get qprocess output in slot

Question

i have a problem with a small program (I am a beginner with c++ and qt). On button press it starts a cli application with qprocess and the output should be displayed in a text field as soon as the cli app writes it to stdout or stderr.

i read that its a good idea to use signals and slots for this but it isnt working.

the compiler throws an error that in my slot getOutput() the "process" object isn't declared (C2065)

here is the code.

processgui.cpp:

#include "processgui.h"
#include "ui_processgui.h"
#include <QProcess>

processGui::processGui(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::processGui)
{
    ui->setupUi(this);
}

processGui::~processGui()
{
    delete ui;
}

void processGui::on_startProcess_clicked() {

    QProcess *process = new QProcess(this);
    QString program = "tracert";
    QString arguments = "";

    process->setReadChannelMode(QProcess::MergedChannels);

    process->start(program, QStringList() << arguments);

    process->waitForStarted();

    QObject::connect(process, SIGNAL(readyReadStandardOutput()), this, SLOT(getOutput()));

}

void processGui::getOutput() {

    QByteArray strdata = process->readAllStandardOutput();

    ui->textLog->append(strdata);

}

processgui.h :

#ifndef PROCESSGUI_H
#define PROCESSGUI_H

#include <QMainWindow>

namespace Ui {
class processGui;
}

class processGui : public QMainWindow
{
    Q_OBJECT

public:
    explicit processGui(QWidget *parent = 0);
    ~processGui();

private slots:
    void on_startProcess_clicked();

    void getOutput();

private:
    Ui::processGui *ui;
};

#endif // PROCESSGUI_H

thanks in advance

score 1 · Accepted Answer · answered Jun 27 '13 at 09:05

1

Move QProcess *process to your header and initialize it with process = new QProcess(this) in your constructor. That way you can access it in your slot.

answered Jun 27 '13 at 09:05

thuga

12,601
42
52

score 1 · Answer 2 · answered Jun 27 '13 at 09:06

1

 QProcess *process = new QProcess(this);

is declared in:

void processGui::on_startProcess_clicked()

it's a scope problem, process is a local variable not available in the whole class.

answered Jun 27 '13 at 09:06

ariwez

1,309
17
20

I fixed it with thugas advice. I thought that the connect made the process avaiable in the slot but you are right. Thanks for the explanation. – arkhon Jun 27 '13 at 09:30

score 0 · Answer 3 · answered May 15 '18 at 07:55

0

You can access QProcess object inside a slot with sender(), like this:

void processGui::getOutput() 
{
    QProcess* process = qobject_cast<QProcess*>(sender());
    QByteArray strdata = process->readAllStandardOutput();    
}

answered May 15 '18 at 07:55

lena

1,181
12
36

get qprocess output in slot

3 Answers3