Segmentation fault while passing IO/file handles

[xfurrier]

I'm not quite sure what can be done with file/IO handles - can they be copied, passed as an argument, etc. I have to be honest, these are still not completely clear to me despite my efforts to understand it.

I've attached a sample program to get a better idea what I'm trying to do.

In my program I want to select a csv file (FileSelect) and pass a handle to another class (MyDialog). The file might have headers it its first row (name,surname,eid) or not - that info is provided by a user by (un)ticking a checkbox.

Bits in MyDialog constructor (init headers) work as I want. However, I cannot pass 'stop 2' in setHeaders as I get "Segmentation fault".

Any help would be appreciated. Thanks.

#include "mydialog.h"
 
MyDialog::MyDialog(QWidget *parent, QIODevice *handle) : QDialog(parent)
{
	m_handle = handle;
 
	// get the number of columns
	QTextStream in(m_handle);
	m_nColumns = in.readLine().split(',').length();
	qDebug() << "Number of Columns" << m_nColumns;
 
	QCheckBox *checkbox = new QCheckBox("&Header row", this);
	checkbox->setCheckState(Qt::Checked);
 
	// init headers - works fine
	m_tableWidget = new QTableWidget(0, m_nColumns);
	in.seek(0);
	QStringList headers = in.readLine().split(',');
	m_tableWidget->setHorizontalHeaderLabels(headers);
 
	QVBoxLayout *mainLayout = new QVBoxLayout;
	mainLayout->addWidget(checkbox);
	mainLayout->addWidget(m_tableWidget);
	setLayout(mainLayout);
 
	connect (checkbox, SIGNAL(stateChanged(int)), this, SLOT(headerRowStateChanged(int)));
}
 
 
void MyDialog::headerRowStateChanged(int nState)
{
	qDebug() << "Checkbox state changed" << nState;
 
	if (nState == Qt::Unchecked)
		setHeaders(false);
	else if (nState == Qt::Checked)
		setHeaders(true);
 
	return;
}
 
void MyDialog::setHeaders(bool bHeaderRow)
{
	QStringList headers;
 
	qDebug() << "stop 1";
	if (bHeaderRow) {
		qDebug() << "stop 2";
		QTextStream in(m_handle);
		qDebug() << "stop 3";
		QStringList headers = in.readLine().split(',');
		qDebug() << "stop 4";
	} else {
		for (int i = 0; i < m_nColumns; i++)
			headers << QString::number(i+1);
	}
	qDebug() << "stop 5";
 
	m_tableWidget->setHorizontalHeaderLabels(headers);
	qDebug() << "stop 6" << headers;
 
	return;
}

#include "mydialog.h"

MyDialog::MyDialog(QWidget *parent, QIODevice *handle) : QDialog(parent)
{
	m_handle = handle;

	// get the number of columns
	QTextStream in(m_handle);
	m_nColumns = in.readLine().split(',').length();
	qDebug() << "Number of Columns" << m_nColumns;

	QCheckBox *checkbox = new QCheckBox("&Header row", this);
	checkbox->setCheckState(Qt::Checked);

	// init headers - works fine
	m_tableWidget = new QTableWidget(0, m_nColumns);
	in.seek(0);
	QStringList headers = in.readLine().split(',');
	m_tableWidget->setHorizontalHeaderLabels(headers);

	QVBoxLayout *mainLayout = new QVBoxLayout;
	mainLayout->addWidget(checkbox);
	mainLayout->addWidget(m_tableWidget);
	setLayout(mainLayout);

	connect (checkbox, SIGNAL(stateChanged(int)), this, SLOT(headerRowStateChanged(int)));
}


void MyDialog::headerRowStateChanged(int nState)
{
	qDebug() << "Checkbox state changed" << nState;

	if (nState == Qt::Unchecked)
		setHeaders(false);
	else if (nState == Qt::Checked)
		setHeaders(true);

	return;
}

void MyDialog::setHeaders(bool bHeaderRow)
{
	QStringList headers;

	qDebug() << "stop 1";
	if (bHeaderRow) {
		qDebug() << "stop 2";
		QTextStream in(m_handle);
		qDebug() << "stop 3";
		QStringList headers = in.readLine().split(',');
		qDebug() << "stop 4";
	} else {
		for (int i = 0; i < m_nColumns; i++)
			headers << QString::number(i+1);
	}
	qDebug() << "stop 5";

	m_tableWidget->setHorizontalHeaderLabels(headers);
	qDebug() << "stop 6" << headers;

	return;
}

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[spirit]

the problem was in that you created QFile in the stack, try this

void FileSelect::processFile()
{
	QString strFilename = QFileDialog::getOpenFileName(this, "Select CSV File", ".", "Comma Separated Values (*.csv)");
	qDebug() << "got filename" << strFilename;
 
	QFile *file = new QFile(strFilename, this);
	if (!file->open(QIODevice::ReadOnly)) {
		qDebug() << "cannot read" << strFilename;
		return;
	}
 
	MyDialog *a = new MyDialog(this, file);
	a->show();
 
	return;
}

void FileSelect::processFile()
{
	QString strFilename = QFileDialog::getOpenFileName(this, "Select CSV File", ".", "Comma Separated Values (*.csv)");
	qDebug() << "got filename" << strFilename;

	QFile *file = new QFile(strFilename, this);
	if (!file->open(QIODevice::ReadOnly)) {
		qDebug() << "cannot read" << strFilename;
		return;
	}

	MyDialog *a = new MyDialog(this, file);
	a->show();

	return;
}

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[xfurrier]

You're absolutely right. Thanks.