Serial.write crashes program in Qt (C++) - c++

Question

I am attempting to write a command to a serial port that will change my TV input, but when I try to write the necessary command to the port, I get a very strange output.
#include <QCoreApplication>
#include <QSerialPort>
#include <Windows.h>
int set_id = 0;
int fd = -1;
int main(int argc, char *argv[])
{
QCoreApplication app{argc, argv};
int timeInSeconds=0;
while(timeInSeconds>0)
{
printf("%d...\n",timeInSeconds);
Sleep(1000);
timeInSeconds--;
}
QSerialPort serial;
serial.setBaudRate(QSerialPort::Baud9600);
serial.setDataBits(QSerialPort::Data8);
serial.setParity(QSerialPort::NoParity);
serial.setStopBits(QSerialPort::OneStop);
serial.setFlowControl(QSerialPort::NoFlowControl);
serial.setPortName("com3");
serial.open(QIODevice::ReadWrite);
/*char cmd1='x';
char cmd2='b';
int value=20;
char cmd[20];
int len;
if (value >= 0x100)
len = sprintf(cmd, "%c%c %02x %02x %02x\r", cmd1, cmd2, set_id, value>>8, value&255);
else
{
len = sprintf(cmd, "%c%c %02x %02x\r", cmd1, cmd2, set_id, value);
}
serial.write(cmd, len);
*/
char cmdHex[5]="0xc5";
serial.write(cmdHex);
serial.close();
int stall;
scanf("%d",&stall);
//return a.exec();
}
The code is supposed to change the tv input to av. (Starting from HDMI 1) Also, the block that is commented out is my first attempt at sending the command.

Answer 1

You should study the QSerialPort examples shipped with Qt.
There's the terminal project, which is interactive (nice for testing ports), and the cwritersync does what you're trying to do.
Here is the full cwritersync code:
/****************************************************************************
**
** Copyright (C) 2013 Laszlo Papp <lpapp#kde.org>
** Contact: http://www.qt.io/licensing/
**
** This file is part of the QtSerialPort module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL21$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see http://www.qt.io/terms-conditions. For further
** information use the contact form at http://www.qt.io/contact-us.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 or version 3 as published by the Free
** Software Foundation and appearing in the file LICENSE.LGPLv21 and
** LICENSE.LGPLv3 included in the packaging of this file. Please review the
** following information to ensure the GNU Lesser General Public License
** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** As a special exception, The Qt Company gives you certain additional
** rights. These rights are described in The Qt Company LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** $QT_END_LICENSE$
**
****************************************************************************/
#include <QtSerialPort/QSerialPort>
#include <QTextStream>
#include <QCoreApplication>
#include <QFile>
#include <QStringList>
QT_USE_NAMESPACE
int main(int argc, char *argv[])
{
QCoreApplication coreApplication(argc, argv);
int argumentCount = QCoreApplication::arguments().size();
QStringList argumentList = QCoreApplication::arguments();
QTextStream standardOutput(stdout);
if (argumentCount == 1) {
standardOutput << QObject::tr("Usage: %1 <serialportname> [baudrate]").arg(argumentList.first()) << endl;
return 1;
}
QSerialPort serialPort;
QString serialPortName = argumentList.at(1);
serialPort.setPortName(serialPortName);
int serialPortBaudRate = (argumentCount > 2) ? argumentList.at(2).toInt() : QSerialPort::Baud9600;
serialPort.setBaudRate(serialPortBaudRate);
if (!serialPort.open(QIODevice::WriteOnly)) {
standardOutput << QObject::tr("Failed to open port %1, error: %2").arg(serialPortName).arg(serialPort.errorString()) << endl;
return 1;
}
QFile dataFile;
if (!dataFile.open(stdin, QIODevice::ReadOnly)) {
standardOutput << QObject::tr("Failed to open stdin for reading") << endl;
return 1;
}
QByteArray writeData(dataFile.readAll());
dataFile.close();
if (writeData.isEmpty()) {
standardOutput << QObject::tr("Either no data was currently available on the standard input for reading, or an error occurred for port %1, error: %2").arg(serialPortName).arg(serialPort.errorString()) << endl;
return 1;
}
qint64 bytesWritten = serialPort.write(writeData);
if (bytesWritten == -1) {
standardOutput << QObject::tr("Failed to write the data to port %1, error: %2").arg(serialPortName).arg(serialPort.errorString()) << endl;
return 1;
} else if (bytesWritten != writeData.size()) {
standardOutput << QObject::tr("Failed to write all the data to port %1, error: %2").arg(serialPortName).arg(serialPort.errorString()) << endl;
return 1;
} else if (!serialPort.waitForBytesWritten(5000)) {
standardOutput << QObject::tr("Operation timed out or an error occurred for port %1, error: %2").arg(serialPortName).arg(serialPort.errorString()) << endl;
return 1;
}
standardOutput << QObject::tr("Data successfully sent to port %1").arg(serialPortName) << endl;
return 0;
}