. The cmd object appears to be destroyed after calling the send_command function. How do I create an object on the heap and access the query_string.
std::list<my_command_message_que*> my_command_que;
void loop(){
if(my_command_que.size() > 0){
my_command_message_que * cmd = my_command_que.front();
std::cout << cmd->query_string;
[Code] ....
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May 7, 2013
I am new to C++ programming and i have a small assignment.
How to implement a thread safe class to manage a queue of objects. Accessing the front of the queue should be a blocking operation when the queue is empty.
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Dec 4, 2014
Alright, so I'm making a windows form with a few hundred buttons, and one button will change color based on data the program receives over a socket. This is what I have, and it kind of works, but I don't want to have to make another if statement for all 260 buttons.
void hitmiss(std::string u){
std::string^ ind = reccdata2();
if (u == "button6"){
if (ind == "1"){
this->button6->BackColor = System::Drawing::Color::Red;
this->textBox2->Text = L"hit";
[Code] .....
What I want to do is make it more like
void hitmiss(System::String^ u){
std::string^ ind = reccdata2();
if (ind == "1"){
this->u->BackColor = System::Drawing::Color::Red;
this->textBox2->Text = L"hit";
[Code] ....
But it returns the error that u is not a part of Form1.
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Feb 13, 2013
My goal is accessing c++ objects within c by using wrapper and externals. To get the pointer to the c++ object I use a type "void *".
But i get an error while linking: undefined reference to "create_mycpp".
Should I take an other way to access c++ objects?
Code:
//-------------------------------------
//mycpp.cpp
#include "mycpp.h"
Mycpp::void func(int i)
{
i += 1;
[Code] ....
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Dec 13, 2012
Table with primary key already set-down in ACCESS. when insert records into the table by Execute() function of cdaodatabase, to some extense, the records are not put behind the last record as wished, otherwise randomly into other places!
now i want to do some kind of operation to order the table after insertion by cdaodatabase or some others. how to?
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Jul 30, 2014
I have a class which I wrote and one of its object is "SerialPort" .NET class. In my MainWindow I created instance of my class called "SerialPortComm", then I send through some functions of mine, commands to the Serial Port, and I receive answers through "DataReceived" event.
But when I trying to use Dispatcher.BeginInvoke to write my data I have received (successfully), nothing shows on the RichTextBox which I'm trying to write to.
What can caused that, and How I can make it works?
SerialPortComm.cs
public partial class SerialPortComm : UserControl {
public SerialPort mySerialPort = new SerialPort();
public void Open_Port(string comNumber, int baudRate) {
mySerialPort.PortName = comNumber;
mySerialPort.BaudRate = baudRate;
[Code] ....
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Sep 9, 2013
if we don't provide the acces modifiers for base class and we need to manipulate the private data of base class in derived class. Is there anyway to acces the private data members? Here's a coding example
class A {
private :
int a;
};
class B : public class A {
public :
void displayA() { cout<<a<<endl; }
};
how i can acces the a of base class A in derived class B without acces modifiers.
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Nov 12, 2014
This has been bothering me for a while now, and I finally put together an example:
#include <iostream>
#include <string>
using namespace::std;
[Code]....
In the code above, the two classes hold pointers to each other, and that's fine but it doesn't seem right since C++ prefers to pass by reference. Yes, it can still do that (see testbox and testball) but even that seems odd to me because still you need to use pointer notation for the enclosed object. Am I the only one who feels this way, and should I just get over it? Or am I missing something that would allow an object to hold a reference?
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May 9, 2013
I've been using threading for a while, that was no needing parameters. so I used for example the following line :
_beginthread(functionName, 0, (void*)10);
and it worked great...
but now I have a function that has an int parameter (int num), and I dont know how to transfer it using _beginthread...
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Mar 3, 2013
I was working on a problem that was best solved with chaining threads together using a blocking thread-safe queue. Eg threads A and B pass data to each other using a queue ... a simple producer consumer design A -> B. This has two benefits: 1) being that there is a buffer between the two threads to cache for a slow consumer and 2) allows for better throughput when loads of data are high because the two can run in parallel. Most of the time the design works well under load. but I found when pushing data through the threads intermittently, i.e. once about 0.5 seconds it ran poorly, mostly from what seemed to be latency introduced during the OS waking up of the consumer thread B.
What i have come up with to solve this issue is what i call an .... Its a wrapper around a basic thread safe queue and adds one extra function called .... The idea here is that if you have a simple case (or perhaps a slightly more complicated case) of two threads in a prod cons design and you know the producer will create or received the data, process it, and then push onto the queue, why not give the consumer thread a heads up to let it know the data is about to arrive. In this case call .... In this way you can have the consumer thread in a polling state anticipating the arrival of data and avoid the time to schedule it back to a running state.
Anyway, i have some code below and I was looking to get some feedback. I have tested it somewhat and it does improve the responsiveness quite substantially.
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Apr 28, 2014
I don't know if I've setup the thread correctly or not, but its behavoir isn't what I'd expect. I'm creating the thread within a BN_CLICKED message
typedef struct my_TNFO {
HANDLE h_event;
HANDLE h_thread;
DWORD thread_id;
BOOL running;
BOOL init;
BOOL canceled;
[Code] ....
progd->count was devised to stop the thread when the recursion ended by posting a message to the main window. When it reaches 1, the def procedure sends the WMU_DISC_DONE message to set the event
All that *appears* to work; however, if I cancel the recursion thread, the list view continues to populate for a bit and then deletels all but 1 item though I send the message LVM_DELETEALLITEMS.
If I move the (tmp->canceled == TRUE) test inside of the do-while, the app gets loopy.
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Feb 15, 2015
Startthread get called to launch to update list box.
a)is it the only way to pass string to the PostMessage?. my concern is that allocate using new in each iteration each time slows it down a bit.
b)does OnAddToListBox look memory leak free?.
c)What is the best way handle m_pThread at the end?. Any way to improve it?.
Code:
UINT CMyDlg::Dump(LPVOID lparam) {
HWND *pHndl = static_cast<HWND *>(lparam);
char buffer[200];
for (int i = 0; i < 100; i++) {
sprintf_s(buf,"user %d, data %s",i, "Connected");
[Code] ....
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Feb 12, 2013
I use MFC Find console window and send key to console like this.
Code:
HWND w;
w = FindWindow(NULL, L"c:userspkrudocumentsvisual studio 2010ProjectsCleanVirusDebugCleanVirus.exe");
[Code]....
After program process success in console it not close console windows but it show like this in Output
The thread 'Win32 Thread' (0x1300) has exited with code 0 (0x0).
I think if I can check when VC will show this line, then I can use FreeConsole(); for close console windows.
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Jun 7, 2014
There are gnu thread, c thread, posix thread and win32 thread which all can be used on windows platform.
How, why and when do I need them?
Code:
#ifndef C_THREAD_H_
#define C_THREAD_H_
extern "C"
{
#include <cthread.h>
[code]....
This simply won't compile with Visual C++ because there isn't any cthread.h header file there.
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May 5, 2014
I want to add a timer(clock) to my application so that it displays the system time and refreshes every second.
I have this code but it only fires once.
// this is at the top of the application
Code:
HANDLE m_threadClockTime= NULL; Code: int APIENTRY _tWinMain(_In_ HINSTANCE hInstance,
_In_opt_ HINSTANCE hPrevInstance,
_In_ LPTSTR lpCmdLine,
_In_ int nCmdShow)
[Code] ....
But this code only fires once? How can I get this to fire every second (without locking up the entire application in between)....
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Nov 24, 2014
How to call a thread by a function pointer?
I get "error C2059: syntax error : '(' " on the indicated line.
Code:
#include <windows.h>#include <iostream>
using namespace std;
DWORD WINAPI Thread() {
cout << "ok" << endl;
return 0;
[Code] ....
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Aug 27, 2013
I am writing a program, the trouble is is that it uses a single thread and is SLOW.
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Apr 30, 2012
After i've created a thread,
Code:
Thread thread = new Thread(new ThreadStart(alpha.ThreadProc)); h
How to wait for that thread to finish without using Sleep?
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Jul 28, 2013
I have a small problem with my program. It is kinda a mess but I will try to explain you what I am trying to do. I have some threads. One of it, it attempts to detect a game client. So my code is sort of like that:
DWORD ProcessID; // The process ID of the game client
void test() {
char* text;
[Code]....
So basically, its like the variable changes, but only inside the thread... why does that happen?
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Jul 25, 2014
When I write a code in c++ includes thread library it says "thread:no such file or directory". How can ı use thread library .
I think I should download boost or c++11 but I couldn't do it .
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Apr 11, 2013
I recently picked up multithreading with OpenMP, so it is still new to me. While processing data, I would like to store it in a vector, as shown here:
vector<int> vect;
#pragma omp parallel for
for(int c=0; c<500; ++c) {
vect.push_back(c)
}
However, since it is multithreaded, I would like (and need!) to have one dedicated vector per thread. I haven't been able to find an example of how to do this online. Is it even possible?
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Aug 25, 2013
I have a function :
void UpdateNotefications(vector <string> &Notefic)
Where I change a vector...
I called it with a thread :
thread t1 (UpdateNotefications, Notefic);
t1.detach();
Though I see that inside the func, Notefic has a val, and outside, it is still empty (after the function is over)...
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Feb 14, 2014
I have an issue where I iterate through devices and make driver API calls. Unfortunately, these calls take too much time and they are interrupting my real-time scheduler. I have 12 cores, of which one is 100% and the others are < 1%.
I'd like to multi-thread this thing. So far, I've replaced:
for (DeviceIterator d = devices.begin(); d != devices.end(); ++d) {
d->Write(words, numwords);
}
with
void* ThreadedWrite(void* p) {
WritePackage* wp = (WritePackage*)p;
wp->device->Write(wp->words, wp->numwords);
delete[] wp->words;
delete wp;
[Code]...
My problem is that this didn't improve performance at all. The main thread still takes too long to execute. Is there something I need to do to prevent the main thread from blocking?
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Jan 25, 2014
I'm trying to create a thread to a class function, but it doesnt work for me...
The function : void Server::RecMsg(SOCKET &socket)
the call : std::thread GetMessages(&Server::RecMsg, ClientSocket);
I get the error : "Error1error C2064: term does not evaluate to a function taking 1 arguments"
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May 29, 2014
// mergefile2norecreation.cpp : definisce il punto di ingresso dell'applicazione console.
//
// Filemerge.cpp : definisce il punto di ingresso dell'applicazione console.
//
#include "stdafx.h"
int _tmain(int argc, _TCHAR* argv[]) {
TCHAR inputfile1[MAX_PATH];
TCHAR inputfile2[MAX_PATH];
TCHAR outputfile[MAX_PATH];
[Code] .....
There is a smart way to make a merge sort between 2 file already ordered? I had try it ,and above there is my result,it works but i think that it's possible to do it in a smart way...
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Mar 31, 2013
the compiler doesnt accept void functions used with threads (for the first time and all of sudden!?)
#include <cstdlib>
#include <thread>
#include <windows.h>
[Code]....
this is a sigment of my code. Compiler says that the error occurs in line 47 (marked by ***). Leaving out the braces makes it even worse.
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