How to use QDebug in QT console

[victor wang]

Hi All,
I'm using qt5.5 on my computer and Linux+QT for my OS system.
I'm using qtcreator to creat a new project with QT Console.
And this is my program.

#include <QCoreApplication>
#include <QDebug>
#include <QtSerialPort/QSerialPort>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    bool ignition_bios_name_error=false;
    QSerialPort comport;
    QString comportstring="/dev/ttymxc2";
    comport.setPortName(comportstring);
    comport.setBaudRate(QSerialPort::Baud9600);
    comport.setDataBits(QSerialPort::Data8);
    comport.setParity(QSerialPort::NoParity);
    comport.setStopBits(QSerialPort::OneStop);

    const char BIOS_COM[4]={0x04,0xA0,0x00,0x5C};
    const char BIOS_name[4]={0x04,0xA0,0x01,0x5B};

    if (!comport.open(QIODevice::ReadWrite)) {
        qDebug("cannot open");//<<comport.errorString();
    }
    qint64 bytesWritten = comport.write(BIOS_COM,sizeof(BIOS_COM));

    if (bytesWritten == -1)
    {
        qDebug("Failed to write the data to port");
    }
    else if (!comport.waitForBytesWritten(80))
    {
        qDebug("Operation timed out or an error occurred for port");
    }
    QByteArray readData=comport.readAll();
    while(comport.waitForReadyRead(80))
        readData.append(comport.readAll());
    if (comport.error() == QSerialPort::ReadError)
    {
        QDebug("read error");
        ignition_bios_name_error = true;
    }
    else if (comport.error() == QSerialPort::TimeoutError && readData.isEmpty())
    {
        QDebug("timed out");
        ignition_bios_name_error = true;
    }
    if(readData.contains("93FA1000WN0A"))
    {
        qDebug()<<"NAME: "+readData.constData();
    }
    else
    {
        qDebug("wrong data");
        ignition_bios_name_error = true;
    }
    bytesWritten = comport.write(BIOS_name,sizeof(BIOS_name));

    if (bytesWritten == -1)
    {
        qDebug("Failed to write the data to port");
    }
    else if (!comport.waitForBytesWritten(80))
    {
        qDebug("Operation timed out or an error occurred for port");
    }
    readData=comport.readAll();
    while(comport.waitForReadyRead(80))
        readData.append(comport.readAll());
    if (comport.error() == QSerialPort::ReadError)
    {
       QDebug("BIOS read error");
    }
    else if (comport.error() == QSerialPort::TimeoutError && readData.isEmpty())
    {
        QDebug("BIOS timed out");
    }
    else if(readData.contains("FA3A110-000000000-000-VV120-WN"))
    {
        if(!ignition_bios_name_error)
        {
            qDebug()<<"BIOS_version: "+readData.constData()+"  And BIOS_name error";
        }
        else
        {
            qDebug()<<"BIOS_version: "+readData.constData();
        }
    }

    return a.exec();
}

When I compile with qmake then it will give me the error.

arm-poky-linux-gnueabi-g++  -march=armv7-a -mfloat-abi=hard -mfpu=neon -mtune=cortex-a9 --sysroot=/mnt/raid115/victor/freescale/opt/fsl-imx-wayland/4.1.15/sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi -c -pipe  -O2 -pipe -g -feliminate-unused-debug-types -O2 -DLINUX=1 -DEGL_API_FB=1 -Wall -W -D_REENTRANT -fPIC -DQT_NO_DEBUG -DQT_SERIALPORT_LIB -DQT_CORE_LIB -I. -I../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5 -I../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtSerialPort -I../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore -I. -I../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/lib/qt5/mkspecs/linux-oe-g++ -o main.o main.cpp
main.cpp: In function 'int main(int, char**)':
main.cpp:41:28: error: no matching function for call to 'QDebug::QDebug(const char [11])'
         QDebug("read error");
                            ^
In file included from ../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/QDebug:1:0,
                 from main.cpp:2:
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:89:12: note: candidate: QDebug::QDebug(const QDebug&)
     inline QDebug(const QDebug &o):stream(o.stream) { ++stream->ref; }
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:89:12: note:   no known conversion for argument 1 from 'const char [11]' to 'const QDebug&'
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:88:12: note: candidate: QDebug::QDebug(QtMsgType)
     inline QDebug(QtMsgType t) : stream(new Stream(t)) {}
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:88:12: note:   no known conversion for argument 1 from 'const char [11]' to 'QtMsgType'
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:87:12: note: candidate: QDebug::QDebug(QString*)
     inline QDebug(QString *string) : stream(new Stream(string)) {}
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:87:12: note:   no known conversion for argument 1 from 'const char [11]' to 'QString*'
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:86:12: note: candidate: QDebug::QDebug(QIODevice*)
     inline QDebug(QIODevice *device) : stream(new Stream(device)) {}
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:86:12: note:   no known conversion for argument 1 from 'const char [11]' to 'QIODevice*'
main.cpp:46:27: error: no matching function for call to 'QDebug::QDebug(const char [10])'
         QDebug("timed out");
                           ^
In file included from ../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/QDebug:1:0,
                 from main.cpp:2:
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:89:12: note: candidate: QDebug::QDebug(const QDebug&)
     inline QDebug(const QDebug &o):stream(o.stream) { ++stream->ref; }
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:89:12: note:   no known conversion for argument 1 from 'const char [10]' to 'const QDebug&'
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:88:12: note: candidate: QDebug::QDebug(QtMsgType)
     inline QDebug(QtMsgType t) : stream(new Stream(t)) {}
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:88:12: note:   no known conversion for argument 1 from 'const char [10]' to 'QtMsgType'
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:87:12: note: candidate: QDebug::QDebug(QString*)
     inline QDebug(QString *string) : stream(new Stream(string)) {}
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:87:12: note:   no known conversion for argument 1 from 'const char [10]' to 'QString*'
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:86:12: note: candidate: QDebug::QDebug(QIODevice*)
     inline QDebug(QIODevice *device) : stream(new Stream(device)) {}
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:86:12: note:   no known conversion for argument 1 from 'const char [10]' to 'QIODevice*'
main.cpp:51:47: error: invalid operands of types 'const char [7]' and 'const char*' to binary 'operator+'
         qDebug()<<"NAME: "+readData.constData();
                                               ^
main.cpp:73:32: error: no matching function for call to 'QDebug::QDebug(const char [16])'
        QDebug("BIOS read error");
                                ^
In file included from ../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/QDebug:1:0,
                 from main.cpp:2:
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:89:12: note: candidate: QDebug::QDebug(const QDebug&)
     inline QDebug(const QDebug &o):stream(o.stream) { ++stream->ref; }
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:89:12: note:   no known conversion for argument 1 from 'const char [16]' to 'const QDebug&'
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:88:12: note: candidate: QDebug::QDebug(QtMsgType)
     inline QDebug(QtMsgType t) : stream(new Stream(t)) {}
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:88:12: note:   no known conversion for argument 1 from 'const char [16]' to 'QtMsgType'
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:87:12: note: candidate: QDebug::QDebug(QString*)
     inline QDebug(QString *string) : stream(new Stream(string)) {}
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:87:12: note:   no known conversion for argument 1 from 'const char [16]' to 'QString*'
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:86:12: note: candidate: QDebug::QDebug(QIODevice*)
     inline QDebug(QIODevice *device) : stream(new Stream(device)) {}
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:86:12: note:   no known conversion for argument 1 from 'const char [16]' to 'QIODevice*'
main.cpp:77:32: error: no matching function for call to 'QDebug::QDebug(const char [15])'
         QDebug("BIOS timed out");
                                ^
In file included from ../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/QDebug:1:0,
                 from main.cpp:2:
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:89:12: note: candidate: QDebug::QDebug(const QDebug&)
     inline QDebug(const QDebug &o):stream(o.stream) { ++stream->ref; }
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:89:12: note:   no known conversion for argument 1 from 'const char [15]' to 'const QDebug&'
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:88:12: note: candidate: QDebug::QDebug(QtMsgType)
     inline QDebug(QtMsgType t) : stream(new Stream(t)) {}
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:88:12: note:   no known conversion for argument 1 from 'const char [15]' to 'QtMsgType'
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:87:12: note: candidate: QDebug::QDebug(QString*)
     inline QDebug(QString *string) : stream(new Stream(string)) {}
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:87:12: note:   no known conversion for argument 1 from 'const char [15]' to 'QString*'
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:86:12: note: candidate: QDebug::QDebug(QIODevice*)
     inline QDebug(QIODevice *device) : stream(new Stream(device)) {}
            ^
../../../sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/include/qt5/QtCore/qdebug.h:86:12: note:   no known conversion for argument 1 from 'const char [15]' to 'QIODevice*'
main.cpp:83:59: error: invalid operands of types 'const char [15]' and 'const char*' to binary 'operator+'
             qDebug()<<"BIOS_version: "+readData.constData()+"  And BIOS_name error";
                                                           ^
main.cpp:87:59: error: invalid operands of types 'const char [15]' and 'const char*' to binary 'operator+'
             qDebug()<<"BIOS_version: "+readData.constData();
                                                           ^
make: *** [main.o] Error 1

How to fix this problem?

Thanks in Advanced!

[joeQ]

@victor-wang hi,friend,welcome.

You write qDebug() to QDebug(), Note qDebug

if (comport.error() == QSerialPort::ReadError)
    {
        QDebug("read error"); ///< use qDebug("......");
        ignition_bios_name_error = true;
    }
    else if (comport.error() == QSerialPort::TimeoutError && readData.isEmpty())
    {
        QDebug("timed out"); ///< use qDebug("......");
        ignition_bios_name_error = true;
    }

[jsulm]

@joeQ @victor-wang Actually it should be:

if (comport.error() == QSerialPort::ReadError)
{
    qDebug() << "read error"; ///< use qDebug("......");
    ignition_bios_name_error = true;
}
else if (comport.error() == QSerialPort::TimeoutError && readData.isEmpty())
{
    qDebug() << "timed out"; ///< use qDebug("......");
    ignition_bios_name_error = true;
 }

It is explained in the documentation even with examples: http://doc.qt.io/qt-5/qdebug.html

[joeQ]

@jsulm

Thank you.

is it also OK ?

some one used to use C printf format, so, he like below format

///< int num. char* pstr
qDebug("%d %s",num,pstr); ///< it also can run.

// or
str = QString("xxxxxx");
qDebug("%s",qPrintable(str));

does it must be qDebug() << XXX ?

maybe qDebug() << XXX is strict.

oh, I find the Qt Reference

If you pass the function a format string and a list of arguments, it works in similar way to the C printf() function. The format should be a Latin-1 string.
Example:

qDebug("Items in list: %d", myList.size());

[victor wang]

@joeQ
@jsulm
Thank you so much for helping me.
I have to apologize that i make a such stupid mistake.
I do not see that I type qDebug -> QDebug.

And I've try both two command as following, It all works perfectly.

qDebug("text");
qDebug()<<"test";

Also I've try modify my wrong program from

qDebug()<<"BIOS_version: "+readData.constData()+"  And BIOS_name error";

to

qDebug()<<"BIOS_version: ";
qDebug("%s",readData.constData());
qDebug()<<"  And BIOS_name error";

And It works also perfectly!

Again thanks for helping me!