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Thread: QFileSystemWatcher with a Qwt Real-time plot

  1. 24th June 2010, 22:37 #1
    gen_mass
    gen_mass is offline Novice
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    Default 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:
    Qt Code: 
    1. //////////////////////////////////////////////////////////////////////////////////////////////////////////////
    2. //The following class (data) is used as a sampling thread with the QFileSystemWatcher.
    3. // It puts the significant values extracted from the text file in a data buffer. This data buffer 
    4. //is passed to another class (plot) who take cares of displaing these datas.
    5.  
    6. #ifndef DATA_H
    7. #define DATA_H
    8.  
    9. #include <QtGui>
    10. #include <QFileSystemWatcher>
    11. #include <QString>
    12. #include <QFile>
    13. #include <QVector>
    14. #include <string>
    15. #include <iostream>
    16. #include <sstream>
    17. #include <fstream>
    18. #include <QFileInfo>
    19.  
    20.  
    21. using namespace::std;
    22.  
    23. class Data: public QObject
    24. {
    25.   Q_OBJECT
    26.  
    27. public:
    28.     Data(double* &_voies,QObject*p=NULL);
    29.     void on_watcher();
    30. private:
    31.     QFileSystemWatcher *m_watcher;
    32.     QFile file;
    33.     QString file_name;
    34.     double *voies;
    35.     qint64 size1;
    36.     qint64 size2;
    37.     int m_position;
    38.     int m_num;
    39.     std::string line;
    40.     std::string contractions_hex;
    41.     std::string valeur_cardio_connecte;
    42. public slots:
    43.       void onFileChanged(const QString& file_name);
    44.  
    45. };
    46.  
    47. #endif // DATA_H
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    data.cpp:
    Qt Code: 
    1. #include "data.h"
    2.  
    3. Data::Data(double * &_voies, QObject*p):
    5. {
    6.  
    7.     _voies = voies= new double[2];
    8.  
    9.     file_name = "Portmon.log";
    10.     QFile file2(file_name);
    11.     size2 = QFileInfo(file2).size();
    12.     m_position =0;
    13.     m_num = 0;
    14.  
    15. }
    16. void Data::on_watcher()
    17. {
    18.     m_watcher = new QFileSystemWatcher();
    19.      m_watcher->addPath(file_name);
    20.     QObject::connect(m_watcher, SIGNAL(fileChanged(const QString&)), this, SLOT(onFileChanged(const QString&)));
    21. }
    22.  
    23.  
    24. //------------------------------------------------------------------------------
    25. // plot::Traitement()
    26. //When the file is detected as changed, 
    27. //the text file is opened and the data forming the signal
    28. // is extracted
    29. // //------------------------------------------------------------------------------
    30.  
    31. void Data::onFileChanged( const QString& file_name)
    32. {
    33.     int nb_data =0;
    34.     double perSec=1;
    35.  
    36.  
    37.      ifstream file("Portmon.log");
    38.     file.clear();
    39.     file.seekg(m_position,ios::beg);
    40.     while(getline(file,ligne))
    41.             {
    42.                 string::size_type loc = line.find("Length 13:",0);
    43.                 if (loc != string::npos)
    44.                 {
    45.  
    46.                  contractions_hex = ligne.substr (loc+14,2); // Data collecting              
    47.                 valeur_cardio_connecte = ligne.substr(loc+26,2);//
    48.                  m_position = file.tellg();//position of the file cursor
    49.                  std::istringstream iss (contractions_hex); //Conversion from hexadecimal to int.
    50.                  iss >> std::hex >> m_num;
    51.                  double y1 =m_num/2;
    52.                  double temps = nb_data*perSec;
    53.                  //Adding data to the data buffer, another class is in charge of displaying the data on the plot
    54.                  voies[0]=temps;
    55.                  voies[1]=y1;
    56.                  nb_data++;
    57.  
    58.                 }
    59.  
    60.   }
    61.  
    62. }
    To copy to clipboard, switch view to plain text mode 

    Here's an example at of a text file:

    Qt Code: 
    1. [\\ISTILPORT06]
    2. 1179  10:06:58  SUCCESS  
    3. 1180  10:06:59  dacspy.exe  IRP_MJ_READ  Serial0  Length 100
    4. 1180  10:06:59  SUCCESS  Length 14: 10 02 43 80 02 00 00 00 00 00 00 00 00 00 
    5. 1181  10:06:59  dacspy.exe  IOCTL_SERIAL_GET_COMMSTATUS  Serial0  
    6. 1181  10:06:59  SUCCESS  
    7. 1182  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
    8. 1182  10:06:59  SUCCESS  
    9. 1183  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
    10. 1183  10:06:59  SUCCESS  
    11. 1184  10:06:59  dacspy.exe  IRP_MJ_READ  Serial0  Length 100
    12. 1184  10:06:59  SUCCESS  Length 14: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
    13. 1185  10:06:59  dacspy.exe  IOCTL_SERIAL_GET_COMMSTATUS  Serial0  
    14. 1185  10:06:59  SUCCESS  
    15. 1186  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
    16. 1186  10:06:59  SUCCESS  
    17. 1187  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
    18. 1187  10:06:59  SUCCESS  
    19. 1188  10:06:59  dacspy.exe  IRP_MJ_READ  Serial0  Length 100
    20. 1188  10:06:59  SUCCESS  Length 13: 00 0A 0B 0C 0A 00 00 08 00 10 03 92 38 
    21. 1189  10:06:59  dacspy.exe  IOCTL_SERIAL_GET_COMMSTATUS  Serial0  
    22. 1189  10:06:59  SUCCESS  
    23. 1190  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
    24. 1190  10:06:59  SUCCESS  
    25. 1191  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
    26. 1191  10:06:59  SUCCESS  
    27. 1192  10:06:59  dacspy.exe  IRP_MJ_READ  Serial0  Length 100
    28. 1192  10:06:59  SUCCESS  Length 14: 10 02 43 80 02 00 00 00 00 00 00 00 00 00 
    29. 1193  10:06:59  dacspy.exe  IOCTL_SERIAL_GET_COMMSTATUS  Serial0  
    30. 1193  10:06:59  SUCCESS  
    31. 1194  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
    32. 1194  10:06:59  SUCCESS  
    33. 1195  10:06:59  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
    34. 1195  10:06:59  SUCCESS  
    35. 1196  10:07:00  dacspy.exe  IRP_MJ_READ  Serial0  Length 100
    36. 1196  10:07:00  SUCCESS  Length 14: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
    37. 1197  10:07:00  dacspy.exe  IOCTL_SERIAL_GET_COMMSTATUS  Serial0  
    38. 1197  10:07:00  SUCCESS  
    39. 1198  10:07:00  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
    40. 1198  10:07:00  SUCCESS  
    41. 1199  10:07:00  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
    42. 1199  10:07:00  SUCCESS  
    43. 1200  10:07:00  dacspy.exe  IRP_MJ_READ  Serial0  Length 100
    44. 1200  10:07:00  SUCCESS  Length 13: 00 07 08 08 08 00 00 08 00 10 03 58 C9 
    45. 1201  10:07:00  dacspy.exe  IOCTL_SERIAL_GET_COMMSTATUS  Serial0  
    46. 1201  10:07:00  SUCCESS  
    47. 1202  10:07:00  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0  
    48. 1202  10:07:00  SUCCESS  
    49. 1203  10:07:00  dacspy.exe  IOCTL_SERIAL_WAIT_ON_MASK  Serial0
    To copy to clipboard, switch view to plain text mode 


    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 !!
    Last edited by gen_mass; 24th June 2010 at 23:12.
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  2. 25th June 2010, 21:28 #2
    JohannesMunk
    JohannesMunk is offline Advanced user
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    Default Re: QFileSystemWatcher with a Qwt Real-time plot

    Reduce the problems complexity. Don't put the stuff into a graph but write a message to the debug output if you get a file change notification. That way you make sure its not your output that is a problem!

    If nothing is triggered, try to get some events when you change the log file manually...

    HIH

    Johannes
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