[SOLVED] Segmentation Fault with QProcess, but in console works all fine

I-sty

Hi all,

I would like to create a simple app what writes the windows processes.

@#include <QtDebug>

#include <QTimer>
#include <QProcess>
#include <QPlainTextEdit>
#include <QString>
#include <QStringList>

#include "mainwindow.h"
#include "ui_mainwindow.h"

//
// Global variables
//
QString p_stdout;

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
QProcess proc;
runScript();

//QTimer *timer = new QTimer(this);
//connect(timer, SIGNAL(timeout()), this, SLOT(refreshList()));
//timer->start(10000);

ui->setupUi(this);

}

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

void MainWindow::splitText(QString text)
{
QStringList list;

list = text.split(QRegExp("\\s+"));

for (int i = 0; i < list.size(); i += 3)
{
    QString temp = list[i];
    temp.append(" ");
    temp.append(list[i+1]);
    temp.append(" ");
    temp.append(list[i+2]);
    temp.append("\n");
    ui->textBox->setPlainText(temp);
}

}

void MainWindow::runScript()
{
//proc->setReadChannelMode(QProcess::SeparateChannels);
proc.start("WMIC path win32_process get Caption,Processid,Commandline"); //this command list the processes
//connect (proc,SIGNAL(finished(int)), this, SLOT(stopped()));
connect(&proc,SIGNAL(readyReadStandardOutput()),this,SLOT(readyReadStandardOutput()));
connect(&proc,SIGNAL(readyReadStandardError()),this,SLOT(readyReadStandardError()));

proc.waitForFinished(-1); //here are the "Segmantation Fault"

if (proc.exitStatus() == QProcess::NormalExit)
{
    QApplication::beep();
}
else
    MainWindow::close();

QByteArray p_stdout = proc.readAll();
QString p_stderr = proc.readAllStandardError();
splitText(p_stdout);

/*if (!proc->waitForFinished())
{
    ui->textBox->setPlainText(QString(proc->readAllStandardError()));
    qDebug() << QString(proc->readAllStandardOutput());
    qDebug() << proc->exitCode();
    qDebug() << proc->exitStatus();
}
else
{
    qDebug() << proc->readAll();
    QByteArray result = proc->readAll();
}*/

}

void MainWindow::readyReadStandardOutput(){
qDebug() << proc.readAllStandardOutput();
ui->textBox->setPlainText(proc.readAllStandardOutput());
}

void MainWindow::readyReadStandardError(){
qDebug() << proc.readAllStandardError();
ui->textBox->setPlainText(proc.readAllStandardError());
}

void MainWindow::refreshList()
{
runScript();
ui->textBox->update();
//ui->textBox->setPlainText(p_stdout);
}

void MainWindow::on_actionE_xit_triggered()
{
MainWindow::close();
}
@

The code is actualy not complete, because I can not debug by the error.

Thanks,
I-sty

AlekseyOk

Hi.
You declared local variable @proc@ in constructor and try to use it in another function! This code shouldn't compile.

P.S. also take a look to "global QProcess...":http://www.qtcentre.org/threads/11696-QProcess-*proc-at-top-of-source-(global-)

I-sty

@void MainWindow::runScript()
{
QProcess *proc = new QProcess();

proc->start("WMIC path win32_process get Caption,Processid,Commandline");
proc->waitForReadyRead();

QString p_stdout = proc->readAll();
QString p_stderr = proc->readAllStandardError();
splitText(p_stdout);

}@

Thanks Aleksey.
I declared local in constructor, I changed the wairForFinished() to waitForReadyRead() and now it's working :D

But, ....

@void MainWindow::splitText(QString text)
{
QStringList list;

list = text.split(QRegExp("\\s+"));

for (int i = 3; i < list.size(); i += 3)
{
    QString temp = list[i];
    temp.append(" ");
    temp.append(list[i+1]);
    temp.append(" ");
    temp.append(list[i+2]);
    temp.append("\n");
    ui->textBox->setPlainText(temp); //here I give "Segmentation Fault"
}

}@

I get a SegFault. Why?

Jeroentjehome

Hi, normally you get the segmentation fault if you want to write or read data from a non-allocated memory location. Why don't you set a break point before the ui->... line and check if the ui pointer is there at all.
Btw there is no check of a full list, so what happens if the list gives e.g. 20 results in stead of 21? The last index of the list will not be there causing the temp.append(list[i+2]) to read from unallocated or at least wrong data.
greetz and enjoy live!

I-sty

I changed the QPlainText to QTextEdit.

@ for (int i = 3; i < list.size(); ++i)
{
/QString temp;
temp.append(list[i]);
temp.append(" ");
temp.append(list[i+1]);
temp.append(" ");
temp.append(list[i+2]);
temp.append("\n\r");/
ui->textBox->setText("hello"); //SegFault
}@

But, I give segfault, anyway. :(

franku

In which context do you call void MainWindow::refreshList() ? If you write to the ui not within the gui thread, you also can get a segment fault. This makes sense, since your console application does not fail.

AlekseyOk

Also, you have a memory leak in runScript() method.
Do you really need to allocate proc in heap?

I-sty

@void MainWindow::runScript()
{
proc->start("WMIC path win32_process get Caption,Processid,Commandline");
proc->waitForReadyRead();
QApplication::beep();
//splitText(QString(proc->readAllStandardOutput()));
}
@

I changed proc.

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

proc = new QProcess();

....

}@

AlekseyOk

Memory leak still exists))

try to change to:

@
proc = new QProcess(this);
@

Did you run your app in debug mode (e.g. via F5 shortcut)?