QFileSystemWatcher with a Qwt Real-time plot

Hi,

I work on Windows XP, andI want to plot a signal coming from a device. This device is connected to my PC by a RS232 serial port. I can't access directly to the data coming in my PC by the serial port, but only from a log text file.

I know that new data enters the text file every second, but because I want to be sure of the synchronisation between the entering of data and the plotting, I try to implement a QFileSystemWatcher: Everytime the file changes, a fileChanged signal is emitted and received by a function who opens the text file, read the just entered new data and close the file.

data.h:

Code:

//////////////////////////////////////////////////////////////////////////////////////////////////////////////
//The following class (data) is used as a sampling thread with the QFileSystemWatcher.
// It puts the significant values extracted from the text file in a data buffer. This data buffer 
//is passed to another class (plot) who take cares of displaing these datas.
 
#ifndef DATA_H
#define DATA_H
 
#include <QtGui>
#include <QFileSystemWatcher>
#include <QString>
#include <QFile>
#include <QVector>
#include <string>
#include <iostream>
#include <sstream>
#include <fstream>
#include <QFileInfo>
 
 
using namespace::std;
 
class Data: public QObject
{
  Q_OBJECT
 
public:
    Data(double* &_voies,QObject*p=NULL);
    void on_watcher();
private:
    QFileSystemWatcher *m_watcher;
    QFile file;
    QString file_name;
    double *voies;
    qint64 size1;
    qint64 size2;
    int m_position;
    int m_num;
    std::string line;
    std::string contractions_hex;
    std::string valeur_cardio_connecte;
public slots:
      void onFileChanged(const QString& file_name);
 
};
 
#endif // DATA_H

data.cpp:

Code:

#include "data.h"
 
Data::Data(double * &_voies, QObject*p):
        QObject(p)
{
 
    _voies = voies= new double[2];
 
    file_name = "Portmon.log";
    QFile file2(file_name);
    size2 = QFileInfo(file2).size();
    m_position =0;
    m_num = 0;
 
}
void Data::on_watcher()
{
    m_watcher = new QFileSystemWatcher();
     m_watcher->addPath(file_name);
    QObject::connect(m_watcher, SIGNAL(fileChanged(const QString&)), this, SLOT(onFileChanged(const QString&)));
}
 
 
//------------------------------------------------------------------------------
// plot::Traitement()
//When the file is detected as changed, 
//the text file is opened and the data forming the signal
// is extracted
// //------------------------------------------------------------------------------
 
void Data::onFileChanged( const QString& file_name)
{
    int nb_data =0;
    double perSec=1;
 
 
     ifstream file("Portmon.log");
    file.clear();
    file.seekg(m_position,ios::beg);
    while(getline(file,ligne))
            {
                string::size_type loc = line.find("Length 13:",0);
                if (loc != string::npos)
                {
 
                 contractions_hex = ligne.substr (loc+14,2); // Data collecting              
                valeur_cardio_connecte = ligne.substr(loc+26,2);//
                 m_position = file.tellg();//position of the file cursor
                 std::istringstream iss (contractions_hex); //Conversion from hexadecimal to int.
                 iss >> std::hex >> m_num;
                 double y1 =m_num/2;
                 double temps = nb_data*perSec;
                 //Adding data to the data buffer, another class is in charge of displaying the data on the plot
                 voies[0]=temps;
                 voies[1]=y1;
                 nb_data++;
 
                }
 
  }
 
}

Here's an example at of a text file:

Code:

[\\ISTILPORT06]
1179  10:06:58  SUCCESS  
1180  10:06:59  dacspy.exe  IRP_MJ_READ  Serial0  Length 100
1180  10:06:59  SUCCESS  Length 14: 10 02 43 80 02 00 00 00 00 00 00 00 00 00 
1181  10:06:59  dacspy.exe  IOCTL_SERIAL_GET_COMMSTATUS  Serial0  
1181  10:06:59  SUCCESS  
1182  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
1182  10:06:59  SUCCESS  
1183  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
1183  10:06:59  SUCCESS  
1184  10:06:59  dacspy.exe  IRP_MJ_READ  Serial0  Length 100
1184  10:06:59  SUCCESS  Length 14: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
1185  10:06:59  dacspy.exe  IOCTL_SERIAL_GET_COMMSTATUS  Serial0  
1185  10:06:59  SUCCESS  
1186  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
1186  10:06:59  SUCCESS  
1187  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
1187  10:06:59  SUCCESS  
1188  10:06:59  dacspy.exe  IRP_MJ_READ  Serial0  Length 100
1188  10:06:59  SUCCESS  Length 13: 00 0A 0B 0C 0A 00 00 08 00 10 03 92 38 
1189  10:06:59  dacspy.exe  IOCTL_SERIAL_GET_COMMSTATUS  Serial0  
1189  10:06:59  SUCCESS  
1190  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
1190  10:06:59  SUCCESS  
1191  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
1191  10:06:59  SUCCESS  
1192  10:06:59  dacspy.exe  IRP_MJ_READ  Serial0  Length 100
1192  10:06:59  SUCCESS  Length 14: 10 02 43 80 02 00 00 00 00 00 00 00 00 00 
1193  10:06:59  dacspy.exe  IOCTL_SERIAL_GET_COMMSTATUS  Serial0  
1193  10:06:59  SUCCESS  
1194  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
1194  10:06:59  SUCCESS  
1195  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
1195  10:06:59  SUCCESS  
1196  10:07:00  dacspy.exe  IRP_MJ_READ  Serial0  Length 100
1196  10:07:00  SUCCESS  Length 14: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
1197  10:07:00  dacspy.exe  IOCTL_SERIAL_GET_COMMSTATUS  Serial0  
1197  10:07:00  SUCCESS  
1198  10:07:00  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
1198  10:07:00  SUCCESS  
1199  10:07:00  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
1199  10:07:00  SUCCESS  
1200  10:07:00  dacspy.exe  IRP_MJ_READ  Serial0  Length 100
1200  10:07:00  SUCCESS  Length 13: 00 07 08 08 08 00 00 08 00 10 03 58 C9 
1201  10:07:00  dacspy.exe  IOCTL_SERIAL_GET_COMMSTATUS  Serial0  
1201  10:07:00  SUCCESS  
1202  10:07:00  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
1202  10:07:00  SUCCESS  
1203  10:07:00  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0

When I try to run this code, no data is added to the plot, and I get an empty plot.

I know that the problem is with the QFileSystemWatcher because everything else has been tested and debugged before.
I have put my text file in the debug file of my project (I'm in debug mode) and my whole project including Qt Creator implementation is on an external disk (:G), I don't know if that changes something..

Thanks for your help !!