Problem with my class and QProcess

Piotrek102

Hi all,
I want to create my own class to make it easier to execute powershell commands with QProcess. For testing, I wrote the code so that it returned to me the current location of the process (pwd).

MyProcess myprocess;
qDebug() << myprocess.RunCommand("pwd");

Unfortunately, the following errors appear to me:
qt.core.qobject.connect: QObject::connect: No such slot QObject::processStarted() in ..\WinConfigurator\myprocess.cpp:12

qt.core.qobject.connect: QObject::connect: No such slot QObject::readyReadStandardOutput() in ..\WinConfigurator\myprocess.cpp:13

My class:

myprocess.h

#ifndef MYPROCESS_H
#define MYPROCESS_H

#include <QProcess>
#include <QTime>
#include <QCoreApplication>
#include <QObject>

class MyProcess : public QObject
{
public:
	MyProcess();
	QStringList RunCommand(QString command);

private slots:
	void processStarted();
	void readyReadStandardOutput();
	void encodingFinished();

private:
	QProcess* process;
	void SetupProcess();
	void delay_MSec(unsigned int msec);
	bool process_ok;
	QStringList stream_data;

};

#endif // MYPROCESS_H

myprocess.cpp

#include "myprocess.h"

MyProcess::MyProcess()
{
	SetupProcess();
}

void MyProcess::SetupProcess()
{
	process = new QProcess(this);
	process->setWorkingDirectory(qApp->applicationDirPath());
	connect(process, SIGNAL(started()), this, SLOT(processStarted()));
	connect(process,SIGNAL(readyReadStandardOutput()),this,SLOT(readyReadStandardOutput()));
	connect(process, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
			[=](int exitCode, QProcess::ExitStatus exitStatus){ encodingFinished(); });
}

void MyProcess::delay_MSec(unsigned int msec)
{
	QTime _Timer = QTime::currentTime().addMSecs(msec);
	while( QTime::currentTime() < _Timer )
	QCoreApplication::processEvents(QEventLoop::AllEvents, 100);
}

void MyProcess::processStarted()
{
	qDebug() << "START";
	stream_data.clear();
}

void MyProcess::readyReadStandardOutput()
{
	QString data = process->readAllStandardOutput();
	stream_data << data;
}

void MyProcess::encodingFinished()
{
	qDebug() << "END";
	process_ok=true;
}

QStringList MyProcess::RunCommand(QString command)
{
	QString cmd = "powershell.exe";
	QStringList parameters{command};
	process_ok=false;
	process->start(cmd, parameters);
	while(process_ok!=true) delay_MSec(100);
	process->close();
	return stream_data;
}

Does anyone know why I get these errors and how to solve it? Thank you in advance for your help!

JonB

@Piotrek102
Do the errors go away if you put the Q_OBJECT macro into your class MyProcess definition (and of course force rebuild)?

On a separate note: it seems a shame you still use SIGNAL/SLOT macros when your third connect() uses nicer new style syntax.

Piotrek102

@JonB said in Problem with my class and QProcess:

put the Q_OBJECT

forgot to mention it so i tried put the Q_OBJECT into my class. But I was getting other errors.

#ifndef MYPROCESS_H
#define MYPROCESS_H

#include <QProcess>
#include <QTime>
#include <QCoreApplication>
#include <QObject>

class MyProcess : public QObject
{
	Q_OBJECT
	
public:
	MyProcess();
	QStringList RunCommand(QString command);

private slots:
	void processStarted();
	void readyReadStandardOutput();
	void encodingFinished();

private:
	QProcess* process;
	void SetupProcess();
	void delay_MSec(unsigned int msec);
	bool process_ok;
	QStringList stream_data;

};

#endif // MYPROCESS_H

New errors:
debug/mainwindow.o:mainwindow.cpp (.rdata$.refptr._ZTV9MyProcess[.refptr._ZTV9MyProcess]+0x0): undefined reference to `vtable for MyProcess'

collect2.exe: error: ld returned 1 exit status

[Makefile.Debug:88: debug/WinConfigurator.exe] Error 1

As for connect (), I'm learning all the time and hope my code will be better in the future

Piotrek102

@JonB
Thank you so much, I forgot to rebuild my app. After rebuilding, everything works great! Thank you very much again! I mark the topic as solved.

I would have written earlier but I had to wait 600 seconds to replay you one more time

JonB

@Piotrek102
I was not sure whether you needed the Q_OBJECT macro. I had thought it was only required if the class emits signals, but yours seemed to be required because your class had slots, which I was not sure mattered. It seems it does!

Yes, anytime you change anything about Q_OBJECT in a class you must do a full rebuild. undefined reference to 'vtable for MyProcess' is the error you will get without rebuild.

Your 3rd connect() uses the new-style syntax (with a lambda). You could rewrite the first two as:

	connect(process, &QProcess::started, this, &MyProcess::processStarted);
	connect(process, &QProcess::readyReadStandardOutput, this, &MyProcess::readyReadStandardOutput);

The advantage is that you get compile-time checking for compatibility. Then you will never (except in unusual circumstances) need to use SIGNAL or SLOT macros again!

SGaist

Hi,

A full rebuild is not strictly required however running qmake before building is when adding or removing the Q_OBJECT macro as moc must do its job when added and otherwise not run when removed. But when I doubt, full rebuild often helps.