Question about QPID and QProcess

[Naahmi]

Hello


I have a small example:

main.cpp

#include <QtCore/QCoreApplication>
#include "process.h"
 
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    Process *proc = new Process;
    proc->startProcess();
 
    return a.exec();
}

#include <QtCore/QCoreApplication>
#include "process.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    Process *proc = new Process;
    proc->startProcess();
    
    return a.exec();
}

To copy to clipboard, switch view to plain text mode 

process.h

#ifndef PROCESS_H
#define PROCESS_H
 
#include <QProcess>
 
class Process : public QProcess
{
public:
    Process();
    void startProcess();
};
 
#endif // PROCESS_H

#ifndef PROCESS_H
#define PROCESS_H

#include <QProcess>

class Process : public QProcess
{
public:
    Process();
    void startProcess();
};

#endif // PROCESS_H

To copy to clipboard, switch view to plain text mode 

process.cpp

#include "process.h"
#include <QDebug>
#include <QDir>
#include <QFileInfo>
#ifdef Q_WS_WIN
#include <windows.h>
#endif
 
Process::Process()
{
 
}
void Process::startProcess()
{
 
#ifdef Q_WS_WIN
 
    qDebug() << "Bin dran!";
 
    QString fileName = "69874.ods";
 
    fileName = QDir::tempPath() + "/" + fileName;
    QFileInfo fileInfo(fileName);
 
    this->start(QString("rundll32 url.dll,FileProtocolHandler \"%1\"").arg( fileInfo.absoluteFilePath()));
 
    struct _PROCESS_INFORMATION *procInfo = this->pid();
 
    qDebug() << "PID: " << procInfo->dwProcessId;
 
#endif
 
#ifndef Q_WS_WIN
 
#endif
}

#include "process.h"
#include <QDebug>
#include <QDir>
#include <QFileInfo>
#ifdef Q_WS_WIN
#include <windows.h>
#endif

Process::Process()
{

}
void Process::startProcess()
{

#ifdef Q_WS_WIN

    qDebug() << "Bin dran!";

    QString fileName = "69874.ods";

    fileName = QDir::tempPath() + "/" + fileName;
    QFileInfo fileInfo(fileName);

    this->start(QString("rundll32 url.dll,FileProtocolHandler \"%1\"").arg( fileInfo.absoluteFilePath()));

    struct _PROCESS_INFORMATION *procInfo = this->pid();

    qDebug() << "PID: " << procInfo->dwProcessId;

#endif

#ifndef Q_WS_WIN

#endif
}

To copy to clipboard, switch view to plain text mode 

i want to open a document (works fine) and get the process for (in my case) for soffice/excel. But qt returned another pid (i think its the qprocess pid and not soffice).

We have a client-server architecture and i want to write back the file to the server if the editor is closed.

Is there a way to get the PID from the childprocess?

proc->state() returned always is runned.

[Santosh Reddy]

You need to wait until the process has started. Use this->waitForStarted();, to block until the process starts

[Naahmi]

Same result wrong pid.

this->start(QString("rundll32 url.dll,FileProtocolHandler \"%1\"").arg( fileInfo.absoluteFilePath()));
this->waitForFinished();
struct _PROCESS_INFORMATION *procInfo = this->pid();
qDebug() << "PID: " << procInfo->dwProcessId;

this->start(QString("rundll32 url.dll,FileProtocolHandler \"%1\"").arg( fileInfo.absoluteFilePath()));
this->waitForFinished();
struct _PROCESS_INFORMATION *procInfo = this->pid();
qDebug() << "PID: " << procInfo->dwProcessId;

To copy to clipboard, switch view to plain text mode 

[wysota]

Why not use QDesktopServices::openUrl() instead?

[Santosh Reddy]

Why wait for finished ?

[Naahmi]

Why not use QDesktopServices::openUrl() instead?

openurl doesn't wait until the editor is closed

We have a client-server architecture and i want to write back the file to the server if the editor is closed.

[wysota]

openurl doesn't wait until the editor is closed

Ah ok.

I'd suggest using the variant of QProcess::start() that accepts arguments as a separate list of strings. You are trying to quote the filename to compensate for spaces in its path but it won't work because quotes are interpreted by the shell (cmd) which in this case is not used. The docs clearly say start() that you use separates arguments based on spaces. So instead use do this:

start("rundll32", QStringList() << "url.dll,FileProtocolHandler" << fileInfo.absoluteFilePath());

start("rundll32", QStringList() << "url.dll,FileProtocolHandler" << fileInfo.absoluteFilePath());

To copy to clipboard, switch view to plain text mode 

Or with Qt5 and C++11:

start("rundll32", { "url.dll,FileProtocolHandler", fileInfo.absoluteFilePath() });

start("rundll32", { "url.dll,FileProtocolHandler", fileInfo.absoluteFilePath() });

To copy to clipboard, switch view to plain text mode 

[Naahmi]

Ah ok.

I'd suggest using the variant of QProcess::start() that accepts arguments as a separate list of strings. You are trying to quote the filename to compensate for spaces in its path but it won't work because quotes are interpreted by the shell (cmd) which in this case is not used. The docs clearly say start() that you use separates arguments based on spaces. So instead use do this:

start("rundll32", QStringList() << "url.dll,FileProtocolHandler" << fileInfo.absoluteFilePath());

start("rundll32", QStringList() << "url.dll,FileProtocolHandler" << fileInfo.absoluteFilePath());

To copy to clipboard, switch view to plain text mode 

Or with Qt5 and C++11:

start("rundll32", { "url.dll,FileProtocolHandler", fileInfo.absoluteFilePath() });

start("rundll32", { "url.dll,FileProtocolHandler", fileInfo.absoluteFilePath() });

To copy to clipboard, switch view to plain text mode 

Thanks for the info but the file opens correct but the pid is wrong and ne process doesn't wait. i have no idea to handle this problem.
I'm using Qt4.

Santosh Reddy
Re: Question about QPID and QProcess

Why wait for finished ?

Sorry copy & paste error i have:

this->start(QString("rundll32 url.dll,FileProtocolHandler \"%1\"").arg( fileInfo.absoluteFilePath()));
this->waitForStarted();
struct _PROCESS_INFORMATION *procInfo = this->pid();
qDebug() << "PID: " << procInfo->dwProcessId;

this->start(QString("rundll32 url.dll,FileProtocolHandler \"%1\"").arg( fileInfo.absoluteFilePath()));
this->waitForStarted();
struct _PROCESS_INFORMATION *procInfo = this->pid();
qDebug() << "PID: " << procInfo->dwProcessId;

To copy to clipboard, switch view to plain text mode 

[wysota]

Maybe the issue is with how rundll32 works? It probably "forks" (or rather spawns the handling app) and ends its own process thus you get pid of the parent that is already dead.

You can check that by executing your command in cmd. If you get a new prompt immediately then what I said is true. If on the other hand you get new prompt only after you close the handler program then it means run32 doesn't return immediately.

[Naahmi]

Maybe the issue is with how rundll32 works? It probably "forks" (or rather spawns the handling app) and ends its own process thus you get pid of the parent that is already dead.

You can check that by executing your command in cmd. If you get a new prompt immediately then what I said is true. If on the other hand you get new prompt only after you close the handler program then it means run32 doesn't return immediately.

Can't see a new promt.

[wysota]

Try running the handler not with QProcess but rather with the system() call. If rundll32 doesn't return immediately, it should do exactly what you want.

[Naahmi]

Try running the handler not with QProcess but rather with the system() call. If rundll32 doesn't return immediately, it should do exactly what you want.

i have tested:

system("rundll32 url.dll,FileProtocolHandler C:/Users/da/AppData/Local/Temp/70233.ods");
qDebug() << "at the end";

system("rundll32 url.dll,FileProtocolHandler C:/Users/da/AppData/Local/Temp/70233.ods");
qDebug() << "at the end";

To copy to clipboard, switch view to plain text mode 

and the display is before the editor is closed. the program doesn't wait :-/

[wysota]

So rundll32 doesn't wait too and there is no solution for what you want that uses rundll32. When I asked you about an immediate prompt after you run rundll32 I guess we had to misunderstand each other -- if system() behaves the way you describe it then rundll32 must have returned immediately.

[Naahmi]

Do you have some other ideas?

[wysota]

First of all tell us why you want to halt your application until the editor is closed.

[Naahmi]

First of all tell us why you want to halt your application until the editor is closed.

Hi,

Our client-server architecture requires that the client wait until the user is finish with editing the file. After this the server synchronized the local file with the file from the server.

[wysota]

Maybe it is enough for you to use QFileSystemWatcher to detect changes to the file? Monitoring the editor itself would probably not have worked anyway because if the editor was already open when you tried opening the file, the file might have been loaded into this existing editor instead of launching a new one or a new document might have been created while your editor was open causing a situation that ending work on your file does not close the editor application at all.

If monitoring the file system is not good enough for you then maybe you can have a modal dialog in your app which the user has to close to continue.