[Qt-interest] install message handler

[Sajjad]

Hello Sean,


Thanks for the suggestion. I have tried your code snippet with  very minor
changes and i am getting empty file as before.


*************************************
#include "Util.h"

#include <iostream>

QTextStream g_nonstderr;
QFile g_debugLogFile;
QMutex g_mutex;

void debugMessageHandler(QtMsgType type, const char *msg)
{
    g_mutex.lock();

    switch ( type )
    {
        case QtDebugMsg:
            g_nonstderr << QString( msg ) << endl;
            break;
        case QtWarningMsg:
            g_nonstderr << "Warning:" << msg << endl;
            break;
        case QtCriticalMsg:
            g_nonstderr << "Critical:" << msg << endl;
            break;
        case QtFatalMsg:
            g_nonstderr << "Fatal:" << msg << endl;
            abort();
    }
    g_mutex.unlock();

}



void setupDebugRedirection()
{
    //static QFile *g_debugLogFile = new QFile();

    g_debugLogFile.setFileName("debugOut.txt");
    g_nonstderr.setDevice( &g_debugLogFile );
    g_debugLogFile.open( QIODevice::WriteOnly | QIODevice::Text );
    qInstallMsgHandler( debugMessageHandler );
}


***********************************'***

Any other hint to look for ?



Regards
Sajjad


On Thu, Sep 2, 2010 at 11:45 AM, Sean Harmer <
sean.harmer at maps-technology.com> wrote:

> Hi,
>
> On Thursday 02 September 2010 10:28:17 Sajjad wrote:
> > I am trying all my debug output to a file and i tried using the
> > qInstallMsgHandler.the function pointer contains the following
> definition:
> >
> > ************************************************
> >
> > #include "Util.h"
> >
> > #include <iostream>
> >
> > void debugMessageHandler(QtMsgType type, const char *msg)
> > {
> >     static QFile *file = new QFile(":/H3D/debugOut.txt");
> >
> >     if(!file->exists())
> >         std::cout << "file does not exist" << std::endl;
> >     else
> >         std::cout << "File is there" << std::endl;
> >
> >     QTextStream out(file);
> >     switch(type)
> >     {
> >     case QtDebugMsg:
> >         out << "Debug" << QString(msg);
> >         break;
> >     }
> > }
> >
> > ********************************************************************
> >
> >
> > I install the handler in the main function and  it is supposed to be
> > functional from anywhere in the project, right?
>
> Yes.
>
> > After every debug output with qDebug() i chcek the contents of the file
> and
> > it is still empty.
> >
> > Is there anything i am missing in the process?
>
> Two things by the looks of it.
>
> 1). You are trying to use an internal resource system file since your
> filename
> begins with a ":". This won't work since such resources are compiled into
> your
> application and so are read-only.
>
> 2). You do not open the file for writing anywhere.
>
> In the past we have used something like this:
>
> QFile g_debugLogFile;
> QTextStream g_nonstderr;
> QMutex g_mutex;
>
> void msgRedirection( QtMsgType type, const char *msg )
> {
>    g_mutex.lock();
>    switch ( type )
>    {
>        case QtDebugMsg:
>            g_nonstderr << QString( msg ) << endl;
>            //fprintf(&nonstderr, "Debug: %s\n", msg);
>            break;
>        case QtWarningMsg:
>            g_nonstderr << "Warning:" << msg << endl;
>            //fprintf(&nonstderr, "Warning: %s\n", msg);
>            break;
>        case QtCriticalMsg:
>            g_nonstderr << "Critical:" << msg << endl;
>            //fprintf(&nonstderr, "Critical: %s\n", msg);
>            break;
>        case QtFatalMsg:
>            g_nonstderr << "Fatal:" << msg << endl;
>            //fprintf(&nonstderr, "Fatal: %s\n", msg);
>            abort();
>    }
>    g_mutex.unlock();
> }
>
> void setupDebugRedirection()
> {
>    g_debugLogFile.setFileName( "/var/log/my-log-file.log" );
>    g_nonstderr.setDevice( &g_debugLogFile );
>    g_debugLogFile.open( QIODevice::WriteOnly | QIODevice::Text );
>    qInstallMsgHandler( msgRedirection );
> }
>
> Then just call setupDebugRedirection() somewhere in main(). We used a mutex
> in
> the msg handler function because we were usign qDebug() and friends from
> several threads and QTextStream is not thread-safe.
>
> NB This took us a long time to realise. We thought we had a race condition
> somewhere else in our threading code and the more qDebug() statements we
> added
> the worse the problem got. We had forgotten about the innocent looking msg
> handler function. Oh well, lesson learned ;-)
>
> HTH,
>
> Sean
> _______________________________________________
> Qt-interest mailing list
> Qt-interest at trolltech.com
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>
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