[Solved] C++ thread does not work in Qt?

MohammadReza

Hi friends.

I try to use c++ thread (in 'thread' library in windows) but have 2 problem.

Here is my simple code

mainwindow.h
@
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
void foo2();

private slots:
void on_pushButton_clicked();

private:
Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H
@

mainwindow.cpp
@
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
#include <thread>

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}

MainWindow::~MainWindow()
{
delete ui;
}

void foo()
{
for(int i=0; i<1000000;i++)
qDebug() << i;
}

void MainWindow::foo2()
{
for(int i=0; i<1000000;i++)
qDebug() << i;
}

void MainWindow::on_pushButton_clicked()
{
std::thread t1(foo);
}
@

'foo' doesn`t have a signature but 'foo2' has a signature.

when I use 'foo' function in on_pushButton_clicked() i get this run time error:
!http://8pic.ir/images/tbwhxd5kvdi8g3jaa7b1.jpg(http://8pic.ir/images/tbwhxd5kvdi8g3jaa7b1.jpg)!

when I use 'foo2' function in on_pushButton_clicked() i get this error:
error: C3867: 'MainWindow::foo2': function call missing argument list; use '&MainWindow::foo2' to create a pointer to member

what is the problem?

Thanks a lot.
Ya Ali.

sierdzio

@
std::thread t1(&MainWindow::foo2);
@

MohammadReza

Thanks dear sierdzio but another errors occured:

!http://8pic.ir/images/qdlr3b7qh19it9vec7f9.jpg(http://8pic.ir/images/qdlr3b7qh19it9vec7f9.jpg)!

MohammadReza

Thanks be to GOD. I could solve this problem by defining foo2 as a static function but run time error occoured again. That is, now foo & foo2 has the runtime error!

How can I solve the runtime error?

sierdzio

Please run it with the debugger attached to see where it fails.

MohammadReza

There is no problem in code.
I get the runtime error here:

!http://8pic.ir/images/6xtyikmiv4go892yshbk.jpg(http://8pic.ir/images/6xtyikmiv4go892yshbk.jpg)!

MohammadReza

Thanks be to GOD. I must detach or join the thread like this:

@
void MainWindow::on_pushButton_clicked()
{
std::thread t1(foo);
t1.join();
}
@

Reference: http://stackoverflow.com/questions/15423345/c-stdthread-problems-in-visual-studio-2012

Thanks to dear sierdzio for helping me.

sierdzio

That is NT dll, not interesting in this case. Go back in the stack trace to see where it fails in your code. I would suspect you are using STD threads wrongly, but I am not sure, I always use QThread instead.

SGaist

Hi,

Another point, why use a thread since the first thing you do after creating t1 is to join so you block the calling thread until t1 has finished ?